Research ArticleDesign of an Improved Cooking Stove Using High DensityHeated Rocks and Heat Retaining Techniques

Anthony A Bantu1 Gilbert Nuwagaba1 Sarah Kizza1 and Yonah K Turinayo 2

1Department of Engineering and Environment Uganda Christian University PO Box 4 Mukono Uganda2National Forestry Resources Research Institute (NaFORRI) National Agricultural Research Organisation (NARO)PO Box 1752 Kampala Uganda

Correspondence should be addressed to Yonah K Turinayo t2rinayonahgmailcom

Received 18 July 2018 Accepted 15 October 2018 Published 28 October 2018

Academic Editor Jayanta Mondol

Copyright copy 2018 Anthony A Bantu et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

In sub-Saharan Africa dependence on wood fuel has caused significant depletion of vegetative resources Whereas there existhundreds of improved cooking stoves many have not reached their maximum potential because their designs are predominantlyfocused on either fuel efficiency or reduced smoke This research designed and fabricated an improved charcoal stove using highdensity rocks and heat retaining techniques The aim was to retain heat and minimise heat losses in cooking devices with a solepurpose of reducing the amount of fuel used during cooking The stove design herein incorporates the interaction of physical andthermal properties of granite rocks with heat loss theories to give a thermal efficient unit The stove was estimated to cost US$36 which compared favourably with most of the improved charcoal stoves on international market (US$ 3ndash50 US$) This studyrevealed that by introducing the new stove design and insulation the granite rocks depicted high thermal storage properties withpotential for reducing fuel use by over 78with reference to the open fire stoveThe designed granite rock stove therefore paves wayfor the use of high density rocks in improved cook stoves to achieve high performance energy efficient systems that can sustainablyput to use vegetative resources

1 Introduction

Many of the worldrsquos population living in developing countrieslack access to modern energy services for economic andsocial development Besides its existing energy system isunsustainable [1] A large proportion of the households donot have access to grid electricity Yet those relying onelectricity for cooking experience intermittent power supplyAlthough liquid petroleum gas burns quite effectively itis expensive and not viable for a common man More sothere has been persistent escalating fossil oil prices and fuelcrisis which has drawn attention to the need for producingviable alternatives to kerosene and gas for domestic cooking[2] Solar another potential alternative source of energyis noticeably location-specific in terms of utilisation Itsassociated problems are linked to energy storage for useduring the period of modest or no sunshine as well as needfor technological artifacts which are currently scarce in the

developing countries [3] However several renewable energyresources including hydroelectricity solar and biomass arepromoted due to their high availability and responsiveness tothe environment

In Africa biomass is a traditional and the most reliablefuel source of energy used for cooking by over 69 ofthe population [4] However its increased utilisation byinefficient technologies has raised fears over the long-termforest degradation with loss of environmental services (egwatershed protection) and biodiversity [5] Biomass is quitedifficult to burn completely in the most commonly usedtraditional household-sized stoves [6] Frequent use of stovesdeveloped by improper combustion designs may result intoindoor air pollution impacting negatively on the healthof household members particularly women and children[1] For instance Nahar [7] reported that about 2 millionannual excess deaths of women and children in developingcountries are linked to indoor air pollution precisely due

HindawiJournal of Renewable EnergyVolume 2018 Article ID 9620103 9 pageshttpsdoiorg10115520189620103

2 Journal of Renewable Energy

to exposure to carbon monoxide and the volatiles (benzeneand formaldehyde) liberated in the form of smoke [8] Suchexposures lead to acute respiratory infections low birthweights lung cancer chronic obstructive lung diseases andeyes problems [9] Thus faster technological developmentis vital in advancing charcoal stove and its environmentalperformance

Although charcoal is believed to be an affordable avail-able and the most convenient fuel source for households itsuse in inefficient stoves would produce significant amountsof indoor air pollution and make it unsustainable Thereforecontinual technology development will suppress charcoalrsquosdetriments and enhance its efficient utilisationwhile reducingsignificantly environmental impact

This work therefore aims at developing a more efficientand safe charcoal burning stove that can reduce fuel con-sumption rates and indoor air pollution Even though a lothas been done to promote ldquoimproved cook stovesrdquo in thedeveloping countries little has been emphasised on qualitycombustion during their design and development [10]This isattributed to limited scientific information on design featuresand materials of stove construction In sub-Saharan Africahowever a number of stove models are designed and fabri-cated by local artisans using locally available materials suchas mud clay dry grass ant-hill soil and clay bricks Butno attempts have been made on high density rocks such asgranite

This paper deals with the development of a charcoal stoveprototype from locally available materials including graniterock stainless steel and the glass wool It describes the designfeatures thermodynamic performance and thermophysicalproperties of the granite rock used in thermal-energy storage(TES) system fabrication According to previous studies onthermophysical properties of granite rock a suitable TES sys-tem should have high values of thermal conductivity specificheat capacity material density and low values of porosity [11ndash13] High thermal storage efficiencies are as a result of highvalues of thermal conductivity specific heat capacity anddensity High density and specific heat capacity values leadto a large volumetric heat capacity hence permitting compactstorage in the systems whereas low values of porosity indicatelarge bulk density and uniaxial compressive strength [14 15]

2 Materials and Methods

21 Construction Materials

211 Fiber Glass A section of the stove wall was made fromglass wool because this material is a poor conductor of heatdue to its low thermal conductivity and thus will prevent heatloss by conduction Through saving as much heat as possiblethe fuel combustion efficiency of the stove is improved itmeans saving evenmuchmore fuel In addition the fiber glassmaterial is locally available

212 Stainless Steel Stainless steel was chosen as a materialbecause of its availability on the local market Technically itundergoes allowable deformation and is resistant to corrosionin high temperatures Steel has a longer service life than most

metals and because of this its design life costs are mini-mal

213 Granite Rocks Rocks are considered an attractive stor-age material for thermal-energy storage at high temperaturesdue to their thermal physical and mechanical properties [1112] The rock selected was granite because of its high densitygood thermal properties and ready local availability

22Designing andConstruction of the Stove In order to comeup with the desired stove design and its desired performanceproper reflection into factors such as fuel type calorific valueair flow rate insulation local resources stove power outputsafety consideration reactor cross-sectional area diameterand height are of great importance In the present studythe size of the combustion chamber and the amount of fuelrequired to accomplish the cooking task were evaluated fol-lowing work done by Kiwana [16] andMaxwell [17] as well asreasonable assumptions depicted in Table 1 Fuel (carbonisedagrowaste briquettes and charcoal) for experimental designwas selected based on its local availability within Kampaladistrict

The combustion chamber dimensions were based on theKenyan ceramic jiko stove because of its prominence on theUgandan local market and availability of dimensional dataThe jiko stove has a basal internal diameter of 160mm andfire box depth of 100 mm [17] A combustion chamberwith an internal diameter of 120mm and height 100mm wasfabricated Thus taking the combustion chamber (innerchamber) as the focal point the outer chamber (concentricto the combustion chamber) was fabricated at an internaldiameter of 170 using granite rock glass wool and stainlesssteel at 23mm 48mm and 10mm thick respectively

23 Testing of ermal Properties of Granite Rock andthe Improved Cook Stove

231 SpecificGravity Test of Granite Rock Granite rocks usedwere sampled from the East African granite dealers Kampaladistrict-Uganda These rocks were obtained by randomlyselecting representative samples from the cut debris stockpiles By hand picking samples were collected at randompoints from the stock piles of different rock sizes Specificgravity test was conducted according to AASHTO [18] todetermine the density of granite for the different rockmassesInitially the density of the hand crashed 1410mm graniterock sample was calculated using (1) where M1 is mass of gasjar and plate M2 is mass of gas jar plate and aggregates M3is mass of gas jar plate aggregates and water andM4 is massof gas jar plate and water

119878119901119890119888119894119891119894119888 119892119886119903V119894119905119910 = (1198722 minus1198721)(1198724 minus1198721) minus (1198723 minus1198722) (1)

Given 1 gcm3 as the density of water this implies that itbuoys up anything within it by 1 gram per cubic centimetreof displacement Because of this the weight in air minus theweight in water is equal to the volume of the rock sample incm3

Journal of Renewable Energy 3

Table 1 Thermal design assumptions for the cooking stove

No- Material Parameter Units Values Reference

1 Fuel (carbonised agro-wastebriquettes) Calorific value MJkg 217 Kiwana 2016

2 Charcoal Calorific value MJkg 298 Kiwana 20163 Water Density gltr 1000 Global Alliance for

Clean Cookstoves 20144 Water Specific heat capacity JgK 41865 Granite rock Thermal conductivity Wmminus1 Kminus1 268 Eppelbaum 20146 Air Thermal conductivity Wmminus1 Kminus1 002 Lienhard IV 20007 Stainless steel Thermal conductivity Wmminus1 Kminus1 16 Young 19928 Glass wool Thermal conductivity Wmminus1 Kminus1 004 Young 19929 Flame Theoretical Maximum temperature K 2123 Yusuf 201110 Cook stove Theoretical thermal efficiency 3511 Cook stove Energy loss 65

232 Water Absorption Test In line with AASHTO [18]the water absorption test was conducted to determine theamount of water absorbed under specified conditions Thisis mainly due to the effect water usually has on heat transferin rocks through conduction The data obtained thereforehelped shed light on the performance of the granite rockin humid environments During the experiment the graniterocks were hand crushed to 1410mm aggregates before thetest could be carried out Water absorption was expressed asincrease in weight percent based on (2) whereby A is weightof oven dry sample in air and B is weight of saturated surfacedry sample in air

119908119886119905119890119903 119886119887119904119900119903119901119905119894119900119899 = [(119861 minus 119860)119860 ] times 100 (2)

233 ermal Test of Granite Rock After lining the graniterock chamber with stainless steel charcoal fuel was ignitedwithin the combustion chamber The maximum temperaturereaching the granite rock (423 K) was attained after 41minutes on average and this was recorded

Samples of the rock were as well heated between roomtemperature (2978K) and 567K in anoven to determine theirability to withstand heat without disintegrating The rockswere heated and observations made for change in weight forthe granitematerial under testThiswas done at time intervalsof 20 minutes for 120 minutes with increasing temperaturein the oven Also the changes in the physical structure of therock were noted

234 Water Boiling Test (WBT) WBT assessed the overallperformance of a cookstove via three phases which consistedof (1) bringing water to a boil from a cold start (2) bringingwater to a boil when the stove is hot and (3) maintainingthe water at simmering temperatures In WBT experimentwater was heated to boiling point the time taken to boila given quantity of water specific firewood consumptionbesides evaluating thermal efficiency at both high and lowenergy input was doneThe test was conducted in accordancewith Volunteers in Technical Assistance [19]

Table 2 Summary of laboratory test results for specific gravityand water absorption tests (see Figure S1ndashS3 in the SupplementaryMaterials for comprehensive analysis)

Sample Test Identification Specificgravity

WaterAbsorption

()1410 mm Hand crushed aggregates 272 042

3 Results and Discussion

31 Classification of Granite Rock As presented in Table 2the specific gravity of the granite rock was found to be 272implying that the rock was of high density

Given the fact that there was little (042)water absorbedby the rock (Table 2) negligible amount of heat would berequired to drive it off Therefore the moisture content ofthe rock would not have any significant effect on its heatretention properties This makes it a suitable material for thestove construction

The effect of temperature on the physical properties of therock was also evaluated based on the practical experience ofconstructed stove operations and oven tests From the oventest experiment the granite rock recorded an initial temper-ature of 2978 K and mass of 40165g There was a gradualdecrease in mass with increasing temperature over time(Figure 1 see Figure S4 in the Supplementary Materials forcomprehensive analysis)

After 120 minutes of oven heating the granite rockrecorded a constant mass of 40121g at constant temperatureof 567 K indicating maximum moisture loss from the rockDespite the slight change in colour (dusty pale white) of therock there was no visible fracture observed Similarly themaximum temperature reaching the granite rock in theconstructed stove was recorded as 423 K (after 41 minutes ofoperation) at minimum moisture content (Figure 1) and nosign of fracture This implies that the granite rock would beable to perform in the stove without disintegrating aftersuccessive cooking times

4 Journal of Renewable Energy

273

323

373

423

473

523

573

623

4009401

4011401240134014401540164017

0 20 40 60 80 100 120

Tem

pera

ture

(K)

Mas

s of t

he ro

ck (g

)

Time (minutes)mass (g)Temperature (K)

Figure 1 Relationship between mass of granite rock and tempera-ture with time

32 Choice of Fuel for Experimental Design For the improvedstove design solid fuels were evaluated The selection toevaluate carbonised agrowaste briquettes and charcoal fuelswas taken based on local availability within Kampala district

Based on (3) we need to transmit 1538355J of energyto a pan to boil 49-liter of water (asymp 4900g) from roomtemperature (298 K) to 373 K (at sea level) given its specificheat capacity of 4186 JgK [20 21]

119867 = 119898119888120579 (3)

where H is the heat required m is the mass of substance and120579 is the temperature difference

(4186 Jg119870) x 4900g x (373119870-298119870)= 1 538 355J of energy to water

(4)

At 100 efficiency whereby all the fuel is transferred to thewater we would require

153835521700 = 7089 g of briquettes (5)

Assuming a thermal efficiency of 35 and energy loss of 652025g of briquette fuel would be required to boil 49 liters ofwater as shown below

7089035 = 2025 g of briquettes (6)

Therefore the fuel chamber needs to be designed to hold atleast 2025g of briquettes

Similarly 516g of charcoal with average calorific value= 298 MJKg = 29800Jg [16] would generate 1538355J ofenergy required to boil 49 liters of water (see (3)) if fuelconversion efficiency was 100

153835529800 = 516 g of charcoal (7)

For a thermal efficiency of 35 147g of charcoal fuel istherefore required as shown below

516035 = 147 g of charcoal (8)

Therefore the fuel chamber needs to be designed to hold 147gof charcoal

Since 100 efficiency is not practical for improved cookstoves the decision to use charcoal as a fuel for the stovedesign was based on a more practical 35 efficiency targetIt was observed that more briquettes would be requiredto achieve the same cooking task as charcoal Thereforecharcoal was a preferred choice of fuel

33 Design of the Stove Prototype The convective and con-ductive heat transfer through the stove wall were calculatedusing Fourierrsquos heat relation (see (9))

119876 = 119870119860(1198791 minus 1198792)119883 (9)

where Q is heat flow rate (Wm2) A is total cross-sectionalarea of conducting surface (m2) X is thickness of specimen(m) and T is temperature (K)According to Baldwin [22] use of Fourierrsquos heat equationfor examination of heat transfer across a stove wall generatesvalues that are too large This is because the heat transferredinto and out of an object depends not only on the conductivityto and from the surfaces but also on the conductivity withinthe object itself dirt or oxide layers and air at the surface ofthe material

Thus (9) is arranged using the thermal resistance conceptas shown in

119876 = 119860 (1198791 minus 1198792)1ℎ1 + 119909119870 + 1ℎ1 (10)

where h is the convective heat transfer obtained from

ℎ = 119860(998779119879119871 )lowast119887 (11)

A and b are constants depending on geometry andflow conditionsL denotes length

For vertical cylinders h = 131 (1358)13 [23]

= 1451Wm2K (12)

Given the height (179mm) and the diameter (375mm)Figure 2 the surface area of stove was estimated as 032 m2following (13)

119860 = 120587119903 (2ℎ + 119903)= 314 lowast 1875 (2 lowast 179 + 1875)= 321165125mm2 or 032m2

(13)

This value was used for only stainless steel since granite andfiber glass do not cover the bottom of the stove whereas forgranite and fiber glass the surface area was estimated using

119860 = 2120587119903ℎ= 2 lowast 314 lowast 1875 lowast 179= 2107725mm2 or 021m2

(14)

Journal of Renewable Energy 5

350

1000

2301702004

40

300

390R 17 cm

R 33 cm

R 39 cm

Figure 2 Plan and front elevation drawings of the designed stove (all dimensions in cm)

Taking theoretical maximum temperature = 2123 K [23] andbased on reasonable assumptions thermal conductivity ofgranite Kg = 268 WmK [24] fiber glass Kf = 004 WmK[25] and stainless steel Ks = 16 WmK [25] total resistancewas estimated as 9768 KWminus1 (see (15))

119879119900119905119886119897 119903119890119904119894119904119905119886119899119888119890 = 1ℎ1119860 + 3

119871119904119870119904119860 +

119871119891119870119891119860 +

119871119892119870119892119860

+ 1ℎ2119860

= 11451 lowast 032 + 3 lowast

0001516 lowast 032

+ 0078004 lowast 021 +

0023268 lowast 021

+ 11451 lowast 032

= 0215 + 879 lowast 10minus4 + 9296+ 0041 + 0215

= 9768KWminus1

(15)

Hence the energy lost by the stove would be 18612W basedon

119876 = 998779119879119879119900119905119886119897 119903119890119904119894119904119905119886119899119888119890 (16)

Using room temperature of 305K

= 2123 minus 3059768= 18189768

119876 = 18612W119876 = 18612 lowast 3600 = 670032119869

(17)

Yet it has been found that the stove would release a total of1538355J of energy to water at 100 efficiency (see (3)) Thisimplies that more than half (1538355 ndash 670032 = 868323J)of the energy produced by the charcoal fuel goes to the water

Figure 3 The stove made from granite rock

Thus the losses through the stove wall were workable for thestove design

34 Features of the Stove The stove (Figure 3) consists ofa combustion chamber (inner retort) constructed using a20mm thick stainless-steel material

The combustion chamber is designed to receive solidbiomass fuel (charcoal) and enhance complete combustionof combustible gas released during charcoal burning pro-cess The combustion chamber is imbedded in a cylinder(outer retort) constructed using granite rock and glass wool(Figure 4) The combustion chamber and outer retort aredesigned in a way that a 30mm gap is left in between toprovide a freemovement of air and enhance resistance to heattransfer to the inner wall of the outer retort This minimisesheat loss given the low thermal conductivity (16 Wm-1 K-1) of the granite rock and air (002 to 005 Wm-1 K-1)compared with stainless steel (16 to 64 Wm-1 K-1) usedin the construction of the combustion chamber [26] Thisleads to large amount of heat from the burning charcoal toconcentrate at the bottom of the cooking pan thus increasingthermal efficiency

35 ermal Performance of the Stove Indicators includingthermal efficiency water boiling rate specific fuel consump-tion fire power and fuel use reduction were used to evaluate

6 Journal of Renewable Energy

Stove Lining(Stainless steel)

Combustion Chamber

Air Inlet PerforationsAir gap

Stove Handle

Support

Granite Rock

Glass Wool

Air Inlet Gate Air Inlet Controller

Figure 4 Major components of the stove

the performance of the designed stove Data used in theevaluation (Table 3) were generated by WBT experimentusing a recommended protocol [19]

The thermal efficiency a measure of the fraction of heatproduced by the fuel that made it directly to the water in thepot [20 21] was calculated using

119874V119890119903119886119897119897 119890119891119891119894119888119894119890119899119888119910 = 119879119900119905119886119897 ℎ119890119886119905 119886119887119904119900119903119887119890119889 119887119910 119908119886119905119890119903119905119900119905119886119897 ℎ119890119886119905 119901119903119900119889119906119888119890119889 lowast 100

ℎ119888 = 119867119890119886119905 119890119899119890119903119892119910 119903119890119902119906119894119903119890119889 119905119900 119887119900119894119897 119908119886119905119890119903 + 119864119899119890119903119892119910 119891119900119903 V119890119901119900119903119894119904119886119905119894119900119899119867119890119886119905 119890119899119890119903119892119910 119903119890119897119890119886119904119890119889 119887119910 119886 119892119894V119890119899 119902119906119886119899119905119894119905119910 119900119891 119891119906119890119897 119883 100

= 119872119908119862119908998779119879 +119872119908Vℎ119865119888119898119871119867119881 lowast 100

(18)

where Mw is mass of water in sauce pan Cw is specificheat capacity of water 998779T is local boiling temperature-initialtemperature of water (K) Fcm is fuel consumed (moist)(g) LHV is net calorific value (Jg) Mwv is mass of watervaporised (g) and h is specific enthalpy of vaporisation (Jg)For example for the 2nd test run the thermal efficiency wascalculated as

= 2875 lowast 4186 lowast (968 minus 245) + 100 lowast 2260125 lowast 29800 lowast 100= 294

(19)

While thermal efficiency is a well-known measure of stoveperformance better indicator may be sought especially dur-ing the low power phase of the water boiling test This isbecause a stove that is very slow to boil may have a very goodlooking thermal efficiency since large amount of water wasevaporated However the fuel used per water remaining maybe too high since somuch water was evaporated and somuchtime was taken while bringing the pot to a boil [20 21] Withrespect to this indicators such as specific consumption waterboiling rate fire power and fuel use reductionwere calculatedas well

The water boiling rate was obtained the following equa-tion

= 119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (119898119894119899)119864119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (20)

The water boiling rate for the 2nd test run was calculated as

= 432775 lowast 1000

= 1550 minltr(21)

Specific fuel consumption measures the amount of fuelrequired to boil (or simmer) 1 liter of water It is calculated(see (22)) by the equivalent dry fuel used minus the energyin the remaining charcoal divided by the liters of waterremaining at the end of the test [20 21]

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892)119890119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (22)

The specific fuel consumption for the 2nd test was obtainedusing (24) as

= 1252775 lowast 1000

= 4505 gliter water boiled(23)

Fire power a useful measure of the stoversquos heat output wasalso calculated following (24)

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892) lowast 119871119867119881(119869119892)119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (min) lowast 60 (24)

Journal of Renewable Energy 7

Table 3 Data fromWBT (see Figure S5 in the Supplementary Materials for comprehensive analysis)

sn Parameters Tests (n = 4)1 2 3 4 mean stdev

1 Mass of water boiled (g) 2925 2875 2850 2800 28625 520

2 Specific heat capacity ofwater (JgK) 4186 4186 4186 4186 4186 0

3 Water boilingtemperature (K) 3698 3698 3698 3698 3698 0

4 Initial water temperaturebefore test (K) 2977 2975 2948 2962 29655 134

5 Water vaporised (g) 100 100 75 100 9375 125

6 Latent heat ofveporisation (Jg) 2260 2260 2260 2260 2260 0

7 Fuel consumed (g) 150 125 100 145 130 23

8 Lower Heating Value ofchar (LHV) Jg 29800 29800 29800 29800 29800 0

9 Effective mass of waterboiled (g) 2825 2775 2775 2700 27688 5154

10 Time to boiling water(min) 4200 4300 3900 4000 4100 183

11 Fuel consumed (g) 150 125 100 145 130 2273

Table 4 Summary of results on thermal performance of the stove

Performanceindex

Unit ofmeasure

Tests (n = 4)Sn 1 2 3 4 MEAN STDEV

1 Thermalefficiency 248 294 357 252 288 51

2 Water boilingrate minltr 149 155 141 148 148 06

3 Specific fuelconsumption

gliter waterboiled 531 450 360 537 470 83

4 Fire power kW 177 144 127 180 157 026

5 Fuel UseReduction 761 797 838 758 788 37

The fire power for the 1st test run was calculated as follows

= 150 lowast 2980042 lowast 60= 17738W

(25)

Given the specific fuel consumption of 222 gliter water boiledfor the 3-stone stove (Kris De Decker 2015) the fuel usereduction attained by the developed improved cook stove wasestimated using

= 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) minus 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) lowast 100 (26)

For instance fuel use reduction in the 1st test run wascalculated as

= 222 minus 531222 lowast 100= 761

(27)

Table 4 shows a summary of results on stove performancesIt was found that after 4 test runs of the water boiling testthe designed improved stove had a mean thermal efficiencyof 288This means that 288 of the total energy producedby the fuel is used to boil water in the pot

Comparisons (Figure 5) were made with locally exist-ing stoves such as the Lorena stove brick stove Envirofit

8 Journal of Renewable Energy

Table 5 Comparisons between the cost of the granite rock stove and conventional stoves

StovePerformance

Cook stove technologies

13e GraniteRock Stove

Traditionalwood

burning

Improvedwood-burning

Traditionalcharcoal-burning

Improvedcharcoal-burning

Kerosene Propane(LPG) Electric Source

Capital Cost(US$) 36 5 ndash 50 3 ndash 6 3 ndash 50 10 ndash 60 60 ndash 120 100 ndash 500 Jeuland

andPattanayak

2012Efficiency (MJ usefulenergyMJproducedHeat)

288 7 - 15 13 - 40 18 - 21 15 - 37 40 - 50 50 - 60

0050

100150200250300350400

Designedprototype

Lorenastove

3-stonestove

Molded1-potstove

Trenchfire

Brickstove

Kenyaceramic

Jiko stove

Envirofitsupersaver

premiumcharcoal

stove

metalstove

Types of stoves

Ther

mal

effici

ency

()

Figure 5 Comparisons between thermal efficiencies of differentstoves

supersaver premium stove molded 1-pot stove Kenyaceramic jiko stovemetal stove trench fire and the traditional3-stone stove Previous studies [27 28] show that the above-mentioned stoves had thermal efficiency values of 14 17357 16 245 21 13 and 9 respectively

With a thermal efficiency of 288 the designed proto-type stove achieves tier 2 in the IWA tiers of performance[29] This shows a substantial improvement over the baselinetraditional 3-stone stove

36 Cost of the Granite Rock Cooking Stove versus Conven-tional Stoves Every household cooking system incurs differ-ent costs and benefits depending on diverse energy technolo-gies employed These costs are related to the capital cost ofa newly developed stove andor design modifications costof fuels required cost of stove distribution or marketingmoney and time spent for regular stove operation andmaintenance [30] In this study the capital cost of the graniterock stove was estimated at US$36 and compared favourablywith conventional charcoal burning stoves (US$3ndashUS$50) inaccordance with Jeuland and Pattanayak [30] (Table 5)

Given the fact that the granite rock stove depicts a rela-tively high thermal efficiency (288) and fuel use reduction(788) (Table 4) there is a higher likelihood for it to operateunder reduced cost making it cheaper than the conventionalstoves

4 Conclusions

The improved cooking stove was designed and fabricatedusing locally available materials including granite rocksstainless steel and glass wool and was estimated to cost US$

36 Based on its water boiling test results 788 fuel usereduction was achieved over the baseline open fire stoveThiswas attributed to the thermal retention storage propertiesof the granite rock The granite rock besides glass woolsignificantly contributed to the reduction on estimated heat(about 670kJ) that would be lost through the stove wallThis enhanced its thermal efficiency Based on compar-isons with performance standards and properties of theconventional stoves the designed granite rock stove is asubstantial improvement technology and can thus lessen thepressure put on forestry resources However further studiesincluding carbon and particulate matter (PM) emissions arerecommended for future design improvements to suit publichealth standards Studies on use of other forms of fuel such asbriquettes and wood chippings could as well be conducted toestablish fuel alternatives to charcoal

Data Availability

The data underlying the findings of this research can beaccessed on either the Uganda Christian University Hamu-Mukasa Library online catalogue or other online sourcesThe online sources among others include (i) httpswwwsafefuelandenergyorgfiles517-1pdf (ii) httpswwwunnedungpublicationsfilesimagesUSMAN20OJONIMI20YUSUFpdf (iii) httpswwwamazoncomHow-make--Kenyan-ceramic-jikodpB0007C8G84 and (iv) httpswwwpciaonlineorgtesting

Disclosure

Theauthors received no form of financing in the research andpublication of thiswork All financing directed for this projectwork was of their own resourcing

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors appreciate the intellectual input from all per-sons at the Department of Engineering and EnvironmentUganda Christian University their guidance helped to focus

Journal of Renewable Energy 3

Table 1 Thermal design assumptions for the cooking stove

No- Material Parameter Units Values Reference

1 Fuel (carbonised agro-wastebriquettes) Calorific value MJkg 217 Kiwana 2016

2 Charcoal Calorific value MJkg 298 Kiwana 20163 Water Density gltr 1000 Global Alliance for

Clean Cookstoves 20144 Water Specific heat capacity JgK 41865 Granite rock Thermal conductivity Wmminus1 Kminus1 268 Eppelbaum 20146 Air Thermal conductivity Wmminus1 Kminus1 002 Lienhard IV 20007 Stainless steel Thermal conductivity Wmminus1 Kminus1 16 Young 19928 Glass wool Thermal conductivity Wmminus1 Kminus1 004 Young 19929 Flame Theoretical Maximum temperature K 2123 Yusuf 201110 Cook stove Theoretical thermal efficiency 3511 Cook stove Energy loss 65

232 Water Absorption Test In line with AASHTO [18]the water absorption test was conducted to determine theamount of water absorbed under specified conditions Thisis mainly due to the effect water usually has on heat transferin rocks through conduction The data obtained thereforehelped shed light on the performance of the granite rockin humid environments During the experiment the graniterocks were hand crushed to 1410mm aggregates before thetest could be carried out Water absorption was expressed asincrease in weight percent based on (2) whereby A is weightof oven dry sample in air and B is weight of saturated surfacedry sample in air

119908119886119905119890119903 119886119887119904119900119903119901119905119894119900119899 = [(119861 minus 119860)119860 ] times 100 (2)

233 ermal Test of Granite Rock After lining the graniterock chamber with stainless steel charcoal fuel was ignitedwithin the combustion chamber The maximum temperaturereaching the granite rock (423 K) was attained after 41minutes on average and this was recorded

Samples of the rock were as well heated between roomtemperature (2978K) and 567K in anoven to determine theirability to withstand heat without disintegrating The rockswere heated and observations made for change in weight forthe granitematerial under testThiswas done at time intervalsof 20 minutes for 120 minutes with increasing temperaturein the oven Also the changes in the physical structure of therock were noted

234 Water Boiling Test (WBT) WBT assessed the overallperformance of a cookstove via three phases which consistedof (1) bringing water to a boil from a cold start (2) bringingwater to a boil when the stove is hot and (3) maintainingthe water at simmering temperatures In WBT experimentwater was heated to boiling point the time taken to boila given quantity of water specific firewood consumptionbesides evaluating thermal efficiency at both high and lowenergy input was doneThe test was conducted in accordancewith Volunteers in Technical Assistance [19]

Table 2 Summary of laboratory test results for specific gravityand water absorption tests (see Figure S1ndashS3 in the SupplementaryMaterials for comprehensive analysis)

Sample Test Identification Specificgravity

WaterAbsorption

()1410 mm Hand crushed aggregates 272 042

3 Results and Discussion

31 Classification of Granite Rock As presented in Table 2the specific gravity of the granite rock was found to be 272implying that the rock was of high density

Given the fact that there was little (042)water absorbedby the rock (Table 2) negligible amount of heat would berequired to drive it off Therefore the moisture content ofthe rock would not have any significant effect on its heatretention properties This makes it a suitable material for thestove construction

The effect of temperature on the physical properties of therock was also evaluated based on the practical experience ofconstructed stove operations and oven tests From the oventest experiment the granite rock recorded an initial temper-ature of 2978 K and mass of 40165g There was a gradualdecrease in mass with increasing temperature over time(Figure 1 see Figure S4 in the Supplementary Materials forcomprehensive analysis)

After 120 minutes of oven heating the granite rockrecorded a constant mass of 40121g at constant temperatureof 567 K indicating maximum moisture loss from the rockDespite the slight change in colour (dusty pale white) of therock there was no visible fracture observed Similarly themaximum temperature reaching the granite rock in theconstructed stove was recorded as 423 K (after 41 minutes ofoperation) at minimum moisture content (Figure 1) and nosign of fracture This implies that the granite rock would beable to perform in the stove without disintegrating aftersuccessive cooking times

4 Journal of Renewable Energy

273

323

373

423

473

523

573

623

4009401

4011401240134014401540164017

0 20 40 60 80 100 120

Tem

pera

ture

(K)

Mas

s of t

he ro

ck (g

)

Time (minutes)mass (g)Temperature (K)

Figure 1 Relationship between mass of granite rock and tempera-ture with time

32 Choice of Fuel for Experimental Design For the improvedstove design solid fuels were evaluated The selection toevaluate carbonised agrowaste briquettes and charcoal fuelswas taken based on local availability within Kampala district

Based on (3) we need to transmit 1538355J of energyto a pan to boil 49-liter of water (asymp 4900g) from roomtemperature (298 K) to 373 K (at sea level) given its specificheat capacity of 4186 JgK [20 21]

119867 = 119898119888120579 (3)

where H is the heat required m is the mass of substance and120579 is the temperature difference

(4186 Jg119870) x 4900g x (373119870-298119870)= 1 538 355J of energy to water

(4)

At 100 efficiency whereby all the fuel is transferred to thewater we would require

153835521700 = 7089 g of briquettes (5)

Assuming a thermal efficiency of 35 and energy loss of 652025g of briquette fuel would be required to boil 49 liters ofwater as shown below

7089035 = 2025 g of briquettes (6)

Therefore the fuel chamber needs to be designed to hold atleast 2025g of briquettes

Similarly 516g of charcoal with average calorific value= 298 MJKg = 29800Jg [16] would generate 1538355J ofenergy required to boil 49 liters of water (see (3)) if fuelconversion efficiency was 100

153835529800 = 516 g of charcoal (7)

For a thermal efficiency of 35 147g of charcoal fuel istherefore required as shown below

516035 = 147 g of charcoal (8)

Therefore the fuel chamber needs to be designed to hold 147gof charcoal

Since 100 efficiency is not practical for improved cookstoves the decision to use charcoal as a fuel for the stovedesign was based on a more practical 35 efficiency targetIt was observed that more briquettes would be requiredto achieve the same cooking task as charcoal Thereforecharcoal was a preferred choice of fuel

33 Design of the Stove Prototype The convective and con-ductive heat transfer through the stove wall were calculatedusing Fourierrsquos heat relation (see (9))

119876 = 119870119860(1198791 minus 1198792)119883 (9)

where Q is heat flow rate (Wm2) A is total cross-sectionalarea of conducting surface (m2) X is thickness of specimen(m) and T is temperature (K)According to Baldwin [22] use of Fourierrsquos heat equationfor examination of heat transfer across a stove wall generatesvalues that are too large This is because the heat transferredinto and out of an object depends not only on the conductivityto and from the surfaces but also on the conductivity withinthe object itself dirt or oxide layers and air at the surface ofthe material

Thus (9) is arranged using the thermal resistance conceptas shown in

119876 = 119860 (1198791 minus 1198792)1ℎ1 + 119909119870 + 1ℎ1 (10)

where h is the convective heat transfer obtained from

ℎ = 119860(998779119879119871 )lowast119887 (11)

A and b are constants depending on geometry andflow conditionsL denotes length

For vertical cylinders h = 131 (1358)13 [23]

= 1451Wm2K (12)

Given the height (179mm) and the diameter (375mm)Figure 2 the surface area of stove was estimated as 032 m2following (13)

119860 = 120587119903 (2ℎ + 119903)= 314 lowast 1875 (2 lowast 179 + 1875)= 321165125mm2 or 032m2

(13)

This value was used for only stainless steel since granite andfiber glass do not cover the bottom of the stove whereas forgranite and fiber glass the surface area was estimated using

119860 = 2120587119903ℎ= 2 lowast 314 lowast 1875 lowast 179= 2107725mm2 or 021m2

(14)

Journal of Renewable Energy 5

350

1000

2301702004

40

300

390R 17 cm

R 33 cm

R 39 cm

Figure 2 Plan and front elevation drawings of the designed stove (all dimensions in cm)

Taking theoretical maximum temperature = 2123 K [23] andbased on reasonable assumptions thermal conductivity ofgranite Kg = 268 WmK [24] fiber glass Kf = 004 WmK[25] and stainless steel Ks = 16 WmK [25] total resistancewas estimated as 9768 KWminus1 (see (15))

119879119900119905119886119897 119903119890119904119894119904119905119886119899119888119890 = 1ℎ1119860 + 3

119871119904119870119904119860 +

119871119891119870119891119860 +

119871119892119870119892119860

+ 1ℎ2119860

= 11451 lowast 032 + 3 lowast

0001516 lowast 032

+ 0078004 lowast 021 +

0023268 lowast 021

+ 11451 lowast 032

= 0215 + 879 lowast 10minus4 + 9296+ 0041 + 0215

= 9768KWminus1

(15)

Hence the energy lost by the stove would be 18612W basedon

119876 = 998779119879119879119900119905119886119897 119903119890119904119894119904119905119886119899119888119890 (16)

Using room temperature of 305K

= 2123 minus 3059768= 18189768

119876 = 18612W119876 = 18612 lowast 3600 = 670032119869

(17)

Yet it has been found that the stove would release a total of1538355J of energy to water at 100 efficiency (see (3)) Thisimplies that more than half (1538355 ndash 670032 = 868323J)of the energy produced by the charcoal fuel goes to the water

Figure 3 The stove made from granite rock

Thus the losses through the stove wall were workable for thestove design

34 Features of the Stove The stove (Figure 3) consists ofa combustion chamber (inner retort) constructed using a20mm thick stainless-steel material

The combustion chamber is designed to receive solidbiomass fuel (charcoal) and enhance complete combustionof combustible gas released during charcoal burning pro-cess The combustion chamber is imbedded in a cylinder(outer retort) constructed using granite rock and glass wool(Figure 4) The combustion chamber and outer retort aredesigned in a way that a 30mm gap is left in between toprovide a freemovement of air and enhance resistance to heattransfer to the inner wall of the outer retort This minimisesheat loss given the low thermal conductivity (16 Wm-1 K-1) of the granite rock and air (002 to 005 Wm-1 K-1)compared with stainless steel (16 to 64 Wm-1 K-1) usedin the construction of the combustion chamber [26] Thisleads to large amount of heat from the burning charcoal toconcentrate at the bottom of the cooking pan thus increasingthermal efficiency

35 ermal Performance of the Stove Indicators includingthermal efficiency water boiling rate specific fuel consump-tion fire power and fuel use reduction were used to evaluate

6 Journal of Renewable Energy

Stove Lining(Stainless steel)

Combustion Chamber

Air Inlet PerforationsAir gap

Stove Handle

Support

Granite Rock

Glass Wool

Air Inlet Gate Air Inlet Controller

Figure 4 Major components of the stove

the performance of the designed stove Data used in theevaluation (Table 3) were generated by WBT experimentusing a recommended protocol [19]

The thermal efficiency a measure of the fraction of heatproduced by the fuel that made it directly to the water in thepot [20 21] was calculated using

119874V119890119903119886119897119897 119890119891119891119894119888119894119890119899119888119910 = 119879119900119905119886119897 ℎ119890119886119905 119886119887119904119900119903119887119890119889 119887119910 119908119886119905119890119903119905119900119905119886119897 ℎ119890119886119905 119901119903119900119889119906119888119890119889 lowast 100

ℎ119888 = 119867119890119886119905 119890119899119890119903119892119910 119903119890119902119906119894119903119890119889 119905119900 119887119900119894119897 119908119886119905119890119903 + 119864119899119890119903119892119910 119891119900119903 V119890119901119900119903119894119904119886119905119894119900119899119867119890119886119905 119890119899119890119903119892119910 119903119890119897119890119886119904119890119889 119887119910 119886 119892119894V119890119899 119902119906119886119899119905119894119905119910 119900119891 119891119906119890119897 119883 100

= 119872119908119862119908998779119879 +119872119908Vℎ119865119888119898119871119867119881 lowast 100

(18)

where Mw is mass of water in sauce pan Cw is specificheat capacity of water 998779T is local boiling temperature-initialtemperature of water (K) Fcm is fuel consumed (moist)(g) LHV is net calorific value (Jg) Mwv is mass of watervaporised (g) and h is specific enthalpy of vaporisation (Jg)For example for the 2nd test run the thermal efficiency wascalculated as

= 2875 lowast 4186 lowast (968 minus 245) + 100 lowast 2260125 lowast 29800 lowast 100= 294

(19)

While thermal efficiency is a well-known measure of stoveperformance better indicator may be sought especially dur-ing the low power phase of the water boiling test This isbecause a stove that is very slow to boil may have a very goodlooking thermal efficiency since large amount of water wasevaporated However the fuel used per water remaining maybe too high since somuch water was evaporated and somuchtime was taken while bringing the pot to a boil [20 21] Withrespect to this indicators such as specific consumption waterboiling rate fire power and fuel use reductionwere calculatedas well

The water boiling rate was obtained the following equa-tion

= 119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (119898119894119899)119864119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (20)

The water boiling rate for the 2nd test run was calculated as

= 432775 lowast 1000

= 1550 minltr(21)

Specific fuel consumption measures the amount of fuelrequired to boil (or simmer) 1 liter of water It is calculated(see (22)) by the equivalent dry fuel used minus the energyin the remaining charcoal divided by the liters of waterremaining at the end of the test [20 21]

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892)119890119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (22)

The specific fuel consumption for the 2nd test was obtainedusing (24) as

= 1252775 lowast 1000

= 4505 gliter water boiled(23)

Fire power a useful measure of the stoversquos heat output wasalso calculated following (24)

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892) lowast 119871119867119881(119869119892)119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (min) lowast 60 (24)

Journal of Renewable Energy 7

Table 3 Data fromWBT (see Figure S5 in the Supplementary Materials for comprehensive analysis)

sn Parameters Tests (n = 4)1 2 3 4 mean stdev

1 Mass of water boiled (g) 2925 2875 2850 2800 28625 520

2 Specific heat capacity ofwater (JgK) 4186 4186 4186 4186 4186 0

3 Water boilingtemperature (K) 3698 3698 3698 3698 3698 0

4 Initial water temperaturebefore test (K) 2977 2975 2948 2962 29655 134

5 Water vaporised (g) 100 100 75 100 9375 125

6 Latent heat ofveporisation (Jg) 2260 2260 2260 2260 2260 0

7 Fuel consumed (g) 150 125 100 145 130 23

8 Lower Heating Value ofchar (LHV) Jg 29800 29800 29800 29800 29800 0

9 Effective mass of waterboiled (g) 2825 2775 2775 2700 27688 5154

10 Time to boiling water(min) 4200 4300 3900 4000 4100 183

11 Fuel consumed (g) 150 125 100 145 130 2273

Table 4 Summary of results on thermal performance of the stove

Performanceindex

Unit ofmeasure

Tests (n = 4)Sn 1 2 3 4 MEAN STDEV

1 Thermalefficiency 248 294 357 252 288 51

2 Water boilingrate minltr 149 155 141 148 148 06

3 Specific fuelconsumption

gliter waterboiled 531 450 360 537 470 83

4 Fire power kW 177 144 127 180 157 026

5 Fuel UseReduction 761 797 838 758 788 37

The fire power for the 1st test run was calculated as follows

= 150 lowast 2980042 lowast 60= 17738W

(25)

Given the specific fuel consumption of 222 gliter water boiledfor the 3-stone stove (Kris De Decker 2015) the fuel usereduction attained by the developed improved cook stove wasestimated using

= 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) minus 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) lowast 100 (26)

For instance fuel use reduction in the 1st test run wascalculated as

= 222 minus 531222 lowast 100= 761

(27)

Table 4 shows a summary of results on stove performancesIt was found that after 4 test runs of the water boiling testthe designed improved stove had a mean thermal efficiencyof 288This means that 288 of the total energy producedby the fuel is used to boil water in the pot

Comparisons (Figure 5) were made with locally exist-ing stoves such as the Lorena stove brick stove Envirofit

8 Journal of Renewable Energy

Table 5 Comparisons between the cost of the granite rock stove and conventional stoves

StovePerformance

Cook stove technologies

13e GraniteRock Stove

Traditionalwood

burning

Improvedwood-burning

Traditionalcharcoal-burning

Improvedcharcoal-burning

Kerosene Propane(LPG) Electric Source

Capital Cost(US$) 36 5 ndash 50 3 ndash 6 3 ndash 50 10 ndash 60 60 ndash 120 100 ndash 500 Jeuland

andPattanayak

2012Efficiency (MJ usefulenergyMJproducedHeat)

288 7 - 15 13 - 40 18 - 21 15 - 37 40 - 50 50 - 60

0050

100150200250300350400

Designedprototype

Lorenastove

3-stonestove

Molded1-potstove

Trenchfire

Brickstove

Kenyaceramic

Jiko stove

Envirofitsupersaver

premiumcharcoal

stove

metalstove

Types of stoves

Ther

mal

effici

ency

()

Figure 5 Comparisons between thermal efficiencies of differentstoves

supersaver premium stove molded 1-pot stove Kenyaceramic jiko stovemetal stove trench fire and the traditional3-stone stove Previous studies [27 28] show that the above-mentioned stoves had thermal efficiency values of 14 17357 16 245 21 13 and 9 respectively

With a thermal efficiency of 288 the designed proto-type stove achieves tier 2 in the IWA tiers of performance[29] This shows a substantial improvement over the baselinetraditional 3-stone stove

36 Cost of the Granite Rock Cooking Stove versus Conven-tional Stoves Every household cooking system incurs differ-ent costs and benefits depending on diverse energy technolo-gies employed These costs are related to the capital cost ofa newly developed stove andor design modifications costof fuels required cost of stove distribution or marketingmoney and time spent for regular stove operation andmaintenance [30] In this study the capital cost of the graniterock stove was estimated at US$36 and compared favourablywith conventional charcoal burning stoves (US$3ndashUS$50) inaccordance with Jeuland and Pattanayak [30] (Table 5)

Given the fact that the granite rock stove depicts a rela-tively high thermal efficiency (288) and fuel use reduction(788) (Table 4) there is a higher likelihood for it to operateunder reduced cost making it cheaper than the conventionalstoves

4 Conclusions

The improved cooking stove was designed and fabricatedusing locally available materials including granite rocksstainless steel and glass wool and was estimated to cost US$

36 Based on its water boiling test results 788 fuel usereduction was achieved over the baseline open fire stoveThiswas attributed to the thermal retention storage propertiesof the granite rock The granite rock besides glass woolsignificantly contributed to the reduction on estimated heat(about 670kJ) that would be lost through the stove wallThis enhanced its thermal efficiency Based on compar-isons with performance standards and properties of theconventional stoves the designed granite rock stove is asubstantial improvement technology and can thus lessen thepressure put on forestry resources However further studiesincluding carbon and particulate matter (PM) emissions arerecommended for future design improvements to suit publichealth standards Studies on use of other forms of fuel such asbriquettes and wood chippings could as well be conducted toestablish fuel alternatives to charcoal

Data Availability

The data underlying the findings of this research can beaccessed on either the Uganda Christian University Hamu-Mukasa Library online catalogue or other online sourcesThe online sources among others include (i) httpswwwsafefuelandenergyorgfiles517-1pdf (ii) httpswwwunnedungpublicationsfilesimagesUSMAN20OJONIMI20YUSUFpdf (iii) httpswwwamazoncomHow-make--Kenyan-ceramic-jikodpB0007C8G84 and (iv) httpswwwpciaonlineorgtesting

Disclosure

Theauthors received no form of financing in the research andpublication of thiswork All financing directed for this projectwork was of their own resourcing

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors appreciate the intellectual input from all per-sons at the Department of Engineering and EnvironmentUganda Christian University their guidance helped to focus

4 Journal of Renewable Energy

273

323

373

423

473

523

573

623

4009401

4011401240134014401540164017

0 20 40 60 80 100 120

Tem

pera

ture

(K)

Mas

s of t

he ro

ck (g

)

Time (minutes)mass (g)Temperature (K)

Figure 1 Relationship between mass of granite rock and tempera-ture with time

32 Choice of Fuel for Experimental Design For the improvedstove design solid fuels were evaluated The selection toevaluate carbonised agrowaste briquettes and charcoal fuelswas taken based on local availability within Kampala district

Based on (3) we need to transmit 1538355J of energyto a pan to boil 49-liter of water (asymp 4900g) from roomtemperature (298 K) to 373 K (at sea level) given its specificheat capacity of 4186 JgK [20 21]

119867 = 119898119888120579 (3)

where H is the heat required m is the mass of substance and120579 is the temperature difference

(4186 Jg119870) x 4900g x (373119870-298119870)= 1 538 355J of energy to water

(4)

At 100 efficiency whereby all the fuel is transferred to thewater we would require

153835521700 = 7089 g of briquettes (5)

Assuming a thermal efficiency of 35 and energy loss of 652025g of briquette fuel would be required to boil 49 liters ofwater as shown below

7089035 = 2025 g of briquettes (6)

Therefore the fuel chamber needs to be designed to hold atleast 2025g of briquettes

Similarly 516g of charcoal with average calorific value= 298 MJKg = 29800Jg [16] would generate 1538355J ofenergy required to boil 49 liters of water (see (3)) if fuelconversion efficiency was 100

153835529800 = 516 g of charcoal (7)

For a thermal efficiency of 35 147g of charcoal fuel istherefore required as shown below

516035 = 147 g of charcoal (8)

Therefore the fuel chamber needs to be designed to hold 147gof charcoal

Since 100 efficiency is not practical for improved cookstoves the decision to use charcoal as a fuel for the stovedesign was based on a more practical 35 efficiency targetIt was observed that more briquettes would be requiredto achieve the same cooking task as charcoal Thereforecharcoal was a preferred choice of fuel

33 Design of the Stove Prototype The convective and con-ductive heat transfer through the stove wall were calculatedusing Fourierrsquos heat relation (see (9))

119876 = 119870119860(1198791 minus 1198792)119883 (9)

where Q is heat flow rate (Wm2) A is total cross-sectionalarea of conducting surface (m2) X is thickness of specimen(m) and T is temperature (K)According to Baldwin [22] use of Fourierrsquos heat equationfor examination of heat transfer across a stove wall generatesvalues that are too large This is because the heat transferredinto and out of an object depends not only on the conductivityto and from the surfaces but also on the conductivity withinthe object itself dirt or oxide layers and air at the surface ofthe material

Thus (9) is arranged using the thermal resistance conceptas shown in

119876 = 119860 (1198791 minus 1198792)1ℎ1 + 119909119870 + 1ℎ1 (10)

where h is the convective heat transfer obtained from

ℎ = 119860(998779119879119871 )lowast119887 (11)

A and b are constants depending on geometry andflow conditionsL denotes length

For vertical cylinders h = 131 (1358)13 [23]

= 1451Wm2K (12)

Given the height (179mm) and the diameter (375mm)Figure 2 the surface area of stove was estimated as 032 m2following (13)

119860 = 120587119903 (2ℎ + 119903)= 314 lowast 1875 (2 lowast 179 + 1875)= 321165125mm2 or 032m2

(13)

This value was used for only stainless steel since granite andfiber glass do not cover the bottom of the stove whereas forgranite and fiber glass the surface area was estimated using

119860 = 2120587119903ℎ= 2 lowast 314 lowast 1875 lowast 179= 2107725mm2 or 021m2

(14)

Journal of Renewable Energy 5

350

1000

2301702004

40

300

390R 17 cm

R 33 cm

R 39 cm

Figure 2 Plan and front elevation drawings of the designed stove (all dimensions in cm)

Taking theoretical maximum temperature = 2123 K [23] andbased on reasonable assumptions thermal conductivity ofgranite Kg = 268 WmK [24] fiber glass Kf = 004 WmK[25] and stainless steel Ks = 16 WmK [25] total resistancewas estimated as 9768 KWminus1 (see (15))

119879119900119905119886119897 119903119890119904119894119904119905119886119899119888119890 = 1ℎ1119860 + 3

119871119904119870119904119860 +

119871119891119870119891119860 +

119871119892119870119892119860

+ 1ℎ2119860

= 11451 lowast 032 + 3 lowast

0001516 lowast 032

+ 0078004 lowast 021 +

0023268 lowast 021

+ 11451 lowast 032

= 0215 + 879 lowast 10minus4 + 9296+ 0041 + 0215

= 9768KWminus1

(15)

Hence the energy lost by the stove would be 18612W basedon

119876 = 998779119879119879119900119905119886119897 119903119890119904119894119904119905119886119899119888119890 (16)

Using room temperature of 305K

= 2123 minus 3059768= 18189768

119876 = 18612W119876 = 18612 lowast 3600 = 670032119869

(17)

Yet it has been found that the stove would release a total of1538355J of energy to water at 100 efficiency (see (3)) Thisimplies that more than half (1538355 ndash 670032 = 868323J)of the energy produced by the charcoal fuel goes to the water

Figure 3 The stove made from granite rock

Thus the losses through the stove wall were workable for thestove design

34 Features of the Stove The stove (Figure 3) consists ofa combustion chamber (inner retort) constructed using a20mm thick stainless-steel material

The combustion chamber is designed to receive solidbiomass fuel (charcoal) and enhance complete combustionof combustible gas released during charcoal burning pro-cess The combustion chamber is imbedded in a cylinder(outer retort) constructed using granite rock and glass wool(Figure 4) The combustion chamber and outer retort aredesigned in a way that a 30mm gap is left in between toprovide a freemovement of air and enhance resistance to heattransfer to the inner wall of the outer retort This minimisesheat loss given the low thermal conductivity (16 Wm-1 K-1) of the granite rock and air (002 to 005 Wm-1 K-1)compared with stainless steel (16 to 64 Wm-1 K-1) usedin the construction of the combustion chamber [26] Thisleads to large amount of heat from the burning charcoal toconcentrate at the bottom of the cooking pan thus increasingthermal efficiency

35 ermal Performance of the Stove Indicators includingthermal efficiency water boiling rate specific fuel consump-tion fire power and fuel use reduction were used to evaluate

6 Journal of Renewable Energy

Stove Lining(Stainless steel)

Combustion Chamber

Air Inlet PerforationsAir gap

Stove Handle

Support

Granite Rock

Glass Wool

Air Inlet Gate Air Inlet Controller

Figure 4 Major components of the stove

the performance of the designed stove Data used in theevaluation (Table 3) were generated by WBT experimentusing a recommended protocol [19]

The thermal efficiency a measure of the fraction of heatproduced by the fuel that made it directly to the water in thepot [20 21] was calculated using

119874V119890119903119886119897119897 119890119891119891119894119888119894119890119899119888119910 = 119879119900119905119886119897 ℎ119890119886119905 119886119887119904119900119903119887119890119889 119887119910 119908119886119905119890119903119905119900119905119886119897 ℎ119890119886119905 119901119903119900119889119906119888119890119889 lowast 100

ℎ119888 = 119867119890119886119905 119890119899119890119903119892119910 119903119890119902119906119894119903119890119889 119905119900 119887119900119894119897 119908119886119905119890119903 + 119864119899119890119903119892119910 119891119900119903 V119890119901119900119903119894119904119886119905119894119900119899119867119890119886119905 119890119899119890119903119892119910 119903119890119897119890119886119904119890119889 119887119910 119886 119892119894V119890119899 119902119906119886119899119905119894119905119910 119900119891 119891119906119890119897 119883 100

= 119872119908119862119908998779119879 +119872119908Vℎ119865119888119898119871119867119881 lowast 100

(18)

where Mw is mass of water in sauce pan Cw is specificheat capacity of water 998779T is local boiling temperature-initialtemperature of water (K) Fcm is fuel consumed (moist)(g) LHV is net calorific value (Jg) Mwv is mass of watervaporised (g) and h is specific enthalpy of vaporisation (Jg)For example for the 2nd test run the thermal efficiency wascalculated as

= 2875 lowast 4186 lowast (968 minus 245) + 100 lowast 2260125 lowast 29800 lowast 100= 294

(19)

While thermal efficiency is a well-known measure of stoveperformance better indicator may be sought especially dur-ing the low power phase of the water boiling test This isbecause a stove that is very slow to boil may have a very goodlooking thermal efficiency since large amount of water wasevaporated However the fuel used per water remaining maybe too high since somuch water was evaporated and somuchtime was taken while bringing the pot to a boil [20 21] Withrespect to this indicators such as specific consumption waterboiling rate fire power and fuel use reductionwere calculatedas well

The water boiling rate was obtained the following equa-tion

= 119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (119898119894119899)119864119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (20)

The water boiling rate for the 2nd test run was calculated as

= 432775 lowast 1000

= 1550 minltr(21)

Specific fuel consumption measures the amount of fuelrequired to boil (or simmer) 1 liter of water It is calculated(see (22)) by the equivalent dry fuel used minus the energyin the remaining charcoal divided by the liters of waterremaining at the end of the test [20 21]

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892)119890119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (22)

The specific fuel consumption for the 2nd test was obtainedusing (24) as

= 1252775 lowast 1000

= 4505 gliter water boiled(23)

Fire power a useful measure of the stoversquos heat output wasalso calculated following (24)

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892) lowast 119871119867119881(119869119892)119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (min) lowast 60 (24)

Journal of Renewable Energy 7

Table 3 Data fromWBT (see Figure S5 in the Supplementary Materials for comprehensive analysis)

sn Parameters Tests (n = 4)1 2 3 4 mean stdev

1 Mass of water boiled (g) 2925 2875 2850 2800 28625 520

2 Specific heat capacity ofwater (JgK) 4186 4186 4186 4186 4186 0

3 Water boilingtemperature (K) 3698 3698 3698 3698 3698 0

4 Initial water temperaturebefore test (K) 2977 2975 2948 2962 29655 134

5 Water vaporised (g) 100 100 75 100 9375 125

6 Latent heat ofveporisation (Jg) 2260 2260 2260 2260 2260 0

7 Fuel consumed (g) 150 125 100 145 130 23

8 Lower Heating Value ofchar (LHV) Jg 29800 29800 29800 29800 29800 0

9 Effective mass of waterboiled (g) 2825 2775 2775 2700 27688 5154

10 Time to boiling water(min) 4200 4300 3900 4000 4100 183

11 Fuel consumed (g) 150 125 100 145 130 2273

Table 4 Summary of results on thermal performance of the stove

Performanceindex

Unit ofmeasure

Tests (n = 4)Sn 1 2 3 4 MEAN STDEV

1 Thermalefficiency 248 294 357 252 288 51

2 Water boilingrate minltr 149 155 141 148 148 06

3 Specific fuelconsumption

gliter waterboiled 531 450 360 537 470 83

4 Fire power kW 177 144 127 180 157 026

5 Fuel UseReduction 761 797 838 758 788 37

The fire power for the 1st test run was calculated as follows

= 150 lowast 2980042 lowast 60= 17738W

(25)

Given the specific fuel consumption of 222 gliter water boiledfor the 3-stone stove (Kris De Decker 2015) the fuel usereduction attained by the developed improved cook stove wasestimated using

= 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) minus 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) lowast 100 (26)

For instance fuel use reduction in the 1st test run wascalculated as

= 222 minus 531222 lowast 100= 761

(27)

Table 4 shows a summary of results on stove performancesIt was found that after 4 test runs of the water boiling testthe designed improved stove had a mean thermal efficiencyof 288This means that 288 of the total energy producedby the fuel is used to boil water in the pot

Comparisons (Figure 5) were made with locally exist-ing stoves such as the Lorena stove brick stove Envirofit

8 Journal of Renewable Energy

Table 5 Comparisons between the cost of the granite rock stove and conventional stoves

StovePerformance

Cook stove technologies

13e GraniteRock Stove

Traditionalwood

burning

Improvedwood-burning

Traditionalcharcoal-burning

Improvedcharcoal-burning

Kerosene Propane(LPG) Electric Source

Capital Cost(US$) 36 5 ndash 50 3 ndash 6 3 ndash 50 10 ndash 60 60 ndash 120 100 ndash 500 Jeuland

andPattanayak

2012Efficiency (MJ usefulenergyMJproducedHeat)

288 7 - 15 13 - 40 18 - 21 15 - 37 40 - 50 50 - 60

0050

100150200250300350400

Designedprototype

Lorenastove

3-stonestove

Molded1-potstove

Trenchfire

Brickstove

Kenyaceramic

Jiko stove

Envirofitsupersaver

premiumcharcoal

stove

metalstove

Types of stoves

Ther

mal

effici

ency

()

Figure 5 Comparisons between thermal efficiencies of differentstoves

supersaver premium stove molded 1-pot stove Kenyaceramic jiko stovemetal stove trench fire and the traditional3-stone stove Previous studies [27 28] show that the above-mentioned stoves had thermal efficiency values of 14 17357 16 245 21 13 and 9 respectively

With a thermal efficiency of 288 the designed proto-type stove achieves tier 2 in the IWA tiers of performance[29] This shows a substantial improvement over the baselinetraditional 3-stone stove

36 Cost of the Granite Rock Cooking Stove versus Conven-tional Stoves Every household cooking system incurs differ-ent costs and benefits depending on diverse energy technolo-gies employed These costs are related to the capital cost ofa newly developed stove andor design modifications costof fuels required cost of stove distribution or marketingmoney and time spent for regular stove operation andmaintenance [30] In this study the capital cost of the graniterock stove was estimated at US$36 and compared favourablywith conventional charcoal burning stoves (US$3ndashUS$50) inaccordance with Jeuland and Pattanayak [30] (Table 5)

Given the fact that the granite rock stove depicts a rela-tively high thermal efficiency (288) and fuel use reduction(788) (Table 4) there is a higher likelihood for it to operateunder reduced cost making it cheaper than the conventionalstoves

4 Conclusions

The improved cooking stove was designed and fabricatedusing locally available materials including granite rocksstainless steel and glass wool and was estimated to cost US$

36 Based on its water boiling test results 788 fuel usereduction was achieved over the baseline open fire stoveThiswas attributed to the thermal retention storage propertiesof the granite rock The granite rock besides glass woolsignificantly contributed to the reduction on estimated heat(about 670kJ) that would be lost through the stove wallThis enhanced its thermal efficiency Based on compar-isons with performance standards and properties of theconventional stoves the designed granite rock stove is asubstantial improvement technology and can thus lessen thepressure put on forestry resources However further studiesincluding carbon and particulate matter (PM) emissions arerecommended for future design improvements to suit publichealth standards Studies on use of other forms of fuel such asbriquettes and wood chippings could as well be conducted toestablish fuel alternatives to charcoal

Data Availability

The data underlying the findings of this research can beaccessed on either the Uganda Christian University Hamu-Mukasa Library online catalogue or other online sourcesThe online sources among others include (i) httpswwwsafefuelandenergyorgfiles517-1pdf (ii) httpswwwunnedungpublicationsfilesimagesUSMAN20OJONIMI20YUSUFpdf (iii) httpswwwamazoncomHow-make--Kenyan-ceramic-jikodpB0007C8G84 and (iv) httpswwwpciaonlineorgtesting

Disclosure

Theauthors received no form of financing in the research andpublication of thiswork All financing directed for this projectwork was of their own resourcing

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors appreciate the intellectual input from all per-sons at the Department of Engineering and EnvironmentUganda Christian University their guidance helped to focus

Journal of Renewable Energy 5

350

1000

2301702004

40

300

390R 17 cm

R 33 cm

R 39 cm

Figure 2 Plan and front elevation drawings of the designed stove (all dimensions in cm)

Taking theoretical maximum temperature = 2123 K [23] andbased on reasonable assumptions thermal conductivity ofgranite Kg = 268 WmK [24] fiber glass Kf = 004 WmK[25] and stainless steel Ks = 16 WmK [25] total resistancewas estimated as 9768 KWminus1 (see (15))

119879119900119905119886119897 119903119890119904119894119904119905119886119899119888119890 = 1ℎ1119860 + 3

119871119904119870119904119860 +

119871119891119870119891119860 +

119871119892119870119892119860

+ 1ℎ2119860

= 11451 lowast 032 + 3 lowast

0001516 lowast 032

+ 0078004 lowast 021 +

0023268 lowast 021

+ 11451 lowast 032

= 0215 + 879 lowast 10minus4 + 9296+ 0041 + 0215

= 9768KWminus1

(15)

Hence the energy lost by the stove would be 18612W basedon

119876 = 998779119879119879119900119905119886119897 119903119890119904119894119904119905119886119899119888119890 (16)

Using room temperature of 305K

= 2123 minus 3059768= 18189768

119876 = 18612W119876 = 18612 lowast 3600 = 670032119869

(17)

Yet it has been found that the stove would release a total of1538355J of energy to water at 100 efficiency (see (3)) Thisimplies that more than half (1538355 ndash 670032 = 868323J)of the energy produced by the charcoal fuel goes to the water

Figure 3 The stove made from granite rock

Thus the losses through the stove wall were workable for thestove design

34 Features of the Stove The stove (Figure 3) consists ofa combustion chamber (inner retort) constructed using a20mm thick stainless-steel material

The combustion chamber is designed to receive solidbiomass fuel (charcoal) and enhance complete combustionof combustible gas released during charcoal burning pro-cess The combustion chamber is imbedded in a cylinder(outer retort) constructed using granite rock and glass wool(Figure 4) The combustion chamber and outer retort aredesigned in a way that a 30mm gap is left in between toprovide a freemovement of air and enhance resistance to heattransfer to the inner wall of the outer retort This minimisesheat loss given the low thermal conductivity (16 Wm-1 K-1) of the granite rock and air (002 to 005 Wm-1 K-1)compared with stainless steel (16 to 64 Wm-1 K-1) usedin the construction of the combustion chamber [26] Thisleads to large amount of heat from the burning charcoal toconcentrate at the bottom of the cooking pan thus increasingthermal efficiency

35 ermal Performance of the Stove Indicators includingthermal efficiency water boiling rate specific fuel consump-tion fire power and fuel use reduction were used to evaluate

6 Journal of Renewable Energy

Stove Lining(Stainless steel)

Combustion Chamber

Air Inlet PerforationsAir gap

Stove Handle

Support

Granite Rock

Glass Wool

Air Inlet Gate Air Inlet Controller

Figure 4 Major components of the stove

the performance of the designed stove Data used in theevaluation (Table 3) were generated by WBT experimentusing a recommended protocol [19]

The thermal efficiency a measure of the fraction of heatproduced by the fuel that made it directly to the water in thepot [20 21] was calculated using

119874V119890119903119886119897119897 119890119891119891119894119888119894119890119899119888119910 = 119879119900119905119886119897 ℎ119890119886119905 119886119887119904119900119903119887119890119889 119887119910 119908119886119905119890119903119905119900119905119886119897 ℎ119890119886119905 119901119903119900119889119906119888119890119889 lowast 100

ℎ119888 = 119867119890119886119905 119890119899119890119903119892119910 119903119890119902119906119894119903119890119889 119905119900 119887119900119894119897 119908119886119905119890119903 + 119864119899119890119903119892119910 119891119900119903 V119890119901119900119903119894119904119886119905119894119900119899119867119890119886119905 119890119899119890119903119892119910 119903119890119897119890119886119904119890119889 119887119910 119886 119892119894V119890119899 119902119906119886119899119905119894119905119910 119900119891 119891119906119890119897 119883 100

= 119872119908119862119908998779119879 +119872119908Vℎ119865119888119898119871119867119881 lowast 100

(18)

where Mw is mass of water in sauce pan Cw is specificheat capacity of water 998779T is local boiling temperature-initialtemperature of water (K) Fcm is fuel consumed (moist)(g) LHV is net calorific value (Jg) Mwv is mass of watervaporised (g) and h is specific enthalpy of vaporisation (Jg)For example for the 2nd test run the thermal efficiency wascalculated as

= 2875 lowast 4186 lowast (968 minus 245) + 100 lowast 2260125 lowast 29800 lowast 100= 294

(19)

While thermal efficiency is a well-known measure of stoveperformance better indicator may be sought especially dur-ing the low power phase of the water boiling test This isbecause a stove that is very slow to boil may have a very goodlooking thermal efficiency since large amount of water wasevaporated However the fuel used per water remaining maybe too high since somuch water was evaporated and somuchtime was taken while bringing the pot to a boil [20 21] Withrespect to this indicators such as specific consumption waterboiling rate fire power and fuel use reductionwere calculatedas well

The water boiling rate was obtained the following equa-tion

= 119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (119898119894119899)119864119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (20)

The water boiling rate for the 2nd test run was calculated as

= 432775 lowast 1000

= 1550 minltr(21)

Specific fuel consumption measures the amount of fuelrequired to boil (or simmer) 1 liter of water It is calculated(see (22)) by the equivalent dry fuel used minus the energyin the remaining charcoal divided by the liters of waterremaining at the end of the test [20 21]

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892)119890119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (22)

The specific fuel consumption for the 2nd test was obtainedusing (24) as

= 1252775 lowast 1000

= 4505 gliter water boiled(23)

Fire power a useful measure of the stoversquos heat output wasalso calculated following (24)

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892) lowast 119871119867119881(119869119892)119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (min) lowast 60 (24)

Journal of Renewable Energy 7

Table 3 Data fromWBT (see Figure S5 in the Supplementary Materials for comprehensive analysis)

sn Parameters Tests (n = 4)1 2 3 4 mean stdev

1 Mass of water boiled (g) 2925 2875 2850 2800 28625 520

2 Specific heat capacity ofwater (JgK) 4186 4186 4186 4186 4186 0

3 Water boilingtemperature (K) 3698 3698 3698 3698 3698 0

4 Initial water temperaturebefore test (K) 2977 2975 2948 2962 29655 134

5 Water vaporised (g) 100 100 75 100 9375 125

6 Latent heat ofveporisation (Jg) 2260 2260 2260 2260 2260 0

7 Fuel consumed (g) 150 125 100 145 130 23

8 Lower Heating Value ofchar (LHV) Jg 29800 29800 29800 29800 29800 0

9 Effective mass of waterboiled (g) 2825 2775 2775 2700 27688 5154

10 Time to boiling water(min) 4200 4300 3900 4000 4100 183

11 Fuel consumed (g) 150 125 100 145 130 2273

Table 4 Summary of results on thermal performance of the stove

Performanceindex

Unit ofmeasure

Tests (n = 4)Sn 1 2 3 4 MEAN STDEV

1 Thermalefficiency 248 294 357 252 288 51

2 Water boilingrate minltr 149 155 141 148 148 06

3 Specific fuelconsumption

gliter waterboiled 531 450 360 537 470 83

4 Fire power kW 177 144 127 180 157 026

5 Fuel UseReduction 761 797 838 758 788 37

The fire power for the 1st test run was calculated as follows

= 150 lowast 2980042 lowast 60= 17738W

(25)

Given the specific fuel consumption of 222 gliter water boiledfor the 3-stone stove (Kris De Decker 2015) the fuel usereduction attained by the developed improved cook stove wasestimated using

= 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) minus 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) lowast 100 (26)

For instance fuel use reduction in the 1st test run wascalculated as

= 222 minus 531222 lowast 100= 761

(27)

Table 4 shows a summary of results on stove performancesIt was found that after 4 test runs of the water boiling testthe designed improved stove had a mean thermal efficiencyof 288This means that 288 of the total energy producedby the fuel is used to boil water in the pot

Comparisons (Figure 5) were made with locally exist-ing stoves such as the Lorena stove brick stove Envirofit

8 Journal of Renewable Energy

Table 5 Comparisons between the cost of the granite rock stove and conventional stoves

StovePerformance

Cook stove technologies

13e GraniteRock Stove

Traditionalwood

burning

Improvedwood-burning

Traditionalcharcoal-burning

Improvedcharcoal-burning

Kerosene Propane(LPG) Electric Source

Capital Cost(US$) 36 5 ndash 50 3 ndash 6 3 ndash 50 10 ndash 60 60 ndash 120 100 ndash 500 Jeuland

andPattanayak

2012Efficiency (MJ usefulenergyMJproducedHeat)

288 7 - 15 13 - 40 18 - 21 15 - 37 40 - 50 50 - 60

0050

100150200250300350400

Designedprototype

Lorenastove

3-stonestove

Molded1-potstove

Trenchfire

Brickstove

Kenyaceramic

Jiko stove

Envirofitsupersaver

premiumcharcoal

stove

metalstove

Types of stoves

Ther

mal

effici

ency

()

Figure 5 Comparisons between thermal efficiencies of differentstoves

supersaver premium stove molded 1-pot stove Kenyaceramic jiko stovemetal stove trench fire and the traditional3-stone stove Previous studies [27 28] show that the above-mentioned stoves had thermal efficiency values of 14 17357 16 245 21 13 and 9 respectively

With a thermal efficiency of 288 the designed proto-type stove achieves tier 2 in the IWA tiers of performance[29] This shows a substantial improvement over the baselinetraditional 3-stone stove

36 Cost of the Granite Rock Cooking Stove versus Conven-tional Stoves Every household cooking system incurs differ-ent costs and benefits depending on diverse energy technolo-gies employed These costs are related to the capital cost ofa newly developed stove andor design modifications costof fuels required cost of stove distribution or marketingmoney and time spent for regular stove operation andmaintenance [30] In this study the capital cost of the graniterock stove was estimated at US$36 and compared favourablywith conventional charcoal burning stoves (US$3ndashUS$50) inaccordance with Jeuland and Pattanayak [30] (Table 5)

Given the fact that the granite rock stove depicts a rela-tively high thermal efficiency (288) and fuel use reduction(788) (Table 4) there is a higher likelihood for it to operateunder reduced cost making it cheaper than the conventionalstoves

4 Conclusions

The improved cooking stove was designed and fabricatedusing locally available materials including granite rocksstainless steel and glass wool and was estimated to cost US$

36 Based on its water boiling test results 788 fuel usereduction was achieved over the baseline open fire stoveThiswas attributed to the thermal retention storage propertiesof the granite rock The granite rock besides glass woolsignificantly contributed to the reduction on estimated heat(about 670kJ) that would be lost through the stove wallThis enhanced its thermal efficiency Based on compar-isons with performance standards and properties of theconventional stoves the designed granite rock stove is asubstantial improvement technology and can thus lessen thepressure put on forestry resources However further studiesincluding carbon and particulate matter (PM) emissions arerecommended for future design improvements to suit publichealth standards Studies on use of other forms of fuel such asbriquettes and wood chippings could as well be conducted toestablish fuel alternatives to charcoal

Data Availability

The data underlying the findings of this research can beaccessed on either the Uganda Christian University Hamu-Mukasa Library online catalogue or other online sourcesThe online sources among others include (i) httpswwwsafefuelandenergyorgfiles517-1pdf (ii) httpswwwunnedungpublicationsfilesimagesUSMAN20OJONIMI20YUSUFpdf (iii) httpswwwamazoncomHow-make--Kenyan-ceramic-jikodpB0007C8G84 and (iv) httpswwwpciaonlineorgtesting

Disclosure

Theauthors received no form of financing in the research andpublication of thiswork All financing directed for this projectwork was of their own resourcing

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors appreciate the intellectual input from all per-sons at the Department of Engineering and EnvironmentUganda Christian University their guidance helped to focus

6 Journal of Renewable Energy

Stove Lining(Stainless steel)

Combustion Chamber

Air Inlet PerforationsAir gap

Stove Handle

Support

Granite Rock

Glass Wool

Air Inlet Gate Air Inlet Controller

Figure 4 Major components of the stove

the performance of the designed stove Data used in theevaluation (Table 3) were generated by WBT experimentusing a recommended protocol [19]

The thermal efficiency a measure of the fraction of heatproduced by the fuel that made it directly to the water in thepot [20 21] was calculated using

119874V119890119903119886119897119897 119890119891119891119894119888119894119890119899119888119910 = 119879119900119905119886119897 ℎ119890119886119905 119886119887119904119900119903119887119890119889 119887119910 119908119886119905119890119903119905119900119905119886119897 ℎ119890119886119905 119901119903119900119889119906119888119890119889 lowast 100

ℎ119888 = 119867119890119886119905 119890119899119890119903119892119910 119903119890119902119906119894119903119890119889 119905119900 119887119900119894119897 119908119886119905119890119903 + 119864119899119890119903119892119910 119891119900119903 V119890119901119900119903119894119904119886119905119894119900119899119867119890119886119905 119890119899119890119903119892119910 119903119890119897119890119886119904119890119889 119887119910 119886 119892119894V119890119899 119902119906119886119899119905119894119905119910 119900119891 119891119906119890119897 119883 100

= 119872119908119862119908998779119879 +119872119908Vℎ119865119888119898119871119867119881 lowast 100

(18)

where Mw is mass of water in sauce pan Cw is specificheat capacity of water 998779T is local boiling temperature-initialtemperature of water (K) Fcm is fuel consumed (moist)(g) LHV is net calorific value (Jg) Mwv is mass of watervaporised (g) and h is specific enthalpy of vaporisation (Jg)For example for the 2nd test run the thermal efficiency wascalculated as

= 2875 lowast 4186 lowast (968 minus 245) + 100 lowast 2260125 lowast 29800 lowast 100= 294

(19)

While thermal efficiency is a well-known measure of stoveperformance better indicator may be sought especially dur-ing the low power phase of the water boiling test This isbecause a stove that is very slow to boil may have a very goodlooking thermal efficiency since large amount of water wasevaporated However the fuel used per water remaining maybe too high since somuch water was evaporated and somuchtime was taken while bringing the pot to a boil [20 21] Withrespect to this indicators such as specific consumption waterboiling rate fire power and fuel use reductionwere calculatedas well

The water boiling rate was obtained the following equa-tion

= 119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (119898119894119899)119864119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (20)

The water boiling rate for the 2nd test run was calculated as

= 432775 lowast 1000

= 1550 minltr(21)

Specific fuel consumption measures the amount of fuelrequired to boil (or simmer) 1 liter of water It is calculated(see (22)) by the equivalent dry fuel used minus the energyin the remaining charcoal divided by the liters of waterremaining at the end of the test [20 21]

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892)119890119891119891119890119888119905119894V119890 119898119886119904119904 119900119891 119908119886119905119890119903 119887119900119894119897119890119889 (119892) lowast 1000 (22)

The specific fuel consumption for the 2nd test was obtainedusing (24) as

= 1252775 lowast 1000

= 4505 gliter water boiled(23)

Fire power a useful measure of the stoversquos heat output wasalso calculated following (24)

= 119891119906119890119897 119888119900119899119904119906119898119890119889 (119892) lowast 119871119867119881(119869119892)119905119894119898119890 119905119900 119887119900119894119897 119908119886119905119890119903 (min) lowast 60 (24)

Journal of Renewable Energy 7

Table 3 Data fromWBT (see Figure S5 in the Supplementary Materials for comprehensive analysis)

sn Parameters Tests (n = 4)1 2 3 4 mean stdev

1 Mass of water boiled (g) 2925 2875 2850 2800 28625 520

2 Specific heat capacity ofwater (JgK) 4186 4186 4186 4186 4186 0

3 Water boilingtemperature (K) 3698 3698 3698 3698 3698 0

4 Initial water temperaturebefore test (K) 2977 2975 2948 2962 29655 134

5 Water vaporised (g) 100 100 75 100 9375 125

6 Latent heat ofveporisation (Jg) 2260 2260 2260 2260 2260 0

7 Fuel consumed (g) 150 125 100 145 130 23

8 Lower Heating Value ofchar (LHV) Jg 29800 29800 29800 29800 29800 0

9 Effective mass of waterboiled (g) 2825 2775 2775 2700 27688 5154

10 Time to boiling water(min) 4200 4300 3900 4000 4100 183

11 Fuel consumed (g) 150 125 100 145 130 2273

Table 4 Summary of results on thermal performance of the stove

Performanceindex

Unit ofmeasure

Tests (n = 4)Sn 1 2 3 4 MEAN STDEV

1 Thermalefficiency 248 294 357 252 288 51

2 Water boilingrate minltr 149 155 141 148 148 06

3 Specific fuelconsumption

gliter waterboiled 531 450 360 537 470 83

4 Fire power kW 177 144 127 180 157 026

5 Fuel UseReduction 761 797 838 758 788 37

The fire power for the 1st test run was calculated as follows

= 150 lowast 2980042 lowast 60= 17738W

(25)

Given the specific fuel consumption of 222 gliter water boiledfor the 3-stone stove (Kris De Decker 2015) the fuel usereduction attained by the developed improved cook stove wasestimated using

= 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) minus 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) lowast 100 (26)

For instance fuel use reduction in the 1st test run wascalculated as

= 222 minus 531222 lowast 100= 761

(27)

Table 4 shows a summary of results on stove performancesIt was found that after 4 test runs of the water boiling testthe designed improved stove had a mean thermal efficiencyof 288This means that 288 of the total energy producedby the fuel is used to boil water in the pot

Comparisons (Figure 5) were made with locally exist-ing stoves such as the Lorena stove brick stove Envirofit

8 Journal of Renewable Energy

Table 5 Comparisons between the cost of the granite rock stove and conventional stoves

StovePerformance

Cook stove technologies

13e GraniteRock Stove

Traditionalwood

burning

Improvedwood-burning

Traditionalcharcoal-burning

Improvedcharcoal-burning

Kerosene Propane(LPG) Electric Source

Capital Cost(US$) 36 5 ndash 50 3 ndash 6 3 ndash 50 10 ndash 60 60 ndash 120 100 ndash 500 Jeuland

andPattanayak

2012Efficiency (MJ usefulenergyMJproducedHeat)

288 7 - 15 13 - 40 18 - 21 15 - 37 40 - 50 50 - 60

0050

100150200250300350400

Designedprototype

Lorenastove

3-stonestove

Molded1-potstove

Trenchfire

Brickstove

Kenyaceramic

Jiko stove

Envirofitsupersaver

premiumcharcoal

stove

metalstove

Types of stoves

Ther

mal

effici

ency

()

Figure 5 Comparisons between thermal efficiencies of differentstoves

supersaver premium stove molded 1-pot stove Kenyaceramic jiko stovemetal stove trench fire and the traditional3-stone stove Previous studies [27 28] show that the above-mentioned stoves had thermal efficiency values of 14 17357 16 245 21 13 and 9 respectively

With a thermal efficiency of 288 the designed proto-type stove achieves tier 2 in the IWA tiers of performance[29] This shows a substantial improvement over the baselinetraditional 3-stone stove

36 Cost of the Granite Rock Cooking Stove versus Conven-tional Stoves Every household cooking system incurs differ-ent costs and benefits depending on diverse energy technolo-gies employed These costs are related to the capital cost ofa newly developed stove andor design modifications costof fuels required cost of stove distribution or marketingmoney and time spent for regular stove operation andmaintenance [30] In this study the capital cost of the graniterock stove was estimated at US$36 and compared favourablywith conventional charcoal burning stoves (US$3ndashUS$50) inaccordance with Jeuland and Pattanayak [30] (Table 5)

Given the fact that the granite rock stove depicts a rela-tively high thermal efficiency (288) and fuel use reduction(788) (Table 4) there is a higher likelihood for it to operateunder reduced cost making it cheaper than the conventionalstoves

4 Conclusions

The improved cooking stove was designed and fabricatedusing locally available materials including granite rocksstainless steel and glass wool and was estimated to cost US$

36 Based on its water boiling test results 788 fuel usereduction was achieved over the baseline open fire stoveThiswas attributed to the thermal retention storage propertiesof the granite rock The granite rock besides glass woolsignificantly contributed to the reduction on estimated heat(about 670kJ) that would be lost through the stove wallThis enhanced its thermal efficiency Based on compar-isons with performance standards and properties of theconventional stoves the designed granite rock stove is asubstantial improvement technology and can thus lessen thepressure put on forestry resources However further studiesincluding carbon and particulate matter (PM) emissions arerecommended for future design improvements to suit publichealth standards Studies on use of other forms of fuel such asbriquettes and wood chippings could as well be conducted toestablish fuel alternatives to charcoal

Data Availability

The data underlying the findings of this research can beaccessed on either the Uganda Christian University Hamu-Mukasa Library online catalogue or other online sourcesThe online sources among others include (i) httpswwwsafefuelandenergyorgfiles517-1pdf (ii) httpswwwunnedungpublicationsfilesimagesUSMAN20OJONIMI20YUSUFpdf (iii) httpswwwamazoncomHow-make--Kenyan-ceramic-jikodpB0007C8G84 and (iv) httpswwwpciaonlineorgtesting

Disclosure

Theauthors received no form of financing in the research andpublication of thiswork All financing directed for this projectwork was of their own resourcing

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors appreciate the intellectual input from all per-sons at the Department of Engineering and EnvironmentUganda Christian University their guidance helped to focus

Journal of Renewable Energy 7

Table 3 Data fromWBT (see Figure S5 in the Supplementary Materials for comprehensive analysis)

sn Parameters Tests (n = 4)1 2 3 4 mean stdev

1 Mass of water boiled (g) 2925 2875 2850 2800 28625 520

2 Specific heat capacity ofwater (JgK) 4186 4186 4186 4186 4186 0

3 Water boilingtemperature (K) 3698 3698 3698 3698 3698 0

4 Initial water temperaturebefore test (K) 2977 2975 2948 2962 29655 134

5 Water vaporised (g) 100 100 75 100 9375 125

6 Latent heat ofveporisation (Jg) 2260 2260 2260 2260 2260 0

7 Fuel consumed (g) 150 125 100 145 130 23

8 Lower Heating Value ofchar (LHV) Jg 29800 29800 29800 29800 29800 0

9 Effective mass of waterboiled (g) 2825 2775 2775 2700 27688 5154

10 Time to boiling water(min) 4200 4300 3900 4000 4100 183

11 Fuel consumed (g) 150 125 100 145 130 2273

Table 4 Summary of results on thermal performance of the stove

Performanceindex

Unit ofmeasure

Tests (n = 4)Sn 1 2 3 4 MEAN STDEV

1 Thermalefficiency 248 294 357 252 288 51

2 Water boilingrate minltr 149 155 141 148 148 06

3 Specific fuelconsumption

gliter waterboiled 531 450 360 537 470 83

4 Fire power kW 177 144 127 180 157 026

5 Fuel UseReduction 761 797 838 758 788 37

The fire power for the 1st test run was calculated as follows

= 150 lowast 2980042 lowast 60= 17738W

(25)

Given the specific fuel consumption of 222 gliter water boiledfor the 3-stone stove (Kris De Decker 2015) the fuel usereduction attained by the developed improved cook stove wasestimated using

= 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) minus 119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899119904119901119890119888119894119891119894119888 119891119906119890119897 119888119900119899119904119898119901119905119894119900119899 (3 minus 119904119905119900119899119890 119904119905119900V119890) lowast 100 (26)

For instance fuel use reduction in the 1st test run wascalculated as

= 222 minus 531222 lowast 100= 761

(27)

Table 4 shows a summary of results on stove performancesIt was found that after 4 test runs of the water boiling testthe designed improved stove had a mean thermal efficiencyof 288This means that 288 of the total energy producedby the fuel is used to boil water in the pot

Comparisons (Figure 5) were made with locally exist-ing stoves such as the Lorena stove brick stove Envirofit

8 Journal of Renewable Energy

Table 5 Comparisons between the cost of the granite rock stove and conventional stoves

StovePerformance

Cook stove technologies

13e GraniteRock Stove

Traditionalwood

burning

Improvedwood-burning

Traditionalcharcoal-burning

Improvedcharcoal-burning

Kerosene Propane(LPG) Electric Source

Capital Cost(US$) 36 5 ndash 50 3 ndash 6 3 ndash 50 10 ndash 60 60 ndash 120 100 ndash 500 Jeuland

andPattanayak

2012Efficiency (MJ usefulenergyMJproducedHeat)

288 7 - 15 13 - 40 18 - 21 15 - 37 40 - 50 50 - 60

0050

100150200250300350400

Designedprototype

Lorenastove

3-stonestove

Molded1-potstove

Trenchfire

Brickstove

Kenyaceramic

Jiko stove

Envirofitsupersaver

premiumcharcoal

stove

metalstove

Types of stoves

Ther

mal

effici

ency

()

Figure 5 Comparisons between thermal efficiencies of differentstoves

supersaver premium stove molded 1-pot stove Kenyaceramic jiko stovemetal stove trench fire and the traditional3-stone stove Previous studies [27 28] show that the above-mentioned stoves had thermal efficiency values of 14 17357 16 245 21 13 and 9 respectively

With a thermal efficiency of 288 the designed proto-type stove achieves tier 2 in the IWA tiers of performance[29] This shows a substantial improvement over the baselinetraditional 3-stone stove

36 Cost of the Granite Rock Cooking Stove versus Conven-tional Stoves Every household cooking system incurs differ-ent costs and benefits depending on diverse energy technolo-gies employed These costs are related to the capital cost ofa newly developed stove andor design modifications costof fuels required cost of stove distribution or marketingmoney and time spent for regular stove operation andmaintenance [30] In this study the capital cost of the graniterock stove was estimated at US$36 and compared favourablywith conventional charcoal burning stoves (US$3ndashUS$50) inaccordance with Jeuland and Pattanayak [30] (Table 5)

Given the fact that the granite rock stove depicts a rela-tively high thermal efficiency (288) and fuel use reduction(788) (Table 4) there is a higher likelihood for it to operateunder reduced cost making it cheaper than the conventionalstoves

4 Conclusions

The improved cooking stove was designed and fabricatedusing locally available materials including granite rocksstainless steel and glass wool and was estimated to cost US$

36 Based on its water boiling test results 788 fuel usereduction was achieved over the baseline open fire stoveThiswas attributed to the thermal retention storage propertiesof the granite rock The granite rock besides glass woolsignificantly contributed to the reduction on estimated heat(about 670kJ) that would be lost through the stove wallThis enhanced its thermal efficiency Based on compar-isons with performance standards and properties of theconventional stoves the designed granite rock stove is asubstantial improvement technology and can thus lessen thepressure put on forestry resources However further studiesincluding carbon and particulate matter (PM) emissions arerecommended for future design improvements to suit publichealth standards Studies on use of other forms of fuel such asbriquettes and wood chippings could as well be conducted toestablish fuel alternatives to charcoal

Data Availability

The data underlying the findings of this research can beaccessed on either the Uganda Christian University Hamu-Mukasa Library online catalogue or other online sourcesThe online sources among others include (i) httpswwwsafefuelandenergyorgfiles517-1pdf (ii) httpswwwunnedungpublicationsfilesimagesUSMAN20OJONIMI20YUSUFpdf (iii) httpswwwamazoncomHow-make--Kenyan-ceramic-jikodpB0007C8G84 and (iv) httpswwwpciaonlineorgtesting

Disclosure

Theauthors received no form of financing in the research andpublication of thiswork All financing directed for this projectwork was of their own resourcing

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors appreciate the intellectual input from all per-sons at the Department of Engineering and EnvironmentUganda Christian University their guidance helped to focus

8 Journal of Renewable Energy

Table 5 Comparisons between the cost of the granite rock stove and conventional stoves

StovePerformance

Cook stove technologies

13e GraniteRock Stove

Traditionalwood

burning

Improvedwood-burning

Traditionalcharcoal-burning

Improvedcharcoal-burning

Kerosene Propane(LPG) Electric Source

Capital Cost(US$) 36 5 ndash 50 3 ndash 6 3 ndash 50 10 ndash 60 60 ndash 120 100 ndash 500 Jeuland

andPattanayak

2012Efficiency (MJ usefulenergyMJproducedHeat)

288 7 - 15 13 - 40 18 - 21 15 - 37 40 - 50 50 - 60

0050

100150200250300350400

Designedprototype

Lorenastove

3-stonestove

Molded1-potstove

Trenchfire

Brickstove

Kenyaceramic

Jiko stove

Envirofitsupersaver

premiumcharcoal

stove

metalstove

Types of stoves

Ther

mal

effici

ency

()

Figure 5 Comparisons between thermal efficiencies of differentstoves

supersaver premium stove molded 1-pot stove Kenyaceramic jiko stovemetal stove trench fire and the traditional3-stone stove Previous studies [27 28] show that the above-mentioned stoves had thermal efficiency values of 14 17357 16 245 21 13 and 9 respectively

With a thermal efficiency of 288 the designed proto-type stove achieves tier 2 in the IWA tiers of performance[29] This shows a substantial improvement over the baselinetraditional 3-stone stove

36 Cost of the Granite Rock Cooking Stove versus Conven-tional Stoves Every household cooking system incurs differ-ent costs and benefits depending on diverse energy technolo-gies employed These costs are related to the capital cost ofa newly developed stove andor design modifications costof fuels required cost of stove distribution or marketingmoney and time spent for regular stove operation andmaintenance [30] In this study the capital cost of the graniterock stove was estimated at US$36 and compared favourablywith conventional charcoal burning stoves (US$3ndashUS$50) inaccordance with Jeuland and Pattanayak [30] (Table 5)

Given the fact that the granite rock stove depicts a rela-tively high thermal efficiency (288) and fuel use reduction(788) (Table 4) there is a higher likelihood for it to operateunder reduced cost making it cheaper than the conventionalstoves

4 Conclusions

The improved cooking stove was designed and fabricatedusing locally available materials including granite rocksstainless steel and glass wool and was estimated to cost US$

36 Based on its water boiling test results 788 fuel usereduction was achieved over the baseline open fire stoveThiswas attributed to the thermal retention storage propertiesof the granite rock The granite rock besides glass woolsignificantly contributed to the reduction on estimated heat(about 670kJ) that would be lost through the stove wallThis enhanced its thermal efficiency Based on compar-isons with performance standards and properties of theconventional stoves the designed granite rock stove is asubstantial improvement technology and can thus lessen thepressure put on forestry resources However further studiesincluding carbon and particulate matter (PM) emissions arerecommended for future design improvements to suit publichealth standards Studies on use of other forms of fuel such asbriquettes and wood chippings could as well be conducted toestablish fuel alternatives to charcoal

Data Availability

The data underlying the findings of this research can beaccessed on either the Uganda Christian University Hamu-Mukasa Library online catalogue or other online sourcesThe online sources among others include (i) httpswwwsafefuelandenergyorgfiles517-1pdf (ii) httpswwwunnedungpublicationsfilesimagesUSMAN20OJONIMI20YUSUFpdf (iii) httpswwwamazoncomHow-make--Kenyan-ceramic-jikodpB0007C8G84 and (iv) httpswwwpciaonlineorgtesting

Disclosure

Theauthors received no form of financing in the research andpublication of thiswork All financing directed for this projectwork was of their own resourcing

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors appreciate the intellectual input from all per-sons at the Department of Engineering and EnvironmentUganda Christian University their guidance helped to focus

Journal of Renewable Energy 9

this research The authors also appreciate the personnel atNational Forestry Resources Research Institute (NaFORRI)National Agricultural Research Organisation (NARO) forallowing them to use their facilities and equipment to carryout the water boiling test which helped them describe thethermal performance of the designed stove

Supplementary Materials

Figure S1 certificate of analysis for specific gravity andwater absorption tests carried out Figure S2 water absorp-tion results for granite rock aggregates Figure S3 spe-cific gravity results for granite rock aggregates Figure S4thermal test results Figure S5 water boiling test results(Supplementary Materials)

References

[1] K R Smith ldquoFuel combustion air pollution exposure andhealth the situation in developing countriesrdquo Annual Review ofEnvironment and Resources vol 18 pp 529ndash566 1993

[2] A Olorunsola ldquoThe development and performance evaluationof a briquette burning stoverdquoNigerian J Renewable Energy vol7 no 1 pp 91ndash95 1999

[3] B O Bolaji ldquoThe Use of Sawdust as an Alternative Source ofEnergy for Domestic Cooking and as a Means of ReducingDeforestationrdquo Global Journal of Environmental Sciences vol 4no 1 pp 73ndash76 2005

[4] J S Sawin ldquoRenewables 2017Global Status Reportrdquo 2013 httpwwwren21netwp-contentuploads201706GSR2017 Ful

[5] ESMAP ldquoIntroducing Energy-efficient Clean Technologies inthe Brick Sector of Bangladesh Washington DC Energy SectorManagement Assistance Program (ESMAP) 2011rdquo

[6] WEO ldquoEnergy for Cooking in Developing Countries 2006rdquohttpswwwieaorgpublicationsfreepublicationspublicationcookingpdf

[7] M K M Nahar ldquoIndoor Air Pollutants and RespiratoryProblems among Dhaka City Dwellersrdquo Archives of CommunityMedicine and Public Health pp 32ndash36 2016

[8] N R P Bruce ldquondoor air pollution in developing countriesa major environment and public challengerdquo 2000 Bulletin ofthe World Health Organization httpswwwpeertechzcomarticlesindoor-air

[9] J K Kaoma ldquoEfficiency and emission characteristics of twoZambia cookstoves using charcoal and coal briquettes Stock-holm Environment Institute 1994rdquo

[10] O Adria ldquoResidential Cooking Stoves and Ovens Good Prac-tice Technology Rocket StoveWuppertal Institute for ClimateEnvironment and Energy 2014rdquo

[11] V Becattini ldquoDetermination of specific heat capacity of rocksby DSC before and after high temperature thermal recyclingZurich Deprtment of earth sciences 2017rdquo

[12] V Becattini T Motmans A Zappone C Madonna A Hasel-bacher and A Steinfeld ldquoExperimental investigation of thethermal and mechanical stability of rocks for high-temperaturethermal-energy storagerdquo Applied Energy vol 203 pp 373ndash3892017

[13] S Khare M DellrsquoAmico C Knight and S McGarry ldquoSelectionof materials for high temperature sensible energy storagerdquo SolarEnergy Materials amp Solar Cells vol 115 pp 114ndash122 2013

[14] F G Bell Engineering in rock masses Elsevier 2013[15] W E Lee Ceramic microstructures property control by process-

ing Springer Science amp Business Media 1994[16] D Kiwana ldquofuel perfomance of feacal sludge briquettes in

Kampala Uganda Centre for Research in Energy and EnergyConservation 2016rdquo

[17] K L C Maxwell ldquoHow to make the Kenyan ceramic jikoNairobi Ministry of energy 1983rdquo

[18] AASHTO ldquoStandard Method of Test for Specific Gravity andAbsorption of Coarse Aggregate T8485rdquoAmerican Associationof State Highway and Transportation Officials 2014

[19] Volunteers in Technical Assistance ldquoesting the Efficiency ofWood-burning Cookstoves Provisional International Stan-dards The partnership for clean indoor air 1985rdquo

[20] Global Alliance for Clean Cookstoves ldquoHandbook for BiomassCookstove Research Design and Development A practicalguide to implement recent advances 2014rdquo

[21] Global Alliance for Clean Cookstoves ldquoThe water boilingtest 423 cookstoves emissions and efficiency in a controlledlabaratory setting 2014rdquo

[22] S F Baldwin ldquoBiomass Stoves Engineering Design Develop-ment and Dissemmination Virginia Volunteers in TechnicalAssistance 1987rdquo

[23] U O Yusuf ldquoExperimental perfomance evaluation of charcoalstove Department of mechanical engineering-University ofNigeria 2011rdquo

[24] L Eppelbaum I Kutasov and A Pilchin ldquoThermal Propertiesof Rocks andDensity of Fluidsrdquo inApplied Geothermics LectureNotes in Earth System Sciences pp 99ndash149 Springer BerlinGermany 2014

[25] H D Young Physics vol 1 Addison-Wesly Publishing Com-pany amp Inc 18th edition 1992

[26] J H IV Lienhard A Heat Transfer Textbook CambridgeMass USA 3rd edition httpwwwmieuthgrlabslttegrkpubsahttpdf

[27] Envirofit ldquoSmart cooking technology for better living 2016product catalogue 2016rdquo

[28] M J Turinayo ldquoPerformance characterization of improvedwood cooking stoves for monitoring household energy inter-ventions in Uganda Kampala National Forestry ResourcesResearch Institute (NaFORRI) 2011rdquo

[29] ISOTMBG Technical Management Board- groups ldquoIWA112012 Guidelines for Evaluating Cook stove Perfomance ISO2012rdquo

[30] M A Jeuland and S K Pattanayak ldquoBenefits and costs ofimproved cookstoves Assessing the implications of variabilityin health forest and climate impactsrdquo PLoS ONE vol 7 no 2Article ID e30338 2012

Hindawiwwwhindawicom Volume 2018

Nuclear InstallationsScience and Technology of

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

OpticsInternational Journal of

Hindawiwwwhindawicom Volume 2018

Antennas andPropagation

International Journal of

Hindawiwwwhindawicom Volume 2018

Power ElectronicsHindawiwwwhindawicom Volume 2018

Advances in

CombustionJournal of

Hindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

Renewable Energy

Acoustics and VibrationAdvances in

Hindawiwwwhindawicom Volume 2018

EnergyJournal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Hindawiwwwhindawicom Volume 2018

International Journal ofInternational Journal ofPhotoenergy

Hindawiwwwhindawicom Volume 2018

Solar EnergyJournal of

Hindawiwwwhindawicom Volume 2018

Shock and Vibration

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

International Journal of

RotatingMachinery

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawiwwwhindawicom Volume 2018

Active and Passive Electronic Components

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Submit your manuscripts atwwwhindawicom