Thermal Performance of Corrugated Solar Air Heater Integrated … · 2019. 11. 9. · by 45 % - 79 % compared with a solar air collector without PCM. Also, the heat losses for evacuated

International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:05 1

193205-8484-IJMME-IJENS © October 2019 IJENS I J E N S

Thermal Performance of Corrugated Solar Air Heater

Integrated with Nanoparticles to Enhanced the

Phase Change Material (PCM)

Ali Mohammed Hayder1,2, Azwan Bin Sapit1, Qahtan Adnan Abed2, Mohammed Saad Abbas1,2 , Bassam Abed

Saheb2 , Nawfel Muhammed Baqer Mohsin3 1Faculty of Mechanical and Manufacturing Engineering, University Tun Hussein Onn Malaysia, Batu Pahat, Johor, Malaysia.,

([email protected] ) 2Al-Furat Al-Awsat Technical University, Al Najaf, Iraq([email protected])

3Al-Furat Al-Awsat Technical University, Al Najaf, Iraq([email protected])

Abstract-- The purpose of this study is to design, fabricate and evaluate the performance of SAH with integrated

nanoparticles enhanced phase change material (PCM)

absorber storage system ,the central problem of the solar

energy is that it is an intermittent source, due to it dependence

on the period of solar radiation. Consequently, thermal energy

storage is considered a perfect option to solve this issue Three

different of the SAH configurations have been designed and

studied; without thermal storage, with thermal storage using

paraffin wax as a PCM and with thermal storage using Al2O3-

paraffin wax. All configurations are fabricated and tested

under the climatic conditions of middle Iraq according to

ASHRAE standard tests at different air mass flow rates. The

two steps method is used to prepare the mixture of

nanoparticles with PCM and ultrasonic device is used to

suspend the nanoparticles in the PCM. The experimental

results show that improvement in the efficiency of the SAH

integrated with storage compared to SAH without storage.

Moreover, the discharging time of heat stored took 5.5, 5, 4.5

and 4 hours at the air mass flow rate 0.03, 0.04, 0.05 and 0.06

kg/s, respectively. The experimental results also show that

increment in the thermal conductivity of PCM with the

dispersion 1wt. % Al2O3 which led to raise the outlet air

temperature and thermal efficiency of the SAH compared to

SAH with pure PCM. Index Term-- Corrugated solar air heater, Nanoparticles,

thermal efficiency, air mass flow rate, phase change material

(PCM).

1. INTRODUCTION In some case, solar energy has occupied graded prime

position in the renewable energy research field, caused

from an inexhaustible energy source [1, 2]. A

thermal energy storage unit works to enhance

the conservation of energy and hence, improve

the performance of the solar heating system [3]. The most

important components in the solar heat systems are thermal

solar collector and thermal energy storage system [4]. The

improvement of mechanism technical methods of the

thermal energy storage systems is essential to taking

advantage of solar radiation falling on the ground for

generating thermal energy effectively [5]. It is

necessary to determine a thermal energy storage method and

a material used for thermal energy storage systems. Using

thermal storage materials in solar energy systems not only

reduces the mismatch between request and supply of energy,

but also improves the performance and reliability of solar

energy systems as well [6]. Therefore, using the thermal

storage materials in solar energy systems is appropriate in cities where there is a significant difference in temperature

between day and night such as desert cities [7]. The

development of heat energy storage systems, the thermal

performance of storage materials is enhanced by mixing it

with nanoparticle to increase the thermal conductivity for

storage materials [8, 9]. The thermo-physical properties of

the storage materials are affected after being mixed with

nanoparticles and leads to enhancement of the heat transfer

characteristics of the storage materials [10]. The use of high

thermal conductivity nanoparticles in increasing thermal

conductivity of thermal storage materials is a simpler thermal conductivity enhancement method than thermal

storage materials integration into porous material [11].

Therefore, the thermal conductivity and heat transfer

characteristics of the thermal storage materials are important

factors to develop thermal performance of the solar energy

systems.

The solar energy systems integrated with a thermal energy

storage unit has been a subject of interest for scientists and

researchers in the past decades. Numerical and experimental

studies have been reported in order to increase the output

temperature of the solar energy heater, increase the thermal

conductivity of the material used for thermal

energy storage, and reduce the thermal losses of the heating

solar systems. The thermal storage in solar energy system

gives rise to a high thermal efficiency of the system, which

may be exploited in many applications such as space heating

of buildings, drying agricultural crops and heating of water

in homes. One of the most significant things to emerge from

this study is the investigation of the effect of using latent

thermal energy storage materials. Many types of research have shown that when solar energy is stored in the form of

latent heat by using PCMs, it gives a good performance.

This is due to the fact that the PCMs provide suitable

temperature rates during the melting and freezing processes

[12]. Consequently, using PCMs is a more effective way to

mailto:[email protected]:[email protected]:[email protected]



meet the request of energy and balance between request and

supply of energy and is the most common storage types in

heating solar systems [13]. An experimental study have

been carried out by Khadraoui et al. [14] to improve the performance of SAH by using a paraffin wax as a PCM. The

PCM is filled in rectangular container as a thermal storage

unit. The experimental tests were conducted on two solar air

collector (with and without PCM). They found that the PCM

increases the outlet air temperature from 3 °C to 7 °C

compared with a SAH without PCM during the night. Also,

the daily efficiency of collector reached 33 % and 17 % with

and without PCM, respectively.

Felinski and Sekret [15] presented the optimized design of

evacuated tube collector with paraffin wax as a PCM. The

experimental tests conducted to study the impact of paraffin wax on the thermal performance of the evacuated tube

collector. They found that the total quantity of useful heat

for evacuated tube collector integrated with PCM increases

by 45 % - 79 % compared with a solar air collector without

PCM. Also, the heat losses for evacuated tube collector

integrated with PCM decreased by 31 % - 32 % compared to

without PCM.

Shalaby et al. [16] evaluated the performance of the

corrugated absorber solar collector with and without paraffin wax. The collector is tested with and without the

paraffin wax by using different water masses. The hourly

production of the system with and without the PCM

depending on the temperature difference between water and

glass cover. They observed that the daylight productivity

decreases by 7.4 % whereas, overnight productivity

increases by 72.7 % when the PCM is used. Kabeel et al.

[17] performed an experimental investigation of the finned

absorber plate solar air collector with paraffin wax as a PCM. The suggested finned solar air collector was

fabricated and tested under the climate condition of Tanta

city Egypt. The authors found that the daily efficiency of

finned solar air collector with PCM was increased by 10.8

% - 13.6 % compared to a finned solar air collector without

PCM. Also, the finned solar air collector with PCM

continues to four hours after sunset to be the outlet air

temperature 8.6 °C higher than ambient temperature. Rabha

and Muthukumar [18] provided a detailed analysis of energy

and exergy of novel double pass solar air collector dryer

integrated with the paraffin wax as a PCM. The dryer was

operated for ten hours every day from 8 AM. to 6 PM. to dry 20 kg of red chili. They found that the values of energy

and exergy efficiency for thermal storage unit are between

43.6 % - 49.8 % and 18.3 % - 20.5 %, respectively while,

the average exergy efficiency of the drying chamber is 52.2

% and the overall efficiency of the drying system is 10.8 %.

An experimental study was conducted by Arfaoui et al. [19]

to evaluate the performance of solar air collector integrated

with AC27 as a PCM under climate condition of Tunisia.

They found that the outlet air temperature is almost constant

which is 27 °C at nights during the discharge period and the

daily energy efficiency amounted to about 47 %.

Wang et al. [20] developed a novel experimental

investigation for the flat micro heat pipe arrays collectors

integrated with a lauric acid as a PCM. The results showed

that the high air flow rate achieves high thermal collector

efficiency and low charging and discharging period which

lead to improved heat transfer, whilst the air flow rate of 60 m3/h achieves a constant outlet temperature during the

discharge period. Hamed et al. [21] presented a Numerical

analysis of a solar water collector with and without PCM.

They found that the maximum outlet water temperatures

obtained from the collector with and without PCM are 62.52

°C and 64.10 °C, respectively. In addition, the final melting

period for PCM is shorter than the freezing period because

of the rise heat transfer coefficient during melting period.

Miqdam et al. [22] conducted an experimental study of the

novel solar air collector consists of vertical and horizontal

parts. The vertical part consists of five pipes filled with

paraffin wax as a PCM while, the horizontal part is filled with the black colored iron chip. Two tests were conducted

at the natural and forced convection of the air movement.

The authors found that the efficiencies in natural and forced

convection were close. However, the use of PCM extends

the work time of the collector for 14 hours during the day.

Although PCMs have been widely used on the thermal

energy storage in many applications. On the other hand, the

low thermal conductivity of the PCMs leads to low heat

transfer rate [23] as well as increases the melting and

solidification time [24]. The heat transfer rate is an

important factor in evaluating the performance of thermal

energy storage system, and the enhancement of thermal

conductivity is considered as an effective method to

improve thermal energy storage system [25]. The high

thermal conductivity is an important property of materials

used for thermal energy storage. Therefore, various types of

metals such as nanoparticles are added to enhance the

thermal conductivity of thermal energy storage materials

[26]. The addition of nanoparticles to latent thermal energy

storage materials leads to improving the thermal

conductivity and achieves a good thermal performance of

energy storage systems. However, nanoparticles can't be

added excessively to thermal energy storage materials

because this increases their dynamic viscosity [27]. The

enhancement of materials properties used for latent thermal

energy storage by nanotechnology gives us a great

opportunity to be used in various industrial and engineering

applications such as; communication engineering systems,

fields of electronic industries, boilers for power plants and

building heating systems etc. [28]. The heat transfer

properties of the thermal energy storage materials after the

addition of nanoparticles could be affected by several

parameters; type of thermal energy storage material,

nanoparticles concentration, nanoparticles shape,

nanoparticles size, and method of preparation. The

nanoparticles concentration is considered the major



parameter that has the most influence and it has a direct

relationship in enhancement of the thermal conductivity

[29]. There is a large volume of recent studies focusing on

how to enhance the thermal conductivity of the latent

thermal energy storage material. Therefore, Table 1 presents

the summary of the previous studies for the latent thermal

energy storage materials with nanoparticles of the solar

system

TABLE I

Summary of the previous studies for the latent thermal energy storage materials with nanoparticles of the solar system

Author Year Type of nanoparticles

Size of nanoparticles

Type of PCM

wt. % Result

Shaikhc et al.

[30]

2008 SWCNTs,

MWCNTs,

CNFs

1 nm

10 nm 100 nm

Paraffin

wax

0.1-1 The various types of nanoparticle are

additives to paraffin wax leads to

improve the latent energy of wax.

The maximum improvement in

SWCNTs nanoparticle at the mass fraction 1 % which reached 13 %.

Mahmud et

al. [31]

2009 Al2O3 80 μm Paraffin

wax

5 The performance of collector

enhanced by adding the Al2O3 to paraffin wax. The flow rate affects

the discharging time so that at the

flow rate of 0.19 kg/s took a

discharge time 3.5 h, while at the

flow rate of 0.05 kg/s took a

discharge time of 8 h.

Alkilani et al.

[32]

2011 Al2O3 70 μm Paraffin

wax

5 By adding nanoparticles to wax gives

a better storage efficiency from the

pure wax. Accordingly, the storage

efficiency attained the maximum

value 71.9 % for pure wax and 77.18 % when the wax-nanoparticles at the

mass flow rate of 0.05 kg/s.

Guo and

Wang [33]

2012 Al2O3 50 nm Paraffin

wax

1, 5, 10 The thermal energy storage rate of

paraffin wax-nanoparticles is better

than conventional pure paraffin wax

due to an increase in the thermal

conductivity and melting rate.

Hence, it will lead to an

improvement in the efficiency of

heat transfer.

Teng and Chieh Yu

[34]

2012 Al2O3, TiO2,

SiO2, ZnO

20-30 nm Paraffin wax

1.2, 3 By adding TiO2 nanoparticles to PCM gives a better performance than

the other nanoparticles in the

improvement of the heat conduction.

In addition, TiO2 decreases the start

of melting temperature and increases

the start of freezing temperature of

PCM.



Dhaidan et al.

(a) [35]

2013 CuO 9 nm Paraffin

wax

1, 3, 5 The addition of CuO nanoparticles to

paraffin wax leads to enhancing the

thermal conductivity of paraffin wax

and increasing the heat transfer rate

which leads to decreasing the charging time. Also, the increasing

concentration of nanoparticles results

in increasing viscosity,

agglomeration and precipitation of

the composite.

Dhaidan et al.

(b) [36]

2013 CuO 9 nm Paraffin

wax

1, 3, 5 The addition of the CuO

nanoparticles with paraffin wax

resulted in improvement of melting

characteristics as well as an increase

in both the thermal conductivity and

natural convection. Therefore, the

properties of compound decreased by increasing the concentration

nanoparticles due to increase

viscosity, agglomeration and

precipitation.

Pise et al.

[37]

2013 Al2O3 20 nm Paraffin

wax

1, 3, 5 The suspend of nanoparticles with

paraffin increases the heat transfer

rate, thermal energy charging rate

and heat release rate compared with

the pure paraffin.

Wang et al.

[38]

2014 TiO2 20 nm Paraffin

wax

0.3, 0.5,

0.7, 0.9,

1, 3, 5, 7

The difference in mass fraction of

TiO2 nanoparticles leads to

difference in latent thermal capacity

and phase change temperature. They

found that the mass fraction 1 wt. %

or less which results in latent thermal

capacity increases and decreases the

phase change temperature. The mass

fraction of 3wt. % or more results in the latent thermal capacity decreases

and increases the phase change

temperature.

Chaichan and

Kazem [39] 2015 Al2O3 45 μm Paraffin

wax 1 The results proved that the addition

of Al2O3 nanoparticles to paraffin

wax increases productivity and time

of distillation as well as improving

thermal conductivity.

Baydaa J.

Nabhan [40]

2015 TiO2 10 nm Paraffin

wax

1, 3, 5 The phase change temperature varies

depending on mass fraction for TiO2

nanoparticles, at the mass fraction

5wt. % the thermal conductivity

increases by around 10 % with

increasing temperature 15 ⁰C.



Chaichan et

al. [41]

2015 Al2O3,

TiO2

30-60 nm

20-50 nm

Paraffin

wax

1, 2, 3, 4,

5

The thermal conductivity of wax

increased by addition the

nanoparticles so that the increase was

found 65 % and 40 % at mass

fraction 5 % for Al2O3 and TiO2, respectively.

Nourani et al.

[42]

2016 Al2O3 10-20 nm Paraffin

wax

2.5, 5,

7.5, 10

The best improvement of thermal

conductivity was the mass fraction

10wt. % by 13 %, and increasing the

melting rate by 27 %.

Arya et al. [43]

2016 Al2O3 80 lm Paraffin wax

1.3, 4, 5 Based on the results, the low thermal conductivity for the paraffin wax

could be increased by adding various

types of nanoparticles with various

types of mass fractions.

Singh et al.

[44]

2017 Al2O3, CuO 40-50 nm Myo-

inositol

1.2, 3 It was found that the myo-inositol

with nanoparticles could be used for high temperature applications from

160 ⁰C to 260 ⁰C. They found also that the Al2O3 is more suitable for

this applications due to an increase in

melting temperature.

Mohamed et

al. [45]

2017 α-Al2O3 2-4 nm Paraffin

wax

0.5, 1, 2 The α-Al2O3 nanoparticles additive

to paraffin wax leads to enhancement

in the latent heat and thermal

conductivity by 2 % with the highest

effect at 50 ⁰C. Chaichan et

al. [46]

2017 Al2O3 30-60 nm Paraffin

wax

1.2, 3 Adding the Al2O3 nanoparticles with

paraffin wax leads to change in many properties of the wax paraffin such

as the color and thermal

conductivity. The thermal

conductivity of paraffin wax was

enhanced by 18 %, 21 %, and 30 %

at the mass fraction 1 %, 2 % and 3

%, respectively.

Tarish and

Alwan [47]

2017 CuO 70 μm Paraffin wax

10 The thermal storage rate of the CuO nanoparticles with paraffin wax is

increased by 30.7 % compared with

pure paraffin.

Saeed et al.

[48]

2017 Fe3O4 16.6-30.1 nm Paraffin

wax

1, 5, 10 Enhancement of the activation

energy and latent heat for the paraffin wax after addition of Fe3O4

nanoparticles compared with

pure paraffin. But the range of

melting temperature stay the same

and unaffected.

Qian et al.

[49]

2018 Na2SiO3 - Paraffin

wax

5 The thermal conductivity increasing

by 60 % when adding Na2SiO3

nanoparticles to paraffin wax as well

as enhancement of the thermal

storage efficiency and release.



Purohit et al.

[50]

2018 CuO 5-17 nm Paraffin

wax

1, 2, 3, 4,

5

Increasing the concentration of CuO

nanoparticles increases both the

latent heat and melting temperature

even for mass fraction of 2 %. On the

other hand, the latent heat and melting temperature were decreased

at the mass fraction higher than 2 %.

Shalaby et al.

[51]

2018 α-Al2O3 71.5 nm Paraffin

wax

3 The using of α-Al2O3 nanoparticles

with a mass fraction 3% increasing

the thermal conductivity by 18.6 %,

and also increasing the thermal

effusively by 28.2 %.

NOMENCLATURE

TI Solar irradiance on the tilt surface (W/m2)

convh Convection heat transfer coefficient (W/m2 K)

radh Radiation heat transfer coefficient (W/m2 K)

condh Conduction heat transfer coefficient (W/m2 K)

outT Output temperature (°C)

inT Inlet temperature (°C)

ambT Ambient temperature (°C)

pT Absorber plate surface temperature (°C)

gT Glass cover surface temperature (°C)

skyT Sky temperature (°C)

mT Mean temperature (°C)

PCMT PCM Temperature (°C)`

k Thermal conductivity (W/m K)

LU Overall heat loss coefficient (kJ/kg K)

tU Top heat loss coefficient (kJ/kg K)

bU Bottom heat loss coefficient (kJ/kg K)

eU Edges heat loss coefficient (kJ/kg K)

S (W) The Absorbed Solar Irradiance by a Collector

PC Coefficient heat capacity (kJ/kg K)

uQ Useful energy of collector (W)

airm Air mass flow rate (kg/s) .g w Glass Wool

cA Cross section area of collector (m2)

l Absorber to glass cover distance (m)

HD Hydraulic diameter of the air flow channel (m)

chH Depth of air flow channel (m)

cW Width of air flow channel (m)

cL Length of the Collector (m)

eR Reynolds number (Dimensionless)

rP Prandtl number (Dimensionless)

aR Rayleigh number (Dimensionless)

uN Nusselt number (Dimensionless) Greek Symbols

Density (kg/m3) Stephan constant (W/m2 K) Transmittance (Dimensionless) Absorptance (Dimensionless) Emissivity (Dimensionless) Kinetic viscosity (m2 /s) Dynamic Viscosity (kg/m s)

th Thermal efficiency (%)

Volumetric coefficient of expansion (1/ K)

II. MATERIALS AND METHODS

Thermal Energy Storage Material (PCM)

Phase change material storage is preferable to sensible

material storage in low temperature applications because of

its isothermal storing mechanism and high storage density.

Paraffin wax is commonly used as a PCM in most thermal energy storage systems because to it melts at

fixed temperatures, unreactive, inexpensive and available.

The PCM used in the current experiences is Iraqi paraffin

wax. It was purchased from the Al-Dora Factory in

Baghdad-Iraq. The paraffin wax was placed inside the

containers of the novel designed collector, each container

was filled with 80 % due to the expansion of paraffin wax

size when melts. Each container has 0.515 kg paraffin wax

and the total paraffin wax of the collector is 8.76 kg as Table 2 indicates the thermo-physical properties of paraffin

wax used in the experiments. Paraffin wax absorbs the

excessive thermal energy during the charging period in



daytime and releases the absorbed thermal energy later

during the discharging period in night-time. The thermal

energy storage could be dimensioned in a way that the

storage temperature is kept in a specified temperature level

while the excess external thermal energy is stored at the

same time. TABLE II

Thermo-physical properties of paraffin wax

Property Value

Latent Heat 176 KJ/kg

Thermal Conductivity 0.21 W/m K

Specific Heat Capacity 2.871 KJ/kg K

Melting Temperature 60 ºC

Freezing Temperature 55 ºC

Liquid Density 770 kg/ m3

Solid Density 850 kg/ m3

Dynamic viscosity 0.03499 KJ/m.s

Alumina (Al2O3) Nanoparticles

Although the paraffin wax have been widely used for the

thermal energy storage in applications of solar systems, but

the low thermal conductivity for the paraffin wax generates

high thermal resistance for a heat transfer between the

surface and wax. This high thermal resistance may not melt

the entire depth of the PCM. To overcome this problem and

give the best condition for the PCM, paraffin wax was

mixed with nanoparticles. Alumina Al2O3 nanoparticles are

thermodynamically stable particles over a wide temperature

range as well as it has a high thermal conductivity [52], so it

is used as thermal conductivity enhancer. In general, Al2O3

nanoparticles have several interesting properties, for

example high solidity, high stability, high insulation, and

transparency [53]. They have been widely used in many

applications such as catalysts, sensors, semiconductors,

capacitors, batteries, fire retard, surface protective coating,

composite materials, pharmaceutical industry and

biomedical field [54]. The thermo-physical properties of

Al2O3 nanoparticles are presented in Table III.

TABLE III

Thermo-physical properties of Al2O3 nanoparticles

Property Value

Color White

Morphology Spherical

Purity 99 % (trace metals basis)

Average Particle Size (APS)

40 nm

SSA 60 m2 /g

Thermal Conductivity 40 W/m K

Specific Heat Capacity 765 J/kg K

Density 3970 kg/m3

Thermal Diffusivity 1.31×10-5 m2/s

Preparation of Mixture (Nanoparticles with PCM)

The mass fraction ( ) of nanoparticles was calculated by the following equation:

(1)

The two steps method are used to prepare the mixture of

Al2O3 nanoparticles and paraffin wax with mass fraction by

1wt. %. Paraffin wax is melted at 60 ℃ and the dispersion of nanoparticles is done directly in flask with capacity of

1000 ml that could be closed by a PVC cap. The ultrasonic

water bath used Elmasonic P180H type with tank and its

capacity is of 18 liters. The flask was fixed to the stainless

steel basket inside the ultrasonic water path. The tank of the

ultrasonic device is filled with distilled water above the

level of mixture in the flask about 3 cm as shown in Figure

1. Then, the degas mode is switched on to remove the air

from the mixture. After that, the flask is closed by the cap

and oscillated continuously for 2 hours in the ultrasonic path

water with working frequency of 37 kHz and power

efficiency of 100 % at 70 ℃, until Al2O3 nanoparticles are uniformly suspended in paraffin wax as shown in figure 2.

Fig. 1. Suspension of nanoparticles in PCM

by ultrasonic water bath (Elmasonic P180H)



Fig. 2. View of the (a) pure paraffin wax, (b) Al2O3 nanoparticle suspended

in paraffin wax with concentration 1wt. %

Thermo-physical properties of Mixture

The uniform distribution of nanoparticles in the paraffin

wax affects the thermo-physical properties of the mixture

such as thermal conductivity, density, specific heat capacity

and viscosity. In this section the thermo-physical properties

of mixture were determined to define the heat transfer

coefficient of the mixture.

a. Thermal Conductivity of Mixture

Suspension of nanoparticles in PCM with a low mass

fraction is to give stability to the mixture for a longer period

of time more than the mixture with a high mass fraction. The thermal conductivity of the mixture depends on the

thermal conductivities of constituents, the concentration of

nanoparticles and dispersed nanoparticles in PCM. In the

current study, Maxwell’s equation is adopted evaluating the

effective thermal conductivity of mixture, as given by this

equation [55].

2 2 ( )

2 ( )

np PCM np PCM

mix PCM

np PCM np PCM

k k k kk k

k k k k

(2)

b. Density of Mixture

The density of the mixture is affected by the concentration

ratio of nanoparticles and type of base fluid (PCM) while

the shape and size of nanoparticles do not affect the density

of the mixture. The density equation of the mixture can be written as following [56].

(1 ) mix PCM np (3)

c. Specific Heat Capacity of Mixture

The specific heat capacity of the mixture depends on the

concentration ratio of nanoparticles, the density of the

mixture and the heat capacity of mixture components. The

specific heat capacity equation is given by the following

[56].

(1 )( ) ( )

mix

p PCM p np

p

mix

C CC

(4)

d. Viscosity of Mixture

The viscosity is considered as an important property of

fluids thermal applications and it describes the internal

resistance of fluids to flow. The heat transfer coefficient

depends mainly by viscosity and it is also important in

thermal conductivity in thermal systems. The viscosity of

the mixture depends on the viscosity of base fluid (PCM)

and concentration ratio of nanoparticles. The shape and size

of nanoparticles affect the viscosity of the mixture. In this

study, Brinkman equation [57] to compute the viscosity of

the mixture was adopted. It is an equation used to calculate the viscosity of the mixture containing suspensions of small

spherical particles as following.

2.5(1 )

PCMmix

(5)

Field Emission Scanning Electron Microscopy (FESEM)

The Field Emission Ecanning Electron Microscope

(FESEM) was conducted for a sample of Al2O3 nanoparticles with paraffin wax. FESEM device is a

microscope that works by electrons instead of light, these

electrons are liberated by a field emission source. Figure 3

shows image of FESEM for the sample of Al2O3

nanoparticles suspension with paraffin wax. The figure

indicates that the mixture of Al2O3 nanoparticles with

paraffin wax has non porous structure. Also, the figure

shows that there is an acceptable dispersion of Al2O3

nanoparticles in paraffin wax.

Fig. 3. FESEM image of 1wt. % Al2O3 nanoparticles with paraffin

wax

a b



Experimental Setup

The experimental tests were conducted in the current study

on three configurations of the single pass solar air heater.

The first configuration represents a solar air heater without

storage (SAHWOS), the second configuration represents a

solar air heater with paraffin wax as PCM (SAHWP) and the third configuration represents a solar air heater with

nanoparticles and PCM (SAHWNP) as shown in Figure 4.

The experimental prototypes of the solar air collector were

fabricated using locally available materials and tested under

actual outdoor operating weather conditions. The

experimental tests were conducted in the Technical College

Najaf, Al-Furat Al-Awsat Technical University located in

the center of Iraq 31°57 N and 44°15 E [58]. The dimensions and specifications of the Solar Air Heaters

(SAH) configurations are summarized in Table 4. The air

temperatures were measured in the experimental tests

by using K-type thermocouples which were distributed in

different places of the SAH. Furthermore, all the K-

type thermocouples were fitted in a data logger, and all the

data was registered automatically.

Fig. 4. Photographic view of the experimental setup of the SAH

TABLE IV

Dimensions and specifications of the solar air heaters

Parameters Measurement

Thickness of plywood used

for the fabrication

16 mm

Thickness of

transparent glass

4 mm

Thickness of glass-wool 20 m

Distance between glazing

and absorber plate

10 mm

Length of the air flow

channel

1.8 m

Width of the air flow channel

0.7 m

Height of the air flow 0.07 m

channel

Area of transparent glass 1.8 × 70 m2

Cross sectional area of

SAHWOS

3.6 × 0.7 m2

Cross sectional area of

SAHWS

2.75 × 0.7 m2

Distance after the axial fan 0.3 m

Distance before the axial fan 0.3 m

Capacity of axial fan 50 W

Collector tilt angle 42º

Air flow rates 0.03, 0.04, 0.05,

0.05 kg/s

Thickness of absorber plate 0.8 mm

Type of absorber plate Aluminum

4. Thermal Analysis of the SAH

In this round, the thermal analysis of the SAH were

presented. The experimental useful energy from the SAH

can be calculated by the following equation [59]:

( )u air P out inQ m C T T (6)

The thermal efficiency is considered the primary indicator

to evaluate the performance of a solar air collector. In

general, thermal efficiency for a solar collector is defined as

the ratio of the obtained useful thermal energy to the overall

absorbed thermal energy. Consequently, the thermal

efficiency equation of the solar collector is written as follows:

( )

.

air p out in

th

T c

m C T T

I A

(7)

The difference between thermal heat losses energy and the

absorber solar irradiance was identified by using the Hottel-

Whillier equation.

[ ( )]u c R L out inQ A F S U T T (8)

Where to determine how to absorb energy ( )RF is used,

while the method of loss energy is determined by R LF U ,

RF is defined as the removal factor and given by the

following equation.

1 expp c L

R

c L p

mC A U FF

A U mC

(9)

Where F is collector efficiency factor, can be calculated by the following equation:



1

1

( )

( ) ( )

1

1 1

L

conv p air

conv p air rad p b

UF

hh h

(10)

Therefore, the steady state efficiency of the

collector is given by the following equation, known as

Hottel-Whillier–Bliss equation.

( )( ) out inth R R L

T

T TF F U

I

(11)

The convection and radiation heat transfer

coefficient between the transparent glass cover and

the ambient is given by the following equations.

0.6

( ) 0.4

8.6 (w )

( )

vconv g amb w

c

h hL

(12)

2 2

( )

( ) (T )( )

( )

g sky

rad g sky g g amb g amb

g amb

T Th T T T

T T

(13)

1.50.0552sky ambT T (14)

The convection and radiation heat transfer

coefficient between the absorber plate surface and the transparent glass cover is given by the following equations.

( )

( )

u p g air

conv p g

N kh

l

(15)

0.2917

( ) 0.1673 ( cos )u p g aN R (16)

3

2

g. . ra p g

PR T T l

(17)

1

mT (18)

2

p g

m

T TT

(19)

2 2

( ) 1 11

p g p g

rad p g

p g

T T T Th

(20)

The convection heat transfer coefficient between the

corrugated absorber plate surface and air flow channel is

given by the following equation.

( )

( )

.u p air airconv p air

D

N kh

H

(21)

4 2

2

c chD ch

c

W HH H

W

(22)

0.76

( ) 0.0743 ( )u p air eN R (23)

air De

v HR

(24)

The overall heat losses from the system can be calculated by

the following equation:

1

( ) ( ) ( )

1 1

( ) ( )t

conv p g rad p g w rad g sky

Uh h h h

(25)

.

.

g w

b

g w

kU

t (26)

.

.

g w c c

e

g w c

k p HU

t A (27)

III. RESULTS AND DISCUSSION

Thermal Performance Test of the SAH

The thermal performance tests of the solar heater was

performed according to ASHRAE [60] standard. In this work, four thermal efficiency curves were established at

different air mass flow rates. The efficiency curve equation

for each air mass flow rate was obtained to calculate SAH

characteristic parameters. The equation (11) mentioned in

above indicates that if efficiency th is plotted against Tout – Tin / IT, it well be resulted in a straight line where the slope

is equal to FRUL and the y-intercept is equal to FR(τα).

Figure 5 to Figure 7 illustrate the typical efficiency curves

for SAHWOS, SAHWP and SAHWNP collectors,

respectively, at different air mass flow rates. It is clearly

seen that the efficiency increases considerably as the air

mass flow rate increases. From these figures it is also

observed that the slope of the efficiency curves decreases with the increase of air mass flow rate which means a

decrease in the heat loss coefficient with the increase of the

air mass flow rates. This result is due to the lower plate

temperature with increased air mass flow rate resulting in

lower heat loss coefficient. It can also be seen from the



curves that the loss coefficient is higher in the SAHWOS

collector, followed by SAHWP collector and least in

SAHWNP collector for the same air mass flow rates.

Fig. 5. Efficiency curve for SAHWOS at different air mass flow rates

Fig. 6. Efficiency curve for SAHWP at different air mass flow rates

Fig. 7. Efficiency curve for SAHWNP at different air mass flow rates

The incidence angle modifier of the collector is important to

predict efficiency during a day of normal collector

efficiency [60]. The incidence angle modifier for flat plate

collectors was explained in detail in Ref. [61], whilst the

incidence angle modifier for corrugated plate collectors is

not yet determined. The incidence angle sensitivity of corrugated plate collectors is different from the flat plate

collectors because of shading between aspects of the

corrugated plate. This may lead to the incidence angle

modifier of corrugated plate collectors is a lower than flat

plate collectors. Furthermore, the solar air collector with a

single glass cover is insensitive for incidence angle modifier

as stated by Hill et al. [62].

The incidence angle modifier for corrugated solar air

collectors was investigated by the method of ASHRAE

standard. Three pairs separate from efficiency values of the

solar collector about solar noon at early and late in the time

of day have been selected, when the incidence angles of

beam radiation are almost 30 , 45 and 60 . It was observed that the average incidence angle of both data

values was the same, as well as the efficiency value for the

incidence angle, is equal to the average of those two values.

Figure 8 shows the variation between incidence angle modifier Kατ and the incidence angle. Therefore, the

relationship between incidence angle modifier Kατ and the

collector efficiency is given by the following equation.

,( )R e nK

F

(28)

Fig. 8.Variation incidence angle modifier Kατ

Experimental Performance Results of The SAH

Figure 9 to Figure 12 presents the hourly solar irradiance

and the performance of SAHWOS collector for different air

mass flow rates in the entire daytime. It is clearly seen from

the figures that the solar irradiance increases from 8:00

(Tout

-Tin)/I

T(

oC.m

2/W)

Eff

icie

ncy

(%)

0 0.01 0.02 0.03 0.04 0.050

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Air mass flow rate = 0.03 kg/s




(Tout

-Tin)/I

T(

oC.m

2/W)

Eff

icie

ncy

(%)

0 0.01 0.02 0.03 0.04 0.050

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1





(Tout

-Tin)/I

T(

oC.m

2/W)

Eff

icie

ncy

(%)

0 0.01 0.02 0.03 0.04 0.050

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1





Incidence Angle (degrees)

In

cid

en

tA

ng

leM

od

ifie

r

0 10 20 30 40 50 60 700

0.2

0.4

0.6

0.8

1

1.2



A.M. to 12:30 P.M. Then, the sun irradiation begins

declining toward the end of the day at 6:00 P.M. From the

temperature measurements it can be seen that the

temperature of air at the outlet of the collector in the

beginning increased at a slower rate, because of the low

irradiation rate. After that, the increase in outlet temperature

is at a faster rate which is due to the increase in the

insolation rate. After 12:00 P.M., the increase in

temperature is slightly reduced, and this increase continues

until 1:00 P.M. The little irradiation in the increase of

temperature is due to the increase in the average air

temperature of the collector. After 2:00 P.M. there is a clear

linear drop in outlet air temperature even 6:00 P.M. at all

cases, which is in direct proportion to the reduction in the

solar irradiance.

Fig. 9. Hourly solar irradiance and mean temperature of (Tamb, Tout,

Tg and Tp) for the SAHWOS at m = 0.03 kg/s Fig. 10. Hourly solar irradiance and mean temperature of (Tamb, Tout,

Tg and Tp) for the SAHWOS at m = 0.04 kg/s


Tg and Tp) for the SAHWOS at m = 0.05 kg/s Fig. 12. Hourly solar irradiance and mean temperature of (Tamb, Tout,

Tg and Tp) for the SAHWOS at m = 0.06 kg/s

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

7 8 9 10 11 12 13 14 15 16 17 18 190

100

200

300

400

500

600

700

800

900

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

7 8 9 10 11 12 13 14 15 16 17 18 190

100

200

300

400

500

600

700

800

900

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

Time of Day (Hrs)

so

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

7 8 9 10 11 12 13 14 15 16 17 18 190

100

200

300

400

500

600

700

800

900

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

7 8 9 10 11 12 13 14 15 16 17 18 190

100

200

300

400

500

600

700

800

900

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature




Tg, Tp and Tpcm) for the SAHWP at m = 0.03 kg/s Fig. 14. Hourly solar irradiance and mean temperature of (Tamb, Tout,

Tg, Tp and Tpcm) for the SAHWP at m = 0.04 kg/s


Tg, Tp and Tpcm) for the SAHWP at m = 0.05 kg/s Fig. 16. Hourly solar irradiance and mean temperature of (Tamb, Tout,

Tg, Tp and Tpcm) for the SAHWP at m = 0.06 kg/s


Tg, Tp and Tpcm) for the SAHWNP at m = 0.03 kg/s Fig. 18. Hourly solar irradiance and mean temperature of (Tamb, Tout,

Tg, Tp and Tpcm) for the SAHWNP at m = 0.04 kg/s

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

8 10 12 14 16 18 20 22 240

100

200

300

400

500

600

700

800

900

10

20

30

40

50

60

70

80

90

100

110

Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

PCM temperature

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

8 10 12 14 16 18 20 220

100

200

300

400

500

600

700

800

900

10

20

30

40

50

60

70

80

90

100

110

Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

PCM temperature

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

per

atu

re(o

C)

8 10 12 14 16 18 20 220

100

200

300

400

500

600

700

800

900

10

20

30

40

50

60

70

80

90

100

110Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

PCM temperature

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

per

atu

re(o

C)

8 10 12 14 16 18 200

100

200

300

400

500

600

700

800

900

10

20

30

40

50

60

70

80

90

100

110Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

PCM temperature

Time of Dat (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 230

100

200

300

400

500

600

700

800

900

10

20

30

40

50

60

70

80

90

100

110

120

Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

PCM temperature

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 220

100

200

300

400

500

600

700

800

900

10

20

30

40

50

60

70

80

90

100

110

120

Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

PCM temperature

Melting

Solidification

Liquid




Tg, Tp and Tpcm) for the SAHWNP at m = 0.05 kg/s Fig. 20. Hourly solar irradiance and mean temperature of (Tamb, Tout,

Tg, Tp and Tpcm) for the SAHWNP at m = 0.06 kg/s Figure 13 to Figure 16 presents the effect of using paraffin

wax on the performance of the SAH. These Figures illustrates

the variation of outlet air temperatures, plate temperature,

glass temperature and PCM temperature. Hourly variations of

measured solar irradiance intensity and ambient temperature

are also shown during the day. Measured data for all cases

explain that the maximum temperatures are obtained about

1:00 P.M. The move of the peaks location for different

temperatures versus time curves compared to solar irradiance

curve are due to the heat stored on the PCM during charging period. In all cases, it was observed that the absorber plate

surface temperature exhibited the highest temperature from

1:00 P.M. until 3:00 P.M. After this time, the PCM

temperature will be the highest. From these figures, it was

clearly seen that the heating rate of PCM during the solid

sensible heating is slow and increases at a higher rate beyond

60 °C. After that, the PCM has changed its phase completely

into liquid. Hence, the experiment is continued until the exit

air temperature is equal to the ambient temperature. It can be

seen that the absorber plate surface temperature in general

increases with the increasing intensity of solar irradiance that

leads to melt the paraffin wax.

Figure 17 to Figure 20 illustrate the variation of the outlet air

temperatures, plate temperature, glass temperature and PCM

temperature. Hourly variations of measured solar irradiance

intensity and ambient temperature are also shown during the

day for the SAHWNP. Measured data for all cases explains

that the maximum temperatures are obtained at about 1:00

P.M. which is the same with SAHWP. In all results, it was

observed that the temperature difference between absorber

plate surface and PCM is small compared to the case of

SAHWP due to the effect of nanoparticles (Alumina). The

effect of nanoparticles was to increase the thermal conductivity and thermal diffusivity. It was also found that the

maximum temperatures of PCM vary with different values of

air mass flow rate.

Figure 21, 22 and 23 shows the variation of the thermal

efficiency of SAHWOS, SAHWP and SAHWNP

respectively, at different air mass flow rates. The thermal

efficiency increases with the day time due to increasing solar

irradiance which leads to increase in the air flow temperature.

Furthermore, the thermal efficiency increases with the

increasing of the air mass flow rate until the value of 0.06

kg/s. Moreover, the use of PCM leads to increasing the

thermal efficiencies as the time increases to obtain their peak

values about 2:00 P.M. and decrease slowly at about 5:00 P.M. Then, the thermal efficiencies increase sharply due to the

large heat supply from the PCM during discharging process.

Fig. 21. A instantaneous thermal efficiency versus time of day at different air

mass flow rates for SAHWOS

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

7 8 9 10 11 12 13 14 15 16 17 18 19 20 210

100

200

300

400

500

600

700

800

900

10

20

30

40

50

60

70

80

90

100

110

Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

PCM temperature

Time of Day (Hrs)

So

lar

Irra

dia

nce

(W/m

2)

Tem

pera

ture

(oC

)

7 8 9 10 11 12 13 14 15 16 17 18 19 200

100

200

300

400

500

600

700

800

900

10

20

30

40

50

60

70

80

90

100

110

Solar irradiance

Ambient temperature

Outlet temperature

Glass temperature

Plate temperature

PCM temperature

Time of Day (Hrs)

Insta

nta

neo

us

Th

erm

al

Eff

icie

ncy

(%)

7 8 9 10 11 12 13 14 15 16 17 18 190

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Air mass flow rates = 0.03 kg/s



Air mass flow rates = 0.06kg/s




mass flow rates for SAHWP


mass flow rates for SAHWNP

Finally, the results of the all configurations in current

experiments can be summarized in Table 5 which represents a

comparison of different configuration in terms of Tin, Tout, T

and th.

TABLE V

Change of (Tin, Tout, T and th) for different configuration of the SAH at different air mass flow rates and solar irradiance of 800 W/m2

Configuration

m

(kg/s)

Tin

(C)

Tout

(C)

T

(C)

th

(%)

SAHWOS

0.03 28.9 57.2 28.3 44

0.04 29.7 55.5 25.8 53

0.05 28.4 53.3 24.9 60

0.06 30.3 50.5 20.2 66

SAHWP

0.03 28.9 52.5 23.6 41

0.04 29.7 50.5 20.8 49

0.05 28.4 46.8 18.4 56

0.06 30.3 44.4 14.1 60

SAHWNP

0.03 28.9 55.1 26.2 43

0.04 29.7 53.0 23.3 52

0.05 28.4 49.9 21.5 59

0.06 30.3 47.4 17.1 64

IV. CONCLUSIONS

The main aim of this paper is to present the actual SAH

collector's experimental performance and efficiency results for

various design configurations of SAH. In thermal

performance, those parameters such as; plate temperature,

glass temperature, inlet and outlet air temperature, ambient

temperature, solar irradiance, thermal efficiency and air mass

flow rate have been investigated thoroughly.

The air mass flow rate is an important and factor influential on results of SAH temperatures. Increment in air mass flow rate

will result to more and more air volume which entering the air

flow channel. It has been noted from the results the outlet air

temperature decreased because of the increase in air velocity

inside a flow channel.

It is clearly there is enhancement in performance of SAH with

thermal storage by using paraffin wax compared to SAH

without storage. Furthermore, the discharging of heat is

possible for duration of 5.5 , 5, 4.5, and 4 hours at the air mass

flow rates of 0.03, 0.04, 0.05 and 0.06 kg/s, respectively.

There is also an increase in the thermal conductivity of

paraffin wax with the dispersion of 1wt. % alumina nanoparticles which led to raise the outlet air temperature and

increased the thermal efficiency of the SAH compared with

pure paraffin wax.

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Thermal Performance of Corrugated Solar Air Heater Integrated … · 2019. 11. 9. · by 45 % - 79 % compared with a solar air collector without PCM. Also, the heat losses for evacuated