Abstract - WordPress.com · Web viewNatural zeolites (88 to 95% clinoptilolite) in adsorbent bed with a grain size of 0.6 mm is used as an adsorbent. The thermal characteristics of

ISSN 2456-8066International Journal of Advanced Engineering and Management

Vol. 4, No. 3, pp. 20-31, 2019

Design and Experimental Evaluation of Zeolite–Water Adsorption Cooling UnitAfzal Ahmad1, Muhammad Hamza Tahir2*, Nouman Zaffar3,Muhammad Asad Saeed3,

Muhammad Arsalan Malik3

1 Head of Department, Mechanical Engineering Department, Pakistan Institute of Engineering and Technology, Multan, Pakistan

2 Research Assistant. Mechanical Engineering Department, Pakistan Institute of Engineering and Technology, Multan, Pakistan

3Undergraduate Students. Mechanical Department, Pakistan Institute of Engineering and Technology, Multan, Pakistan

*Corresponding author E-mail: [email protected]

AbstractThis paper presents the design and experimental

evaluation of zeolite adsorption system operated through renewable heat solar power. The adsorbent FAM Z01 is used in the adsorption chiller. Because of its pore volume, it is highly affected for water vapor adsorption. The principal edge of the Zeolite system are: (i) it does not have many parts and therefore needs less maintenance; (ii) it has the efficient cooling method with a low-temperature adsorbent process; (iii) it substitutes for the use of vapor pipes and (iv) it is environmentally beneficial. The testing of the cooling unit was performed on conditions: (i) the temperature of source, (ii) cycle time and (iii) the time of heat recovery. Under the experimental parameters of 47 LC adsorption, 153 LC desorption, 34 LC condenser and 27.5 LC, 17 LC and 11 LC evaporator temperatures, the adsorption cooling unit COP is around 0,59 and cooling mass adsorbent (CSC) density per kg and cooling power density of 5.21 kW / m3 and 7.2 W / kg.Keywords

Absorption Cooling System, Cost Efficient, Zeolite , Green Energy, Solar Energy Harvesting

I. INTRODUCTION

In typical vapor compression cooling systems, cooling and heating uses refrigerants that deplete ozone, for example chlorofluorocarbons (CFCs). Although refrigerant less damaging to ozone layer like hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are increasing, they continue to contribute to the undesirable global

warming effect. In addition, electricity is being used as source in such systems. With increasing demand for climate change and refrigeration increasing, energy consumption will also increase. This inherently results in a faster depletion, higher emissions and high energy demand, of known fossil fuel reserves. Such environmental problems have intensified the efforts of research into the production of environmentally friendly coolants and energy saving refrigeration technology.

Pakistan has been under development and for the next ten years the demand for electricity is expected to increase by 6%–8% annually[1]. Pakistan's rise in electricity demand is partly motivated by the increase in cooling demand because of long and warm summers in the subcontinent. This surge in air conditioning demand in Pakistan is linked to the protection of resources, depletion, emissions and the outdated infrastructure as well as to climate change. Such issues with increasing demand for air conditioning are not specific to Pakistan and have previously been addressed in the literature. [2]–[7].

One way to provide alternatives to the vapor compression system is through the Adsortion System. For last few decades adsorption methods have been used primarily to isolate and purify gas It is now only used to generate heating and cooling phenomena.⠀ The technological innovation include a liquid absorption heat-driven cooling system[8],[9] and solid heat-adsorption pumps[9]. As waste heat or solar energy can be used and environmentally sound chemicals are applied, both their ODPs (ozone depletion potentiality) and GWPs (global warming potential) are almost nil[10]. Over the past

Afzal Ahmad, Muhammad Hamza Tahir, Nouman Zaffar, Muhammad Asad Saeed, Muhammad Arsalan Malik “Design and Experimental Evaluation of a Natural Zeolite–Water Adsorption Cooling Unit” International Journal of Advanced Engineering and Management, Vol. 4, No. 3, pp. 20-31, 2019


Vol. 4, No. 3, pp. 20-31, 2019

decades, many kinds, such as exhaust-gas driven adsorbent-cooling air-conditioners [11]–[13], exhaust-gas-driven ice makers [14],[15] solar-powered adsorption air-conditioners [16]–[19] and ice makers/ solar-powered adsorption systems [20]–[22] have been developed and designed and experimentally tested. Table 1 illustrates the characteristics of some systems with basic conditions. These systems are used with different pairs of adsorbent coolants, including 13xwater, silica gel-methanol, charcoal-methanol active ingredient, and activated ammonia. Zeolite is a naturally or synthetically available resource. A lot of zeolites do not worsen with usage and are ideal for reversible adsorption processes. In addition, ice is firmly binds in contrast with other potential coolants, and it is non-flammable, and non-toxic as compared to many other refrigerants.[23]–[29]

Cycles of adsorption process utilizing silica–water[30], [31], carbon–methanol[30], [31] and zeolite–air[32]–[35] have a clear advantage, as the energy is relatively low near ambient temperatures, ensuring the recovery of waste heat under 80 LC[36]. In addition, these systems are non-corrosive and almost do not require any moving components that reduce maintenance. There are many advantages towards this adsorption chiller, fewer moving

components, easy assembling, able to drive waste heat up to 60 lc. Adsorption systems can therefore deal with the abundant supply of waste heat in an economic and technological way.

Current research aims to build a cooling system for thermal adsorption using zeolite-water as an adsorber / coolant to evaluate efficiencies of the cooling unit at

different temperatures. In this study the machine is very efficient and could easily be worked because of lack of vacuum sealing problems. However, the condenser manufactured is new in comparison to the ones mentioned. A large condensing area is available to the condenser and this reduces the time of desorption when the coolant steam is low and the condensation surface contains non-condensable gasses[37]. However, the operating principle of current system is distinct from those used in previous literature.

II. DESCRIPTION OF THE ABSORPTION COOLING UNIT

A laboratory model was designed and fabricated and its efficiency under different working conditions was analysed experimentally. Figure 1 and 2 illustrate a schematic and graphical model of proposed design. A shell, adsorbent bed, evaporator, condenser, heating and cooling bed, measuring devices and additional components are primary elements of


Table 1. Specifics of some cooling systems

Coolant pair Heat Source Purpose COPSCP

(W/kg)Cycle time

Power(kW)

Zeolite13x–H2O [23] Exhaust Air-conditioner 0.381 26.72

Zeolite13x– H2O [24] Exhaust Air-conditioner 0.153 4.1Consolidated C–CH3OH

[25]Exhaust Refrigeration 0.124 31.61 3961

Activated C–CH3OH [26] Waste heat Refrigeration 0.131 3.61 (kgice) 6004

Silica gel– H2O [27] Solar heat Air-conditioner 0.361 441 4.3

Silica gel– H2O [28] Solar heat Air-conditioner 0.374 64.41 902 7.61

Activated C–CH3OH [29] Solar heat Refrigeration 0.11–0.154.61(k

gice)


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the design.

Fig.1 Schematic Diagram of Absorption Cooling Unit

Fig.2 Graphical Model of Absorption Cooling Unit

Detailed descriptions of each component are as follows:A. Shell Adsorbent Bed

The most important element of refrigerating unit is the adsorbent bed. Due to its poor conductivity, the adsorbent should be carefully considered during the bed's layout if heat transfer conditions are compromised by system performance. Therefore, the cycle time and weight of the bed may be significantly reduced by taking these effects into account.In this study the heat properties of the bed are found to be enhanced by the adsorbent bed. The bed is made up of a tube inserted inside a tubular shell lined with zeolite (zeolite). Natural zeolites (88 to 95% clinoptilolite) in adsorbent bed with a grain size of 0.6 mm is used as an adsorbent. The thermal characteristics of the zeolite are given in Table 2. In accordance to the adsorption capability of balance, Solmus et al.[37] consider isosteric water adsorption energy into natural zeolite.

Table 2. Thermo properties of zeolite

Appearance Ivory white

Porosity (%) 44–51Pore diameter (A) 3pH 7.1–8.2Density (kg m 3) 652–851Melting Point (LC) 1303Surface area (m2 g 1) 27Thermal conductivity(W m K 1) 0.153

Figure 3a, 3b and adsorbent bed components respectively illustrate the adsorbent bed and zeolite tube schemes. The tube is 73 mm in diameter and 765 mm in length of the stainless-steel tube. The ten-meter tube is filled with zeolite around 9/10, and the rest of the top one tenth is a vapor divide. The zeolite used in this refresher system is poor thermal conductor with small cereals which, when packed, result in large resistance. The zeolite is compressed using a stainless-steel disc, known as the compression plate, to maximize heat transfer and thereby increasing thermal response time. In order to ensure that mass transfers are not significantly affected, compression should be restricted within the scope (e.g., 20-25 kPa). In order to achieve a temperature distribution in the zeolite, three thermocouples are distributed on the same axial range. The thermocouples penetrate the coat via a thermocouple feed on the top cover. The adsorber bed coat has a width of 136 mm and a stainless-steel pipe of 821 mm with covers.

(a)



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(b)Fig: 3(a), 3(b) Schematic Diagram Zeolite tube

Fig. 4 Adsorbent Bed ComponentsB. Evaporator

The evaporator consists of a 11 mm diameter and 2.5 m long stainless-steel coil and a thermocouple feed through used to obtain the refrigerant temperatures at the bottom, middle and top of the coil enclosed in housing with blower that act as the output section of cooling unit. Evaporator tube and housing is shown in Figure 5a and 5b.

(a)

(b)Fig. 5 Evaporator (a) Cooling Tube (b) Housing

C. Condensor

As shown in figure 6 the condenser comprises of a pipe bundle and container. The tube pack consists of tubes that condense the refrigerant, 23.5 mm in diameter and 12.5 mm long. A 12v dc fan is attached to condenser to pass more and more air through it to gain more heat exchanging phenomenon through fins of condenser.

Fig. 6 Condenser Tubes

D. Heating and Cooling UnitsA pump heats and cools zeolite alternatively for the heat exchange in the heating and cooling baths. The heating and cooling baths can accommodate 29L. In the heating bath, there are two 1.6 kW electric heaters. A vapor cooling system evaporator is installed in the cooling bath Heat and cooling baths temperature are measured by means of thermocouples. Graphical model ofboth baths is shown in figure 7.

Fig. 7 Graphical Model of Heating and Cooling UnitE. Measurement Instruments

a. ThermocoupleBoth thermo-pairs are K-types in the experimental

model. Thermocouples were connected to vacuum chamber wall to measure temperature of the refrigerant and zeolite.

b. Pressure Gauges In vacuum tube, evaporator and condenser, three bourdon

pressure gages measure the coolant vapour pressure.



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F. Supplementary System ComponentsFor connection of the adsorbed bed, capacitor and

evaporator, the supplementary unit components are:a. Vaccume Ball ValveSix vacuum ball valves are used to control the different

components of experimental system.b. Throttling ValveA throttle device is used to reduce the refrigerant

pressure. Therefore, the capillary tube is used to achieve the required pressure and after the throttling valve is about 0.6 m long.

III. EXPERIMENTAL PROCEDUREThe experimental model is designed by using Solmus et al.[37] method before starting the experiments. The zeolite tube has a specified mass and volume of zeolite. The mass and volume are 1.98 kg and 2.71 liter The adsorbent shell and tube are mounted to the evaporator condenser line, so that the pressure inside the system is below 0.1 kPa. The prototype of the laboratory cools off since only one bed has to be adsorbed. The Dühring diagram in the figure 8 is used to describe an entire adsorption cycle, which includes adsorption and desorption processes. The cycle starts in point A where the adsorbent bed's temperature and pressure are Tadc and Pad, and the zeolite's adsorption capability is limited. The system pressure decreases from PI to Pef as zeolite adsorption capability gradually increasing. This is due to the cooling of the evaporator bath between Tei and Tef. The adsorption stops at B, where the zeolite has maximum adsorption ability. The zeolite heating isosteric ally increases the pressure from Pef to Pc (C).The pressure of the condenser (Pc) is the saturated water pressure corresponding to the condenser's water bath temperature, i.e. Tc. The desorption process begins further heating of the zeolite. Zeolite heat decreases the amount of water absorbed from C to D points at a constant pressure. At D, the zeolite has a minimum adsorption capacity. By comparing the water levels of the condenser at points A and B and water enthalpy of the evaporation, the cooling capacity of prototype can be estimated.

Fig. 8 Adsorption Cooling Cycle (Dühring diagram)

IV. RESULTS AND DICUSSIONThe performance was tested at several temperatures. The power supplies to the system were determined by an hour-watt meter via the electric heaters in the oil bath during the desorption process. The heat loses to the atmosphere from the adsorbent bed result in energy consumption. The performance has been calculated using two different methods. During the desorption process, the first approach was to measure the energy consumption and neglect all the heat loses on the environment and the efficiency. This first method is a hypothetical (ideal) scenario to be followed, but never achieved by the actual system. This was done using an empty adsorbent bed and a time-based measurement of the amount of energy absorbed. The energy consumption in the empty adsorbent bed by the model was separated from the energy supplied during desorption, and the gap between these two factors resulted in net energy (Qu). The second method is to ensure that when desorbing, energy supplied to the system is equal to the amount of energy supplied to the heaters (QI), which are responsible for all atmospheric heat losses, thermal losses and thermal liquids. At least theoretical opportunities for increased system performance are demonstrated by the deviation between these performance measures.The refrigeration capacity was evaluated using the following equation.

Qr=m ad L( Xmax−X min)



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D–A formulas used in the Solmus et al. adsorption and desorption processes[39] are applied to the natural zeolite adsorption potential for both Xmax and XMin. The following equations are used in the estimation of the COP, power density (SCPv) and average mass specific cooling power density (SCP). The operating conditions and results are listed in Table 3.

COP1=Q r

QuCOP2=

Q r

Qi

SCPv=Qr

tcy V ad

SCP=Q r

t cy mad

Table 3. Experimental results and operating conditionsTe (LC)

10 16 21.5

ta 202 213 223td 191 182 182tcy 392 393 404

Tad-h (LC) 151 152 152Tad-c (LC) 52 44 46Tc (LC) 33 32 33Te-i (LC) 11 16 22.45Te-f (LC) 11 12.55 17.45Qi (kJ) 10,612 10,540 10,448Ql (kJ) 9556 9258 9268Qu (kJ) 934 1142 1240Qr (kJ) 254 284 316COP1 0.54 0.53 0.55COP2 0.025 0.026 0.027

SCPv(kW/m3) 4.4 4.81 5.24SCP (W/kg) 5.77 6.53 7.1

A limited number of experimental data was presented in this study as the effect of system parameters on system performance is minimal due to the low adsorption capacity and high energy consumed by the system in the process of desorption of natural zeolite-Water working pairs. The balanced adsorption capacity of water in a natural zeolite at a varying (40–150 LC) temperature and pressure (0.88–7.48 kPa) were previously studied.[37].

In these conditions, Natural Zeolite's maximum adsorption capacity is approximately 0.13 kgw/kgad for 41 LC and 7.48 kPa. The cyclic adsorption range between 45 LC and 150 LC for bed temperature, the maximum steam pressure of 4.35 kPa and the minimum steam pressure 2.83, 1.81 and 1.33 kPa vary from 0.065 to 0.077 kgw/kgad. This is relatively small by the number of other working pairs [37].Table 3 illustrates that the process of adsorption is longer than the desorption. In accordance with some previous studies in the literature[10], [16], the average period of the model is 395 Minutes. This is primarily due to the existing heat transfer limitations in the adsorbent bed Through these limitations the cycle duration of the research model has to be reduced and this is our primary objective for the follow-up research.The cooling capacities of prototype at 11, 16 and 21.5 LC evaporator temperatures are 243, 275 and 324 kJ, respectively. The COP value of the experimental model is around 0.58 at 45 LC adsorption, 140 LC desorption, 35 LC condenser temperature and 21.5LC evaporator, 15LC and 10. The average system COP value is almost 0.027 when considered under the same operating conditions. The mean volumetric cooling power density of the experimental unit is 5.2 kW / m3 and 7 W / kg per m3. With the increasing temperature of the evaporator, SCPv and SCP values for the experimental prototype increase due to an increased adsorbent adsorption capability with an increase in the evaporator temperature.The temperature variation and the coolant pressure in the process of adsorption and desorption in the Duhrings graph and the temporary change in the temperature of the evaporator bath are shown in Fig. 9 for the top and bottom temperature of the initial evaporator. It is noticeable in Fig. 9 that the adsorbent bed temperature during adsorption is not constant unlike the ideal cycle. This increase in temperature due to thermal transfer restriction, the speed at which the heat from the adsorption process is released is higher than the rate of heat transfer from a bed to the atmosphere.



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(a)

(b)

(c)Fig 9. The change in the temperature of zeolite and the pressure of refrigerants during the process of adsorption and desorption and the change in the temperature of the evaporator bath.

When the experiments were performed, the ambient temperature was above the initial temperature of the evaporator. This led to a net transfer of heat from the atmosphere to the evaporator bath Due to its high initial adsorption rate the evaporator bath temperature decreased by about 80 minutes from 22.5 to 17.5 LC, which is then almost constant until the end of the process.

V. CONCLUSIONA thermally powered cooling adsorption system was

developed and fabricated utilizing natural zeolite-water as the working pair. The performance of the experimental model was tested and illustrated through various evaporator temperatures. Mean values for the COP, SCPv and SCP of model were 0.59, 5.3kW / m3 and 6.9W / kg. The experimental prototype's mean cycle duration is about 385min and the adsorption process is longer than the desorption.This research is a basis for our study in the cooling systems of thermal adsorption. Research will be carried out on the new experimental model with the different adsorbed working pairs and the experimental design will be powered by the solar energy. On the other hand, solar-powered adsorption systems that use zeolite water as a working pair could be a reliable and cost-effective alternative that can partially satisfy this increasing refrigeration demand. Pakistan has great potential for solar energy and natural Zeolite resources.

Nomenclature

COP coefficient of performancem mass (kg)P saturation pressure (kPa)SCPv volumetric cooling power density (kW/m3)SCP mass specific cooling power density(W/kg)t time (min)T temperature (LC)

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Abstract - WordPress.com · Web viewNatural zeolites (88 to 95% clinoptilolite) in adsorbent bed with a grain size of 0.6 mm is used as an adsorbent. The thermal characteristics of