THERMODYNAMIC ANALYSIS OF ADSORPTION COOLING CYCLE USING CONSOLIDATED COMPOSITE ADSORBENTS - ETHANOL PAIRS

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1 VOL., NO. 2, OCTOBER 26 ISSN Asian Research Publishing Network (ARPN). All rights reserve. THERMODYNAMIC ANALYSIS OF ADSORPTION COOLING CYCLE USING CONSOLIDATED COMPOSITE ADSORBENTS - ETHANOL PAIRS Animesh Pal,2,5, Ibrahim I. El-Sharkawy 2,,4, Biyut Baran Saha,2,, Khairul Habib 6, Takahiko Miyazaki 2,4 an Shigeru Koyama 2,4,5 Kyushu University Program for Leaing Grauate School, Green Asia Eucation Center, Interisciplinary Grauate School of Engineering Sciences, Kyushu University, Fukuoka, Japan 2 International Institute for Carbon-Neutral Energy Research, Kyushu University, Fukuoka, Japan Mechanical Power Engineering Department, Faculty of Engineering, Mansoura University, El-Mansoura, Egypt 4 Faculty of Engineering Sciences, Kyushu University, Fukuoka, Japan 5 Interisciplinary Grauate School of Engineering Sciences, Kyushu University, Fukuoka, Japan 6 Department of Mechanical Engineering, Universiti Teknologi Petronas, Perak Darul Rizuan, Malaysia saha.baran.biyut.2@m.kyushu-u.ac.jp ABSTRACT This stuy eals with the thermoynamic analysis of asorption cooling cycle using consoliate composite asorbents-ethanol pairs. The stuie composites are name as composite A (5% Maxsorb III, 4% expane graphite (EG), % biner) an composite C (% Maxsorb III, 2% expane graphite (EG), % biner). The Dubinin- Raushkevich (D-R) an Dubinin Astakhov (D-A) equation are use to raw pressure-temperature-concentration (P-T-W) iagrams of the assorte pairs. The specific cooling effect (SCE) an coefficient of performance (COP) of both pairs have been simulate for esorption temperatures ranging from 4 to 9 ºC at ifferent evaporator temperatures along with a heat sink at ºC by consiering a time inepenent thermoynamic moel. The imum COPs of composite A-ethanol an composite C-ethanol base cooling systems are foun to be.69 an.65, respectively. Keywors: consoliate composite asorbent, asorption cooling system, ethanol, performance evaluation. INTRODUCTION Asorption cooling systems have attracte much attention in the last two ecaes as it can be riven by low temperature waste heat an can utilize environmentally frienly asorbents-rigerants pairs such as silica gelwater, activate carbon (AC) fibers-ethanol, an AC power-ethanol [-8]. However, the main ifficulty for spreaing this technology is the poor system performance an bulkiness that is ue to the limitation of sorption capacity an low heat transfer rate insie the asorber/esorber reactors. Enhancement of heat an mass transfer rate insie absorber be coul be one of the possible methos to enhance the system performance an size reuction. Recently, several notable researchers have been focuse on composite material in orer to improve the system performance. Following are some representative examples; El-Sharkawy et al. [9] prepare consoliate composite asorbents an experimentally investigate the asorption uptake an thermal conuctivities. Authors reporte the thermal conuctivity of composite asorbents showe up to times than that of Maxsorb III. Cacciola et al. [] evelope asorbent materials as a block using polytetrafluorethylene biner an AC. Results showe effective thermal conuctivity ranging between. an.2 W m - K -. Jin et al. [] stuie consoliate AC with chemical biner, an consoliate AC with expane natural graphite. The thermal conuctivity of granular AC with ifferent sizes almost maintains a constant at.6 Wm - K -, while the value moestly increases to.4 Wm - K - for the consoliate AC with chemical biner. Zhao et al. [2] use granular AC with thermal conuctivity is.6 Wm - K -. Results showe that with the aition of ENG-TSA, the thermal conuctivity of composite AC is increase significantly. This stuy aims to evaluate the performance of an ieal asorption cooling cycle in terms of SCE an COP using consoliate composite asorbents-ethanol pairs for further improvement of asorption cooling cycle. NOMENCLATURE Cp specific heat (kj kg - K - ) COoefficient of performance (-) E asorption characteristics (kj kg - K - ) LH latent heat (kj kg - K - ) n exponent of D-A equation quilibrium pressure (kpa) P s saturation pressure (kpa) R g gas constant (kj kg - K - ) T temperature (K or C) Q h heat ae (kj kg - ) Q st heat of asorption (kj kg - ) SCE specific cooling effect (kj kg - ) Ts,a temperature at the starting of asorption ( C) a temperature at the en of asorption ( C) Ts, temperature at the starting of esorption ( C) temperature at the en of esorption ( C) W asorption uptake at equilibrium (kg kg - ) W imum asorption uptake (kg kg - ) Subscripts a asorbent c conenser e evaporator 224

2 VOL., NO. 2, OCTOBER 26 ISSN Asian Research Publishing Network (ARPN). All rights reserve. s sens rigerant saturation sensible imum imum Ln(P) ADSORPTION COOLING CYCLE The schematic iagram of asorption cooling system an the thermoynamic processes of a basic asorption cycle are shown in Figures- an, respectively. It consists of an evaporator, a conenser, an asorber/esorber, an a throttling valve or a bening capillary tube, which is use to connect the conenser an the evaporator. As can be seen from Figure- the ieal cycle consists of four steps, which are pre-heating, esorption process, pre-cooling, an asorption process. In the first step, the asorber is isconnecte from both the evaporator an the conenser. It is then heate by external heat source at constant rigerant concentration, which results in the temperature increase of rigerant from a to Ts,. The asorber pressure increases from the evaporating pressure up to the conensing pressure. In the secon step, asorber is connecte to the conenser an the heat ae from external source continues in this process. The rigerant vapor is esorbe at constant pressure, Pc, while the temperature increases until it reaches the esorption temperature,. The esorbe rigerant vapour is liquefie in the conenser an the conensing heat is remove by coolant of temperature Tc that flows insie the conenser heat transfer tubes. In the pre-cooling process, the asorber is isolate from both the evaporator an the conenser. It is then coole own at constant rigerant concentration from to Ts,a by coolant. The pressure of the asorber ecreases from conenser pressure own to the evaporator pressure. In the last step, the asorber is connecte to the evaporator an asorb the rigerant vapour from the evaporator. During the asorption process the asorber is coole from Ts,a to a. Asorption heat is remove by coolant that flows insie the asorber. Figure-. Thermoynamic process of the basic asorption cooling cycle. THERMODYNAMIC FRAMEWORK In this stuy two types of consoliate composite asorbents have been use, namely composite A, an composite C for investigating the performance of ieal asorption cooling cycle. Composite A comprises of 5% Maxsorb III, 4% EG, % biner whilst composite C contains % Maxsorb III, 2% EG, % biner. The preparation process; porous properties; asorption uptake measurement proceure; an thermal conuctivities of these asorbents can be foun in El-Sharkawy et al. [9]. Dubinin Raushkevich (D-R) an Dubinin Astakhov (D- A) equations are use, respectively, to fit asorption uptakes of composite A an composite C as written by Equation. () an Equation. (2) below. The estimate fitting parameters reporte by El-Sharkawy et al. [9] are furnishe in Table-. 2 R g T P s () W W exp ln E P W W Te Tc a R gt P s exp ln E P Asorption n Ts, Ts,a T T (2) Specific cooling effect (SCE) can be efine as the following equation: SCE W W LH Tc Te Cp T () The coefficient of performance (COP) can be written as: SCE COP (4) Q sens Q latent where, Ts, Q Cp T W Cp T WCp T (5) sens an, a a W a Ts, Q Q W (6) latent st W Figure-. Schematic iagram of basic asorption cooling system. 225

3 VOL., NO. 2, OCTOBER 26 ISSN Asian Research Publishing Network (ARPN). All rights reserve. Table-. Fitting parameters of D-R an D-A equation of stuie composite asorbents-ethanol pairs [9]. Composite A: 5% Maxsorb III, 4% EG, % biner C: % Maxsorb III, 2% EG, % biner W [kg kg - ] E [kj kg - ] n [-] In Equation (5), the first term efines the sensible heat ae to the asorbent consequently its temperature increases from a to whilst the secon an thir terms are represente sensible heat ae to the rigerant uring pre-heating an the esorption process, respectively. The specific heat capacity of asorbent (Cp a) is calculate accoring to El-Sharkawy et al. [9] an has been taken constant for the range of temperature utilize. Q st is the heat of asorption in Equation. (6). Clausius Clapeyron equation (Equation. ) is use to compute the average value of heat of asorption. It is foun that value of the average heat of asorption (Q st) for the composite A an composite C are 995 kj kg - an 96 kj kg -, respectively. Q Asorption Uptake [kg kg - ] Rgln P T st W cons tan t () Asorption Uptake [kg kg - ] Asorption temperature, C Asorption temperature, C RESULTS AND DISCUSSIONS The asorption isotherms as shown in Figures-2. a-2.b for composite A-ethanol pair an composite C- ethanol pair are preicte from measure ata, where experiments have been conucte at three evaporator temperatures of 5,, an 5 C whilst changing the asorption temperature from 2 to C [9]. The pressure-temperature-concentration (P-T-W) iagram is use to analysis the performance of an ieal asorption cooling cycle. It shows the thermoynamic relation between the equilibrium pressure, asorbent temperature an asorption capacity at equilibrium conitions. The D- R equation has been use to raw the P-T-W iagram of composite A-ethanol pair, whilst D-A equation is use to raw the P-T-W iagram of composite C-ethanol pair, which are shown in Figure-.a an Figure-.b, respectively. Figures-4.a-4.b show the effect of esorption temperature on the SCE of composite A-ethanol an composite C-ethanol pair, respectively, at ifferent evaporator temperatures, namely,, an 5 C. It is seen that the SCE increases linearly with the increases of esorption temperature. This is ue to the increases of concentration ifference with the increases of esorption temperature at constant asorption an evaporator temperatures.. T e Asorption a T Ts,a Ts, c Temperature [ºC] Asorption T e a T Ts,a Ts,. c Temperature [ºC] Figure-. P-T-W iagram of composite A-ethanol pair, an composite C-ethanol pair Figure-2. Preicte asorption isotherms of composite A-ethanol pair, an composite C-ethanol pair. 226

4 VOL., NO. 2, OCTOBER 26 ISSN Asian Research Publishing Network (ARPN). All rights reserve. SCE [kj kg - ] SCE [kj kg - ] Evapoartor temperature [ºC] Figure-4. Specific cooling effect (SCE) of composite A, an composite C with function of esorption temperature. It is observe that consoliate composite A- ethanol asorption cycle can achieve SCE as about 98 kj kg - at evaporation 5 ºC along heat source 9 ºC whilst composite C-ethanol pair gives about 56 kj kg -. Figures- 5.a-5.b show the effect of esorption temperature on COP of both pairs, respectively. It can be seen that the COP increases sharply only when the esorption temperature is below C. After that, the increase in COP is marginal even though the SCE increases. This happens ue to the requirement of heat input becomes significantly large when the temperature ifference between heat source an heat sink is relatively high. The imum COPs of composite A-ethanol an composite C-ethanol base cooling systems are foun to be.69 an.65, respectively. In aition, both consoliate composite asorbents show much higher thermal conuctivity compare to parent material Maxsorb III, which is reporte by El-Sharkawy et al. [9]. COP [-] COP [-] Figure-5. Effect of esorption temperature on COP for composite A, an composite C. CONCLUSIONS The ieal asorption cooling cycle base on consoliate composite, namely, composite A an composite C, asorbents-ethanol pairs has been investigate. The Dubinin-Raushkevich (D-R) an Dubinin Astakhov (D-A) equations have been use to raw P-T-W iagrams of the assorte pairs. The specific cooling effect (SCE) an coefficient of performance (COP) of both pairs have been estimate for esorption temperatures ranging from 4 to 9 ºC at ifferent evaporator temperatures along with a heat sink at ºC. It is foun that consoliate composite A-ethanol asorption cycle can achieve SCE an COP as about 98 kj kg - an.69, respectively, at evaporation 5 ºC along heat source 9 ºC whilst composite C-ethanol pair gives about 56 kj kg - an.65. Both pairs show high SCE an COP with much higher thermal conuctivity compare to Maxsorb III, which may lea to compact esign of asorption cooling systems. REFERENCES Saha B.B., Koyama S., Kashiwagi T., Akisawa A., Ng K.C., an H. T. Chua, Waste heat riven ual-moe, multi-stage, multi-be regenerative asorption system, Int. J. Refrig. 26 (2) Habib K., Saha B.B., Koyama S., Stuy of various asorbent rigerant pairs for the application of solar 22

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