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Composite Sorbent of Methanol “Lithium Chloride in Mesoporous Silica Gel” for Adsorption Cooling Machines: Performance and Stability Evaluation Larisa G. Gordeeva,*,† Angelo Freni,‡ Yuri I. Aristov,† and Giovanni Restuccia‡ BoreskoV Institute of Catalysis, NoVosibirsk, Russia, and Istituto di Tecnologie AVanzate per l’Energia “Nicola Giordano”, Messina, Italy
In this paper, a novel composite sorbent of methanol “lithium chloride in mesoporous silica gel” is proposed for adsorption cooling machines. Methanol sorption isotherms were measured by a thermogravimetric technique. This composite demonstrated outstanding methanol sorption ability (up to 0.6 g of methanol per 1 g of dry sorbent). The thermodynamic coefficient of performance (COP), calculated by mathematical modeling for a basic cooling cycle, can reach 0.72 at desorption temperature of 343 K. The real performance was measured by testing this novel material in a lab-scale adsorption chiller. The specific cooling power of 210-290 W/kg and real cooling COP of 0.32-0.4 were obtained. Cycling stability of the sorbent was successfully verified. Such results indicate that the new composite sorbent “lithium chloride in mesoporous silica gel” can be recommended for application in adsorption cooling machines driven by low temperature heat. 1. Introduction The interest in adsorption cooling (or heating) machines driven by low-grade waste heat or solar energy has recently increased. The feasibility of this technology has been demonstrated by realization of prototypes of solar air conditioners, trigenerative systems, and automotive air conditioners.1-3 The level of competitiveness of adsorption machines has been increasing continuously, so that, such systems can be considered almost ready for the market.4,5 Mostly, adsorption machines are realized by using microporous silica gel or zeolite as adsorbent and water as refrigerant. Indeed, water is the perfect refrigerant for adsorption air conditioning/heat pumping except the very low operating pressure. This drawback implies severe mass transfer limitations through the components of the machine and through the adsorbent bed itself. Furthermore, the eventual presence of small amount of air or other inert gases could easily stop the adsorption/desorption process.6 Methanol is considered an interesting alternative to water, due to the higher operating pressure and the lower freezing temperature. However, the low latent heat of methanol and the low sorption ability of common sorbents reduce the efficiency of an adsorption machine using methanol as refrigerant. An attractive way to overcome the poor thermodynamic properties of methanol, is to develop sorbents with outstanding methanol sorption ability. For this reason, a new family of composite sorbents “inorganic salts confined in porous matrices”, has been recently designed specifically for methanol sorption.7 Among the different sorbents synthesized and properly characterized, the composite “lithium chloride in mesoporous silica gel” presents a very high methanol sorption capacity w ) 0.8 kg/kg,8 that is much higher than that of conventional methanol adsorbents, like activated carbons. The aim of this paper is an evaluation of the performance of the composite “lithium chloride in mesoporous silica gel” as a methanol adsorbent for adsorption cooling machines driven by low temperature heat sources (343 K < T < 363 K). First, the isotherms of methanol sorption were measured by a thermo* To whom correspondence should be addressed. E-mail: gordeeva@ catalysis.ru. Tel.: +7 383 326 94 54. Fax. +7 383 330 95 73. Address: Ac. Lavrentiev av. 5, Novosibirsk, 63 00 90, Russia. † Boreskov Institute of Catalysis. ‡ Istituto di Tecnologie Avanzate per l’Energia “Nicola Giordano”.
gravimetric technique via a magnetic suspension balance. Experimental equilibrium curves were used to calculate a thermodynamic cooling coefficient of performance (COP). Afterward, a granulated bed of this composite sorbent was tested in a lab-scale adsorption chiller in order to measure the real performance in terms of COP and specific cooling power (SCP). Finally, a portion of the cycled sorbent was extracted from the experimental setup and properly characterized to verify its stability after 100 cycles. 2. Experimental Researches 2.1. Synthesis of the Composite. Commercial silica gel KSK (average pore diameter dav ) 15 nm, specific surface Ssp ) 300 m2/g, pore volume Vp ) 1.0 cm3/g) was used as a host matrix. The composite LiCl(20%)/SiO2 was synthesized by dry impregnation of the host matrix with an aqueous solution of lithium chloride, followed by thermal drying at 473 K. The salt content in the composite was 20 wt %. 2.2. Characterization. Isotherms of methanol sorption were measured at T ) 311, 324, 328, 335, 353 K and pressure PMeOH ) 4-50 kPa by a thermogravimetric technique based on the use of a magnetic suspension balance Rubotherm.9 About 500 mg of sample was loaded in the balance measuring cell. Preliminarily, the sample was heated up to 373 K under continuous evacuation (residual pressure 0.01 kPa) until reaching the dry weight m0. Afterward, the sample was cooled down to a fixed temperature and then exposed to methanol vapor with a fixed pressure to start equilibrium tests. The methanol vapor pressure was imposed over the sample by connecting the measuring cell with an evaporator filled with liquid methanol. Saturated pressure of liquid methanol in the evaporator was set by a thermostat with an accuracy of (0.1 K. The amount of methanol sorbed at equilibrium m(PMeOH,T) was measured as the final increase in the sample weight at fixed T and PMeOH. The methanol sorption was characterized by the methanol uptake w ) m(PMeOH,T)/m0. Nitrogen adsorption isotherms were measured by a Sorptomatic 1990 instrument at 77 K to obtain Ssp (BET), Vp, and dav (BET). Phase composition of the composites was characterized in situ by an X-ray diffraction (XRD) using a Philips PW diffractometer with Cu KR radiation in an air environment at
10.1021/ie8016303 CCC: $40.75 2009 American Chemical Society Published on Web 05/22/2009
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∑ (m˙ c ∆T ) i p
COP )
i ev∆t
i
∑ (m˙ c ∆T ) i p
(2)
i bed∆t
i
where m ˙ i and ∆Ti are the instantaneous mass flow and the instantaneous difference in temperature between the inlet and outlet of the external heat transfer fluids through the evaporator or the adsorbent bed. 3. Results and Discussion
Figure 1. Scheme of the lab-scale chiller: (1) heat storage tank, (2) heat exchanger (heating loop), (3) heat exchanger (cooling loop), (4) adsorbent bed, (5) vacuum chamber, (6) evaporator, (7) condenser, (8, 9) thermocryostats. Table 1. Main Properties of the Tested Adsorbent Bed mass of sorbent, kg sorbent particle size, mm mass of metal, kg heat exchanger area, m2 heat exchanger size, mm metal to adsorbent ratio
3.1. Methanol Sorption Equilibrium. Methanol sorption isotherms presented in Figure 2a demonstrate a little uptake at low methanol pressure that can be attributed to the adsorption on the active centers of the silica gel surface. At increasing methanol pressure, the salt starts to sorb methanol due to reaction LiCl + 3CH3OH ) LiCl · 3CH3OH and transforms to LiClmethanol solution inside silica pores.8 A sharp rise in the uptake in a narrow pressure range corresponds to this transformation. Further increase in methanol pressure leads to gradual uptake growth that is typical for the salt solution. The total amount of methanol sorbed reaches 0.6 g/g that is significantly larger than that typical of the conventional methanol adsorbents like activated carbons and zeolites (0.2-0.4 g/g).10-12 Methanol uptake presented as a function of the free sorption energy ∆F ) RT ln(Ps/PMeOH) (Figure 2b) agrees well with that on
0.62 0.2-0.4 0.86 2.9 300 × 300 × 23 1.38
room temperature. The diffraction patterns were recorded by 0.05° step scanning at the 2θ angle range from 25 to 65°. 2.3. Description of the Experimental Setup. Figure 1 shows the scheme of the lab-scale chiller used to evaluate the dynamic performance for the proposed composite sorbent. The main component of the chiller is a vacuum chamber where an adsorber is placed. The chamber is connected to an evaporator and a condenser by means of vacuum valves. An external circuit allows the heating/cooling of the adsorber by means of two plate heat exchangers connected respectively to an electric boiler of diathermic oil and to a water chiller. The adsorber was realized by embedding 0.62 kg of sorbent grains inside a compact heat exchanger of a finned flat-tube type. This configuration presents the following peculiarities: (i) compactness and low weight, as the heat exchanger is made of aluminum; (ii) good heat transfer properties, due to the high heat transfer area; (iii) high vapor permeability, due to a granular shape of the sorbent. Table 1 shows the main properties of the adsorbent bed. The adsorption cooling cycles were simulated by properly setting the inlet temperature of the external heat transfer fluids of the adsorbent bed, evaporator, and condenser. Since the experimental unit was a single-bed system, the useful effect was intermittent. The SCP was calculated as a ratio between the useful cooling effect and the total time cycle multiplied by the sorbent mass; the COP was calculated as a ratio of the useful cooling effect and the total amount of energy supplied for desorption from the external heating source:
∑ (m˙ c ∆T ) i p
SCP )
i ev∆t
i
msτcycle
(1)
Figure 2. Isotherms (a) and temperature independent curves (b) of methanol sorption on (solid symbols, s), and desorption from (open symbols, - -), LiCl(20%)/SiO2 composite and LiCl(31%)/SiO2(Grace 8926.02) composite (---).8 T ) 311 (1), 324 (2), 328 (3), 335 (4), and 353 (5) K.
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Figure 3. The isosteric chart for LiCl(20%)/SiO2 composite and typical ice making and air conditioning cycles.
Figure 5. Ideal and experimental cooling cycles plotted over the Clapeyron diagram.
Figure 4. Cooling COP for composite LiCl(20%)/SiO2 (1) and commercial activated carbon AC35 (2), calculated at Tev ) 283 K and Tcon ) Tads ) 308 K.
Figure 6. Evolution of the inlet (s) and outlet (- - -) temperature of the external heat transfer fluid of the adsorber and the mean temperature of the bed (---) during four continuous cycles. Tev ) 283 K, Tcon ) Tads ) 303 K, Tdes ) 358 K.
LiCl(31%)/SiO2(Grace 8926.02) composite,8 but demonstrates reduced sorption capacity due to lower salt content. This indicates an identical sorption mechanism on both the composites. Figure 3 shows the equilibrium set of isosteric curves for LiCl(20%)/SiO2 that was designed on the basis of the experimental isotherms. The same figure presents also typical thermodynamic cycles for an adsorption ice-maker (Tev ) 271 K, Tcon ) Tads ) 303 K) and an air conditioner (Tev ) 280 K, Tcon ) Tads ) 308 K). The composite shows an outstanding uptake variation per these cooling cycles (∆w ) 0.27 g/g for ice maker, ∆w ) 0.58 g/g for air conditioner). Moreover, the required desorption temperature is low (Tdes ) 348-353 K for ice maker, Tdes ) 353-358 K for air conditioner), that allows efficient utilization of low grade waste heat or solar energy. 3.2. Calculation of the Cooling COP. The thermodynamic cooling COP for the working pair LiCl(20%)/SiO2-methanol was calculated by a mathematical model, previously developed and presented.13 The calculations were performed on the basis of the experimental equilibrium curves previously discussed. Figure 4 shows the single-bed cooling COP as a function of the desorption temperature. The other operating conditions are as follows: evaporator temperature Tev ) 283 K, condenser temperature Tcon ) 303 K, minimum temperature of adsorption Tads ) 308 K. The COP calculated for commercial activated carbon AC35 was added for comparison purposes. The results obtained indicate that the novel sorbent presents the COP between 0.72 and 0.77 for the desorption temperature range of 343-358 K. Such values are noticeably higher than COP values calculated for AC35 (Figure 4) and comparable with those
typical of best water sorbents. The attractive estimated ideal performance of composite LiCl(20%)/SiO2 is evidently due to its high methanol sorption ability that compensates the intrinsically low heat of methanol evaporation. The simulation model used for this thermodynamic evaluation does not take into account the mass of metal of the heat exchanger as well as other parameters (parasitic losses, heat exchanger efficiency, etc.) that surely leads to a real COP lower than the calculated one. Aim of the following evaluation of the experimental performance is to directly quantify such a value. 3.3. Experimental Evaluation of the Performance. Figure 5 shows a typical experimental cycle (Tev ) 283 K, Tcon ) Tads ) 303 K, Tdes ) 358 K) plotted on the isosteric diagram reported above. It is evident that the experimental cycle fits quite well with the ideal one; the isosteric heating/cooling phases follow satisfactorily the theoretical isosters. During the isobaric phases, the pressure inside the bed tends to a constant value which is slightly lower/higher than the methanol vapor pressure fixed at the evaporator/condenser. This effect is probably due to the under-sized evaporator and condenser, which are not able to provide the proper heat transfer and consequently evaporation/ condensation rate. Figure 6 shows the evolution of the inlet/outlet temperature of the external heat transfer fluid through the adsorbent bed and the mean temperature of the bed during four continuous cycles. The fluctuating temperatures at the inlet of the external heating/ cooling heat transfer fluid were due to insufficient power level of the heat source/sink. Notwithstanding the granular shape of the sorbent, the measured cycle time was relatively short (about
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Figure 7. Heat transfer rate for the heating/desorption and adsorption/ evaporation phases. Tev ) 283 K, Tcon ) Tads ) 303 K, Tdes ) 358 K.
Figure 8. Experimental specific cooling power and cooling COP for composite LiCl(20%)/SiO2 vs desorption temperature (Tev ) 283 K, Tcon ) Tads ) 303 K).
16 min). This good result depends on several factors which influence the heat and mass transfer properties of the adsorbent bed: (i) large heat transfer area of the finned flat-tube type heat exchanger; (ii) narrow distance between fins; (iii) low metal to adsorbent mass ratio; (iv) small particle size of the adsorbent; (v) low mass transfer resistance due to the relatively high pressure of the methanol vapor and to the highly porous adsorbent bed. As a consequence, the thermal power exchanged was quite high, as shown in Figure 7, in which the profile of heat transfer rate is presented for the heating/desorption and evaporation phases. The intermittent useful effect produced is due to the single bed configuration of the chiller. During the adsorption phase, the mean instantaneous useful effect was 376 W. The corresponding specific cooling power SCP, calculated considering the total cycle time, was 272 W/kg of dry sorbent. The instantaneous mean power supplied during the heating/desorption phase was 900 W. The corresponding experimental cooling COP was 0.35. The obtained COP is sensibly lower than the value calculated by the thermodynamic model. This result was expected, as the real performance of the chiller is influenced by the inert masses, heat losses, etc. However, a cooling COP in the range 0.3-0.4 can be considered sufficient for those applications that use waste or solar heat as the driving source. It is worthy to mention that the temperatures of the heat source/
sink for heating/cooling the adsorbent bed were set at 363 and 298 K, respectively, giving ∆T ) Th - Tdes ) Tads - Tc ) 5 K (Th and Tc are the inlet temperature of the external heating and cooling fluid, respectively). The above-described results of the base-case were extended measuring the experimental cooling COP and SCP for different maximum desorption temperatures. The other operating conditions were fixed as: Tev ) 283 K, Tcon ) Tads ) 303 K. Figure 8 shows the obtained results putting in evidence that composite LiCl(20%)/SiO2 provides high performance for the investigated desorption temperature range. Indeed, a cooling COP ) 0.32-0.40 and a SCP ) 210-290 W/kg were measured. Increase in the desorption temperature over 368 K does not provide evident benefit, because the composite already desorbed the majority of methanol, so that the cycle is prolonged without an additional useful effect. To have a more general idea about the performance of the proposed working pair, Table 2 shows the performance comparison with other working pairs tested by the authors in the same lab-scale chiller. All test were carried out in similar conditions setting ∆T ) Th - Tdes ) Tads - Tc ) 5 K. The hydrophobic zeolite CBV901 was proposed as methanol adsorbent and tested in the lab-scale chiller as a finned-tube stainless steel heat exchanger coated with a consolidate zeolite layer.14 The obtained performance was quite poor, mainly due to the limited heat transfer efficiency of the stainless steel heat exchanger and the insufficient adsorption capacity of this zeolite (lower than 0.18 g of methanol per 1 g of dry sorbent). The composite water sorbent SWS-1 L “calcium chloride in mesoporous silica gel” was proposed by the authors for adsorption air conditioning. A finned-tube stainless steel heat exchanger filled with loose grains of sorbent was previously tested,15 showing high cooling COP. It was caused by very high water sorption capacity of SWS-1 L (more than 0.7 g of water per 1 g of dry sorbent). Low SCP was due to the poor heat transfer properties of the granulated adsorbent bed. Afterward, a finned-tube aluminum heat exchanger was coated with an SWS-1 L layer of 5 mm thickness.16 This arrangement made it possible to reduce the cycle time and thus to increase noticeably the SCP up to few hundreds W/kg. However, it was found that the consolidated layer of sorbent was too thick, so that the mass transfer became the new limiting factor. As a result, the amount of water adsorbed/desorbed was reduced that affected the cooling COP. Differently, in this paper it is demonstrated that an adsorbent bed made of finned flat-tube heat exchanger with high heat exchange area, filled with grains of the new composite sorbent of methanol possesses high sorption capacity and good heat and mass transfer properties. A further performance improvement could be obtained realizing heat exchangers coated with a layer of sorbent. In this case, the thickness of the coating has to be limited to a few millimeters, to prevent mass transfer limitations. 3.4. The Composite Stability. The adsorbent durability upon adsorption/desorption cycles is of primary importance for evaluating the practical potential of the material. Changes in the material adsorption properties can be caused by destroying the microstructure or phase transformation in the adsorbent.
Table 2. Performance of Various Working Pairs Measured in the CNR-ITAE Lab-Scale Adsorption Chillers adsorbent bed configuration
adsorbate
COP
Tdes, K
SCP, W/kg
cycle time, min
LiCl in SiO2 loose grains on finned flat-tube heat exch. CBV901 zeo coated on finned tubes heat exch. SWS-1 L loose grains on finned tubes heat exch. SWS-1 L coated on finned tubes heat exch.
methanol methanol water water
0.32-0.4 0.1-0.12 0.4-0.6 0.15-0.3
353-368 353-368 363-373 363-373
210-290 30-60 20-40 150-200
8-18 15-20 90-150 15-20
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tion of LiCl-CH3OH solution inside pores. No crystalline solvates were observed in silica pores during sorption. Subsequently, destruction of the composite structure is not expected. Nevertheless, to demonstrate that the properties of LiCl(20%)/ SiO2 composite are stable, a portion of the tested sorbent was extracted from the lab-scale chiller after cycling (100 cycles were carried out) and characterized. In particular, the sorbent porous structure, phase composition, and methanol sorption equilibrium were measured and compared with the fresh sample. The XRD patterns of both the fresh and tested composites (Figure 9a) indicate the crystalline phases of LiCl with cubic structure (JCPDS No. 04-0664) and monohidrate LiCl · H2O formed due to sorption of water vapor from the air LiCl + H2O ) LiCl · H2O at ambient temperature.17,18 At increasing temperature the monohydrate transforms back to anhydrous LiCl (Figure 9a). The size of coherently scattering domains of both the composites was 20-30 nm, which was close to the pore diameter of the silica gel. Bulk crystals of LiCl were not detected in the composites indicating no salt leakage from the pores. The data on low temperature nitrogen adsorption (Figure 9b) presented similar characteristics for both the freshly prepared and tested composites: Ssp ) 166 and 163 m2/g, Vp ) 0.58 and 0.61 cm3/g and dav ) 14.0 and 14.9 nm, respectively. Finally, the data on methanol sorption of tested composites agree well with that measured for the fresh sample. In conclusion, the porous structure, phase composition, and sorption properties of the composite remain stable after cycling, which allows us to expect good durability of LiCl(20%)/SiO2 composite upon further cycling. 4. Conclusions The novel composite sorbent “lithium chloride in mesoporous silica gel” demonstrated very high methanol sorption ability (up to 0.6 g of methanol per 1 g of dry sorbent) and a relatively low regeneration temperature (T < 363 K). The performance of the working pair in the adsorption cooling cycle were evaluated by calculating the cooling COP and by testing the sorbent in a lab-scale chiller. The calculated thermodynamic cooling COP reached 0.72 at the maximum desorption temperature 343 K. The testing in the lab-scale chiller showed that is possible to reach a SCP of 290 W/kg and cooling COP of 0.4. The attractive performance measured, together with the successful verification of the cycling stability, demonstrates that the new composite sorbent of methanol can be efficiently used for realization of light and compact adsorption chiller driven by low grade waste or solar heat. Acknowledgment This work was performed in the frame of cooperation agreement between CNR and RAS. The Russian authors thank the Russian Foundation for Basic Researches (Grant 08-0800808) and SB RAS (Integration project N 11) for partial financial support of this work. Figure 9. XRD pattern (a) and pore size distribution (b) of the fresh (1, 3) and tested (2) LiCl(20%)/SiO2 composites. XRD patterns were measured at T ) 298 (1, 2) and 383 K (3).
Nomenclature
These transformations can be expected due to successive formation and decomposition of the crystalline solvates inside the pores. Actually, if the molar volume of dry salt and its solvate differ significantly, the adsorption is accomplished by the swelling of the salt crystallites that can destroy the matrix. Our previous study,8 showed that the methanol sorption on LiCl(31%)/SiO2(Grace 8926.02) composite results in the forma-
COP ) coefficient of performance cp ) heat capacity, J/(g K) dav ) average pore diameter, nm ∆F ) Dubinin-Polanyi potential, J/mol m ) mass of methanol adsorbed, g m0 ) mass of dry sorbent, g m ˙ i ) mass flow, g/s PMeOH ) methanol pressure, Pa
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Ps ) saturation pressure, Pa R ) gas universal constant, J/(mol K) SCP ) specific cooling power, W/kg Ssp ) specific surface, m2/g T ) temperature, K ∆Ti ) difference in inlet/outlet temperature, K τ ) total time of cycle, s Vp ) pore volume, cm3/g w ) methanol uptake, g/g ∆w ) variation of uptake per cycle, g/g Subscripts ads ) adsorption con ) condensation des ) desorption ev ) evaporation h ) heating fluid c ) cooling fluid s ) sorbent
Literature Cited (1) Critoph, R. E.; Zhong, Y. Review of trends in solid sorption refrigeration and heat pumping technology. Proc. IMechE., Part E. 2005, 219, 285. (2) Henning, H. M. Solar assisted air conditioning of buildingssan overview. Appl. Therm. Eng. 2007, 27, 1734. (3) de Boer, R.; Chwieduk, D.; Critoph, R. E.; Malvicino, C.; Restuccia G. SOCOOL - Solid Sorption System for Cooling in Tri-generation, Proceedings of the 3rd International Conference on Heat Powered Cycles, HPC 2004, Cyprus, October 11-13, 2004, ISBN 01874418353, paper 1212. (4) Paulusen, S.; Braunschweig, N.; Mittelbach, W. A novel compact adsorption chiller in the range of 10 kW of cooling power, Proceedings of the Solar Air-Conditioning International Conference, Germany, October 67, 2005; Bildungszentrum der Hanns-Seidel-Stiftung e.V. Kloster Banz 96231 Bad Staffelstein. (5) Wang, R. Z.; Oliveira, R. G. Adsorption refrigeration-an efficient way to make good use of waste heat and solar energy. Prog. Energy Combust. Sci. 2006, 32, 424. (6) Glaznev, I. S.; Aristov, Yu. I. Kinetics of water adsorption on loose grains of SWS-1L under isobaric stages of adsorption heat pumps: The effect of residual air. Int. J. Heat Mass Transfer 2008, 51, 5823.
(7) Gordeeva, L. G.; Freni, A.; Restuccia, G.; Aristov, Yu. I. Influence of characteristics of methanol sorbents “salt in mesoporous silica” on the performance of adsorptive air conditioning cycle. Ind. Eng. Chem. Res. 2007, 46, 2747. (8) Gordeeva, L. G.; Freni, A.; Krieger, T. A.; Restuccia, G.; Aristov, Yu. I. Composite sorbents “LiCl in silica gel pores”: methanol sorption equilibrium. Microporous Mesoporous Mater. 2008, 112, 254. (9) Dreisbach, F.; Lo¨sch, H. W.; Harting, P. Highest pressure adsorption equilibria data: Measurement with magnetic suspension balance and analysis with a new adsorbent/adsorbate-volume. Adsorption 2002, 8, 95. (10) Wang, L. W.; Wang, R. Z.; Wu, J. Y.; Wang, K.; Wang, S. G. Adsorption ice makers for fishing boats driven by the exhaust heat from diesel engine: Choice of adsorption pair. Energy ConVers. Manage. 2004, 45, 2043. (11) Restuccia, G.; Freni, A.; Vasta, S.; Russo, F.; Brigandi, A. Hydrophobic zeolite/methanol experiments on a lab scale refrigeration system with a thermally efficient coated heat exchanger, Proceedings of the 5th International Seminar, Heat Pipes, Heat Pumps, Refrigerators, Minsk, Belarus, September 8-11, 2003, p 281. (12) Hamamoto, Y.; Alam, K. C. A.; Saha, B. B.; Koyama, S.; Akisawa, A.; Kashiwagi, T. Study on adsorption refrigeration cycle utilizing activated carbon fibers. Part 1. Adsorption characteristics. Int. J. Refrig. 2006, 29, 305. (13) Cacciola, G.; Restuccia, G. Reversible adsorption heat pump: A thermodynamic model. Int. J. Refrig. 1995, 18, 100. (14) Restuccia, G.; Freni, A.; Russo, F.; Vasta, S. Experimental investigation of a solid adsorption chiller based on a heat exchanger coated with hydrophobic zeolite. Appl. Therm. Eng. 2005, 25, 1419. (15) Restuccia, G.; Freni, A.; Vasta, S.; Aristov, Yu. I. Selective water sorbent for solid sorption chiller: Experimental results and modelling. Int. J. Refrig 2004, 27, 284. (16) Freni, A.; Russo, F.; Vasta, S.; Tokarev, M.; Aristov, Yu. I.; Restuccia, G. An advanced solid sorption chiller using SWS-1L “CaCl2 in mesoporous silica gel”. Appl. Therm. Eng. 2007, 27, 2200. (17) Lerner, H.-W.; Bolte, M. An orthorombic modification of lithium chloride monohydrate. Acta Crystallogr. 2003, 59, 20. (18) Gordeeva, L. G. Novel adsorbents for thermal-chemical energy conversion. Ph.D. Thesis. Boreskov Institute of Catalysis, Novosibirsk, Russia, 1998.
ReceiVed for reView October 27, 2008 ReVised manuscript receiVed April 29, 2009 Accepted May 5, 2009 IE8016303
