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1 Thermal Analyi Of A Silicagel Methanol Adortion Refrigeration Sytem Mr.Anirban Sur 1 Dr.Randi.K.Da 2 1 Aitent Profeor Mechanical Engg. Deartment Inderraatha Engineering College Plot No:63, Site 4, Indutrial Area, Sahibabad Ghaziabad, Uttar Pradeh Profeor Mechanical and Mining machinery Engineering Deartment Indian School Of Mine Dhanbad Jharkhand India 1 ur-anirban@rediffmail.com ABSTRACT A newly deigned adortion ilica gel methanol ytem ha been analyzed in thi aer. In thi adortion refrigeration cycle ytem, two thermal comreor have been ued imultan-eouly. So when one of them i in adortion hae another i in deortion condition. Thu, the roblem of non continuity of refrigeration effect occurring in the conventional adortion ytem ha been removed in thi ytem. To utilize heat energy from low temerature heat ource with temerature ranging from 70 C to 90 C, ilica gel methanol ha been elected a working air. The exerimental reult roved that it i able to roduce a cooling ower of 16.4 kw with a COP of about Although the ytem erformance imrove with increae of regeneration temerature, in thi model deortion roce i retricted due to low temerature (85 C) heat ource. The erformance of the ytem were analyzed for varied regeneration temerature. The adortion cycle ha been decribed with the hel of the analyi reult. Keyword: Adorbate; Adorbent; Adortion; Performance; ilica gel, Methanol 1. INTRODUCTION Adortion i the roce by which molecule of a fluid are fixed on the wall of a olid material. The adorbed molecule undergo no chemical reaction but imly loe energy when being fixed. In adortion roce the hae change from fluid to adorbate (adorbed hae) i exothermic. Adortion occur at the urface interface of two hae, where coheive force including electrotatic force and hydrogen bonding, act between the molecule of all ubtance irreective of their tate of aggregation. Unbalanced urface force at the hae boundary caue change in the concentration of molecule at the olid/fluid interface. The roce of adortion involve earation of a ubtance from one hae accomanied by it accumulation or concentration at the urface of another. The adorbing hae i the adorbent, and the material concentrated or adorbed at the urface of that hae i the adorbate. Aumtion: The baic adortion cycle ha been dicued elewhere and i not reeated here. For theoretical analyi of the cycle the following aumtion are adoted: The thermodynamic equilibrium of the adorbent / adorbate ytem in all oint of the adorber and any given moment; Diffuion occur only in the gaeou hae; The reitance to ma diffuion though the inter article void and the ore i neglected; The adorbate adorbent ytem i treated a a continuou medium for the thermal conduction effect; The reure i aumed to be uniform in the reactor ( = 0); The ytem i conidered to be one-dimenional. Thu, the adorbent temerature i a function of radial direction only. The convection effect within the orou bed are negligible; The wall adorber i homogeneou, thu the thermo hyical roertie of them will be the ame at all oint; The ecific heat of the adorbed methanol i equal to that of the bulk liquid methanol; In the hae adortion-evaoration and deortion-condenation the vaor reure equal the aturation reure at the evaoration and condenation temerature, reectively. In thi analyi, ilica gel-methanol ha been elected a the adorbent adorbate air. Comared with other adorbent, ilica gel can be regenerated at a relatively low temerature (below 100 C, and tyically about 85 C). It i evident that, the COP of water/ ilica gel baed refrigeration ytem i higher than of a methanol/ilica gel baed refrigeration ytem due to the higher latent heat of evaoration of water and latent heat of deortion under ame oerating condition. But, ecific heat of methanol i much lower than that of the water o it require le heat inut comare to water. Water/ilica gel, methanol/ilica gel i the ideal air which may get activated even at a temerature of C. But water i not a uitable refrigerant for ub-zero temerature alication hence for thi ytem methanol/ilica gel adorbent/ refrigerant ha been elected.

2 2. THERMAL ANALYSIS The time behaviour of adortion rate can be decribed by the differential equation given by Sakoda and Sujuki[9] dq( T ) k a ( qmax qo )...(1) K a i the overall ma tranfer coefficient and it can be calculated by an equation rooed by Polanyi. k a 15Do ex( E / RT) 2 a R....(2) Thi equation i uitable for adortion in micro orou material. Adortion rate i controlled by urface diffuion inide a article and the urface diffuivity, and it i given a a function of temerature. In thi equation, D o i the re-exonent contant, E a i the activation energy of urface diffuion and R i the ize of the adorbent article. Adortion equilibrium (q*)kg/kg i varied for different adorber bed temerature a hown in Fig(2) i decribed by Chihara et al[10] by the equation Q*=k(P/P ) 1/n.(3) Where, q* i the amount of adorbent (kg/kg) in equilibrium at reure P (bar). P i the aturation vaour reure of the adorbent and, k & n are contant. Again the value of k can be found by an equation given by Chihara et al[10] K = * /...(4) Where, * i the denity of methanol in adortion hae, i the ore fraction in a article, i the article denity of ilicajel. Adorbate releaed from the adorber bed and deorber bed er kg of adorbent( q) i calculated alo by the equation given by Sakoda A, Suzuki M[9]: P ( Tev ) P ( Tcond ) q k{ }...(5) 1/ n P ( T ) P ( T ) a reg P i the aturation vaour reure of the adorbent at it ecific temerature(t) and, k & n are contant. Adortion and deortion heat energy (ΔH) J/Kg, i required during adortion and deortion rocee can be calculated by heat of ortion of methanol and i calculated a (Tamainot-Telto and Critoh,2001)[8]: ΔH = ART /T at..(6) Where R i the ga contant (R = 260 J/kg K for methanol), T i the amle temerature (K), T at (K) i the aturation temerature correonding to the ga reure P and A i a contant correonding to the loe of the aturation curve on a lot of ln veru -1/T at (Claeyron diagram)[1]. For methanol, A ha been calculated a 4666 K. At an ideal ytem the cooling ower or ecific coling caacity (Q 0 ) of the evaorator i calculated by the equaution Qo. Hev.(7) Where can be calculated by the equation (1) and δh ev i the change in enthaly of methanol in the evaorator. It i calculated by the roerty table of methanol correonding the inlet and outlet condition of methanol. The COP of the ytem i defined a the ratio of heat tranferred in the evaorator ( Q 0 ) to the heat required for regeneration (Q H ) Qo COP.(8) QH Secific cooling ower i the refrigerating effect or cooling ower er kg of refrigerant. It can be found out by the hel of methanol roertie in-late outlet of evaorator. It unit i kw/kg.

3 Reult and Dicuion: Methanol roertie are obtained from Peary and Chilton (1973) a Ln P = a b/(t+ c).. (9) where P i aturation reure in mm Hg, at a given temerature, T and the value of the contant a = , b = K, c = K. Secific heat of methanol i calculated a: Peary and Chilton (1973) C m = a + bt + ct (10) Where contant are: a = kj/kg-k, b = kj/kg, c = 2.59e kj/kg-k, d =-2.85 x kj/kg-K 2 and T in K. Fig. 1 i drawn to analye the variation of regeneration temerature of methanol vaour and it deortion caacity with reect to variou value of contant n by uing Eqn. (5). From thi grah, it can be een that for a fixed regenaration temerature maximun deortion can occur at a fixed value of n. At each regenartion temerature (between 70 C 95 C) maximumm amount of methanol ha been deorbed when value of n i nearly 1.6. So amount of Δq i deendent on the value of n and for maximum amount of Δq in each temerature conidered n=1.6 Fig-1: Relation between T reg, n and q Adortion rate i deendent uon adobent bed temerature. So the amount of methanol adorbed change with the temerature of ilica-gel bed. Fig. 2 how the variation of adorbed ma of methanol a a function of bed temerature. Thi grah i drawn with the hel of Eqn.(3). The adortion caacity of ilica jet bed diminihe with increae in temerature. Hence, it i neceary to maintain the adorber bed temerature at lower value by circulating cold water through the ilica gel bed. Since the thermal comreor work between two reure limit i.e. Between the evaorator reure and the condener reure, a thermal cycle can be lotted by uing Eqn.(3), for different deortion and adortion bed temerature. The cyle i hown in Fig. 3. Thu for given deortion and adortion bed temerature, q (amount of refrigerant adorbed or deorbed er kg of adorbent) can be obtained. For examle, for deortion bed temearture of 363 K and adorbtion bed temerature of 298 K, q ha been etimated a kg/kg Fig-2: Relation between q * V T bed

4 In the ame manner different value of q can be evaluated by varying T reg, in Fig. 3, keeing the evaorator temerature, condener temerature and ambient condition a contant. Again, ince the regeneration and adortion temeeratiure are een clearly in Fig. (3), the adortion cycle can be eaily decribed with the hel of thi figure. Thi figure alo how the beginning and cloing of adortion and deortion rocee.. Fig-3: Thermal cycle of adortion And de-ortion on the aumtion Of P=P(278K,308K) Fig.(4) clearly how that a the T reg increae, the deortion caacity(δq) alo increae, which mean that higher the thermal ource temerature better will be the erformance of thermal comreor. The value of T reg correonding to q = 0 i the minimum inut temerature required to run the ytem for a articular thermal cycle. Fig-4:Realation between q Kg/Kg v t reg k Uing the equation 5,6,7,8 and uing the value of n=1.6, k = 0.267, T ev = 278K, T a = 298K, T cond = 308K and varying the value T reg from 330K to 400K we can oberve the effect of regeneration temerature on Secific Cooling Caacity(SCP) and the coefficient of erformance(cop) of the ytem. Fig-5:Realation between SCP V T reg

5 The variation of SCP with regeneration temerature i hown in fig.-5 and variation of COP of adortion refrigeration ytem a a function of the regeneration temerature i hown in fig-6. The figure how that the theoretical COP of the ytem lie between 0.05 to 0.38 for the regeneration temerature of 340 K to 360 K. Fig-6:Realation between COP V T reg Concluion: Thi aer ha rooed a deign cheme of olar continuou olid adortion refrigeration and made a thermal analyi on that ytem. The relation between adortion deortion ma rate of methanol with reect to variable regeneration temerature and their effect on ecific cooling ower, coefficient of erformance ha been dicued. Thi aer how that uch ytem ha a great-alied value and the theoretical work on the ytem, will make for the otimization of erformance arameter of the exerimental rototye. Reference: [1] HUBARD SS. EQUILIBRIUM DATA FOR SILICA GEL AND WATER VAPOR.IND ENGG CHEM 1954;46(2): [2] YONEZAWA Y, OHNISHI T, OKUMURA S, SAKAI A, NAKANO H, H.T. CHUA ET AL. / INTERNATIONAL JOURNAL OF REFRIGERATION 22 (1999) [3] YONEZAWA Y, MATSUSHITA M, OKU K, NAKANO H, OKUMURA S,YOSHIHARA M, SAKAI A, MORIKAWA A. ADSORPTION REFRIGERATION SYSTEM. US PATENT NO , [4] HA RKO NEN M, AITTOMA KI A. ANALYTICAL MODEL FOR THE THERMAL WAVE ADSORPTION HEAT PUMP CYCLE. HEAT RECOVERY SYST CHP 1992;12(1): [5] JONES JA, CHRISTOPHILOS V. HIGH-EFFICIENCY REGENERATIVE ADSORPTION HEAT PUMP. ASHRAE TRANS 1993;99(1): [6] MILES DJ, SANBORN DM, NOWAKOWSKI GA, SHELTON SV. GAS FIRED SORPTION HEAT PUMP DEVELOPMENT. HEAT RECOVERY SYST CHP 1993;13(4): [7] ZHENG W, WOREK WM, NOWAKOWSKI G. EFFECT OF DESIGN AND OPERATING PARAMETERS ON THE PERFORMANCE OF TWO-BED SORPTION HEAT PUMP SYSTEMS. J ENERGY RESOURCES TECHNO 1995;117: [8]CRITOPHR.E.: PERFORMANCE LIMITATION OF ADSORPTION CYCLES FOR SOLAR COOLING; SOLAR ENERGY; VOL. 41, NO. 1; PP ; [9] SAKODA A, SUZUKI M: FUNDAMENTAL STUDY ON SOLAR POWERED ADSORPTION COOLING SYSTEM, J. CHEM. ENG. JAPAN, 1 (1989) [10] CHIHARA K ET AL, J. CHEM ENG. JAPAN, 16(1983)