Impacts of desiccant liquid properties on the membrane based heat exchanger performance

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1 4 èe Conférence Interntione des Energies Renouvebes (CIER-2016) Proceedings of Engineering nd Technoogy PET Vo.14, pp Ipcts of desiccnt iquid properties on the ebrne bsed het exchnger perfornce Seifennsr Sbek 1*, Fys Tiss 1, Ridh Chouikh 2, Aenh Guizni 1 1 Ther Process Lbortory Reserch nd Technoogies Center of Energy, Borj-Cedri Science nd Technoogies Prk, BP 95, 2050 H-if, Tunisi 2 Physics Deprtent, Fcuty of Science, King Khid University, P. O. Box 9004, Abh 61413, Sudi Arbi * Seifennsr.sbek@gi.co Abstrct The ebrne bsed het exchnger is new proposition of cen ir conditioning technoogies in which is investigted in this pper. The ir nd desiccnt iquid re used inside ebrne bsed het exchnger. In order to evute the ipcts of desiccnt iquid properties on the het nd ss trnsfer distributions, two-diension ode incuding the oentu, het nd ss trnsport equtions is soved by CFD code. Significnt preters such s inet veocity, teperture nd wter content of desiccnt iquid re entioned. The resuts show tht the incresing of desiccnt iquid veocity iniizes the het nd ss trnsfer rtes between the ir nd desiccnt iquid chnnes. A high inet desiccnt iquid teperture eds to rge (s wter content) specific huidity rtio vues in the outet ir (desiccnt iquid) chnne. In ddition, the inet wter content of desiccnt iquid hs strong effect on the outet huidity nd wter content distributions when it becoes higher. Aso, this investigtion tkes into ccount the effect of desiccnt iquid proprieties which so hve strong effect on the sensibe, tent nd tot effectiveness of studied exchnger. Keywords Mebrne bsed het exchnger; desiccnt iquid; effectiveness. I. INTRODUCTION Energy recovery technoogies cn be cssified into two ctegories; the sensibe het exchngers in which recover ony the sensibe het with gret effectiveness, probe of intennce, nd price; the second ctegory is the tot het exchngers. Tot het exchngers or ebrne bsed het exchngers re new ctegory of recovery equipents in which use porous ebrne. They cn recover both het nd oisture with high effectiveness [1-3]. These ebrne bsed technoogies re ffected by vrious operting nd geoetric preters such s the fuids nture, ebrne properties, inet preters vues, etc. Firsty, the specifictions of porous ebrnes re their proprieties which re perebe ony to the vpour nd used in dehuidifiction nd recovery processes. Sever studies specify to buit nd iprove new ebrnes with high perfornce. Zhng et [4] fbricted nove vpour perebe coposite ebrne in which used poyethersufone (PES) coted into dense poyviny coho (PVA). The uses of ithiu choride (LiC) st ike n dditive to the PVA soution is to fciity nd iprove the oisture peretion. The LiC concentrtion hs gret effect of in the wter vpour perebiity of the hydrophiic poyer ebrne. X.R. Zhng et [5] re used the se pproch to prepre ceuose cette (CA) ebrne. The process invoves chep rw teri of CA, n environent friendy sovent cetic cid, nd dditive deionized wter. The coposite ebrne is fored by coting sovent cetic cid nd dditive de-ionized wter csting soution onto the CA support ebrne. Studies found tht the pproch is successfu in king ebrnes for het nd oisture recovery with high oisture perebiity. The pproch provides n environent friendy yet econoic soution for prepring ebrnes for het nd oisture recovery. Secondy, ny prove tht the ebrne bsed het exchnger perfornce y be reted to the operting nd geoetric conditions. Zhng et [6-8] investigted nd tested the different fow rrngeents (co-current, counter fow, nd cross fow) for ebrne bsed het exchngers. Nusset nd Sherwood nubers re ccuted for the three fow rrngeents. They concuded tht the fow rrngeents hs n effect on the het nd ss trnsfer rtes between the fresh nd exhust chnnes of ebrne bsed het exchngers. Aso, they constructed nd investigted qusi-counter fow pre het exchnger. An experienty nd detied thetic odeing re crried which the oentu, het nd ss trnsport equtions re soved in the different regions of the qusicounter ebrne bsed het exchnger. They found tht qusi-counter fow geoetry hs gret effectiveness then the other ebrne bsed het exchngers [9]. However, recent studies specify tht the desiccnt iquid ir ebrne energy exchnger which used two different fuids. The perfornce of these exchngers y be reted to the desiccnt iquid proprieties. In iterture, sever teris hve been investigted such s Mgnesiu Choride (MgC2) [10], Lithiu Choride (LiC) [11], nd Lithiu Broide (LiBr) [12]. In order to copre nove fow rrngeent configurtion nd to evute their effects on the desiccnt iquid ir ebrne energy exchnger perfornce, Vi et. [13] deveoped nueric ode nd they found tht with the

2 4 èe Conférence Interntione des Energies Renouvebes (CIER-2016) Proceedings of Engineering nd Technoogy PET Vo.14, pp se ebrne re the counter-cross-fow rrngeent is better thn pure counter-fow nd ower thn pure cross-fow. Abdse et. [14] proposed nove desiccnt iquid ir ebrne energy exchnger designs in order to enhnce the cooing cpcity nd contro the fuids teperture. They found tht the sensibe cooing cpcity, oisture reov rte, nd tot effectiveness of the studied exchnger re enhnced respectivey by up to 140%, 54%, nd 39% by copred to nor nor desiccnt iquid ir ebrne energy exchnger with the se design preters. It is obvious tht the choice of desiccnt iquid properties is one of the ost iportnt preters infuencing on het exchnger perfornces. In this study, ebrne bsed het exchnger is nuericy investigted. The desiccnt iquid ipcts on het nd ss distributions re evuted. Aso, their ipcts on the sensibe, tent nd tot effectiveness re estbished. The is of this pper re to show the effects of one coponent fro ny other preters which hve n ipct on the tot het exchnger perfornce. II. MATHEMATICAL FORMULATION A. Description of Mebrne bsed het exchnger A schetic description of ebrne bsed het exchnger is shown in Fig. 1. This syste operted with two different fuids in which the desiccnt iquid fows in the first chnne which is seprted by porous ebrne fro the djcent ir chnne. In this investigtion, the ir stres were hot nd huid; however the desiccnt soution is chrcterized by coo nd concentrted properties. So, the het nd oisture re usuy trnsferred fro the hot nd huid ir to the coo nd concentrted desiccnt soution through the porous ebrne. The two fuids fow inside the tot het exchnger in counter-current fow rrngeent. y x A B C D Huid Air Desiccnt Liquid Fig. 1. Schetic description of the studied exchnger. A nueric ode is crried t different conditions, which consist of the ir chnne, the desiccnt iquid chnne, nd the porous ebrne. Therefore, the governing equtions estbished s shown in Fig. 1. In ddition, the foowing ssuptions re de: The regie inside ir nd desiccnt iquid chnnes is stedy nd inr (Re < 2300). The ebrne is perebe ony to wter vpor. E F G H The ebrne properties re not dependent of the fuids proprieties. Desiccnt soution crystiztion nd ir stre condenstion re negected. The het nd oisture trnsfer between the two fuid chnnes ony nor direction to the ebrne. B. Governing Equtions It cn be observed tht the probe is odeed in the x-y pne. Therefore, the governing equtions incuding the ir chnne, desiccnt iquid chnne nd porous ebrne re written in Crtesin coordintes s foows. 1) Air chnne The oentu conservtion: u x v y 0 (1) where u nd v re respectivey the ir veocities in the x nd y directions. Conservtion of oentu equtions: u 1 u p u u u v x y x x y u v 1 v p v v v x y x x y where ρ represents the ir density (kg. -3 ). Het nd ss trnsfer equtions: T T T T u v x y x y W W W W u v Dv x y x y where α denotes the ther diffusivity of ir. D v nd W represent respectivey the wter vpor diffusivity nd the ir specific huidity. 2) Desiccnt iquid chnne The oentu conservtion: u x v y 0 (6) where u nd v re respectivey the desiccnt iquid veocities in the x nd y directions. Conservtion of oentu equtions: u 1 u p u u u v x y x x y (2) (3) (4) (5) (7)

3 4 èe Conférence Interntione des Energies Renouvebes (CIER-2016) Proceedings of Engineering nd Technoogy PET Vo.14, pp u v 1 v p v v v x y x x y where ρ is the desiccnt iquid density (kg. -3 ). Het nd ss trnsfer equtions: T T T T u v x y x y W W W W u v D x y x y (10) where α nd D denote respectivey the ther nd ss diffusivities of desiccnt iquid. In the previous equtions, W nd W represent respectivey the ir huidity nd desiccnt iquid wter-to-st ss rtios. They re indicted the oisture/wter content of both ir nd desiccnt iquid fows s defined. ss of wter W ss of dry ir ss of wter W ss of st (8) (9) (11) (12) In ddition, the properties of desiccnt iquid hs osty strong ipct in wter content W which known so by iquid huidity rtio s defined. p W v,eq P p v,eq (13) where P denotes the tot pressure however, p v,eq represents the prti pressure of wter vpor under equiibriu condition t the soution-ebrne interfce. 3) Mebrne Due to the geoetric nd physic proprieties of the ebrne (s thickness, ther conductivity ), the ss nd het trnsfer rtes in the x-direction re negigibe. Therefore, the het nd ss trnsfer equtions in the two interfces of porous ebrne cn writhen s. T W 0 ; 0 y y (14) C. Nueric pproch The governing equtions shown in the previous section re soved by using the Successive Over Rextion ethod (SOR) with Chebyshev cceertion one for ech controvoue [15, 16]. Conde corretions [17] re used for the desiccnt iquid properties, which is choride ithiu (LiC) in this study. This nueric ode shoud stisfy the conservtion of the deveoped equtions which depict the het nd ss trnsfer sitution. In ddition, the convergence criteri re ssured. The boundry conditions re shown in bove figure (Fig. 1), in which: AB : T W x 0 ; 0 y H ; 0 ; 0 x x BC T W x 0 ; 0 y H ; 0 ; 0 x x CD: x 0 ; 0 y H ; u u ;,0 v 0 ; T T ; W W, i, i DH y 0 ; 0 x L ; v 0 ; T W u 0 ; 0 ; 0 x x x FG : x L ; 0 y H ; T x AE : W 0 ; 0 x y H ; 0 x L ; v 0 ; T W u 0 ; 0 ; 0 x x x EF : x L ; 0 y H ; u u ;,0 v 0 ; T T ; W W, i, i GH : x 0 ; 0 y H ; T x W 0 ; 0 x BF

4 Effectiveness (-) Teperture ( C) 4 èe Conférence Interntione des Energies Renouvebes (CIER-2016) Proceedings of Engineering nd Technoogy PET Vo.14, pp y H ; 0 x L ; T T ; W W,int,int CG : y H ; 0 x L ; T T ; s s s s,int,int v s,int,int,int,int t s,int s,int W W f P T, W où W W P P P M P v s,int M ( P P )+M P t s,int v s,int P T, W etion. is ccuted by Conde corr v s,int,int In order to evute the perfornce of the desiccnt iquid ir ebrne energy exchnger, the sensibe nd tent effectiveness cn be ccuted by Eqs. (15) nd (16). s ( c p ) T,in T,out in( c p, c p) T,in T,in ( c p ) W,in W,out in( c p, c p) W,in W,in Therefore, the tot effectiveness cn be expressed s: tot ( c p ) H,in H,out in( c p, c p) H,in H,in III. RESULTS AND DISCUSSION (15) (16) (17) In order to exine the nueric ode, this investigtion crried out under inet operting conditions: inet ir teperture 35 C, inet huidity rtio 20g.kg -1, nd inet veocity 1.s -1. A. Inet veocity ipct Firsty, the inet the desiccnt iquid teperture is 25 C nd wter content of desiccnt iquid fow is 70%. However, inet desiccnt iquid veocity vries fro 0.05 to 0.5.s -1. Fig. 2 iustrtes the vritions of outet ir nd desiccnt iquid tepertures for vrious inet desiccnt iquid veocities. The outet teperture vues for both ir nd desiccnt iquid sides decrese sowy when the inet desiccnt iquid veocity vries fro 0.05 to 0.5.s-1. We cn rerk tht the vrition of desiccnt iquid veocity cuses wek effect on the het trnsfer rte between ir nd desiccnt iquid sides which decreses by 0.16 C t the outet ir side, nd decreses by 0.66 C t the outet desiccnt iquid side. Tbe 1 shows the infuence the vrition of outet ir huidity rtio nd the wter content of desiccnt iquid for inet desiccnt iquid veocities. By vrying the inet desiccnt iquid veocity fro 0.05 to 0.5.s-1, the outet ir huidity rtio weky decreses by 0.27 g.kg-1 in ddition, the wter content of desiccnt iquid decreses by 9.29% t the outet desiccnt iquid side. 27,5 27,0 26,5 26,0 25,5 25,0 Fig. 2. Outet teperture vritions of ir nd desiccnt iquid. TABLE I. Inet desiccnt iquid veocity (.s -1 ) Outet ir teperture Outet desiccnt iquid teperture 0,0 0,1 0,2 0,3 0,4 0,5 Inet desiccnt iquid veocity (.s -1 ) OUTLET AIR HUMIDITY RATIO AND WATER CONTENT OF DESICCANT LIQUID. Outet ir huidity rtio (g.kg -1 ) Wter content (%) The sensibe, tent nd tot effectiveness re shown in Fig. 3. As seen, when the inet desiccnt iquid veocity increses fro 0.05 to 0.5.s -1, the sensibe effectiveness decreses by 4% however, the tent effectiveness increses by 2.3%. It is concuded fro these resuts tht the desiccnt iquid veocity hs wek effect on the ss nd het trnsfer rtes in the desiccnt iquid ebrne energy exchnger who decreses tiny under high fuid fow veocities. 0,9 0,8 0,7 0,6 0,5 sensibe tent tot 0,4 0,0 0,1 0,2 0,3 0,4 0,5 Inet desiccnt iquid veocity (.s -1 )

5 Huidity rtio (g.kg s -1 ) Wter content of desiccnt iquid (-) Teperture ( C) Effectiveness (-) 4 èe Conférence Interntione des Energies Renouvebes (CIER-2016) Proceedings of Engineering nd Technoogy PET Vo.14, pp Fig. 3. Sensibe, tent nd tot effectiveness. B. Inet teperture ipct Secondy, the inet the desiccnt iquid teperture vries fro 15 to 35 C, however the wter content of desiccnt iquid fow is 70% nd the inet desiccnt iquid veocity fixed t 0.05.s -1. Fig. 4 shows the outet ir nd desiccnt iquid tepertures increse respectivey by 11 C nd 18.5 C, when desiccnt iquid teperture increses fro 15 to 35 C. This signifies tht the het trnsfer rte in the studied exchnger iproves under ow desiccnt iquid tepertures. Further, Fig. 4b shows the outet wter content of desiccnt iquid decreses fro to 72.51%, whie the huidity rtio vues outet ir chnne increse fro to g.kg -1 when the inet desiccnt iquid teperture vues vry fro 15 to 35 C. It cn be expined tht the desiccnt iquid hve strong ffinity to bsorb the wter vpor under ow desiccnt iquid teperture vues in which cn eds to better ss trnsfer. Therefore, it cn be confired by the decresing of sensibe, tent nd tot effectiveness when the inet teperture vues of desiccnt iquid increse fro 15 to 35 C s shown in Fig Outet ir teperture Outet desiccnt iquid teperture Inet desiccnt iquid teperture ( C) Outet ir huidity rtio Outet wter content Inet desiccnt iquid teperture ( C) b 0,90 0,85 0,80 0,75 0,70 Fig. 4.. outet teperture vritions nd b. outet ir huidity rtio nd wter content of desiccnt iquid. 0,7 0,6 0,5 0,4 0,3 0,2 0, Inet desiccnt iquid teperture ( C) Fig. 5. Sensibe, tent nd tot effectiveness. C. Inet wter content of desiccnt iquid ipct sensibe tent tot Finy, the inet the desiccnt iquid teperture kept t 25 C nd wter content of desiccnt iquid fow vries fro 60% to 90%. However, inet desiccnt iquid veocity is 0.05.s -1. Fig. 6 iustrtes the outet teperture vues of ir nd desiccnt iquid for inet wter content of desiccnt iquid fro 60% to 90%. It cn be seen tht the outet teperture vues of two fuids (ir, desiccnt iquid) re not ffected by the inet wter content vrition of desiccnt iquid. Their vues intined respectivey t 29.7 C nd 26 C, when the inet wter content vue increses fro 60 to 90%. However, Fig. 6b shows the outet vues of ir huidity rtio nd wter content of desiccnt iquid. By chnging the inet wter content vue fro 60% to 90%, the outet wter content of desiccnt iquid increses by 25%. Aso, the outet ir huidity rtio increses grduy nd, finy tends to becoe stbe. It cn be concuded tht the desiccnt iquid begins to bsorb or desorb efficienty under n opti vues which re between 65% nd 75% of inet wter content, then it enters in stbe phse or sturtion phse. The sensibe, tent nd tot effectiveness of desiccnt iquid ir ebrne energy exchnger under vrious inet wter content vues of desiccnt iquid re shown in Fig. 7. The tent nd tot effectiveness increse grduy to finish t constnt vues 25.45% nd 34.34%.However, the sensibe effectiveness intins stbe for different inet wter content vues due to the stbiity of ir nd desiccnt iquid tepertures t outet chnnes.

6 Effectiveness (-) Teperture ( C) Wter content of desiccnt iquid (-) Teperture ( C) 4 èe Conférence Interntione des Energies Renouvebes (CIER-2016) Proceedings of Engineering nd Technoogy PET Vo.14, pp Fig. 7. Sensibe, tent nd tot effectiveness ,5 17,4 17,3 17,2 17,1 17,0 16,9 16, Fig. 6.. outet teperture vritions nd b. outet ir huidity rtio nd wter content of desiccnt iquid. 0,60 0,55 0,50 0,45 0,40 0,35 0,30 0,25 0,20 Outet ir teperture Outet desiccnt iquid teperture Inet wter content of desiccnt iquid (%) Outet ir huidity rtio Outet wter content Inet wter content of desiccnt iquid (%) Sensibe Ltent Tot b 65% < opti vues < 75% Inet wter content of desiccnt iquid (%) 1,00 0,95 0,90 0,85 0,80 0,75 IV. CONCLUSIONS As concuded, the desiccnt iquid properties cuses strong effect on the het nd ss trnsfer rte in the desiccnt iquid ir ebrne energy exchnger which enhnces under the inet opti vues. Genery, the operting conditions hve usuy ipcts on the exchnger s perfornce. These bove resuts confir the efficiency of the desiccnt iquid ir ebrne energy exchnger nd provide soution to iprove the het nd ss trnsfer rtes in the ebrne bsed technoogies REFERENCES [1] L.Z. Zhng, Tot Het Recovery: Het nd Moisture Recovery fro Ventition Air, Nov Science Pubishers Inc., New York, Chp. 1, pp. 2-10, [2] L.Z. Zhng, J.L. Niu, Effectiveness corretions for het nd oisture trnsfer processes in n enthpy exchnger with ebrne cores, ASME Journ of Het Trnsfer, vo. 122, Iss. 5, pp , [3] L.Z. Zhng, Het nd ss trnsfer in pte-fin sinusoid pssges with vpor perebe w teris, Interntion Journ of Het Mss Trnsfer, vo. 51, pp , [4] L.Z. Zhng, Yun-Yun Wng, Ci-Ling Wng, Hui Xing, Synthesis nd chrcteriztion of PVA/LiC bend ebrne for ir dehuidifiction, Journ of Mebrne Science, vo. 308, pp , [5] X.R. Zhng, Li-Zhi Zhng, Hong-Mei Liu, Li-Xi Pei, One-step fbriction nd nysis of n syetric ceuose cette ebrne for het nd oisture recovery, Journ of Mebrne Science, vo. 366, , [6] L.Z. Zhng, Het nd ss trnsfer in cross-fow ebrne-bsed enthpy exchnger under ntury fored boundry conditions, Interntion Journ of Het nd Mss Trnsfer, vo. 50, pp , [7] L.Z. Zhng, Ci-Hng Ling, Li-Xi Pei, Conjugte het nd ss trnsfer in ebrne-fored chnnes in entry regions, Interntion Journ of Het nd Mss Trnsfer, vo. 53, pp , [8] R. A-Wked, M. S. Nsif, G. Morrison, M. Behni, CFD siution of ir to ir enthpy het exchnger, Energy Conversion nd Mngeent, vo. 74, pp , [9] L.Z. Zhng, Het nd ss trnsfer in qusi-counter fow ebrne-bsed tot het exchnger, Interntion Journ of Het nd Mss Trnsfer, vo. 53, pp , [10] M. Seyed-hdi, B. Erb, C.J. Sionson, R.W. Besnt, Trnsient behvior of runround het nd oisture exchnger syste, Prt I: ode forution nd verifiction. Interntion Journ of Het nd Mss Trnsfer vo. 52(25-26), pp , [11] S.M. Hung, L.Z. Zhng, K. Tng, L.X. Pei, Fuid fow nd het ss trnsfer in ebrne pre-ptes chnnes used for iquid desiccnt ir dehuidifiction, Int. J. Het Mss Trnsfer vo. 55 (9-10), pp , [12] H. Fn, C.J. Sionson, R.W. Besnt, W. Shng, Perfornce of runround syste for HVAC het nd oisture trnsfer ppictions using cross-fow pte exchngers couped with queous ithiu broide. HVAC&R Res vo. 12(2), pp , [13] A. Vi, M. G. Ge, R.W. Besnt, C.J. Sionson, Nueric odeing of fuid fow nd couped het nd ss trnsfer in counter-cross-fow pre-pte iquid-to-ir ebrne energy exchnger, Interntion Journ of Het nd Mss Trnsfer,vo. 89, pp , [14] M.R.H. Abdse, C.J. Sionson, R.W. Besnt, Design nd testing of nove 3-fuid iquid-to-ir ebrne energy exchnger (3-fuid LAMEE), Interntion Journ of Het nd Mss Trnsfer, vo. 92, pp , 2016.

7 4 èe Conférence Interntione des Energies Renouvebes (CIER-2016) Proceedings of Engineering nd Technoogy PET Vo.14, pp [15] R. Sebi, R. Chouikh, A. Guizni, Cross-fow ebrne-bsed enthpy exchnger bnced nd unbnced fow, Energy Conversion Mngeent. Vo. 87, pp , [16] T. Fys, R. Chouikh, A. Guizni, A nueric investigtion of rectnt trnsport in PEM fue ce with prtiy bocked gs chnnes, Energy Conversion nd Mngeent vo. 80, pp , [17] R. Conde. Properties of queous soutions of ithiu nd cciu chorides: forutions for use in ir conditioning equipent design. Interntion Journ of Ther Sciences vo. 43, pp , 2004.

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