JJMIE Jordan Journal of Mechanical and Industrial Engineering

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1 JJMIE Jdan Junal f Mechanical and Industial Engineeing Vlue, Nube 2, Dec. 27 ISSN Pages Effects f Cndensate and Initial Fatin f Thin Fst Laye n Evaat Cil Pefance f R i-cnditines hed Haza H. li *, Ibahi M. Isail Deatent f Mechanical Engineeing, Faculty f Engineeing, ssiut Univesity, ssiut 76, Egyt. bstact This study investigated exeientally and theetically, hw cndensate and initial fatin f a thin fst laye n the suface f the evaat affects the evaat efance f ai-cnditines caed t dy cil cnditins. The theetically btained esults wee validated with the easued values in bth wet and initial fst fatin cnditins and a gd celatin was fund. The esults indicated that, at the sae ange f change in face velcity value, the ttal cnductivity f a dy cil (U) dy is inceased by 38.8%. Hweve, when it is cbined with an incease in latent heat t the evaat ttal ing caacity ati value ( lat /) f.6%, the ttal cnductivity f wet cil (U) wet is 4.4%. These esults ealy indicate that the evaat cil is chaacteized by highe efance unde wet cnditins caed t dy cil cnditins. The esults als shw that the ttal cnductivity afte initial fatin f a thin fst laye (U) F has a highe value by abut 8.2% than the dy cil cnditin. Meve, the degadatin in the evaat cil efance unde thin fst with a thickness u t ne is nly abut 6.7%. 27 Jdan Junal f Mechanical and Industial Engineeing. ll ights eseved Keywds: Evaat cil efance; Wet evaat cil; Fsted evaat cil; and i dehuidifying; Nenatue lhabetic Sybls : suface aea, 2 a : cefficient f fictitius enthaly, J/kg b : sle f i vs. T cuve [3], J/kg K c : secific heat, J/kg K d : evaat tube ute diaete, h : heat tansfe cefficient, W/ 2 K i : enthaly, J/kg k : theal cnductivity, W/ K L : length, Le : Lewis nube, - : fin eiete, - & : ass flw ate, kg/s q : heat flux, W/ 2 : ttal heat tansfe ate, W : adius, T : teeatue, K C U : veall heat tansfe cefficient, W/ 2.K {[W/ 2.K]/[J/kg]} V : face velcity, /s W : huidity ati, kg H2O /kg dy ai x, y, z : satial c-dinates, Geek sybls ΔT : lgaithic ean teeatue diffeence, K δ : thickness, φ : elative huidity η : fin efficiency, - Subscits a : ai avg : aveage c : cnvectin : cell eff : effective eq : equivalent f : satuated liquid fin : fin fins f : fst g : satuated va I : inne in : inlet lat : latent heat : ean : ute ut : utlet : ie : efigeant * Cesnding auth. e-ail: ah-haza@aun.edu.eg

2 7 27 Jdan Junal f Mechanical and Industial Engineeing. ll ights eseved - Vlue, Nube 2 (ISSN ) s sv v w wb. Intductin : satuatin : slid-va in subliatin : va : wet : e : wet-bulb The evaat cils in ai cnditining aliances vide the dest suface f cndensate fatin f the ai stea e va cntent in ing eatin de as it s and dehuidifies ind ai. s the aunt f e cndensed n the evaat suface inceases, e dlets ae fed and inteittently dain due t gavity. Se e dlets adhee t the cil by suface tensin henena. This is defined as hld-u cndensate e. This hld-u e eacts with the ind aibne cntainants and duces ld cunds and fuling esistance between the ai and the evaat cil suface, li and Isail []. Meanwhile, thin fst laye fatin ay ccu n the evaat sufaces f a ai-cnditine when it wks as a heat u in winte seasn. In this case, the utd ai teeatue is lw and the evaat eates at cil suface teeatues belw C. It is fund that se dust desits n the utd heat exchange f the ai-cnditine, which sticks n the evaat suface duing the heating seasn with eithe cndensate an initial fst fatin laye. Bth cunds f e/dust desitins n the evaat cil suface f a esistance t the heat tansfe. li and Isail [] esented the effect f fuling desits n ai-cnditine efance. In the liteatue, nueus studies have been cnducted and vide detailed infatin elevant t bth heat and ass tansfe cefficients in the aiside f fin and tube heat exchanges unde dehuidifying cnditins such as Yaun and Tucke [2], Jacbi et al. [3], Piugd et al. [4] and Halici and Tayaz []. Gavity-indeendent e seaatin within the cndensing heat exchanges by the use f a hydhilic fin suface cating, that te the wetting and wicking f the cndensate n the fin, wee investigated by Shin et al. [6] and O Neill et al. [7], while Lee et al. [8] investigated this effect in case f fst fatin. Wette [9] esented a sile siulatin del f a dy finned e-t-ai cil. Osada [] eted that in the evaat cndensed e adhees t the fin suface and thus inceases the essue d f the evaat and degades the heat tansfe efance f the fins wing t luve blckage and e bidging. In additin, nueus studies have been cnducted by using siulatin dels f thick fst laye fatin and edicted the efance f fin and tube evaat unde these cnditins such as [ t 6]. The influence f thick fst fatin n the efance f evaat cils wee investigated by eithe siulatin exeiental studies by [7 t 23]. Hweve, thugh a liteatue suvey it was fund that nueus exeients and dels investigated the effect f e va cndensate n the aiside f evaat sufaces ainly fcused n the evaluatin f bth heat and ass tansfe cefficients. Few exales cited that the cndensate degades the heat tansfe efance f the evaat cil fins as well as causes a decease in the aiflw aea, thus leading t an incease f essue d thugh the evaat cil. li and Isail [] fund in thei exeients that the ean wet-cil efance is highe than the dy-cil cnditin. Nueus studies investigated the influence f a thick fst fatin laye n the evaat cil, while the influence f initiatin and thin fst laye fatin n the evaat cil efance is nt ea. Thus, the efance f an evaat cil f ai-cnditines, when its suface is cveed by eithe cndensate initial fst layes withut dust desitin n the cil, need t be aified. Theefe, f ai-cnditines, this study ais at investigating exeientally and theetically the effect f cndensate and thin fst laye fatin n the suface f evaat cil n the efance f the evaat cil caed t dy cil suface cnditins. Exeients wee caied ut n a flat finned and staggeed tube evaat cil, while the theetical del was used t aify the effect f aaetes n the evaat cil efance which is difficult t easue exeientally. 2. Exeiental aatus, Instuentatin and Pcedue 2.. aatus and Measueents The test facility descibed in li and Isail [] is used t investigate the efance f the evaat cil unde wet and initial fatin f thin fst laye cnditins at vaius aiflw ates with in dificatins in case f fst exeients. The dificatins ae: inceasing the caillay tube length, and ing the last 8 tubes in the cndense by e. scheatic diaga f the aaatus and its diensins is shwn in Figue..9 Evaat.63.2 W Ta, Twb, T a,i Va Twb,i.8 Cndense ing e Rtaete.46 Figue : scheatic diaga f the test facility i blwe Flw nzzle The aaatus ainly cnsists f an ai handling sectin, test sectin and the aiately equied instuents. The ai handling sectins inude a nzzle ete, a vaiable seed aiflw fan, an inlet ai distibutin lenu and a flw staightene (hneycb). The flw staightene vides a unif ai velcity distibutin at the inlet t the evaat cil (test sectin). The evaat cil fntal fined aea diensins ae.24 x.9 (x7.in) with a deth in flw diectin f.2 (6 in). It is a late fin and tubes heat exchange. The fins ae ade f aluinu ally and the tubes ae ade f ce. Fu ws f tubes with fu tubes in deth ae aanged in staggeed anne (2d x 2.d ). The tubes ae f 9.2 (3/4in) in ute diaete (d ), fins itch is fin/4.2 (6 fin/in) and fin thickness is.6. The test cil (evaat) itself is a cnent f a cessin efigeatin cye using R2 as efigeant, see Figue. The the ain cnents f the efigeatin cye inude a heetic cess, an ai-ed cndense, a taete (uncetainty f ±. l/in) f efigeant ass flw easueents, 2 lng caillay tube f efigeant

3 27 Jdan Junal f Mechanical and Industial Engineeing. ll ights eseved - Vlue, Nube 2 (ISSN ) 7 exansin, and 4 essue gauges at inlet and utlet f bth the evaat and cndense with uncetainty f ±. kpa. The inut electic we t the cess was easued by a Wattete with uncetainty f ±W. vaiable electic esist cntlled the inut we t the aiflw fan t. Thus, the aiflw ate is cntlled by the fan seed. The that velcity f the ai assing thugh the nzzle is deteined by easuing the static essue d acss the nzzle using e anete with an accuacy f ±.. data acquisitin syste having a eslutin f. C is used t easue and ecd the teeatues. ll teeatues ae easued by using tye T (ce/cnstantan) thecules with. diaete and an uncetainty f ±. C. The thecules wee used t easue the teeatue at the fllwing lcatins: 2 ints ai dy-bulb and wet-bulb teeatues befe the evaat cil, 6 ints n the evaat cil tubes and fins in additin, tw ints at efigeant inlet and utlet, tw ints f abient ai dy-bulb and wet-bulb teeatues, esectively. The face ai velcity at ai inlet t the evaat was easued using a table digital aneete with uncetainty f ±. /s Exeiental Pcedues and Data Reductin T study the effect f dew fatin n the efance, exeients wee caied ut in a quasisteady state cnditin at diffeent aiflw ates cesnding t a face velcity anging f.62 /s t /s esectively. While f the case f initial fatin f a thin fst laye, the face velcity was.62 /s. This is because with this exeiental aaatus and eating cnditins, the fst is fed nly at this lw face velcity value. Stabilizatin f teeatue eadings t ±. C in all thecule senss was cnsideed an indicatin f eaching a quasi-steady state cnditin, then the aveage f the teeatue values ae ead and ecded. t the sae tie, the eadings f the efigeatin cye essue gauges and taete as well as the anete eadings f the essue diffeence acss the nzzle wee taken. The easueents wee efed at the Heat Labaty, ssiut Univesity, Egyt. The exeiental evaat cil ing caacity has been btained f the enegy balance n bth efigeant and ai sides. It is given by: ( a )/2 [W] () whee a is the aiside caacity f the evaat cil. It is calculated by: a, 2 & a ( ia, ia ) [W] (2) whee the ai enthaly, i, at the inlet and utlet f the evaat cil is calculated by the fula f SHRE [24]. The ai ass flw ate, & a, at the nzzle that is calculated f the essue d acss the nzzle. is the efigeant side ing caacity f the evaat cil. It is calculated by: & ( i i ) [W] (3),, i whee the efigeant enthaly, i, at the inlet and utlet f the evaat cil is btained f [2] as a functin f the teeatue and essue f state int. The efigeant ass flw ate & is estiated f the taete eading and the efigeant density. SHRE [24] elatins wee used t btain the huid ai eties ati, W, at inlet and utlet f the evaat cil f the easued data f ai dy-bulb teeatue, T a, and ai wetbulb teeatue, T wb, esectively. The uncetainties wee calculated thugh the data eductin f the exeiental easueents based n the fula f cuting veall es f [26]; the uncetainty is estiated in deteinatin anging f 9.% t 3.6%. 3. Theal Mdel The theal del is used t investigate the facts influencing the evaat cil efance, which ae hadly t btain by exeiental easueents. These facts ae the ati f wet cil aea t the ttal cil suface aea, the ati f the latent heat subliatin heat caacities t the evaat ttal ing caacity and the effect f initial fatin f thin fst laye thickness n the evaat efance. The del is built f a flat fin ai-t-efigeant heat exchange (evaat cil) with staggeed tubes shwn in (Fig. 2-a). It is based n the discetizatin f the heat exchange int cells. Each cell is ne finned-tube in the efigeant flw diectin z as shwn in Fig. (2-b). a y x b (c) L M & a cndensate fst δ f δ T, & w, if & w d& w, if z (a) Figue 2: Scheatic diaga f flat staggeed fin-and tube evaat cil with cdinate (a), enegy and ass tansfe balance n a cell (b) and hexagnal fin diensin aaetes (c) The efigeant entes the evaat as a tw-hase ixtue f satuated liquid and va with secific quality. Theefe, the enegy vaiatin is assued t be nediensinal in the flw diectin and it is estiated f the enthaly diffeence f the efigeant between inlet and utlet f a cell. In cntast, the ai dy-bulb teeatue and its huidity ati ae vaying in bth x and y diectins ve each cell. Figue (2-b) shws a cell in the geneal case at which the suface culd be dy, wet with a thin fst laye at the cell suface. In the fllwing subsectins, deling f the cil unde these cnditins is esented. 3.. Dy Cil Suface Cnditin F dy cil suface cnditins, it is assued that neithe cndensate n fst is esent n a cell suface shwn in Fig. (2-b). The heat tansfe ate f a cell,, is btained as fllws: cnvectin heat tansfe f the ai stea t the ie ute suface and fins is sensible nly and is calculated by: T,i i T (b) & & a

4 72 27 Jdan Junal f Mechanical and Industial Engineeing. ll ights eseved - Vlue, Nube 2 (ISSN ) h η )( T T ) [W] (4) c, (, fin, whee h c, is the utside cnvective heat tansfe cefficient between ai and dy sufaces f the cell. It is calculated f the celatin f a flat fin-and-tube heat exchange f Wang [27]., and fin ae the ie ute suface aeas and fin aea in a cell, esectively. T is the ai stea dy-bulb teeatue, T, is the ie ute suface teeatue and η is the fin efficiency and is given by SHRE [24] in case f staggeed tubes with cntinuus flat fins. In this study, η is teated as hexagnal fin as shwn in Fig. (2-c) and given by: ( ϕ) tanh η () ϕ whee 2hc,, k finδ fin eq ϕ.3ln eq eq M L.27.3 M whee is the inne adius f the fin, the ie ute adius, see Fig. (2-b), eq is the equivalent adius f the fin, k fin is the fin theal cnductivity, δ fin is the fin thickness and a, b, L and M ae diensin aaetes as shwn in Figue (2-c), esectively. The cnductin thugh the ie wall f ne cell is given by: ln i T 2 πl k ( T,, i ). [W] (6) whee k, T, and T,i ae the ie theal cnductivity, ute and inne suface teeatues, esectively. Cnvectin f inne tube suface t the efigeant f a cell is given by: h T T ) [W] (7) i, i (, i whee h i is the cnvective-evaatin heat tansfe cefficient between the tw-hase efigeant and the inne suface f the ie. It is a functin f the tw-hase efigeant ass flw ate, efigeant quality, essue, teeatue and intenal ie diensins. Thughut the liteatue, nly a few ethds exlained the details f calculating the lcal values f h i such as [28] and [29]. In this study, the value f h i is calculated by the techniques esented in Cbeán [3]. T is the efigeant teeatue. F Eqs. (4), (6) and (7) the value f can be als exessed by: U ΔT [W] (8) whee U is given by: U ln i h πk L η P, i i 2 finhc, P, hc, [W/ 2.K] (9) The lgaithic ean teeatue diffeence, ΔT, between the ai stea and efigeant with the bability f efigeant sueheating at the utlet f the ie at the last cell is given by: ΔT ( Ta,in T,ut ) ( Ta,ut T,in ) ( Ta,in T,ut ) ( ) ln Ta,ut T,in 3.2. Wet Cil Suface Cnditin [K] () s the ist ai is ed and its teeatue deceases belw the e va dew int teeatue, the e va cndenses n the evaat cil suface. F wet cil cnditins, bth the heat tansfe and ass tansfe between the ist ai and a thin cndensate fil takes lace siultaneusly accding t the enthaly diffeence as cited in [3]. In this at f the del the fllwing assutin ae used: the ute suface f fins and tubes ae cveed with a thin e fil, the bunday laye f satuated ist ai is at the thin e fil teeatue, which is equal t bth the tube and dified fins suface teeatue. The equatin f cnvectin heat and ass tansfe between huid ai and wet cell sufaces, shwn in Fig. (2-b), is given by [3] as fllws: hc, c a ( i i ) s, ( W W ) s, ( i g,t Le i f, i g Le) [W] () with ttal ute suface aea f the cell, enthaly i, huidity ati W, secific heat c and Lewis nube Le. T cnside the cnductin acss the e fil thickness shwn in Fig. (2-b), cnductin thugh the ie wall and intenal cnvectin evaatin between the efigeant and inne ie suface value is calculated by; U,w Δi [W] (2) whee U,w is the veall heat tansfe cefficient in wet cnditin based n the enthaly tential. It is given by: U,w b ' b ' ln ' i b 2πk L η h,i hi fin w,w b ', h,w [(W/2)/(J/kg)] (3)

5 27 Jdan Junal f Mechanical and Industial Engineeing. ll ights eseved - Vlue, Nube 2 (ISSN ) 73 ' is, is, whee b, i s, and i s, ae fictitius T T enthalies f satuated ist ai valuated at the ie and efigeant teeatues, esectively. The value f i s, is defined in [3] by i s, a ' ' b T, whee a ' ' and b ae cefficients t be calculated f lts in [3] at the ai satuatin cnditin cesnding t the ie teeatue. ' Siilaly the values f i s,, b ' and b can be calculated, esectively. The wet fin efficiency, η w, is calculated at h,w. The cbined cnvectin and evaatin heat tansfe cefficient, h,w, between ist ai and ute cell sufaces aea is calculated by: h,w c δ a b ' h k c, Δi value is calculated by: Δi ( i is,, 2 ) ( i2 is,, ) ( i is,, 2 ) ln ( i i ) 2 s,, [W/ 2.K] (4) [J/kg] whee i and i 2 ae enthalies f the enteing and leaving ai stea f a cell, i s,, and i s,,2 ae fictitius enthalies f satuated ai calculated at enteing and leaving efigeant teeatues f a cell and ae estiated as defined in [3]. The ie inne suface teeatue is calculated f: T,i T [K] () h i,i The ttal heat tansfeed f the ai stea t the cell suface cnsists f tw ats: the sensible at and the latent at. Using the elatin f cnvective heat and cnvective ass tansfe by Le nube elatin, the ute ie suface teeatue is caed with the inlet ai dew int teeatue t the cell in de t aify at which cell the cndensate begins. It is calculated by: h ( W W ) s, i fg ( T T, )( Le c ( ), a T T, η c, fin [W] (6) whee i fg is the enthaly f latent heat f cndensatin Fst Cil Suface Cnditin In this at f the del, a celatin that cnsides the lecula diffusin f e va inside an initially fed fst laye, ass and heat tansfe between ai stea and fsted cil suface is used t edict the effect f an initial fatin f a thin fst laye n the evaat cil suface and the thin fst thickness effect n the evaat efance. The fllwing assutins ) ae cnsideed: all heat and ass tansfe sufaces ae cveed with thin fst laye and this laye is t be chaacteized by aveage eties; fst theal cnductivity vaies nly with fst density. The ttal heat tansfe ate in a cell with fsted suface cnditins is calculated by: U U, ΔT [W] (7) f whee U,f is given by:, f P,i hi ln 2πk i L δ k f f η finheff h P, eff [W/ 2.K] (8) k f and δ f ae the fst theal cnductivity and thickness, esectively. The equatins esented in [9] f k f and δ f ae used in this study. h eff is effective cbined sensible/ subliatin heat tansfe cefficient. By siilaity with eq. (6) it is calculated by: h eff ( ) ( ) W Ws, f isv c a T Tf, h c, [W/ 2.K] (9) Le whee i sv is the enthaly f heat f subliatin and T f, is the fst laye suface teeatue which is calculated by: T f T [K] (2) h eff 3.4. Slutin Techniques The inlet cnditins f bth the ai and efigeant ae inut int the del. The slutin ethd f the equatin in geneal is based n an iteative slutin cedue f ie teeatues. Fist, a guess is ade f ie teeatue distibutin in each cell, and then the gvening equatins f the efigeant ae slved in an exlicit anne. Once the efigeant eties ae btained f any fluid cell, the ie teeatues at evey ie cell ae estiated f the heat tansfeed acss it. This cedue is eeated until cnvegence is eached. In the aiside, deending n the eating cnditin aaetes, se cells ay eate with a dy suface, and with eainde f its wet suface. Detailed cedues f the slutin f huid ai ae in RI [32] and can be suaized as fllws: the evaat is fist teated as dy, then the inlet dew int teeatue f the ai is caed with the wall teeatue f cells. F the heat tansfe ate equatin the utlet enthaly is calculated, and then the utlet ai teeatue. t cells whee the ie wall teeatue is equal t the inlet ai dew int teeatue f the cell, the calculatin f a wet cil is integated. Then, the latent heat tin is calculated as the diffeence between the ttal heat and the sensible heat. F the latent heat tin, the utlet huidity values f the cells ae calculated. The evaat cil

6 74 27 Jdan Junal f Mechanical and Industial Engineeing. ll ights eseved - Vlue, Nube 2 (ISSN ) diensins descibed in the exeiental sectin with the aid f the equatins f calculatin f and fin, which ae given in RI [32], ae inut int the del. The ean hld-u e thickness, δ, eaining n the evaat sufaces and the fst thickness δ f ae set t. in case f investigating the aaetes than thei thickness. The Lewis nube (Le) is set t. cute ga based n this del was witten in FORTRN language. In the ga, ai eties ae calculated with using SHRE [24] equatins and efigeant eties ae calculated by using subutine PROPERTY f SHRE [2]. 4. Results and Discussin 4.. Effect f Cndensate n Evaat Cil Pefance The esults esented in this study ae based n a quasisteady state cnditin. ng any easueents that wee caied ut f face velcities anging f.62 /s t /s, it was bseved exeientally that thee is n cndensate f exeients efed at face velcities geate than /s. Theefe, thee was a significant cntact tie equied between ist ai and the evaat cil suface f dew fatin. In additin t this fact, the lwe ai elative huidity as seen f Figue (3-a) inside the labaty duing the exeients tie, is anthe fact cntibuting t this effect. Hweve, in de t investigate the effect f cndensate fatin n the evaat cil efance, all exeients wee caied ut with inlet efigeant teeatue highe than C, t avid fst fatin n the cil suface. The easued values f vaiatin f inlet ai dy-bulb teeatue enteing the evaat cil, efigeant inlet teeatue t evaat cil as well as the deteined ai e cntinent huidity ati and elative huidity bth wee calculated f the easued wet-bulb and dy-bulb teeatues at vaius ai face velcity as shwn in Figue (3-a). The calculated values f utlet ai dy-bulb teeatue, ai e cntinent huidity ati and the evaat cil ttal ing caacity, f the inut eating cnditins data t the del that is shwn in Figue (3-a), ae caed with thei cesnding exeientally deteined values as shwn in Figues (3- b,c and d), esectively. s seen f the Figue (3), the del f wet cil cnditin edicts the efance f the evaat cil within % f elative e withut any secific adjustent. Thus, it can be cnsideed that a gd ageeent was btained as the calculated values lay within the ange f exeiental uncetainty. This ageeent validates the calculated esults f the evaat cil efance unde cndensate fatin. The del is used t investigate the chaacteistic aaetes t aify the effect f dew fatin n the evaat cil efance. The btained esults f the wet cil del ae shwn in Figue (4). These esults wee btained with the inut eating cnditins shwn in Figue (3-a). Caing the ttal cnductivity (U) values in bth wet and dy cnditins, thei values esented in Figue (4-a) ae based n lgaithic ean teeatue diffeence f Eq. (). s stated eviusly, in the esented ange f face velcity, dainage f cndensate f the evaat cil is bseved exeientally, until a face velcity value f /s. Teatue, C Teatue, C Evaat caacity, W Huidity ati, (g/kga) T a,in φ% W in T,in Exeiental Calculated Exeiental Calculated 6 Exeiental Calculated (d) Face Velcity, (/s) Figue 3: Measued enteing eating cnditins t the evaat cil at wet cnditin (a), caisn f the calculated values with cesndence easued values, utlet ai dy-bulb teeatue (b), utlet ai huidity ati, (c) and evaat ing caacity (d) (a) (b) (c) φ % and W,(g/kga) In this ange f face velcity, this bsevatin agees with the del esults f % wet cil suface that ae shwn in Figue (4-b). F Figue (4-a), it is ea that bth calculated (U) values, f dy and wet cnditins inceases with incease in the face velcity values. This esult is exected because the heat tansfe cefficient is deendant n the flw Reynlds nube, in which it is a functin f the face velcity. While, the value f (U) in wet cnditins is highe than the case f dy cil and the diffeence between bth (U) values inceases as the latent heat ati value inceases. This can be attibuted t the fllwing: in the esent exeients, the fin itch is 4.23, the etained cndensate dlets n the cil d nt bidge the inte-fin ga but incease the heat tansfe ate. The highe (U) wet value instead f etained cndensate thin laye, which can eesent cnductin esistance, can be exlained with aid f gu in the

7 27 Jdan Junal f Mechanical and Industial Engineeing. ll ights eseved - Vlue, Nube 2 (ISSN ) 7 backets f Eq. (6). The te in the backet is the dy cnvective heat tansfe cefficient lus the tin f latent heat f cndensatin. U, (W/K) % (U) dy (U) wet Wet suface % lat / % (a) (b) Face Velcity, (/s) Figue 4: Chaacteistics f the evaat cil unde wet cnditin The incease in (U) wet value is functin f inlet ai dy-bulb teeatue and huidity ati and efigeant teeatue, with cnsideing the cnductin esistance in the tube wall is vey sall. The ati f the incease n (U) wet value can be ealy exlained in quantity values as fllws: at the latent heat t the evaat ttal ing caacity ati ( lat /) value f 8.2% the values f (U) in bth dy and wet cil wee 2.8 and 23.6 (W/K), esectively. While, at ( lat /) value f 29.64%, U values becae 3.32 and 34.3 (W/K), esectively. Thus, f the sae ange f a change in face velcity value, (U) dy is inceased by 38.76%, while when it is cbined with an incease in ( lat /) value by.64%, the (U) wet is 4.4%. These esults ealy indicate that, an evaat cil with highe fin-itch is chaacteized by highe efance unde wet cnditin than the dy cil suface cnditin and the etained cndensate has an itant effect n the evaat cil efance enhanceent Effect f Initial Fatin f Thin Fst Laye n the Evaat Cil Pefance T investigate the effect f initial fatin f thin fst laye n the evaat cil, the exeiental aaatus had a in dificatin caed t that descibed befe in de t btain enteing efigeant teeatue less than C. With this dificatin, initial fatin f thin fst laye n the cil is built at lw face velcity values nly. n exeient was caied ut f nube f hus with thin fst laye fed n the evaat cil. The easued enteing cnditins t the cil ae shwn in Fig. (-a). The del esults f the utlet ai huidity ati unde fst cnditin wee caed with exeientally btained value as shwn in Figue (-b). It can be seen f Figue (-b) that bth esults ae in gd ageeent with the scale easueents (±7%). The calculated (U) values f bth dy and fsted cil cnditins as well as the subliated heat t the evaat ttal ing caacity ati ( sv /) values ae shwn in (-c). s shwn in Figue (-c), (U) values ae cnstant with tie vaiatin in bth cil cnditins instead f change in ( sv /) values. ls, the esults shwn in the figue indicate that the ttal cnductivity unde initial fatin f thin fst laye (U) f has highe values than dy cil cnditin, f the esented eating cnditins, by abut 8.2%. The highe value f (U) f, instead f the thin fst laye that added cnductin esistance t heat tansfe, can be exlained with the aid f the backets in Eq. (9). The value in the backets is the su f dy cnvective heat tansfe cefficient lus the subliated heat tin ati. Teatue, C W, (g/kga) U, (W/K) (a) (b) (U) dy T a,in T,in W ut exeiental W ut calculated (U) f 7 3 ( sv /) (c) Tie, hs. Figue : Measued enteing eating cnditins t the evaat cil at fst cnditin (a), the calculated utlet ai huidity ati unde fst cnditin caed with cesndence exeiental ne (b) and chaacteistics f the evaat cil unde thin fst fed laye (c) φ φ % (sv/) % Inteetatin f this esults ae based n hlgy diaga esented in Libbecht [33], in which the initial fst laye, at tube teeatue ange f t - C, cnsists

8 76 27 Jdan Junal f Mechanical and Industial Engineeing. ll ights eseved - Vlue, Nube 2 (ISSN ) f a us stuctue csed f individual ice cystals and ai ckets. Based n this hysical stuctue, the initial fst fatin vide e es f diffusin f the diffeence f ai iste cntent (W-W s,f ) int this initial fst laye. This diffeence in the ai huidity is cnveted int fst and cbined by extactin t the subliatin heat f the ai stea, which has a sitive effect n the heat tansfe ate between the ai stea and the cil. These esults ealy indicate that, the evaat cil suface with highe fin-itch has highe efance unde initial fatin f thin fst laye caed with dy cil suface cnditin Effect f Fst Thin Thickness n the Evaat Cil Pefance In the exeients f investigatin f the effect f fst fatin n the cil efance, n instuents wee used t easue the fst thickness due t the difficulty in easuing the fst thickness in a full-scale evaat cil. Theefe, the del is used t investigate the effect f thin fed fst thickness laye n the cil suface u t ne n the evaat cil efance. The esult is esented in the f f the ttal cnductivity unde fst cnditin (U) f. The calculated esult cesndence t the eating cnditins f face velcity equal.62 /s, enteing ai dy-bulb teeatue f C, inlet ai elative huidity f 87.% and inlet efigeant teeatue f -6 C is esented in Figue (6). (U)f, (W/K) φ87.% T a,in C T,in -6 C Face Velcity.62 (/s) δ f, Figue 6: Effect f initial thin fst laye n the evaat cil ttal cnductivity (U)f The esult indicates that the degadatin in (U) f value f fst laye thickness u t ne is nly abut 6.7%. Exlanatin f this esult is as stated in the evius subsectin. Thus, it can be cnuded that, the eductin in cil ttal heat tansfe ate due t initial thin fst laye u t ne at the stated eating cnditin has insignificant effect n the evaat cil efance. While, thugh the afeentined liteatue cncening the degadatin n the evaat cil efance at dee feezing teeatues unde fst cnditin ay be exlained by the fact that, fst fatin n heat exchange suface at these lw teeatue has diffeent cnstuctin, nn-us, as shwn in hlgy diaga esented in [33]. In additin, geate fst thickness with lw fin-itch leads t blcking f the aiflw aths fllwed by a geate eductin f aiflw ate and higheessue d thugh the evaat cil, esulting in a geate eductin f the evaat cil efance. In additin, it causes additinal theal cnductin esistance n the cil suface leading t daatic deceases in the evaat cil efance.. Cnusins This study investigated exeientally and theetically the effects f cndensate and initial fatin f thin fst laye n the evaat cil suface n the efance f the evaat cil f aicnditines caed with dy cil suface cnditins. Exeients wee caied n flat fin and staggeed tube evaat cil, while the theetical del was used t aify the effects f aaetes which ae difficult t easue in the exeients n the evaat cil efance. The btained esults ae suaized as fllws: The del esults wee validated with the easued data in bth wet and initial fst fatin cnditins f the evaat cil, and the edicted esults ae within % f elative e. This validatin is cnsideed a gd ageeent as the calculated values ae within the ange f exeiental uncetainty. F the sae ange f a change in face velcity value, (U) dy is inceased by 38.76%, while when it is cbined by an incease in ( lat /) value by.64%, the (U) wet is 4.4%. The evaat cil with highe fin-itch is chaacteized by highe efance unde wet cnditin than the dy cil suface cnditin. The ttal cnductivity unde initial fatin f thin fst laye (U) f has highe values than dy cil cnditin by abut 8.2% in the ange f eating cnditins f this study. t the stated eating cnditin, the degadatin in (U) f unde thin fst thickness u t ne is nly abut 6.7% that has insignificant effect n the evaat cil efance. Refeences [] li, hed Haza H. and Isail, Ibahi M, Effect f the evaat aiside fuling n efance f ai cnditines and its iact n ind ai quality, SHRE Int. J. f HVC&R Reseach, 27, cceted f ublicatin [2] Yaun Y. H. and Tucke. S., The efance study f a wet six-w heat-ie heat exchange eating in tical buildings. Int. J. Enegy Res., Vl. 27, 23, [3] Jacbi. M., Pak Y., Zhng Y., Michna G., and Xia Y., High Pefance Heat Exchanges f i-cnditining and Refigeatin licatins (Nn-Cicula Tubes). RTI-2CR/6-22-, Final Ret, July 2 [4] Piugd W., Wngwises S. and Wang C., Siultaneus heat and ass tansfe chaacteistics f wavy fin-and-tube heat exchanges unde dehuidifying cnditins. Int. J. f Heat and Mass Tansfe, Vl.49, 26, [] Halici F. and Tayaz I., Exeiental study f the aiside efance f tube w sacing in finned tube heat exchanges. Heat Mass Tansfe, Vl. 42, 26,

9 27 Jdan Junal f Mechanical and Industial Engineeing. ll ights eseved - Vlue, Nube 2 (ISSN ) 77 [6] Shin J. and Ha. S., The effect f hydhilicity n cndensatin ve vaius tyes f fin-and-tube heat exchanges. Int. J. f Refigeatin Vl. 2, 22, [7] O Neill C., Beving D.E., Chen W. and Yan Y., Duability f hydhilic and antiicbial zelite catings unde e iesin. IChE J., Vl. 2, N. 3, 26, 7-6. [8] Lee H., Shin J., Ha S., Chi B. and Lee J., Fst fatin n a late with diffeent suface hydhilicity. Int. J. f Heat and Mass Tansfe Vl. 47, 24, [9] Wette M., Siulatin Mdel Finned Wate-t-i Cil withut Cndensatin. Lawence Bekeley Natinal Labaty Ret LBNL-423, Januay 999. [] Osada H., ki H., Ohaa T. and Kuyanagi I., Reseach n cugated ulti-luveed fins unde dehuidificatin. Heat Tansfe sian Reseach, Vl. 3, N., 2, [] Hng C. H., Mdeling and easueent f fst chaacteistics n heat exchange sufaces. PhD. Thesis, Univesity f Saskatchewan, Saskatn, Canada, 2. [2] Wattes R. J., O Neal D. L. and Yang J., Evaluatin f Fin Staging Methds f Miniizing Cil Fst ccuulatin. SHRE Res. Pject: 2-RP, July 2. [3] Yang J., study f heat u fin staged evaats unde fsting cnditins. PhD Dissetatin, Texas &M Univesity, 23. [4] Chen H., Thas L. and Besant R. W., Fan sulied heat exchange fin efance unde fsting cnditins. Int. J. f Refigeatin Vl. 26, 23, [] Hffenbecke N., Investigatin f ltenative Defst Stategies. M. Sc Thesis Univesity f Wiscnsin-Madisn, 24. [6] Liu Z., Zhu H. and Wang H., Study n tansient distibuted del f fst n heat u evaat. J. f sian chitectue and Building Engineeing, Vl. 4, N., 2, [7] Huz I., Kue E. and Yaankaadeniz R., Exeiental and theetical efance analysis f ai-ed latefinned-tube evaats. Int. C. Heat Mass Tansfe, Vl. 2, N. 6, 998, [8] Vea P., Calsn D. M., Wu Y., Hnjak P. S. and Bullad C. W., Exeientally validated del f fsting f lainfin-und-tube heat exchanges. Pc. f IIF IIR Cissin D/B Ubana, IL, 22. [9] Seke D., Kaatas H., Egican N., Fst fatin n finand-tube heat exchanges. Pat I-Mdeling f fst fatin n fin-and-tube heat exchanges. Int. J. f Refigeatin, Vl. 27, 24, [2] Seke D., Kaatas H., Egican N., Fst fatin n finand- tube heat exchanges. Pat II-Exeiental investigatin f fst fatin n fin-and-tube heat exchanges. Int. J. f Refigeatin, Vl. 27, 24, [2] ljuwayhel N. F., Nueical and Exeiental Study f the Influence f Fst Fatin and Defsting n the Pefance f Industial Evaat Cils. PhD Dissetatin, Univesity f Wiscnsin-Madisn, 26 [22] Muehlbaue, J., Investigatin f Pefance Degadatin f Evaat f Lw Teeatue Refigeatin licatins. M. Sc Thesis, Univesity f Mayland, Cllege Pak, 26. [23] Ya Y., Jiang Y., Deng S. and Ma Z., study n the efance f the aiside heat exchange unde fsting in an ai suce heat u e heate/chille unit. Int. J. f Heat and Mass Tansfe, Vl. 47, 24, [24] SHRE (2). 2 Fundaentals Handbk SI. eican Sciety f Heating, Refigeating and i- Cnditining Enginees. tlanta, Gegia. [2] SHRE, HVC Tlkit: Tlkit f Piay HVC Syste Enegy Calculatins. eican Sciety f Heating, Refigeating and i-cnditining Enginees. tlanta, Gegia, 999. [26] Deblin, E. O. Measueent Systes, licatin and Design. McGaw-Hill Bk C; 99. [27] Wang, C.C., Chi, K.Y., and Chang, C.J., Heat tansfe and fictin chaacteistics f lain fin-and-tube heat exchanges, at II: celatin. Int. J. f Heat Mass Tansfe, Vl. 43, 2, [28] Payne, W. V. and Danski, P.., Ptential Benefits f Sat Refigeant Distibuts. RTI-2CR/6-2-, Final Ret, Januay 23. [29] Cbeán J. M., Fenández de Códba P., Otuñ S., Fei V., Seta T. and Bccadi J., Mdeling f tube and fin cils wking as evaats cndenses. Pc. f thid Euean Theal Sciences Cnf., Heidelbeg, Geany, 2. [3] Cbeán, J. M., Fenández de Códba, P., Otuñ S., Fei, V., Gnzálvez, J., Seta T. and Bccadi J., Mdelling f cact evaats and cndenses. Pc. f Sixth Int. Cnf. n dvanced Cutatinal Methds in Heat Tansfe, Madid, 2. [3] Kuehn T. H., Rasey J. W. and Thelkeld J. L. Theal Envinental Engineeing 3d Ed., Pentice Hall; 998. [32] RI Standad 4-2 with ddendu 2, Fced- Ciculatin i-heating and i-cling Cils. May 2. [33] Libbecht, K. G., The hysics f snw cystals. Institute f Physics Publishing, Rets n Pgess in Physics, Vl. 68, 2, 8 89.

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