Analysis of thermal performance of a car radiator employing nanofluid

Transcription

1 Interntionl Journl of Mechnicl Engineering nd Alictions 2014; 2(4): 4751 Published online Setember 20, 2014 (htt:// doi: /j.ijme ISSN: X (Print); ISSN: (Online) Anlysis of therml erformnce of cr rditor emloying nnofluid Ghnbrli Sheikhzdeh 1, Mohmmdhdi Hjilou 2,, Hmed Jfrin 3 1 Dertment of Mechnicl Engineering, University of Kshn, Kshn , Irn 2 Dertment of Mechnicl Eng., Irn University of Science nd Technology, Tehrn , Irn 3 Dertment of Mechnicl Eng., Trbit Modress University, Tehrn , Irn Emil ddress: Sheikhz@kshnu.c.ir (G. Sheikhzdeh), Hjilou_mh@mecheng.iust.c.ir (M. Hjilou), Hmed.jfrin@modres.c.ir (H. Jfrin) To cite this rticle: Ghnbrli Sheikhzdeh, Mohmmdhdi Hjilou, Hmed Jfrin. Anlysis of Therml Performnce of Cr Rditor Emloying Nnofluid. Interntionl Journl of Mechnicl Engineering nd Alictions. Vol. 2, No. 4, 2014, doi: /j.ijme Abstrct: In this study, therml erformnce of cr rditor with emloyment of Ethylene Glycol/coer nnofluid in disrte environmentl conditions hs been investigted. The governing equtions for het trnsfer in the cr rditor hve been written nd solved by using generted comuter code in different environmentl sttes nd the chnges in the outut nnofluid temerture hve been studied. It hs been shown tht by incresing the vlues of volume frction of nnorticles nd lso, Reynolds number of inlet ir, one cn observe rise in the vlues of overll het trnsfer coefficient of the ir side nd the rte of het trnsfer. Furthermore, it is observed tht by dding nnosized rticles to the coolnt fluid in rditor, one cn significntly reduce its outut temerture. In ddition, it hs been demonstrted tht by dding 5% of nnorticles to the coolnt fluid, therml erformnce of the rditor in hot wether of 50 C cn be better thn its erformnce in the wether of 20 C. Keywords: Nnofluid, Therml Performnce, Cr Rditor, Environmentl Conditions, Numericl Anlysis 1. Introduction Technicl imrovement in cr industries hs ugmented the need for engines with high efficiencies. High efficiency of n engine is not only deendnt on its function, but lso it relies on the otiml fuel consumtion nd lower roduction of ollution. Reducing the weight of cr with otiml design of its rditor is necessity for ecologicl systems. Adding s is one of the wys to increse the rte of cooling in utomobile rditors, in which more mounts of surfce for het trnsfer is creted nd convection het trnsfer of ir cn enhnce. Nonetheless, this method hs been the subject of study of mny reserchers in the st nd hs lmost reched its limit. One of the other roosed wys to increse the rte of het trnsfer in utomobile rditors is the emloyment of coolnt fluid with high conductivity coefficient or ugmenttion of the conductivity in common coolnt fluid. Due to the fct tht the conduction coefficient of coolnt fluids such s wter or ethylene glycol is very low, incresing their conductivity hs been the tken into considertion by numerous scientists. So fr, there hs been vst number of theoreticl nd exerimentl studies on enhncing the conduction het trnsfer of fluid by susending very smll rticles in them, which is new roch in therml sciences. In this regrd, Mxwell [1] did some exeriments in which he dded some rticles in the size of micron nd nno to the fluid. The roblem encountered in these fluids ws the fct tht rticles settled in the bottom of the tnk nd lso the flow rte of fluid reduced. Furthermore, corrosion in the ies nd significnt ressure dros in the flows were nother disdvntges of these fluids. In comrison with micronsized rticles, since nnorticles hve high rtio of re to volume, they cn crete more stble susensions; therefore, they cn highly reduce the mount of sediments in the ies nd chnnels. Adding metllic mterils with the size of nno to common fluids such s wter, ethylene glycol nd industril oil, ws first resented by Choi [2]. In ddition, studies hve demonstrted tht dding metllic rticles to bse fluids cn notbly result in the rise of conductivity in fluids [3.4].

2 48 Ghnbrli Sheikhzdeh et l.: Anlysis of Therml Performnce of Cr Rditor Emloying Nnofluid Concetions for het trnsfer correltion of nnofluids re resented by Xun nd Roetzel [5]. In their work, they hve suggested tht nnofluid behves more like fluid rther thn conventionl solidfluid mixture nd bsed on this roch, they hve roosed two different roches for deriving het trnsfer correltion of the nnofluid. Furthermore, Wng nd Mujumdr [6] hve conducted review on the het trnsfer chrcteristics of nnofluids. They hve climed tht further theoreticl nd exerimentl reserch investigtions re needed to understnd the het trnsfer chrcteristics of nnofluids nd identify new nd unique lictions for these fields. Numerous numericl studies bout the evlution of the effect of using nnofluids in het trnsfer devices hve been crried out. Ds, Choi nd Ptel [7] investigted the utiliztion of nnofluids in het exchngers. They hve reorted tht nnofluids show gret romise for use in cooling nd relted technologies. Also, they hve climed tht metllic nnorticles seem to enhnce therml conductivity nomlously, with very lrge enhncement t very low volume frction. They clim tht this ding oens the rosect of incresing therml conductivity enhncement without mking lrge chnges in viscosity, which cn erode the gin in convective conditions. Moreover, Nguyen, Roy, Guthier nd Glnis[8] exmined the emloyment of Al2O3/wter nnofluid in cooling system of electricl devices. They envisged significnt imrovement of het trnsfer coefficient (round 40%) for the 7% volume frction of nnorticles. It seems tht nnofluids cn be good relcement for the coolnt fluid in utomobile rditors. Yu, Frnce, Choi nd Routbort [9] in reserch on using nnotechnology in trnsorttion hve shown tht 15% to 40% of het trnsfer enhncement cn be chieved by emloying different nnofluids. Owing to this feture, one cn reduce the size nd weight of cr without ny negtive imct on its het trnsfer rte [10]. Performnce investigtion of ethylene glycol/coer nnofluid s the coolnt fluid in cr rditor hs been studied by Leong, Sidur, Kzi nd Mmnuc [11] nd in their work, they hve reorted n enhncement of bout 4% in the rte of het trnsfer with dding 2% of nnorticles to the bse fluid. Recently, Fdhilh et l. [12] resented mthemticl modeling in order to study the thermohysicl roerties of coer/wter nnofluid for utomotive cooling systems. They hve showed in their work tht by offering 10 % of coer nnorticles concentrtion, the het trnsfer coefficient of the nnofluid cn be enhnced u to 92 %. In the current reserch, therml erformnce of cr rditor by using ethylene glycol/coer nnofluid with different volume frctions of nnorticles in disrte environmentl conditions (chnges in the velocity nd temerture of ir) is resented. In ddition, chnges in the overll het trnsfer coefficient of the ir side s well s the rte of het trnsfer in terms of φ (volume frction of nnorticles) nd Reynolds number of the inlet ir hve been demonstrted. Also, outut temerture of nnofluid s function of volume frction of nnorticles is investigted. 2. Problem Deition A smle rditor with generl chrcteristics resented by [13] hs been considered in Tble 1. Also, its secific chrcteristics which is ccording to [14] is reresented in Tble 2. The considered rditor is cross flow comct het exchnger with unmixed fluids. The flow of the Ethylene Glycol/coer nnofluid s the coolnt fluid of engine runs through the rditor tubes s the hot fluid, nd the flow of ir s the cooling fluid is erendiculr to the ned ies. Therml erformnce of the rditor will be nlyzed by considering equtions governing the het trnsfer nd with chnges in the volume frction of nnorticles nd the conditions of the incoming ir to the rditor, the effect of emloying nnofluids s the coolnt fluid of the utomobile rditor in disrte environmentl conditions will be studied. Thermohysicl roerties of ir, ethylene glycol nd coer hve been demonstrted in Tble Governing Equtions Assuming ll the roerties to be constnt, equtions governing het trnsfer in both sides of ir nd nnofluid hve been written. In these equtions, subscrits,, f nd donte chrcteristics of ir, nnofluid, the bse fluid nd the rticles, resectively. Chrcteristics of nnofluid with resect to the ones of nnorticles nd the bse fluid s well s volume frction of nnorticles cn be comuted through the following equtions [16]: ρ = ( 1 ϕ) ρ + ϕρ (1) f ( ρ c ) = (1 ϕ)( ρc ) + ϕ( ρc ) (2) µ f f 2.5 = µ (1 ϕ) (3) Tble 1. Chrcteristics of the smle Rditor [13] Descrition Inlet Temerture (ºC) Core width (m) Core height (m) Core deth (m) Tube size ( cm cm ) Air Coolnt It should be ointed out tht the conduction coefficient of ethylene glycol/coer nnofluid hs been tken from [17]. Vlues of Reynolds number of both flows re resumed to be known. Thus, mss velocity of the two flows cn be determined s follows: = µ Re = µ (4) G / Dh,, G Re / Dh, Also, mss flow rte of nnofluid nd ir re:

3 Interntionl Journl of Mechnicl Engineering nd Alictions 2014; 2(4): mɺ = G A ɺ σ (5) fr, σ, m = GAfr, Tble 2. Surfce Chrcteristics of the smle Rditor [14] Descrition Tube rrngement Fin tye Fin mteril Fin itch (cm/) Fin thickness (cm) Hydrulic dimeter, Dh (cm) Free flow re frontl re, σ Het trnsfer re/totl volume (m 2 /m 3 ), α Fin re/totl re, β Air Stggered Ruffled Coer Coolnt Tble 3. Thermohysicl roerties of ethylene glycol, ir nd coer [15] Thermohysicl Coer Ethylene roerty (365 K) Glycol (365K) Air (365 K) Het Ccity c (J/kg.K) Density ρ (kg/m 3 ) Conduction Coefficient k (W/m.K) Viscosity µ (Ns/m 2 ) Furthermore, the rtes of het ccity of the two forementioned flows re: = ɺ,, = ɺ (6) C mc C mc, Comring the vlues of the rtes of het ccity of the two flows, minimum nd mximum rtes of het ccity nd their rtio cn be determined s: C = C /C (7) Also, het trnsfer coefficient of ir cn be clculted from the following eqution: min mx 2/3 c, / Pr In which the Colburn fctor, J, is: h = J G (8) / Re J = (9) Moreover, totl surfce temerture effectiveness in the ir side follows the subsequent eqution: η = 1 (1 η ) A (10) o A / In which the effectiveness of s (ssuming symmetry between the ies) is: η = tnh( ml ) / ml, m = 2h / k t (11) Het trnsfer coefficient of nnofluid cn be determined by the eqution (12): h = Nu k / D (12) h, Where Nusselt number stnds for the fullydeveloed lminr flow which its vlue is: Nu = (13) Neglecting the sediment fctor nd therml resistnce in the ies, the overll het trnsfer coefficient bsed on the het trnsfer surfce in the ir side cn be exressed s in eqution (14): 1 U 1 1 = + (14) η h h ( α / α ) o And the number of het trnsfer units cn lso be exressed s: min U ( α V ) NTU = (15) C In which V is the volume of the rditor. Considering the vlues of C nd NTU clculted from equtions (7) nd (15), the efficiency of the rditor bsed on crossflow unmixed fluid het exchnger cn be determined from eqution (16): 0.78 [ ex( C NTU ) ] ε = 1 ex NTU 1 (16) C And lly, the overll rte of het trnsfer, Q, is: ( T T ) Q Cmin, i, i = ε (17) Which cn be estblished by mens of therml blncing between the two outut temertures of the two flows. Clcultions using generted comuter code for different conditions hve been conducted nd the results re illustrted in the subsequent rt. 4. Results nd Discussion Some resumtions hve been considered during the course of clcultions, such s the Reynolds number nd the inlet ir temerture re ssumed to hve the constnt vlues of 4000 nd 37.5 ºC, resectively, exect for the rt in which the effect of chnges in the conditions of the inlet ir hs been investigted. Mss flow rte of the coolnt (nnofluid) is lso ssumed to be constnt nd equl to 7 kg/s nd its inut temerture hs been considered 82.5ºC. All the investigtions hve been crried out in the domin of 0 to 5% of volume frction of nnorticles. According to figure (1), the overll het trnsfer coefficient of the ir side rises with n increse in the volume frction of nnorticles. It cn be seen tht with ugmenttion of φ from 0 to 5%, the overll het trnsfer coefficient of the ir side exeriences n increse of bout 64.3% in its vlues. Furthermore, rte of het trnsfer in terms of the volume frction of nnorticles hs been deicted in figure (2).

4 50 Ghnbrli Sheikhzdeh et l.: Anlysis of Therml Performnce of Cr Rditor Emloying Nnofluid As it is rent in this figure, with rise in the vlues of volume frction of nnorticles from 0 to 5%, the rte of het trnsfer increses for 29.6%. Figure 3. Chnges in the overll het trnsfer coefficient s function of Reynolds number of the inlet ir Figure 1. Overll het trnsfer coefficient of the ir side with resect to volume frction of nnorticles Figure 2. Effect of volume frction of nnorticles on the rte of het trnsfer Now, chnges on the inlet ir to the rditor re investigted nd results re exressed in figures (3) to (5). In order to exmine the effect of chnges in the conditions of the inlet ir of the rditor, firstly, the effect of chnges in the Reynolds number of inlet ir is studied. In figure (3), the overll het trnsfer coefficient of the ir side in terms of Reynolds number hs been shown. As it hs been demonstrted, the increse in the vlues of overll het trnsfer coefficient of the ir side for ure ethylene glycol is 4.5%, wheres for nnofluid it is 12.4%. Besides, s the volume frction of nnorticles ugments, not only their vlues of U increses, but lso their rte of chnge exeriences rise in its vlues. Figure (4) illustrtes the chnges in the rte of het trnsfer with resect to Reynolds number of the inlet ir. Enhncement of the Reynolds number will clerly result in rise in the vlues of Q, where the more the volume frction of nnorticles, the more vlues of Q cn be chieved. Also, it is noteworthy to oint out tht n increse in the rte of het trnsfer with chnges in Reynolds number of the inlet ir is 26.16% for nnofluids while for ure ethylene glycol this vlue is 15.6%. Moreover, ccording to figure (4), there seems to be convergence in the vlues of Q s the volume frction of nnorticles tkes higher ercentges. The effect of chnges of the inlet ir temerture on the outut nnofluid temerture (coolnt fluid) hs been shown in figure (5). It cn be observed tht with the inlet ir becoming wrmer, the outut temerture of coolnt will increse too. Besides, the temerture of the outgoing nnofluid from the rditor in terms of volume frction of nnorticles reduces. This mtter cn be vividly seen in figure (5), where if the inut temerture of ir is 20ºC, by dding 5% of nnorticles, the temerture of the outgoing coolnt fluid from the rditor cn be decresed from 86.3 ºC to 78.7 ºC. On the other hnd, if the inlet temerture of ir ugments to 50 ºC, by dding 5% of nnorticles, the outut temerture of the coolnt fluid cn be reduced from 89.6 ºC to 85.2 ºC. In other words, by dding 5% of nnorticles, the erformnce of the rditor in the hot wether of 50 ºC will even be better thn tht of 20 ºC. It should be ointed out tht the ttined results in this reserch re in resonble greement with the ones resented by Leong et l. [11], i.e. the trend of ll the resent figures re comtible with the resented results of [11]. Nonetheless, since the roblem deition in the resent work nd the one in Leong et l. [11] is different, nd lso due to the fct tht the ttemt in this reserch hs been more on the rcticl sects of therml erformnce of the cr rditor rther thn theoreticl ones which re discussed by Leong et l. [11], some differences between the vlues of two works cn be observed. 5. Conclusion In this er, therml erformnce of smle cr rditor with emloyment of nnofluids in different environmentl conditions hs been investigted. According to the ttined results, it could be seen tht with ugmenttion of the volume frction of nnorticles from 0 to 5%, the overll het trnsfer coefficient of the ir side exeriences n increse of bout 64.3% in its vlues nd the rte of het trnsfer cn rise bout 26.9%. Furthermore, s Reynolds number enhnces from 4000 to 6000, vlues of the overll het trnsfer coefficient of the ir side for ure ethylene glycol would increse 4.5%, wheres for nnofluid this rise is 12.4%. Moreover, the rte of het trnsfer with chnges in Reynolds number of the inlet ir

5 Interntionl Journl of Mechnicl Engineering nd Alictions 2014; 2(4): rises 26.16% for nnofluids while for ure ethylene glycol it is 15.6%. In ddition, by dding nnorticles to the bse fluid, one cn reduce the temerture of the outgoing coolnt fluid from rditor. In rticulr, by dding 5% of nnorticles to the coolnt fluid, erformnce of the rditor in the hot wether of 50ºC cn be even better thn tht of 20ºC. [5] Xun, Y., Roetzel, W. (2000) Concetion for het trnsfer correltions of nnofluids. Interntionl Journl of Het nd Mss Trnsfer 43, [6] Wng, X.Q., Mujumdr, A.S. (2007) Het trnsfer chrcteristics of nnofluids: review, Interntionl Journl of Therml Sciences 46, [7] Ds, S., Choi, S., nd Ptel, H., Het trnsfer in nnofluids review. Het Trnsfer Eng, 27(10), [8] Nguyen, C.T., Roy, G., Guthier, C., nd Glnis, N., Het trnsfer enhncement using Al2O3 wter nnofluid for n electronic liquidcooling system. Al. Therm. Eng, 27(8 9), [9] Yu, W., Frnce, D.M., Choi, S.U.S., Routbort, J.L., Review nd Assessment of Nnofluid Technology for Trnsorttion nd Other Alictions (No. ANL/ESD/079). Energy System Division, Argonne Ntionl Lbortory, Argonne. Figure 4. Rte of het trnsfer s function of Reynolds number of the inlet ir [10] Kulkrni, D.P., Vjjh, R.S., Ds, D.K., nd Oliv, D., Aliction of luminum oxide nnofluids in diesel electric genertor s jcket wter coolnt, Al. Therm. Eng, 28(1415), [11] Leong, K.Y., Sidur, R., Kzi, S.N., Mmunc, 2010, Performnce investigtion of n utomotive cr rditor oerted with nnofluidbsed coolnts (nnofluid s coolnt in rditor, Alied Therml Engineering 30, [12] Fdhilh, S.A., Hidyh, I., Hilw, M.Z., Fizh, H.N., Mrhmh, R. S. (2013) Thermohysicl Proerties of Coer/ Wter Nnofluid for Automotive Cooling System Mthemticl Modeling, Journl of Mechnicl Engineering nd Technology, 5(2), 2739 Figure 5. Outut temerture of nnofluid s function of volume frction of nnorticles References [1] Mxwell, J.C., A Tretise on Electricity nd Mgnetism. Clrendon Press, Oxford, UK. [2] Choi, S.U.S., Enhncing therml conductivity of fluids with nnorticles. ASME, FED231/MD, 66, [3] Lee, S., Choi, S.U.S., Li, S., nd Estmn, J.A., Mesuring therml conductivity of fluids contining oxide nnorticles. Journl of Het Trnsfer, 121, [4] Ds, S.K., Putr, N., Thiesen, P., nd Roetzel, W., Temerture deendence of therml conductivity enhncement for nnofluids. Journl of Het Trnsfer, 125, [13] Vsu, V., Krishn, K.R., Kumr, A.C.S., Therml design nlysis of comct het exchnger using nnofluids, Interntionl Journl of Nnomnufcturing, 2 (3), [14] Chryulu, D.G., Singh, G., Shrm, J.K., Performnce evlution of rditor in diesel engine cse study, Alied Therml Engineering, 19, [15] Incroer, F. P., DeWitt, D.P. (1996) Fundmentls of Het nd Mss Trnsfer, John Wiley & Sons, New York [16] Xun, Y., nd Li, Q., Investigtion on convective het trnsfer nd flow fetures of nnofluids. Journl of Het Trnsfer, 125, [17] Estmn, J.A., Choi, S.U.S., Li, S., Yu, W., Thomson, L.J., 2001, Anomlously incresed effective therml conductivities of ethylene glycolbsed nnofluids contining coer nnorticles, Alied Physics Letters 78 (6),