International Journal of Modern Trends in Engineering and Research e-issn No.: , Date: 2-4 July, 2015

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1 International Journal o Modern Trends in Engineering and Researh e-issn No.: , Date: 2-4 July, 2015 Numerial Analysis And Parametri Study o Miro-hannel Heat Exhanger For Single Phase Water Cooling Patil J.D. 1, Gaikwad S.M. 2 1,2 Assistant Proessor, Mehanial Engineering Department, 1 Army Institute o Tehnology, University o Pune, jdpatilaitp@yahoo.om 2 Army Institute o Tehnology, University o Pune, gaikwads.sanjay@gmail.om Abstrat Today with the miniaturization o eletroni omponents with inreased speed o omputational apabilities, thermal management o miroeletroni omponents is a hallenging problem. Overheating o these miro omponents and miro devies led to the use o mini and miro hannels in the above mentioned tehnologies. The aim is to eliminate as ast as possible the maximum heat quantity rom these systems in order to ensure an inreased reliability and untional stability. Miro hannel heat exhangers with diret liquid ooling are apable o removing high heat lux. Whereas, this high heat removal apability o this devie is assoiated with inreased pressure drop penalty. Hene hannel size optimization beomes neessary in seleting orret hannel geometry or desired appliation. Present paper deals with the numerial analysis and parametri study o mirohannel. This parametri study will be useul or seletion o hannel geometry aording to system requirements. The results shows that or the same ooling requirements (or same ambient to juntion temperature dierene 60oC, same hip size 10mmX10mm and same heat lux 300 W/m2) you have a hoie o seleting hannel geometries or: 1) Channel with hydrauli diameter o 100 μm having high onvetive heat transer oeiient o W/m2 K and maximum pressure drop o 35kPa. 2) Channel with hydrauli diameter o 180 μm having low onvetive heat transer oeiient o W/m2 K and minimum pressure drop o 5KPa. Keywords Mirohannels, eletroni ooling, hannel geometry, pressure drop I INTRODUCTION Now days, there is rapid growth o appliations whih requires high heat transer rate and luid low in relatively small hannels. Suh examples inlude eletroni ooling, MEMS devies or biologial and hemial analysis and ooling o laser gun et. Development o new appliations requiring ooling o omponents by passing single phase liquid in mirohannels has motivated researhers to study thermo-hydrodynami perormane o mirohannels. In the present work, numerial analysis is arried out to deide hannel geometry required or thermal perormane with minimum pressure drop ondition. The onstraints or hannel geometry optimization inlude maximum juntion temperature dierene, hip size, heat lux and pressure drop. II LITERATURE REVIEW Mirohannels were irst proposed or eletroni ooling appliations by Tukerman and Pease [1]. They have experimentally demonstrated diret irulation o water in mirohannels abriated in silion hips or eletronis ooling appliations. They proved that mirohannel heat sink was All rights Reserved 1782

2 to dissipate 790 W/m 2 with a maximum substrate temperature to inlet water temperature dierene o 71 C. However, the pressure drop was quite large it is around 200 KPa with plain mirohannels. Mark E, Steinke and Satish G Khandlikar [2], reviewed single phase heat transer tehniques or appliations in miro hannels, minihannels and mirodevies. The major tehniques inlude low disruptions, low pulsations, breakup o boundary layer, entrane region, vibration, eletri ields, swirl low, seondary lows and mixers. In this paper appliability o these tehniques or single phase lows in mini hannel and miro hannel is evaluated. The miro hannel and minihannel single phase heat transer enhanement devies will extend the appliability o single phase ooling or ritial appliations, suh as miroproessors ooling. Satish G Khandlikar and Harshal R Upadhye [3], have done hannel size optimization. As the heat lux inreases beyond about 200W/m 2, the heat transer and pressure drop harateristis o the plain hannels ditate the use o turbulent low through the hannels, whih suers rom an exessive pressure drop penalty. Thereore, they have done theoretial analysis o a m m silion hip inorporating plain mirohannels or heat transer and pressure drop and presented results in parametri plots. These results show that the enhaned strutures are apable o dissipating heat luxes extending beyond 300W/m 2 using water as the oolant in a split-low arrangement with a ore pressure drop o around 35 kpa. Evan G Colgan and et al [4], desribes a pratial implementation o a single-phase Si mirohannel ooler designed or ooling very high power hips suh as miroproessors. Through the use o multiple heat exhanger zones and optimized ooler in designs, a unit thermal resistane C- mm 2 /W rom the ooler surae to the inlet water was demonstrated with a luid pressure drop o 35 KPa. Gaurav Agarwal, Manoj Kumar Moharana and Sameer Khandekar [5], have studied thermohydrodynamis o simultaneously developing single phase low through a mini-hannel array experimentally. They observed that developing low provides very high heat transer oeiients in entrane region and thereore o interest or mini miro sale heat lux removal appliation. J D Patil and Dr. B S Gawali [8], have done numerial analysis o mirohannel heat exhanger that is used to selet appropriate hannel geometry by using least thermal resistane value. Results obtained rom analysis are used to plot onvetive heat transer oeiient, thermal resistane and pressure drop. III TERMS AND TERMINOLOGY USED FOR ANALYSIS Fig. 1 Mirohannel geometry Channel aspet ratio α is deined as the ratio o the hannel width to the hannel All rights Reserved 1783

3 a b Fin aspet ratio α is deined as the ratio o the in thikness to the in height. s b Fin spaing ratio β is deined as the ratio o in aspet ratio to the hannel aspet ratio. Channel width is depend on hip width, number o hannels, and the in spaing ratio by the relation, a n W n 1 Eetive hannel wall heat transer surae area, onsidering in (thikness o hannel wall) eiieny eet, is given by Fin eiieny Where hp m= ka Nusselt number A 2 b a Ln w hd Nu= k tanh mb mb Hydrauli diameter 4ab d= 2 a+b Condution thermal resistane o mirohannel (base thikness o hannel is taken as 1.5 times height o hannel) 1.5 b R ond = k WL Convetive thermal resistane 1 R onv = hl 2 a b All rights Reserved 1784

4 Resistane due to heating o the luid as it absorbs energy passing through the heat exhanger. 1 R heat = Cm Total thermal resistane p t R Total =R ond Ronv R heat IV FLUID FLOW PARAMETERS For the hydrodynamially developing low, the dimension less axial distane x + is deined as + x/d x = Re Axial pressure drop is expressed in terms o the inremental pressure drop as 2 Re umx p= 2 d K x 2 u m 2 Where is Fanning rition ator and K(x) is some times reerred as the inremental pressure deet. It inreases monotonially rom a value o zero at x=0 to a onstant value in the hyrodynamially developed region at x>l hy This onstant value is reerred as Hagenbah s ator. L hy =0.05Re d K x = and Re= Measuring loal pressure along the low is diiult in mirohannel, hene researhers generally measures pressure drop aross the inlet and outlet maniolds. This pressure drop measurement represent the ombined eet o entrane and exit losses, developing region eets and the ore ritional losses. Thus, the measured pressure is sum o these omponents and is alulated by ollowing equation. 2 Re u x u u u p Total = 2 d m m m m K x K Ke Where, K and K e are ontration and expansion loss oeiient due to area hange. The inremental pressure drop, K, K e and rition ator are obtained rom Kakak et al.[6] and Kandlikar, et al.[7] The dimensionless axial distane x * is deined as V HEAT TRANSFER All rights Reserved 1785

5 * x/d x/d x= P e Re Pr The thermal entrane length L th =0.1Re Pr d The loal Nusselt number or thermally developing region are obtained rom Kandlikar, et al.[7] VI OBJECTIVE The objetives o present work are 1. To develop MATLAB program to analyze the heat transer and pressure drop in a miro hannels. 2. To present parametri study o miro hannel geometry. VII ASSUMPTIONS The ollowing assumptions are onsidered or analysis 1. Size o miro hannel hip 10 X 10-3 m X 10 X 10-3 m. 2. Depth o miro hannel, b is 300 X 10-6 m (300μm). 3. Constant heat lux o 300W/m 2 is applied. 4. Inlet temperature o water is taken as 27 o C (300K). 5. Maximum mean temperature o the hannel wall at outset is maintained below 360 K. 6. Constant properties are assumed or ooling luid (water) and the hannel wall material opper. 7. Number o hannels is taken rom 50 to 100 with inrement o Fin spaing ratio is taken rom 0.2 to 1 with inrement o Low starting value o Re is assumed e.g. Re=50 and required analysis is done. 10. Mass low rate in a single hannel m in kg/s is alulated or assumed Re. VIII SOLUTION METHOD One hannel symmetri with enter line o hannel width is onsidered or analysis. Length o hannel is divided into a ertain number o equal divisions, in our analysis 10. Hene one symmetri hannel is divided in ten slies rom inlet to outlet as shown in Figure 2. Heat dissipated per slie Q div is alulated or given data. Energy balane is applied or eah slie starting rom irst slie where inlet temperature, per hannel mass low rate m, speii heat C p and Q div known and T out is alulated or ollowing equation. Q div T out = Tin mc p Fig. 2 Single hannel is divided into smaller number o division or All rights Reserved 1786

6 Pressure Dierene Total Thermal Resiatane This alulated T out is used as T in or next slie. The bulk temperature T b or this slie is taken as the mean o T in and T out. Fluid properties required or urther analysis are taken at this bulk mean temperature. The average surae temperature o this slie is alulated heat transer by mode o onvetion rom this slie by using equation Qdiv T= s Tb hadiv The temperature dierene between this T s and temperature o water at inlet 30 o C is alulated. I this is more than 60 o C then the assumed value o Re is inreased by small inrement and alulations are repeated. This proess is repeated until required temperature dierene o 60 o C is reahed. For the onverged value o Re mass low rate and pressure drop is alulated. This proess is repeated or dierent number o hannels and in spaing ratios. The results obtained are plotted as parametri plots. IX VERIFICATION OF NUMERICAL ANALYSIS Veriiation o numerial analysis is done by omparing experimental results obtained by Tukerman and Pease with numerial results obtained or the same geometri, low and thermal onditions. The results o total thermal resistane and pressure drop or three dierent ases are shown in Fig. 3 (a) & (b). Case 1: a=56μm, s=44 μm,b=320 μm,=4.7m 3 /s and q=181w/m 2, Case 2: a=55μm, s=45 μm,b=287 μm,=6.5m 3 /s and q=277w/m 2, Case 3: a=50μm, s=50 μm,b=302 μm,=8.6m 3 /s and q=790w/m 2. Numerial results are seen to be in good agreement with experimental results. Variation o Experimental and Numerial values 1.40E E E E E-02 Tukerman Experimental Values Our Numerial Values 4.00E E E Expt No Fig 3 (a) Variation o total thermal resistanes or three dierent ases. Variation o Experimental and Numerial Values 3.50E E E E E+05 Tukerman Exprimental values Our Numerial Values 1.00E E E Expt No Fig 3 (b) Variation o pressure drop or three dierent All rights Reserved 1787

7 X RESULT AND DISCUSSION Fig. 4. Shows variation o h with respet to number o hannels and in spaing ratio. It shows that h inreases with inrease in number o hannels and β. As we know that Nu is proportional to produt o h and d. Fig. 5 shows variation o d with respet to number o hannels and in spaing ratio. Highest value o h is W/m 2 o K at n=100 and β =1 where value o d is lowest. Fig. 4 Variation o onvetive heat transer oeiient with number o hannels and in spaing ratio. Fig. 6 shows variation o pressure drop in kpa with respet to number o hannels and in spaing ratio. Highest value o pressure drop o 30 kpa is obtained at n=100 and β =1. Value o pressure drop is diretly depends on resistane to low and resistane to low is diretly depends on hydrauli diameter available or low. Fig. 5 Variation Hydrauli diameter with respet to number o hannels and in spaing All rights Reserved 1788

8 Fig. 6 Contour plot o in spaing ratio β vs number o hannel with pressure drop (red lines) and in thikness in μm as parameter or water low in plane retangular miro hannels at a heat lux o 3MW/m2. From the above plots we an onlude that 1. Perormane with maximum pressure drop: Channels with hydrauli diameter less than 100 μm, number o hannels rom 85 to 100 and in spaing ratio o 0.8 to 1. Convetive heat transer rate in this range is above W/m 2 o K and pressure drop is around 25 kpa. 2. Perormane with minimum pressure drop: Channels with hydrauli diameter slightly greater than 180 μm, number o hannels rom 50 to 65 and in spaing ratio o 0.2 to 0.5. Convetive heat transer rate in this range is above W/m 2 o K and pressure drop is below 5 kpa. Two speial ases in the above mentioned two ategories are ompared to study eet o hannel geometry on thermal resistanes. The variation dierent thermal resistanes or these two ases are shown in Fig 7(a) and (b). Case 1) number o hannels 90 and in spaing ratio o 0.9 Case 2) number o hannels 60 and in spaing ratio o 0.3. In this ase onvetive thermal resistane is more beause o lower onvetive heat transer oeiient where as ondution and heat resistanes are almost same. Thereore total thermal resistane in this ase is more than ase no 1 hene in ase 2 same ooling eet is obtained with slight higher temperature dierene. Fig. 7(a) Case 1) number o hannels 90 and in spaing ratio o 0.9 Rondution=0.0117, Rheat=0.207, Ronvetion= , Rtotal= and All rights Reserved 1789

9 Fig. 7 (b) Case 2) number o hannels 60 and in spaing ratio o 0.3.Rondution=0.0117, Rheat=0.207, Ronvetion= 0.111, Rtotal= 0.33 and Tbase=65.2O CONCLUSION Numerial analysis and parametri study o mirohannels abriated on 10mmX10mm hip size, 300 W/m 2 heat lux and 60 o C juntion to ambient temperature dierene is studied. Results are presented in the orm o ontour plots. This parametri study is used or seletion o hannel geometry aording to system requirements. The results shows that or the same ooling requirements you have a hoie o seleting hannel geometries or: 1) Channel with hydrauli diameter o 100 μm having high onvetive heat transer oeiient o W/m 2 o K and maximum pressure drop o 25kPa. 2) Channel with hydrauli diameter o 180 μm having low onvetive heat transer oeiient o W/m 2 o K and minimum pressure drop o 5kPa. REFERENCES [1] D B Tukerman and R F W Pease, High perormane heat sinking or VLSI, IEEE Eletron devie letters, Vol EDL-2, No 5, May 1981 [2] Marl E Steinke and Satish G Kandlikar, Review o single phase heat transer enhanement tehnique or appliation in mirohannels, minihannels and mirodevies, Heat and mass tehnology, Vol 22, n 2, [3] Satish G Kandlikar and Harshal R Upadhye, Extending the heat lux limit with enhaned mirohannels in diret single phase ooling o omputer hips, 21 st IEEE SEMI-THERM symposium, 2005, [4] Evan G Colgen, Brue Furman, Mihael Gaynes, William s Graham, Nany C, LaBiana, John H Magerlein, Robert J Polastre, Mary Beth Rothwell, R J BenZama,Rehan Choudhary, Kenneth C Marston, Hilton Toy, Jamil Wakil, Jerey A Zitz and Roger R Shmidt, A pratial implementation o silion mirohannel oolers or high power hips, IEEE Transation on omponents and pakaging tehnologies, Vol 30, No 2, June [5] Gaurav agarwal, Manoj Kumar Moharana and Sameer Khandekar, Thermo-Hydrodynamis o developing low in a retangular mini-hannel array, 20 th National and 9 th International ISHMT-ASME Heat and mass transer onerene, [6] Kaka, S., Shah, R. K and Aung, W., Handbook o single phase onvetive heat transer, John Wiley & Sons, (New York, 1987). [7] Satish G. Kandlikar, Srinivas Garimella, Dongqing Li, Stéphane Colin and Mihael R. King, Elervier Ltd, [8] J D Patil and Dr B S Gawali, Numerial analysis and parameteri study o mirohannel heat exhanger or diret liquid ooling o miroproessor All rights Reserved 1790

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