Thermal and Hydraulic Performance of Water/Glycol Mixture and the Application on Power electronics Cooling

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1 ENVIRONMENTAL AND EARTH SCIENCES RESEARCH JOURNAL ISSN: (Print), (Online) Vol. 3, No. 1, March, 016, pp. 1-6 DOI: /eerj A publication o IIETA Thermal and Hydraulic Perormance o Water/Glycol Mixture and the Application on Power electronic Cooling Xiaoze Du, Wei Zhang, Lijun Yang and Yongping Yang * Key Laboratory o Condition Monitoring and Control or Power Plant Equipment (North China Electric Power Univerity), Minitry o Education, Beijing 1006, China duxz@ncepu.edu.cn ABSTRACT Numerical imulation were conducted to tudy thermal and hydraulic perormance o liquid-cooled heat ink on power electronic cooling, in particular with water/glycol mixture. Conidering non-uniorm and dicrete heat ource, geometry and number o cooling channel were analyzed. The reult how that alternating rectangular channel ha high thermal perormance with a little penalty in hydraulic reitance. The number o cooling channel can be optimized to provide the bet thermal perormance, a 40 channel or the analyzed cae. Perormance dierence reulting rom working coolant wa tudied, with 100% de-ionized water, mixture o 50% ethylene glycol and 50% de-ionized water (EGW) by weight, and mixture o 60% propylene glycol and 40% de-ionized water (PGW) by weight. The variation o luid phyical propertie with temperature were taken into account. It ha been concluded that lower coolant temperature doe not necearily lead to better cooling capacity, i.e. a peciic coolant ha an optimum operation temperature to provide the maximum cooling perormance. Keyword: Electronic cooling, Liquid-cooled heat ink, Water/glycol mixture. 1. INTRODUCTION Variable-requency drive (VFD) i widely employed in motor application, o which the unit power requirement ha been upgraded to 30,000kW, with both heat generation and heat denity being increaed igniicantly [1]. Accordingly, the VFD cooling mut be enhanced rom air cooling to liquid cooling. In cold environment, water/glycol mixture i normally elected a working luid to avoid reezing, with a penalty in thermal perormance and hydraulic reitance []. Xie et al. [3] tudied the eect o channel dimenion, channel wall thickne, bottom thickne and inlet velocity on thermal reitance, preure drop and maximum allowable heat lux or a rectangular mini-channel heat ink. With a 3D conjugate heat traner numerical model, Li et al. [4] ound an optimal ize or rectangular channel to obtain minimum thermal reitance and maximum pumping power aving. Uing a novel multi-parameter optimization approach, Wang et al. [5] employed an invere problem method to optimize the geometry or a micro-channel heat ink. Peng et al. [6] perormed an experimental tudy on preure drop and convective heat traner (water a coolant) in traight rectangular microchannel. The reult howed that in both laminar and turbulent low regime, cro-ectional apect ratio had a great inluence on low riction and convective heat traner eiciency. Uing the equential quadratic programming (SQP) method, Hu et al. [7] conducted an optimization tudy, ocuing on the tructure o microchannel. For a given heat ink, the paper give optimal number o the channel, a well a width and height o the channel. Geometric contruction o the channel ha a huge impact on the heat traner and low perormance. In the previou tudy conducted by the author [8], ive kind o cooling channel were tudied with a given cold plate. The reult howed that alternating rectangular channel had the bet thermal perormance with a little penalty in preure drop, and higher channel denity could improve both thermal and hydraulic perormance. Gunnaegaran et al. [9] tudied heat ink perormance o three dierent hape o micro-channel, a rectangular, trapezoidal, and triangular with the Reynold number ranging rom It ha been ound that the heat ink having the mallet hydraulic diameter ha the bet perormance in preure drop and riction actor. Type o coolant ha a igniicant inluence on heat ink perormance. The coolant election i quite diicult becaue many actor mut be taken into the conideration, a corroion reitance, regulatory contraint, thermal propertie, cot, thermal tability, and environmental temperature [10]. Water i an excellent heat traner media, but reezing i a problem. Ethylene glycol and propylene glycol are colorle and odorle liquid that are micible 1

2 with water. Though pure glycol don t have the preponderance a a coolant, they can eiciently lower the reezing point o water when mixed, and hence the water/glycol mixture i widely ued a antireezer and heat traner media. In application, water/glycol mixture between 40% and 60% glycol percentage i typically recommended. Ethylene glycol olution have better thermo-phyical propertie (uch a vicoity) than propylene glycol olution, epecially at lower temperature. However, when the coolant are ued or application involving poible human contact or where mandated by regulation, the le toxic propylene glycol ha it big advantage. In the application or power electronic cooling, water and water/glycol mixture mut be de-ionized. For a ilicon baed mini-channel heat ink, Li et al. [11] numerically tudied the conjugate heat traner and hydraulic perormance with dierent kind o coolant. The reult howed that coolant thermo-phyical propertie had an inluence on both the hydraulic and thermal perormance. Dehghandokht et al. [1] tudied a multi-port erpentine meochannel heat exchanger with water and ethylene glycolwater mixture a coolant. The reult howed that the erpentine meo-channel heat exchanger could be applied a an automotive radiator uing ethylene glycol-water mixture. In the preent tudy, ocuing the application to power electronic cooling, thermal and hydraulic perormance o a liquid-cooled heat ink will be numerically tudied, with an emphai on channel geometry, channel number, and coolant election.. PHYSICAL AND MATHEMATICAL MODEL.1 Model decription Conidering three diode rectiier module (60 mm 14 mm, A1, B1, C1) and our IGBT emiconductor module (140 mm 190 mm, D1, D, E1, E) intalled on both the top and bottom urace o a heat ink, the analyzed heat ink dimenion i given a Figure 1, length L = mm, width W = mm, and thickne t =.9 mm. The heat ink i made o copper, with one inlet and one outlet. In the model, each diode rectiier module i one heat ource with uniorm heat lux, q1 = 88W/m, and each IGBT module i with uniorm heat lux, q = 1710W/m. Cooling channel are arranged a two pae with parallel low. The phyical model i ocued on channel hape and channel number. Baed on the previou tudy [8], two type o channel, traight rectangular channel and alternating rectangular channel are elected or analyi, a the alternating rectangular channel can provide the bet thermal perormance and the traight rectangular channel can be a baeline or comparion. Figure 1. The cheme o the heat ink. Governing equation with boundary condition A three-dimenional numerical imulation model ha been built or the heat ink. Governing equation or liquid coolant are, ( V ) 0 (1) (. ) ( ) V V P V () c V k T (3) P, (. ) ) Energy equation or bae olid copper wall region: k T (4) 0 The boundary condition or the governing equation are given a ollow: In the luid: Inlet: v = w = 0; Outlet: u u in ; and T = Tin (5) p p (6) q w out At heat ink urace covered by heat ource k n At heat ink urace open to the ambient: 0 n At luid-olid interace: T T ; k n k n.3 Analyi conideration Channel geometry, channel number, and coolant election will be analyzed to tudy their eect on heat ink thermal and hydraulic perormance. Three coolant luid are elected or the comparion, a 100% de-ionized water, 50% ethylene glycol/ 50% deionized water by weight (EGW50/50), and 60% propylene glycol/ 40% de-ionized water by weight (PGW60/40). Conidering the temperature variation, cooling perormance rom the three coolant are compared under the ame pumping power, thu the inlet velocity o the coolant, uin, i calculated according to the given preure drop [13]. Thermal propertie o the glycol olution, epecially vicoity, are enitive to temperature. In the analyi, the change in luid propertie with temperature are taken into account. The luid phyical propertie are obtained rom the ASHRAE Handbook [14]. (7) (8) (9)

3 The channel geometry determination and channel number optimization are taken a a deign conideration. The deign criteria are the inlet coolant temperature 308K, the coolant volumetric low rate m3/, the maximum allowable heat ink urace temperature 358K, and the maximum hydraulic preure drop 40,000Pa. PGW60/40 i elected a working coolant, a it provide the wort thermal and hydraulic perormance. 3. NUMERICAL SOLUTION Meng et al. [15] conducted an experimental tudy on thermal and hydraulic characteritic o alternating elliptical channel. A threhold o Reynold (Re) number deining low tate wa given or alternating elliptical channel, a Re<500, the tate i laminar low and Re = 500 ~ i low-re low. It ha been ound in Hu et al. tudy [8] that the Re number threhold can be a low a 00 or alternating rectangular channel, a the diturbance in it i greater than that in alternating elliptical channel. In the analyzed cae, a the Reynold number in the alternating rectangular channel i between 00 and 500, the low tate i conidered in turbulence tranition regime. Accordingly, low-re k- ε turbulent model i employed or the CFD olution. The meh or the alternating rectangular channel and the channel arrangement are hown in Figure and Figure 3, repectively. The computational domain i dicretized to control volume, and grid point are located in the center o each control volume. The conervation equation are ormulated with the parameter at each control volume and the urrounding control volume. The low ield i olved uing the tandard SIMPLE algorithm. Finite Volume Method (FVM) with hybrid dierencing cheme i elected or olving the governing conervation equation with the boundary condition executed on both luid and olid region. Ater a meh independent tudy, hexahedral grid are eventually applied or the numerical computation. Figure.Shape o alternating rectangular channel with meh 4. RESULTS AND DISCUSSIONS 4.1 Channel election Channel geometry play a very important role in improving heat ink perormance. Five cooling channel geometrie have been tudied in Hu et al. work [8], a alternating rectangular channel how the bet heat traner perormance with a little penalty in hydraulic reitance. The comparion between the alternating rectangular channel and the traight rectangular channel i given a Table 1. It can be ound rom Table 1 or the analyzed 16-channel heat ink that the traight rectangular channel reult in the maximum temperature o 400K, much higher than the allowable 358K, while the alternating rectangular channel i only 367K. The two channel how about 50% dierence in the heat traner perormance. The preure drop are cloe, and both are quite within the deign limitation. Thereore, the alternating rectangular channel will be elected or the analyi next on channel number optimization and coolant eect, mainly ocuing on thermal perormance. Table 1. The perormance o the two kind o channel (water a coolant) Parameter aximum urace T (K) heat traner ΔT(K) traight rectangular channel p (Pa) Channel number and arrangement alternating rectangular channel Uniormly located cooling channel are tudied. The inlet temperature o coolant i 308K, and the volumetric low rate i ixed m3/. With an increae in channel number, the pitch between the adjacent cooling channel i kept contant. It mean the channel ize will be maller, and the um o channel urace directly acing the heat ource will become maller. It can be aid that the channel number will aect the entire heat convective traner area contacting with the coolant, a well a the ratio o cooling channel area and non-channel area at heat ink urace. The channel number will alo aect coolant low ditribution in the heat ink. Figure 4 how the velocity proile at the cro-ection o the hal o the heat ink thickne, i.e. z=11.4mm. Each channel i numbered a channel 1, channel...channel N rom top to bottom. For a 16-channel heat ink, the coolant low ditribution per channel i quite uneven, a the ma low rate i increaed igniicantly rom channel 1 to channel 8 at Pa 1 and rom channel 9 to channel 16 at Pa. With 4 channel in the heat ink, the ma low rate i alo increaed rom channel 1 to channel 1 and rom channel 13 to channel 4, but the non-uniormity i not a igniicant a the 16-channel deign. When 36 channel are applied, the coolant low ditribution ha become quite uniorm. Figure 3. Channel arrangement in the heat ink (uniorm arrangement) 3

4 (a) 16 channel The heat ink urace temperature at the heat ource area i illutrated a Figure 6. It can be ound that the maximum heat ink urace temperature i decreaed with the channel number increaing up to 40. At the 16-channel heat ink, the hottet pot occur under module A1 and the lowet temperature i under module D. A the channel number increaing, the urace temperature reduction under module A1 i igniicant, while the eect under module E i little. When the channel number i increaed to 36, the temperature under module A1 and E are almot the ame. At the 40- channel heat ink, the hottet pot exit under module E. The reult how the eect o the channel number increae on both uniormity o coolant ditribution and enhancement o heat convective perormance. (b) 4 channel (c) 36 channel Figure 4. The chematic velocity o urace z=11.43mm (the inlet temperature i K) (a) 16 channel Another important actor aecting the heat ink perormance i the heat traner coeicient. The average heat traner coeicient at cooling channel urace i deined a, Qc h A c m o which, m T T ln T, outlet c, outlet c, inlet, inlet c, outlet, outlet (10), i the log mean temperature dierence between the coolant and channel. When the channel number i increaed, the ize o each channel become maller. It caue an increae in the diturbance o the low in each channel, and hence the heat traner coeicient. The increae o the average urace heat traner coeicient with channel number i hown a Figure 5. The channel number take the thermal eect rom coolant low ditribution, entire heat traner area (including the ratio o heat convection area to heat conduction area), and heat traner coeicient at cooling channel urace. (b) 4 channel (c) 36 channel h (W/m k) water egw50/50 pgw60/ number o channel Figure 5. Variation o urace heat traner coeicient with number o channel (T= K) (d) 40 channel Figure 6. The temperature proile o dierent channel with PGW a coolant 4

5 The heat rom power component i diipated into the coolant with heat conduction and heat convection. A the channel number increae, the heat conduction area (i.e. the area between cooling channel) become larger. Becaue the conduction reitance i higher than the convection reitance or the analyzed cae, a larger heat conduction area mean an eect to increae thermal reitance. When the channel number i increaed to 45, the eect o heat conduction reitance become igniicant, and caue the total thermal reitance increaed and hence heat ink urace temperature increaed. For a heat ink with maller convection reitance, or example water v. PGW60/40, the eect o the conduction reitance i greater. The concluion can be ound rom Figure 7. A hown in Figure 8, the preure drop i alway increaed with the channel number in the heat ink. It i mainly becaue o the minor loe at branching point. Figure 9. Non uniorm arrangement o the luid channel Water EGW50/50 PGW60/40 T max (K) number o channel Figure 7. Maximum urace temperature o dierent number o channel ( T= K) P(Pa) Water EGW50/50 PGW60/ number o channel Figure 8. Preure drop o dierent number o channel (T= K) Fig. 4~8 how the eect rom the cooling channel with uniorm arrangement. Since the heat ource on the heat ink urace are dicrete, the cooling channel can be located accordingly or a cutomized deign. The non-uniorm arrangement o the cooling channel, illutrated a Figure 9, can reduce the maximum urace temperature. Since the preure drop mainly occur at each channel, the non-uniorm channel arrangement ha little impact on coolant low ditribution. Figure 10 how the velocity proile at the croection o z=11.4mm or the non-uniorm channel arrangement cae. Figure 10. The chematic velocity o urace z=11.43mm o the non-uniorm arrangement cae. 4.3 Coolant eect In a cooling deign, it i in general conidered that a lower coolant temperature give higher temperature dierence or the heat traner rom heat diipating component to liquid coolant, and hence reult in higher cooling capacity. However, the concluion may not be accurate or the coolant which phyical propertie change igniicantly with temperature, uch a water/glycol mixture. Baed on the analyzed heat ink cae, the cooling ability o water/glycol mixture i tudied to invetigate the variation with coolant temperature, under the ame pumping power. The reult are hown a Figure 11. It can be ound that the maximum heat ink urace temperature i not alway reduced with a decreae in coolant temperature. There exit an optimal inlet temperature or each coolant, a 88K or EGW50/50 and 68K or PGW60/40. The optimal temperature i reulted rom the aociated eect o temperature dierence, heat convection perormance, and coolant low rate. A the inlet coolant temperature i decreaed, the temperature dierence or heat traner i increaed, while the heat convection perormance at luid/olid interace i decreaed becaue o an increae in coolant vicoity reulting rom lower temperature. In addition, i the ame pumping power i conidered, the coolant low rate will be reduced with the coolant temperature, a hown in Figure 1. Without the conideration o the ame pumping power, the optimal coolant temperature alo exit becaue o the eect rom coolant vicoity and hence heat convection perormance. 5

6 5. CONCLUSIONS Numerical imulation were conducted to tudy the heat traner and luid low characteritic o a liquid-cooled heat ink with water/glycol mixture a working coolant. The analyi wa ocued on channel geometric contruction, channel number, and coolant eect. The concluion have been ummarized. (1) Alternating rectangular channel can provide high heat traner perormance, with a little penalty in hydraulic reitance. Becaue the device temperature i alway the major concern compared to pumping power, the alternating rectangular channel hould be widely applied to power electronic cooling. () The cooling channel in heat ink have an optimal number to provide the maximum thermal perormance and hence the minimum urace temperature. It i reulted rom the aociated eect o heat convection reitance at channel urace and heat conduction reitance in heat ink olid part. The preure drop i alway increaed with channel number. (3) Water/glycol mixture ha an optimal operating temperature to provide the maximum cooling perormance. REFERENCES [1] J. Zhang, J. Waggel, J. Zhao, D. Weber and M. Matuonto, Study or cooling ytem in variable requency drive and aociated control unit, Proc. 4th Int. Green Energy Con., Beijing, October 0-, 008, pp [] E. C. Roger and B. A. Ste, Ethylene glycol: It ue in thermal torage and it impact on the environment, ASHRAE Tran., 99(1993) [3] X. L. Xie, Z. J. Liu, Y. L. He and W. Q. Tao, Numerical tudy o laminar heat traner and preure drop characteritic in a water-cooled minichannel heat ink, Appl. Therm. Eng., 9(009) [4] J. Li and G. P. Peteron, 3-Dimenional numerical optimization o ilicon-baed high perormance parallel microchannel heat ink with liquid low, Int. J. Heat and Ma Tran., 50(007) [5] Z. Wang, X. Wang, W. Yan, Y. Duan, D. Lee and J. Xu, Multi-parameter optimization or microchannel heat ink uing invere problem method, Int. J. Heat and Ma Tran., 54(011) [6] X.F. Peng and G. P. Peteron, Convective heat traner and low riction or water low in microchannel tructure, Int. J. Heat Ma Tran., 39(1996) [7] G. Hu and S. Xu, Optimization deign o microchannel heat ink baed on SQP method and numerical imulation, Proc. 009 IEEE Int. Con. on Appl. Superconductivity and Electromagnetic Device, Chengdu, China, September 5-7, 009. [8] H. Hu, J. Zhang, X. Du and L. Yang, Analyi o liquid-cooled heat ink ued or power electronic cooling, ASME J. Therm. Sci. Eng. Appl., 3(011) [9] P. Gunnaegaran, H. A. Mohammed, N. H. Shuaib and R. Saidur, The eect o geometrical parameter on heat traner characteritic o microchannel heat ink with dierent hape, Heat and Ma Tran., 37(010) [10] S. C. Mohapatra and D. Loikit, Advance in liquid coolant technologie or electronic cooling, Annual IEEE Semiconductor Therm. Meaurement and Management Sym., 005, pp [11] J. Li, G. P. Peteron and P. Cheng, Threedimenional analyi o heat traner in a micro-heat ink with ingle phae low, Int. J. Heat Ma Tran., 47(004) [1] M. Dehghandokht, M. G. Khan, A. Fartaj and S. Sanaye, Flow and heat traner characteritic o water and ethylene glycol-water in a multi-port erpentine meochannel heat exchanger, Int. J. Therm. Sci., 50(011) [13] H. Kou, J. Lee and C. Chen, Optimum thermal perormance o microchannel heat ink by adjuting channel width and height, Heat and Ma Tran., 35(008) [14] ASHRAE Handbook, HVAC Application, American Society o Heating, Rerigerating and Air- Conditioning Engineer, Atlanta, Georgia, Fundamental, 005, pp [15] J. Meng, X. Liang, Z. Chen and Z. Li, Experimental tudy on convective heat traner in alternating elliptical axi tube, Exp. Therm. and Fluid Sci., 9(005) NOMENCLATURES A heat traner area (m) D equivalent diameter (mm) k thermal conductivity (W/(K m)) L length o the heat ink(mm) P preure (Pa) Q total heat generation (W) q heat lux (W/m) Re Reynold number T temperature (K); thickne o the heat ink(mm) u, v, w velocity component along x, y, z (m/) V volume low o the heat ink(m3/) W width o the heat ink(mm) x, y, z coordinate direction (mm) Greek ymbol Δ dierence ρ denity (Kg/m3) μ dynamic vicoity ((N )/ m) λ thermal conductivity (W/(K m)) Subcript in max out w c luid inlet maximum outlet olid wall channel 6