小通道平行流换热器是燃料电池汽车的主要散热部件。吸收了电堆废热的冷却液(50%乙二醇溶液),流过小通道换热管,由换热器外侧空气冷却。在进液温度、进风温度、冷却液流量以及风速变化的试验工况下,测试了换热器的传热流动性能。引入量纲一参数κ,评估了各工况参数对换热量、阻力影响的强弱。接着,分析液侧努谢尔数Nu和摩阻系数f随雷诺数Re的变化趋势,结果显示：在小通道内(当量直径D=2.685 mm),冷却液从层流到湍流的转淚点Rec=1 750,介于微尺度与常规尺度的临界值之间。在此基础上,通过多元回归法,拟合得到层流和湍流的液侧换热系数,摩阻系数的关联式,以及空气侧阻力fa公式。Nu和f的计算值与试验值误差分别在[-7.06%,5.93%]和[-3.95%,4.11%]内,fa的误差在[-2.22%,3.62%]内。基于这些关联式,建立数学模型,可在广泛多变的运行条件下,对换热器的运行性能进行理论预测和评估。
The parallel flow heat exchanger with mini-channel is used as the major radiator for fuel cell vehicle (FCV) to dissipate the waste heat, product by fuel cell stack, from the coolant, a glycol-water mixture with volume concentration of 50%, to the air. Under the operating conditions with varied inlet temperatures of air and coolant, coolant volume flow rate and air velocity, the flow and heat transfer characteristics of the heat exchanger is investigated experimentally. Then, a dimensionless parameter, κ, is defined to quantify the influences of the condition parameters on heat transfer and pressure drop. The trends of coolant-side Nusselt number Nu and friction factor f with Reynolds number Re are investigated. It is observed that the flow transition from laminar to turbulent in the mini-channels (D=2.685 mm) of the heat exchanger occurred at the critical Reynolds number , Rec=1 750, which is lower than that in conventional channels and higher than that in micro-channels. Furthermore, the coolant-side correlations are developed in different forms for laminar and turbulent flows to predict the heat transfer coefficients and friction factors. The correlation of air-side friction coefficient fa is also present. Great agreements between the predicted and experimental values are observed. The deviations of Nu and f are within [-7.06%,5.93%] and [-3.95%,4.11%]. And the errors of fa ranged from -2.22% to 3.62%. Base on these correlations, a mathematical model is built to predict performance of FCV radiators under various operating conditions, especially some extreme but significant conditions that could not realize at labs.
[1] 巫江虹,谢方,刘超鹏,等. 电动汽车热泵空调系统微通道换热器适应性研究[J]. 机械工程学报,2012,48(14)：141-147.
WU Jianghong,XIE Fang,LIU Chaopeng,et al. Adaptability research on micro-channel heat exchanger applied to heat pump air conditioning system for electrical vehicle[J]. Journal of Mechanical Engineering,2012,48(14)：141-147.
[2] QI Z G,CHEN J P,CHEN Z J. Parametric study on the performance of a heat exchanger with corrugated[J]. Applied Thermal Engineering,2007,27：539-544.
[3] TANG L H,ZENG M,WANG Q W. Experimental and numerical investigation on air-side performance of fin-and-tube heat exchangers with various fin patterns[J]. Experimental Thermal and Fluid Science,2009,33：818-827.
[4] LI W,WANG X. Heat transfer and pressure drop correlations for compact heat exchangers with multi-region Louver fins[J]. Internal Journal of Heat Transfer,2010,53：2955-2962.
[5] DAVENPORT C J. Correlation for heat transfer and friction characteristics of louvered[J]. AICHE Symposium Ser,1983,79(25)：19-27.
[6] CHANG Y J. A generalized heat transfer correlation for louver fin geometry[J]. International Journal of Heat and Mass Transfer,1997,40(3)：533-544.
[7] 董军启,陈江平,陈芝久. 百叶窗翅片的传热与阻力性能试验关联式[J]. 制冷学报,2007,28(5)：10-14.
DONG Junqi,CHEN Jiangping,CHEN Zhijiu. Correlation of flow and heat transfer characteristics for multi-louvered fin[J]. Journal of Refrigeration,2007,28(5)：10-14.
[8] 王辉,唐勇,余建军. 相变传热微通道技术的研究进展[J]. 机械工程学报,2010,46(24)：101-106.
WANG Hui,TANG Yong,YU Jianjun. Recent advances of the phase change micro-channel cooling structure[J]. Journal of Mechanical Engineering,2010,46(24)：101-106.
[9] DEHGHANDOKHT M,KHAN M G,FARTAJ A,et al. Flow and heat transfer characteristics of water and ethylene glycol-water in a multi-port serpentine meso-channel heat exchanger[J]. International Journal of Thermal Science,2011,50：1615-1627.
[10] 刘赵淼,逄燕,申峰. 几何尺寸对矩形微通道液体流动和传热性能的影响[J]. 机械工程学报,2012,48(16)：139-145.
LIU Zhaomiao,PANG Yan,SHEN Feng. Effects of geometry on liquid flow and heat transfer in microchannels[J]. Journal of Mechanical Engineering,2012,48(16)：139-145.
[11] HASAN M I,RAGEB A A,YAGHOUBI M,et al. Influence of channel geometry on the performance of counter flow microchannel heat exchanger[J]. International Journal of Thermal Science,2009,48：1607-1618.
[12] 鲁进利,周宾,许忠林,等. 不同截面微通道中流动阻力特性[J]. 东南大学学报,2011, 41(3)：554-557.
LU Jinli,ZHOU Bin,XU Zhonglin,et al. Flow characteristics in microchannel with different cross-section[J]. Journal of Southeast University, 2011, 41(3)：554-557.
[13] KAYS W M,LONDON A L. Compact heat exchangers[M]. 3rd ed. New York：McGraw-Hill,1993.
