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Influence of nanoparticle concentrations on flow boiling heat transfer coefficients of Al_2O_3/R141b in micro heat exchanger by direct metal laser sintering

查看全文 作　　者：Jianyang [1,2]Zhou;Xiaoping [1]Luo;Cong [1]Deng;Mingyu [1]Xie;Lin [1]Zhang;Di [1]Wu;Feng [1]Guo 高影响力作者 机构地区：[1]School of Mechanical and Automobile Engineering, South China University of Technology;[2]School of Mechanical and Marine Engineering, Qinzhou University高影响力机构 出　　处：《Chinese Journal of Chemical Engineering》索引2017年第25卷第12期,共13页高影响力期刊 基　　金：Supported by the National Natural Science Foundation of China[21276090] 摘　　要：Al_2O_3/R141 b + Span-80 nanorefrigerant for 0.05 wt.% to 0.4 wt.% is prepared by ultrasonic vibration to investigate the influence of nanoparticle concentrations on flow boiling heat transfer of Al_2O_3/R141 b + Span-80 in micro heat exchanger by direct metal laser sintering. Experimental results show that nanoparticle concentrations have significantly impact on heat transfer coefficients by homogeneity test of variances according to mathematical statistics. The heat transfer performance of Al_2O_3/R141 b+ Span-80 nanorefrigerant is enhanced after adding nanoparticles in the pure refrigerant R141 b. The heat transfer coefficients of 0.05 wt.%, 0.1 wt.%, 0.2 wt.%, 0.3 wt.%and 0.4 wt.% Al_2O_3/R141 b + Span-80 nanorefrigerant respectively increase by 55.0%, 72.0%, 53.0%, 42.3% and 39.9% compared with the pure refrigerant R141 b. The particle fluxes from viscosity gradient, non-uniform shear rate and Brownian motion cause particles to migrate in fluid especially in the process of flow boiling. This migration motion enhances heat transfer between nanoparticles and fluid. Therefore, the heat transfer performance of nanofluid is enhanced. It is important to note that the heat transfer coefficients nonlinearly increase with nanoparticle concentrations increasing. The heat transfer coefficients reach its maximum value at the mass concentration of 0.1% and then it decreases slightly. There exists an optimal mass concentration corresponding to the best heat transfer enhancement. The reason for the above phenomenon is attributed to nanoparticles deposition on the minichannel wall by Scanning Electron Microscopy observation. The channel surface wettability increases during the flow boiling experiment in the mass concentration range from 0.2 wt.% to 0.4 wt.%. The channel surface with wettability increasing needs more energy to produce a bubble. Therefore, the heat transfer coefficients decrease with nanoparticle concentrations in the range from 0.2 wt.% to 0.4 wt.%. In addition, a new correlation has been proposed by fitting the experimental data considering the influence of mass concentrations on the heat transfer performance. The new correlation can effectively predict the heat transfer coefficient. 关 键 词：NANOPARTICLE 集中 MINICHANNEL SINTERING 流动沸腾 加热转移系数
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