微细通道内表面活性剂对Al2O3/R141b流动沸腾传热的影响

Effects of Surfactants on Flow Boiling Heat Transfer of Al2O3/R141b in Microchannels

为了探究微细通道内表面活性剂对纳米流体制冷剂Al2O3/R141b流动沸腾传热的影响,采用二步法制备了添加0.2%(质量分数,余同)SDBS、0.3%SDBS、0.3%CTAB、0.4%CTAB、0.1%Span80、0.2%Span80的改性纳米流体制冷剂与0.1%Al2O3/R141b纯纳米流体制冷剂共7种实验工质.设计系统压力为170kPa、热流密度为9.4~33.5kW/m2、质量流率为219.9~439.8kg/(m2·s),在高、宽分别为2.0、1.0mm的矩形截面微细通道内进行流动沸腾传热实验.研究结果表明:表面活性剂对纳米流体制冷剂饱和沸腾区的流动沸腾传热系数影响十分显著;在选用的热流密度及质量流率范围内,采用前述6种添加了表面活性剂的纳米流体制冷剂时,饱和沸腾区平均传热系数较采用纯纳米流体制冷剂时分别提升27.7%、17.9%、13.8%、8.9%、7.9%、5.3%;表面活性剂强化因子SEF随质量流率的变化规律不明显,在同一质量流率下SEF随着热流密度的增大而减小,其中阴离子型表面活性剂SDBS对纳米流体流动沸腾传热的效果最好,阳离子型表面活性剂CTAB次之,非离子型表面活性剂Span80最差.

In order to investigate the effect of surfactants on the flow boiling heat transfer of nanofluids refrigerant Al 2 O 3 /R141b in microchannels,a two-step method was used to prepare 0.1% Al 2 O 3 /R141b pure nano-refrigerant and nano-refrigerants respectively modified by 0.2%(mass fraction,the same below)SDBS,0.3% SDBS,0.3% CTAB,0.4% CTAB,0.1% Span80 as well as 0.2% Span80.Then,flow boiling and heat transfer expe-riments of the surfactant-modified nano-refrigerants were carried out in a rectangular microchannel with a height of 2.0mm and a width of 1.0mm at a design system pressure of 170kPa,a heat flux density varying from 9.4 to 33.5 kW/m 2 and a mass flow rate varying from 219.9 to 439.8 kg/(m 2 ·s).The results show that(1)the surfactants all have significant effect on the flow boiling heat transfer coefficient of nano-refrigerants;(2)within the range of selected heat flux and mass flow rate,the average heat transfer coefficient of the modified nano-refrigerants in saturated boiling zone increases by 27.7%,17.9%,13.8%,8.9%,7.9% and 5.3%,respectively;(3)the variation of surface activity enhancement factor(SEF)with the mass flow rate is not obvious,and the SEF decreases with the increase of heat flux density at the same mass flow rate;and(4)anionic surfactant SDBS has the best effect on the fluid boiling heat transfer of nanofluids,the cationic surfactant CTAB takes the second place,while the nonionic surfactant Span80 has the worst effect.