中文摘要：

为探究纳米粒子浓度对纳米流体制冷剂在微细通道中流动沸腾气液两相压降影响,运用超声波振动法制备质量分数为0.05%、0.1%、0.2%、0.3%、0.4%均匀、稳定的Al2O3/R141b纳米流体制冷剂,在直接激光烧结（DMLS）微型换热器中,设计系统压力为176 k Pa,纳米流体制冷剂入口温度为40℃,在热通量21.2-38.2 k W·m-2和质量流率183.13-457.83 kg·m-2·s-1工况下,研究纳米粒子浓度对Al2O3/R141b纳米流体制冷剂流动沸腾气液两相压降影响。研究结果表明：纳米粒子浓度对纳米流体制冷剂在微细通道中流动沸腾气液两相压降有显著影响,气液两相压降随纳米流体制冷剂的纳米粒子浓度增加而减少,在纯制冷剂中R141b加入纳米粒子Al2O3,不同质量分数的纳米流体制冷剂流动沸腾气液两相压降降低5.5%-32.6%;通过SEM和表面静态接触角测试方法,发现纳米流体制冷剂沸腾气液两相压降随质量分数增加而减少的原因是纳米颗粒沉积在通道表面,增加了微通道表面的润湿性;对比国际上3种比较经典流动沸腾两相压降模型,并基于Qu-Mudawar关联式和Zhang关联式进行修正,得出两相压降结果的85%数据点位于修正后的关联式模型值的±15%范围之内,同时实验结果与修正后的模型结果偏差MAE值为11.7%,说明修正后关联式能有效预测本工况下实验值。

英文摘要：

Uniform and stable nanorefrigerant coolants of 0.05%—0.4% Al2O3/R141b（mass fraction） were prepared by ultrasonic vibration and used to investigate nanoparticle concentration on pressure drop of gas-liquid two-phase boiling flow of a nanorefrigerant in micro channels. A micro heat exchanger was fabricated by direct metal laser sintering（DMLS） with designed capacity of system pressure at 176 k Pa and inlet temperature at 40℃. At conditions of heat flux 21.2—38.2 k W·m-2 and mass flow rate 183.13—457.83 kg·m-2·s-1, the experimental results show that the nanoparticle concentration had significant impact on pressure drop of Al2O3/R141 b nanoparticle coolant boiling flow in micro channels and the pressure drop decreased with the increase of nanoparticle concentration. After added Al_2O_3 nanoparticles to pure R141 b coolant, pressure drop of the pure refrigerant in micro channels was reduced by 5.5%—32.6% depending on mass faction of nanoparticles. Scanning electron microscopy（SEM） and static contact angle measurement revealed that deposition of some Al_2O_3 nanoparticles on the microchannel surface increased surface wettability, which might lower pressure drop of Al_2O_3/R141 b upon increase of nanoparticle concentration. Considered three classic pressure drop models and correlations of Qu-Mudawar＇s and Zhang＇s for gas-liquid two-phase boiling flow, a revised correlation was developed that 85% of the experimental data points on pressure drop were fallen within a ±15% range of model calculation. The revised correlation can effectively predict the experimental results under these conditions as supported by small MAE number of 11.7%, which was relative deviation between experimental results and revised model predictions.