Abstract: Nano-refrigerants (0.1%-0.4% Al₂O₃/R141b) which used Span-80 as a dispersant were manufactured by ultrasonic vibration. They were used as working fluids to investigate the effect of nanoparticles concentrations on flow boiling pressure drop fluctuation under the designed conditions. An experiment on flow boiling of nano-refrigerant was conducted in rectangular microchannels with the hydraulic diameter of 1.33mm.The results showed that nanoparticles concentrations have significant impact on flow boiling pressure drop fluctuation of Al₂O₃/R141b. Under certain conditions,the average pressure drop of the 0.1%,0.2%,0.3%,0.4wt% nanofluids decreased by 9.4%,20.1%,23.2% and 36%,respectively,than the pure refrigerant,The standard deviation of the pressure drop was reduced on average 8.0%,22.7%,28.6% and 33.9%,accordingly. That indicates that total pressure drop decreases and the fluctuation is more gradual with the increase of nanoparticles concentrations. Scanning electron microscopy (SEM) and measuring surface static contact angle revealed that the deposition of nanoparticles on the surface of microchannels is more pronounced and the surface static contact angle become smaller with the increase of concentration. It proves that the cause of the influence of nanoparticles concentrations on flow boiling pressure drop and fluctuation is nano-refrigerant with higher concentration deposits more,reducing the roughness of the wall surface but increasing the wettability of the wall surface.

Key words: microchannels, nanoparticles, concentrations, pressure drop fluctuation

摘要： 为探究浓度对纳米制冷剂流动沸腾压降及其波动的影响，使用Al₂O₃纳米颗粒，采用Span-80作为分散剂，并通过超声波振荡技术分别制备出质量分数为0.1%、0.2%、0.3%、0.4%的Al₂O₃/R141b纳米制冷剂。设计系统压力为175.8kPa，进行纳米制冷剂在水力直径为1.33mm矩形微通道内的流动沸腾实验。结果表明：纳米粒子浓度对纳米制冷剂流动沸腾压降及其波动的影响十分显著，实验工况下，0.1%、0.2%、0.3%、0.4%纳米流体的压降平均值比纯制冷剂分别平均降低了9.4%、20.1%、23.2%、36%，压降标准差分别平均降低了8.0%、22.7%、28.6%、33.9%，说明纳米粒子浓度越高，压降越小，波动越平缓。通过对实验后的槽道进行扫描电镜分析及表面静态接触角的测量，发现纳米粒子在槽道表面发生了沉积，浓度越大，沉积作用越明显，表面接触角越小。证明了纳米制冷剂流动沸腾压降随浓度升高而降低、压降波动随浓度升高而更加平缓的原因是：高浓度的纳米流体在微通道壁面的沉积更多，减小了壁面的粗糙度而增大了壁面的润湿性。

关键词: 微通道, 纳米粒子, 浓度, 压降波动