微细通道内纳米制冷剂的流动沸腾传热特性

Heat Transfer Characteristics of Flow Boiling Nano-Refrigerant in Rectangular Microchannel

分别以0、0.031%、0.062%、0.155%、0.248%浓度的Al_2O_3-R141b纳米制冷剂为工质,在水力直径为1.33 mm的矩形铝基微细通道内进行了流动沸腾实验,研究了不同浓度纳米制冷剂实验后槽道表面能的变化情况.结果表明:加入少量纳米颗粒后,壁面形成大量的活化核心,使得沸腾起始点ONB提前,强化了传热;浓度为0.062%纳米制冷剂的强化传热效果最好,传热系数比纯制冷剂最大可提高48.1%;当纳米颗粒浓度超过最佳浓度而继续增大时,颗粒在表面沉积现象越来越严重,使槽道表面能增大,换热热阻也随之增大,强化传热效果反而依次降低.浓度为0.031%、0.062%、0.155%、0.248%纳米制冷剂实验后的槽道表面能,比槽道原始表面能分别增长了0.47、1.39、1.89、2.14倍.

The nano-refrigerants respectively of 0, 0. 031% , 0. 062% , 0. 155% and 0. 248% （volume fraction） Al2O3-R141b particles, were taken as the working fluids to perform flow boiling experiments in the aluminum-based rectangular microchannels of a hydraulic diameter of 1.33 mm, so as to reveal the influence of the nanoparticle con- centrations on the surface energy of the microchannels after the experiments. The results show that （ 1 ） after adding a small amount of nanoparticles, a massive amount of activation nucleuses form on the wall surface, which brings forward the onset of nucleation boiling （ONB） and then enhances the heat transfer; （2） the nanorefrigerant of 0. 062% Al2O3-R141b achieves the best effect in enhancing the heat transfer, and its heat transfer coefficient can be increased by a maximum of 48. 1% in comparison with that of pure R141 b refrigerant; （3） when the nanoparti- cle concentration is greater than the optimal concentration of 0. 062%, the particle deposition on the surface be- comes serious with the increase of the nanoparticle concentration, which causes the surface energy and heat flow re- sistance of microchannels to increase, but with a decrease in the heat transfer enhancement; and （4） the surface energy of the microchannels treated with the nano-refrigerants respectively of 0. 031%, 0. 062%, 0. 155%, 0. 248% Al2O3-R141b particles, increases respectively by 0. 47, 1.39, 1.89 and 2. 14 times, in comparison with that of the original microchannels before the experiments.