壁面润湿性对微细通道内R141b流动沸腾不稳定性的影响

Influence of wall surface wettability on instability of R141b flow boiling in microchannels

为了探究壁面润湿性对制冷剂R141b流动沸腾不稳定性的影响,设计微细通道流动沸腾实验平台,制备3种不同润湿性的矩形微细通道,其壁面接触角分别为62.3°、接近0°和158.7°。以R141b为实验工质,在截面宽×高为1mm×2mm的矩形微细通道内进行流动沸腾换热实验,研究了沿程测点压力波动情况以及影响进出口总压降波动的因素,最后对总压降波动信号进行Hurst指数分析,结果表明:微细通道沿程测点波动方差最大的位置正处于沸腾起始点(ONB)附近,热流密度的减小以及质量通量的增大均会使沸腾起始点推后;进出口总压降波动受热流密度、质量通量和壁面润湿性的影响,相同工况下,热流密度增大和质量通量的减小都会引起系统不稳定性增强,超疏水表面微细通道的总压降波动方差均比其他两种表面的大,是波动方差最小的超亲水表面的1.35～1.84倍;利用Hurst指数分析,表明系统具有混沌现象,超疏水表面微细通道的Hurst指数最大,表现出更强烈的不稳定性。

In order to explore the effect of wall wettability on the flow boiling instability of refrigerant R141b, a microchannel flow boiling experimental platform was designed and three rectangular channels of different wetting properties were fabricated with wall contact angles of 62.3°, close to 0°, and 158.7°, respectively. Using R141b as an experimental working fluids, flow boiling heat transfer experiments were carried out in a rectangular microchannel with a cross-section width × height of 1mm×2mm. The pressure fluctuations at the measuring points along the channel and the factors affecting the fluctuation of the total pressure drop between the inlet and outlet were studied. Finally, the Hurst index analysis of the total pressure drop fluctuation signal were carried out. The results showed that the position with the largest fluctuation variance in the measurement point along the microchannel is near the onset of nucleate boiling (ONB). The decrease of heat flux and the increase of mass flux will delay the onset of nucleate boiling.The fluctuation of total pressure drop at inlet and outlet is influenced by the heat flux, mass flux, and wall wettability. Under the same conditions, the increase of heat flux and the decrease of mass flux will cause the increase of system instability. The total pressure drop fluctuation variance on the superhydrophobic surface of microchannels is larger than that of the other two surfaces, which is 1.35 to 1.84 times larger than that of the superhydrophilic surface with the smallest fluctuation variance. Hurst exponent analysis shows that the system has a chaotic phenomenon, and the Hurst exponent of the super hydrophobic surface microchannel is the largest, showing a more intense instability.