相分离结构微细通道流动沸腾压降分析与可视化

Analysis and visualization of flow boiling pressure drop in microchannels with phase separation structure

为探究相分离结构对微细通道流动沸腾压降的影响,利用数控技术加工了相分离结构微细通道实验段。以质量分数为30%的甘油水溶液作为实验工质,在工质入口温度为70℃、质量流率为121.25kg/(m^(2)·s)、热流密度为76.61~150.70kW/m^(2)的工况下分析了两种(多孔/少孔)相分离结构和无排气孔的普通微细通道的压降变化,同时对通道内气泡行为进行了可视化研究,引入气相分离系数对受限气泡在通道内的生长行为进行定量分析。实验结果表明,相分离结构可以改善通道内两相总压降,在多孔、少孔和普通微细通道中,微细通道的气相转移面积越大,气相分离系数越大,通道内受限气泡长径比越小,两相总压降损失越小。此外,通过对相邻通道增加压差,调整合适的压力切换周期,可以进一步改善相分离膜的气相转移速率,减缓通道内两相总压降。

To investigate the effect of the above phase separation structure on the boiling pressure drop of the flow within the microchannels,an experimental section of the microchannels with the phase separation structure was machined using CNC technology.The pressure drop of two(porous/low-porous)phase separation structures and a normal microchannels without venting holes were analyzed at an inlet temperature of 70℃,a mass flow rate of 121.25kg/(m^(2)·s)and a heat flow density of 76.61—150.70kW/m^(2) using an aqueous glycerol solution with a mass fraction of 30%as the experimental working medium.To examine how different phase separation structures of microchannels affect the length-to-diameter ratio(l/w)of confined bubbles,the bubble dynamics in the channels were visualized and a gas phase separation coefficient was employed to quantify the growth behavior of confined bubbles in the channels.The experimental results showed that the phase separation structure could improve the total pressure drop of the two phases in the channels.In the porous,less porous,and ordinary microchannels,the larger the gas phase transfer area of the microchannels,the larger the gas phase separation coefficient,the smaller the length-diameter ratio of the confined bubbles in the channels,the smaller the total pressure drop loss of the two phases,and could improve the system reliability.In addition,by increasing the pressure difference between adjacent channels and adjusting the appropriate pressure switching period,the gas phase transfer rate of the phase separation membrane could be further improved and the total pressure drop of the two phases in the channels could be slowed down.This study could provide a new design idea for the improvement of flow boiling pressure drop in microchannels.