梯形微通道内乙醇水混合蒸气冷凝流型可视化实验

利用高速摄像系统对梯形硅基微通道进行乙醇水混合蒸气冷凝流型可视化实验。梯形微通道结构为梯形,水力学直径165.87 mm,通道长度50 mm。实验中混合蒸气乙醇质量分数范围为2%～60%。实验发现入口蒸气乙醇浓度对通道内流型有重要影响。沿着冷凝方向,发现环状流、环状条纹流、翻滚流、喷射流/喷射滴状流及气泡流。不同蒸气入口乙醇质量分数有不同的流型分布,低乙醇浓度的蒸气冷凝环状条纹流及喷射流区域出现伪滴状凝结形式,高乙醇浓度的蒸气冷凝出现翻滚流流型。实验以蒸气质量通量及蒸气干度为坐标对不同入口浓度蒸气冷凝建立了两相流型图,并对喷射流发生干度建立了流型转变预测式。

Visualization study of flow patterns for ethanol-water mixtures condensation in microchannels

A visualization experiment was carried out to investigate the condensation flow patterns of the ethanol-water vapor mixtures in an array of microchannels under a wide range of concentration (2%-60%). The microchannel was a trapezoidal silicon one with a hydraulic diameter of 165.87 mm and a length of 50 mm. The visualization study indicated that the ethanol concentration remarkably influenced the flow regimes. Along the flow direction, annular, annular-streak, annular-streak-droplet, annular-churn, injection, droplet-injection and bubble flow patterns were observed in the vapor mixtures condensation of different inlet ethanol concentration (60%, 31%, 20%, 6%, 4%, 2%). Due to the Marangoni effect, the film of the annular flow was more fluctuant comparing with the pure steam condensation. With the decreasing of the ethanol concentration, the injection flow pattern became more regular and the droplet would appear in the injection flow area. The two-phase flow pattern maps of different inlet ethanol concentrations were also developed to describe the experiment. A correlation based on the critical quality correlation was proposed to indicate the transition of the two-phase flow patterns.