高速蒸汽与过冷水直接接触凝结局部换热特性研究

Experimental Study on the Local Heat Transfer Characteristics in the Direct Contact Condensation of Steam Jet with Subcooled Water

针对气液两相流喷射器内高速蒸汽与过冷水直接接触凝结过程,设计并搭建了使用矩形截面喷嘴及混合腔的可视化实验台,在蒸汽质量流率为200~600kg·m^(-2)·s^(-1)、入口过冷水质量流率为4~18t·m^(-2)·s^(-1)、入口过冷水温度为20~50℃的实验条件下,使用图像处理技术分析可视化图像,研究了气液界面的波动特性,建立了局部凝结换热系数的计算方法,并对界面波动与局部凝结换热系数的关系进行了研究。研究结果表明:实验中观察到的界面波是界面不稳定性的一种表现形式;界面波在传播过程中振幅逐渐增加,强度增大,平均振幅在0.12~0.38mm之间;局部凝结换热系数沿流动方向逐渐增大,其值在1.8~5.9 MW·m^(-2)·℃^(-1)之间;界面波振幅与局部凝结换热系数对比的结果表明,界面的波动对汽水直接接触凝结的换热过程具有强化作用。

Aiming at the direct contact condensation process of steam jet with subcooled water,a visualized experimental rig composed of rectangular steam nozzle and mixing chamber was designed and built.The flow field was observed when the steam mass flux,water mass flux and water temperature were in the range of 200-600 kg·m-2·s-1,4-18 t·m-2·s-1 and 20-50℃,respectively.The steam-water interfacial fluctuation was investigated by image processing techniques,and a model for calculating local heat transfer coefficients was established.Besides,the relationship between interfacial fluctuation and local heat transfer characteristic was also studied.The results indicate that the interfacial wave observed in the research implies an interfacial instability,the interfacial wave amplitude and local heat transfer coefficient increase along the interface,and a relatively great local heat transfer coefficient can be achieved at steam jet tail.Furthermore,the interfacial fluctuation can enhance the heat and mass transfer in the condensation process of steam jet in water flow.