蒸汽流量对蒸汽直接接触冷凝的影响

为研究蒸汽流量对蒸汽直接接触凝结及汽泡表面变化过程的影响，利用高速摄像仪记录一定过冷度、不同蒸汽流量条件时过冷水中蒸汽的凝结过程.实验结果表明:蒸汽流量小于0.36m3/h时，汽泡表面始终较光滑；当蒸汽流量升至0.74m3/h时，汽泡表面上出现波动，汽泡最终逐渐分裂成数个小汽泡；当蒸汽流量大于1.13m3/h时，汽泡表面上的波动非常剧烈，汽泡不稳定性增强，并最终破碎成大量微汽泡.且随蒸汽流量增，这些微汽泡的直径减少，喷射速度增加.蒸汽流量超过1.13m3/h后，汽泡在凝结时，其相对半径迅速减小，半径变化率迅速增加.汽泡表面剧烈的波动会极大的增加汽泡有效换热面积，导致蒸汽与过冷水间的传热和传质过程被极具的加强. 

Effect of vapor injection rate on direct contact condensation of vapor

In order to investigate the effect of vapor injection rate on the direct contact condensation and evolution of vapor bubble surface, a high-speed video camera was employed to record the process of vapor condensation in the cold bulk at a certain liquid subcooling and different vapor injection rates. Experimental results showed that the bubble surface was relatively smooth throughout the whole slow process of bubble condensation when the vapor injection rate was less than 0.36m³/h. As the vapor injection rate increased to 0.74m³/h, surface wave appeared on the bubble surface and the bubble was split up into some tiny bubbles finally. When the vapor injection rate was larger than 1.13m³/h, surface wave on the bubble was very violent. The bubble instability was enhanced and the bubble would collapse into many microbubbles. Furthermore, with the increase of the vapor injection rate, the diameter of these microbubbles decreased and the average velocity increased. When the vapor injection rate exceeded 1.13m³/h, the bubble relative radius decreased and the change rate of bubble radius increased rapidly. The strong surface wave on the bubble could increase the bubble effective area of heat transfer significantly, resulting in a substantial enhancement of heat and mass transfer between vapor and cold bulk.