连续液柱流表面真空蒸发模型

Modeling and simulation of vacuum evaporation from surface of a continuous falling liquid column

真空条件下连续液柱流表面蒸发现象及模型表达是低能耗汽-液分离过程设计的重要基础。研究了重力作用下通过孔口的连续液柱流条件,获得了液柱断裂的判据。研究了该体系表面蒸发的机理并建立了数学模型。数值模拟与实验数据较为吻合,结果表明:绝热闪蒸条件下,汽液相界面附近液相侧温度梯度显著,过程阻力主要在液相;增加孔口流速、增加液体过热度、减小孔径均可提高蒸发速率,但必须满足液柱断裂判据的限制。

Modeling and simulation of vacuum evaporation from the surface of a continuous falling liquid column were carried out to obtain a mechanism-based prediction for application in energy-efficient vaporliquid separation process. The parameters governing the continuous flow of falling liquid column out-of an orifice were investigated to determine the critical conditions for breakup of the liquid column. The mechanism of evaporation from the free surface of liquid column was analyzed and a mathematical model of the system was set up. The simulation results were in good agreement with the experimental data. In an adiabatic flash vaporization, the temperature gradient near the interface on the liquid side was a sensitive indicator of evaporation rate. This means that the resistance of heat transfer mainly lies in the liquid phase, so that the evaporation rate can be enhanced by increasing the liquid velocity out-of the orifice and narrowing the orifice diameter but without the breakup of liquid column, or increasing the degree of superheat.