为深入研究液膜内的微观传热机理，对水平管外降膜蒸发的传热特性进行了数值模拟，获得了液膜厚度、液膜速度和传热系数等热力参数在液膜内的分布特性。通过与实验数据的对比验证了数学模型的准确性。研究结果表明：在饱和蒸发温度62 ℃、传热温差2.8 ℃、管外径25.4 mm和液膜入口速度0.071~0.15 m/s条件下，沿圆周方向，液膜厚度减少，传热系数增加，直至达到液膜热力发展区，膜厚和传热系数趋于稳定；受液膜内温度分布变化的影响，液膜内的粘度、表面张力和导热系数的变化对液膜传热特性产生显著影响。

In order to get a better understanding of micro-scale heat transfer mechanism of falling film evaporation outside a horizontal tube, numerical simulation on heat transfer characteristics of falling film was explored. The distributions of thermal parameters, including film thickness, film velocity and local heat transfer coefficient, were obtained. The simulated results agreed well with the experimental, which justifies the expectation that the model is reliable. The results indicate that for inlet velocity between 0.071 and 0.15m/s with saturated evaporation temperature of 62℃, heat transfer temperature difference of 2.8℃and tube diameter of 25.4 mm, the film thickness reduces and local heat transfer coefficient increases along the tube circumference. They begin to stabilize till the film reaches the fully thermal developed region. The variation of viscosity, surface tension and conduction coefficient, which is caused by the temperature distribution inside the liquid film, has an obvious effect on the heat transfer characteristics of the liquid film.

TK124

国家自然科学基金基金