表面张力模型对水平椭圆管外降膜流动传热数值计算结果的影响
Effect of surface tension model on numerical calculation results of heat transfer in falling film flow over horizontal elliptical tubes
摘要：
采用VOF方法对水平椭圆管外降膜流动和换热进行了二维数值分析。研究了4种椭圆管管型在不同表面张力模型下的降膜流动和换热问题。结果表明,在椭圆管近壁处存在极薄的层流底层,对换热影响很大;在滞止区,流体涡流导致壁面换热系数波动较大。同时发现在椭圆管外降膜流动计算中,表面张力不可忽略,连续表面力(CSF)模型和连续表面应力(CSS)模型均能较好地体现椭圆管的壁面流动和换热情况,但CSF模型在上下滞止区的计算更为准确。此外,椭圆度对壁面传热系数影响也较为显著。椭圆度增大,换热增强,特别是当周向角θ=20°～180°时,换热增强尤为明显。
Abstract：
A two-dimensional numerical analysis of the falling film flow and heat exchange in horizontal elliptical tubes is conducted using the volume of fluid (VOF) method. The falling film flow and heat transfer problems of four elliptical tube types under different surface tension models are studied.The results show that there is an extremely thin laminar bottom layer near the wall of the elliptical tube, which has a significant influence on the heat exchange, and in the stagnation zone, the fluid vortex causes the heat transfer coefficient of the wall to fluctuate greatly. At the same time, it is found that the surface tension cannot be ignored in the calculation of the falling film flow over the elliptical tubes, and the continuum surface force (CSF) model and the continuum surface stress (CSS) model can better reflect the wall flow and heat transfer of the elliptical tube, but the CSF model is more accurate in the calculation of the upper and lower stagnation zones. Furthermore, the effect of ellipticity on wall heat transfer coefficient is also significant. With the increase of ellipticity, the heat transfer is enhanced, especially when the circumferential angle θ is 20° to 180°, the heat transfer enhancement is particularly obvious.
Keywords:horizontal elliptical tube; falling film flow; heat exchange; heat transfer; surface tension; stagnation zone