水平降膜管外液膜厚度分布

Distribution of Falling Film Thickness on the Horizontal Tubes

研究了液膜流动破裂的基础机理,构建了考虑表面张力、重力、惯性力及剪切应力等因素的液膜动力模型,采用边界层积分法,引入含有三次项剪切力项的速度分布函数,推导二维稳态水平管外环向液膜的厚度方程.通过数值方法求解该厚度方程,得到水平管外环向液膜厚度的分布规律.结果表明,随环向角度增大,环向液膜厚度先减小后增大,最薄液膜位置角在环向90?之后,且流量、剪切应力系数与管径等因素不改变环向液膜厚度的分布趋势,改变了环向最薄液膜位置角.最薄液膜位置角随流量增大、剪切应力系数减小及管径减小而增大.表面张力是影响环向液膜稳定性不可忽略的因素.

The kinetic modeling of falling film on the horizontal tube is derived using integral boundary layer equation with more realistic velocity distribution. In order to improve the accuracy, the surface tension, gravity force, inertia force and shear stress have been included. The obtained equations are solved numerically. The results showed that compared with Nusselt theory, the equation with surface tension is more accordant with experimental results at same Re. Film thickness decreases first and then increases, and the angle of minimum thickness at circumferential position is bigger than 90~. The increment of flow rate, decrement of shear stress coefficient and diameter can enhance the angle of minimum thickness and the change of parameters will not affect the distribution of liquid film. The angle of minimum thickness will increase when the flow rate increases, the shear stress coefficient decreases or the diameter decreases. Moreover, the surface tension plays an important role on the liquid film flow.