含表面活性剂液滴的受热铺展特性

Spreading of A Liquid Drop Containing Insoluble Surfactant Driven by Thermocapillary

针对壁面均匀加热和非均匀加热情况下含非溶性表面活性剂液滴在预置液膜上的铺展过程,基于边界层流动理论建立了液膜厚度,表面活性剂浓度的非线性演化方程组。利用PDECOL程序对液膜厚度、表面活性剂浓度的演化历程进行了模拟计算,并分析了各参数对铺展特性的影响规律。结果表明,两种加热方式下液滴铺展结构不同,非均匀加热方式下铺展过程较为稳定;两种加热方式下,减少Marangoni数、气液界面的Biot数及增大液滴表面Peclet数均可使液滴铺展过程趋于缓慢;在非均匀加热方式下,选择适宜的加热强度也可以得到更为稳定的铺展过程。与含活性剂、初始厚度均匀的液膜受热流动相比,加热造成的Marangoni效应对液滴的影响更为显著。

The spreading of a liquid drop on thin liquid film in the presence of insoluble surfactant and isothermal or non-uniform heating from below was considered. Coupled nonlinear evolution equations for the film thickness and surfactant concentration were derived on the base of lubrication theory. The spreading processes on different conditions were calculated using PDECOL program and the numerical results were presented, while the effects of parameters on the spreading process were discussed. The results show that complex droplet patterns are obtained for an isothermal underlying substrate. For the case of non-uniform heating condition, more stable double ridges patterns are observed. For all situations, decreasing Marangoni parameter and surface Biot number, increasing surface Peclet number will stabilize the film. On the condition of non-uniform heating, appropriate heating number can also lead to a stable spreading process. Compared to the initial uniform film flow, which is covered by surfactants and on the same heating condition, the Marangoni effect introduced by thermal gradient is more significant on the drop spreading.