Abstract: A liquid film flowing down along a heated solid plate may be remarkably influenced by Marangoni effect. This effect is usually generated by the existence of surface tension gradient that is induced by variations of surface temperature in the transverse direction of the film(due to the flow rate difference between film center and rim), causing notable contraction of the film. The shrinkage effect interacts with the liquid wetting ability and the expansion effect induced by the mass flow, resulting in distinct bulgy structure in the cross-section of the film rim. A mathematical model describing the characteristics of the heated film was derived by taking into account the effect of surface tension gradient on the film flow, as well as the force balance and mass conservation in the bulgy structure. The model indicated that low surface temperature,small liquid-solid contact angle and large mass flux could benefit preferential extension of the liquid film on a solid plate. The comparison of the model with the experimental data, showed that the model could satisfactorily describe the flow characteristics of a falling films on a heated plate. It is expected that the model can be used as a theoretical basis for optimal design and operation of falling film process and equipments.

Key words: 受热降膜, Marangoni效应, 表面张力梯度, 模型

摘要： 在降膜受热流动过程中，由于液膜边缘与膜中央之间存在速度差异，造成液膜横向温度分布不均，由此在液膜横向产生了表面张力梯度, 即引起了自液膜边缘向液膜中央的Marangoni流动，从而使得液膜收缩变形. Marangoni流动引起的收缩效应与液体润湿性及流动压力的扩展效应相互作用, 在液膜边缘形成了凸起区. 根据液膜边缘凸起区内的受力平衡和物料平衡关系，同时考虑温度引起的表面张力梯度对液膜流动的影响，建立了受热降膜收缩模型. 此模型显示, 较低的壁温、较小的固液接触角以及较大的液体流量有利于液膜在加热固体壁面上的扩展. 通过与实验数据的对比显示,该模型较准确地预测了受热液膜下落初始过程中的液膜分布, 能够为传质传热过程及其设备的优化设计提供理论依据.

关键词: 受热降膜, Marangoni效应, 表面张力梯度, 模型