电解质溶液的受热降膜传热与Marangoni效应

采用红外热成像技术研究了电解质Na2SO4-H2O溶液受热降膜传热过程中的Marangoni效应。实验结果表明,降膜表面的流向和径向上存在分别由温度和浓度分布不均引起的热和溶质Marangoni效应。降膜径向热Marangoni效应引起了液膜的收缩,使液膜厚度增加,增大了液膜热阻;流向热Marangoni效应加剧了液膜的湍动,减小了液膜滞流层厚度,降低了液膜热阻;径向溶质Marangoni效应则减弱了热Marangoni效应对液膜的收缩作用,促进了液膜的扩展。分析发现在本实验条件下,表征Marangoni效应大小的Marangoni数Ma不能准确地反映不同雷诺数Re下Marangoni效应对降膜流动的影响,为此引入判断Marangoni效应对降膜流动影响程度的Marangoni效应影响因子ε,ε与实验结果具有较好的一致性。

Heat transfer and Marangoni effect of an aqueous electrolyte heated falling film

An experimental investigation was performed on the Marangoni effect in the heat transfer process of an aqueous Na2SO4 liquid film flowing down a vertical heated plane by using a sensitive infrared technique.It shows that the thermal and solutal Marangoni effects coexist in streamwise and transverse directions on the surface of the liquid film,which are respectively resulted from the local variations of the surface temperature and concentration.The transverse thermal Marangoni effect causes the contraction of the film and thickens the liquid film,resulting in the increase of its heat resistance.Meanwhile,the streamwise one makes the film more turbulent and thins the sticky boundary layer,inducing the decrease of the heat resistance.The solutal Marangoni effect weakens the influence of transverse thermal Marangoni effect on the film and enhances the extension of the film on the heated plane.It showed that the Marangoni number Ma could not adequately clarify the influence of Marangoni effect on the liquid film flow at different Renolds number Re,thus a Marangoni effect impact factor ε was introduced to determine the influence.The analysis indicates that ε is in good agreement with the experimental results.