Gupta Nivedita R, Haj-Hariri Hossein, Borhan Ali
Department of Chemical Engineering, University of New Hampshire, Durham, NH 03824, USA.
J Colloid Interface Sci. 2007 Nov 1;315(1):237-47. doi: 10.1016/j.jcis.2007.06.017. Epub 2007 Jun 16.
Thermocapillary convection within a differentially-heated open rectangular cavity containing two immiscible liquid layers is considered in the absence of gravitational effects. The temperature and flow fields in the two layers are computed using domain mapping in conjunction with a finite-difference scheme on a staggered grid. The melt-encapsulant and air-encapsulant interfaces are allowed to deform, with the contact lines pinned on the solid boundaries. The presence of a free surface at the top leads to increased convection in the encapsulant phase while retarding thermocapillary flow in the melt. The intensity of thermocapillary convection in the encapsulated layer is reduced as the viscosity of the encapsulant is increased or the thickness of the encapsulant layer is decreased. Choosing an encapsulant with a greater sensitivity of interfacial tension to temperature (as compared to that of the melt phase) can almost completely suppress thermocapillary convection in the melt. Deformations of the melt-encapsulant interface in an open cavity are found to be larger than those in a closed cavity with a rigid top surface, due to higher pressure gradients realized in the encapsulant phase. In contrast to interface deformation behavior reported earlier for a double-layer system in a closed cavity, the shape of the melt-encapsulant interface is qualitatively similar for all values of the viscosity ratio, with the interface dipping into the melt near the cold wall, and into the encapsulant near the hot wall. For the double-layers considered in this study, a free surface at the top of the encapsulant layer was found to be more effective than a rigid top in reducing the intensity of thermocapillary convection in the melt.
在不存在重力效应的情况下，研究了包含两个不混溶液体层的差热加热开放式矩形腔内的热毛细对流。利用区域映射结合交错网格上的有限差分格式计算两层中的温度和流场。熔体密封剂和空气密封剂界面允许变形，接触线固定在固体边界上。顶部自由表面的存在导致密封剂相中的对流增加，同时阻碍熔体中的热毛细流动。随着密封剂粘度的增加或密封剂层厚度的减小，密封层内热毛细对流的强度降低。选择一种界面张力对温度更敏感的密封剂（与熔体相比）几乎可以完全抑制熔体中的热毛细对流。由于在密封剂相中实现了更高的压力梯度，发现开放式腔内熔体-密封剂界面的变形大于具有刚性顶面的封闭腔内的变形。与先前报道的封闭腔内双层系统的界面变形行为相反，对于所有粘度比的值，熔体-密封剂界面的形状在定性上是相似的，界面在冷壁附近浸入熔体中，在热壁附近浸入密封剂中。对于本研究中考虑的双层结构，发现密封剂层顶部的自由表面在降低熔体中的热毛细对流强度方面比刚性顶面更有效。
