Phase-separation behavior in a binary mixture fluid layer subjected to a vertical temperature gradient

实验研究了异丁酸(IBA)-水二元混合物层的相分离行为，将厚度为3 mm的层夹在两块蓝宝石玻璃之间，使下层热侧温度T_b高于临界温度T_c，上层冷侧温度T_t低于临界温度T_t，并施加垂直温度梯度。得到以下结论：1。以包含一个液滴的多边形细胞为特征的模式，类似于Assenheimer， Khaykovich和Steinberg（1994）所观察到的，其层比现在的层更薄，在层间温度梯度的有限区域形成，尽管模式最终消失。随着温度梯度ΔT/d增大，相分离液滴的生长速率增大，当温度梯度超过1.7K/mm时，生长速率加快。随着τ(=(T_tT_c)/T_c)的增大，生长速率增大。对液滴的消失速度也观察到这些趋势。包括一个液滴在内的多边形胞型的形成归因于沿液滴表面的热毛细运动，即马兰戈尼对流。层内浓度驱动的瑞利对流促进了相分离液滴的生长。液滴表面的热毛细运动增强了相分离液滴的消光。

The phase separation behaviors in a layer of isobutyric acid (IBA)-water binary mixture were experimentally investigated, where the layer with 3 mm thickness was sandwiched between two sapphire glasses and was subjected to a vertical temperature gradient by keeping the lower hot side temperature T_b above the critical temperature T_c and keeping the upper cold side one T_t below the critical one. The following conclusions were obtained.1. The patterns characterized by a polygonal cell including one droplet, similar to those observed by Assenheimer, Khaykovich & Steinberg (1994) whose layers were thinner than the present ones, are formed in a limited region of temperature gradients across the layer, although the patterns finally disappear.2. The growth rate of the phase-separated droplets increases with temperature gradient ΔT/d, especially increases rapidly beyond 1.7K/mm. In addition, the growth rate increases with increasing of τ(=(T_tT_c)/T_c). These trends were also observed for the extinction rate of the droplets.3. The formation of the polygonal cellular patterns including one droplet is attributed to the thermocapillary motion along the droplet surface, i.e., Marangoni convection.4. The growth of the phase-separated droplets is enhanced by the concentration-driven Rayleigh convection in the layer.5. The extinction of the phase-separated droplets is enhanced by the thermocapillary motion along the droplet surface.