Thermal energy transport at solid-liquid and solid-vapour interfaces

流体的相变被用于无数的工业过程中。它们的一个重要的潜在应用是电子冷却。喷雾冷却正被考虑用于这一应用。与池沸腾相比，喷雾冷却能够从固体中去除更多的热能，但喷雾冷却被认为是一个复杂的过程，其能量传输机制尚不清楚。喷雾冷却的一个基本步骤是固着液滴蒸发。这一过程需要将热能从固体传输到液滴的液-汽界面，在那里液体蒸发，从而降低液体的温度并冷却固体。因此，一个中心问题是热能从热固体传输到液-蒸气界面的机制。在以前的研究中，我们已经建立了一个新的水的表面性质-表面热容-可以用来确定表面张力驱动的对流所传输的能量，最近，我们证实了这种热能传输模式在固着水滴蒸发过程中占主导地位。它比热传导大一个数量级。但这一观察提出了一个问题：所有这些能量是如何到达固着液滴的三相线的？在初步研究的基础上，我们提出了一个假设：我们假设热能沿着液滴的固液界面传导到它的三相线，表面张力驱动的对流然后沿着液-汽界面分配热能，在那里它被用来蒸发液体。我们假设固-液界面上的热能传输是由吸附在那里的液膜促进的。根据最近提出的一个等温线，我们以前已经证明，可以通过测量接触角的压力依赖性来确定吸附量。我们的建议是调查我们的假设。(据我们所知)以前没有人研究过固-液界面上的热能传输。因此，如果我们的假设被证明是有效的，那么固着液滴蒸发过程中的热能传输的概念将会改变。

The phase changes of fluids are used in countless industrial processes. One of their important potential applications is for electronic cooling. Spray cooling is being considered for this application. It is capable of removing more thermal energy from a solid than pool boiling, but spray cooling is recognized to be a complex process for which the energy transport mechanisms are not understood. An essential step in spray cooling is sessile-droplet evaporation. This process requires thermal energy to be transported from the solid to the liquid-vapour interface of the droplet where the liquid evaporates, reducing the temperature of the liquid and cooling the solid. Thus, a central issue is the mechanism by which thermal energy is transported from the hot solid to the liquid-vapour interface. In previous studies, we have established a new surface property of water---the surface-thermal-capacity---that can be used to determine the amount of energy transported by surface-tension-driven convection, and recently, we have confirmed that this mode of thermal-energy transport is dominate during sessile-water-droplet evaporation. It is an order of magnitude greater than thermal conduction. But this observation raises a question: how does all that energy get to the three-phase line of a sessile droplet? Based on preliminary studies, we have formulated a hypothesis: we suppose thermal energy is conducted along the solid-liquid interface of the droplet to its three-phase line, and that surface-tension-driven convection then distributes the thermal energy along the liquid-vapour interface where it is used to evaporate the liquid. We assume the thermal energy transport along the solid-liquid interface is facilitated by the liquid film adsorbed there. Based on a recently proposed isotherm, we have previously shown that the amount adsorbed may be determined by measuring the pressure dependence of the contact angle. Our proposal is to investigate our hypothesis. Thermal energy transport along a solid-liquid interface has not been previously investigated (to our knowledge). Thus, if our hypothesis proves valid, the conception of thermal-energy transport during sessile-droplet evaporation will be changed.