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。它们重要的潜在应用之一是电子冷却。喷雾冷却正在考虑中。它能够从固体中去除比池沸腾更多的热能，但人们认为喷雾冷却是一个复杂的过程，其能量传递机制尚不清楚。喷雾冷却的一个重要步骤是液滴蒸发。这个过程需要热能从固体传递到液滴的液-气界面，在那里液体蒸发，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递到液-汽界面的机制。在之前的研究中，我们已经建立了一种新的水的表面性质——表面热容量，它可以用来确定表面张力驱动的对流输送的能量。最近，我们已经证实，这种热能输送模式在无基水滴蒸发过程中占主导地位。它比热传导大一个数量级。但这个观察结果提出了一个问题：所有这些能量是如何到达一个无根液滴的三相线的？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液滴的三相线，然后由表面张力驱动的对流将热能沿着液汽界面分布，用于蒸发液体。我们假设沿固液界面的热能传递是由固液界面上吸附的液膜促进的。根据最近提出的等温线，我们以前已经表明，吸附量可以通过测量接触角的压力依赖性来确定。我们的建议是调查我们的假设。据我们所知，以前还没有研究过沿固液界面的热能输运。因此，如果我们的假设被证明是正确的，那么在无底液滴蒸发过程中热能输运的概念将会改变。

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.