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。其重要的潜在应用之一是用于电子冷却。目前正在考虑将喷雾冷却用于该应用。与池沸腾相比，它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。喷雾冷却中的一个重要步骤是座滴蒸发。该过程需要将热能从固体输送到液滴的液-气界面，在液滴的液-气界面处液体蒸发，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向液-汽界面传输的机制。在以前的研究中，我们已经建立了一个新的表面性质-表面热容量-可以用来确定由表面张力驱动的对流传输的能量的量，最近，我们已经证实，这种模式的热能传输是占主导地位的座水滴蒸发。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？基于初步的研究，我们已经制定了一个假设：我们假设热能是沿着液滴的固-液界面传导到其三相线，然后表面张力驱动的对流将热能沿着液-汽界面分布，在那里它被用来蒸发液体。我们假设热能的传输沿着固-液界面是由吸附在那里的液膜。基于最近提出的等温线，我们先前已经表明，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。热能传输沿着固-液界面以前没有研究（据我们所知）。因此，如果我们的假设被证明是正确的，在座滴蒸发过程中的热能传输的概念将被改变。

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.