Thermal spraying of high-capillarity porous metal coatings for heat transfer applications

热管是一种广泛用于冷却电子系统的装置。它由一个中空的铜管组成，在其内表面有一个多孔的金属层，里面充满了挥发性液体并密封。当管子一端受热时，液体蒸发，带走大量热量，蒸汽扩散到温度较低的管子另一端，在那里凝结。液体被毛细管力拉回多孔灯芯，流向管的热、干端，形成一个循环回路。热管中的多孔芯通常是通过烧结金属粉末制成的。我们建议通过热喷涂来制作多孔金属层，这是一种将熔化的金属液滴喷射到要涂覆的表面上的过程。水滴在降落时彼此结合，冻结，形成一层固体。我们将喷射两种不同粉末的混合物，然后通过溶解或燃烧从固体涂层中去除其中一种，留下一个多孔层。本提案的目的是开发和测试用于热管和沸腾传热应用的结构，多孔铜和铝表面。在这个项目中，我们将开发制造多孔涂层的方法，这些涂层中有通道等结构，以增加其渗透性。我们将测量这些涂层中液体的毛细上升速率，并建立分析模型来模拟液体在其中的运动。我们还将测量加热时液体从它们表面蒸发的速率。将进行试验来观察这些表面上的核沸腾，以确定沸腾热流增强了多少。能最大限度地传递热量的表面将用于制造电子系统冷却的热管，并使用实验室测试设备测量冷却热流密度。热管也将用于LED灯阵列的冷却。预计该项目将带来一种制造热管的新方法，这种方法将比现有技术快得多，并允许将多孔层应用于比目前可能的更大的区域。

A heat pipe is a device that is widely used for cooling electronic systems. It consists of a hollow copper tube with a porous metal layer on its inner surface that is filled with a volatile liquid and sealed. The liquid evaporates when the tube is heated at one end, carrying away a large amount of heat, and the vapour diffuses to the other end of the tube that is at a lower temperature, where it condenses. The liquid is drawn back through the porous wick by capillary forces towards the hot, dry end of the tube, setting up a circulation loop. The porous wick in a heat pipe is usually made by sintering a metal powder. We propose to make porous metal layers by thermal spraying, a process in which a spray of molten metal droplets is directed onto a surface to be coated. The droplets coalesce with each other when they land, freeze, and form a solid layer. We will spray a mixture of two different powders, and then remove one phase from the solid coating by dissolving or burning it, leaving a porous layer behind. The objective of this proposal is to develop and test structured, porous copper and aluminium surfaces for use in heat pipe and boiling heat transfer applications. In the project we will develop methods of fabricating porous coatings with structures such as channels in them to increase their permeability. We will measure the rate of capillary rise of liquids in these coatings and develop analytic models to simulate the motion of liquid in them. We will also measure the rate at which liquid evaporates from their surface when they are heated. Tests will be done to observe nucleate boiling on these surfaces to determine how much the boiling heat flux is enhanced. The surfaces found to maximize heat transfer will be used to make heat pipes for cooling of electronic systems and the cooling heat flux measured using laboratory test rigs. The heat pipes will also be used for cooling of LED light arrays. It is expected that the project will lead to a new method of fabricating heat pipes that will be much faster than existing techniques and allow porous layers to be applied on much larger areas than currently possible.