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，内表面有一层多孔的金属层，里面充满了挥发性液体并密封。当管子的一端加热时，液体蒸发，带走大量热量，蒸汽扩散到管子的另一端，温度较低，在那里冷凝。在毛细管力的作用下，液体通过多孔芯被拉回管子的热而干的一端，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备多孔金属层，这是一种将熔化的金属液滴直接喷洒到待涂层表面的过程。当它们着陆、冻结并形成固体层时，液滴彼此结合。我们将喷洒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相，留下一层多孔层。该提案的目标是开发和测试热管和沸腾换热应用中使用的结构化、多孔铜和铝表面。在该项目中，我们将开发制造具有通道等结构的多孔涂层的方法，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，并开发分析模型来模拟液体在其中的运动。我们还将测量液体在受热时从其表面蒸发的速度。将进行试验，以观察这些表面上的成核沸腾，以确定沸腾热流增加了多少。被发现的最大限度地散热的表面将被用来制造用于电子系统冷却的热管，并使用实验室试验台测量冷却热流。热管还将用于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，并允许在比目前可能的面积更大的区域上应用多孔层。

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.