Thermal spray fabrication of porous heat exchangers and heat pipes

多伦多大学的先进涂层技术中心（CACT）已经使用热喷涂技术开发了高效热交换器和热管。热交换器的效率可以通过将多孔金属丝网、穿孔板或金属泡沫粘合到热交换器管的表面来提高，从而增加热传递的面积。CACT开发了一种粘结技术，使用电弧喷涂方法，将金属网、泡沫和穿孔板粘结到管上。我们将在各种应用中使用高效热交换器，包括废热回收、燃气加热器和工业烤箱。 热管是广泛用于将热量从一个位置快速传递到另一个位置的装置。传统的热管由中空铜管组成，该铜管在其内表面上具有多孔层，通常通过烧结一层铜粉制成，其充当被挥发性液体饱和的芯。烧结的芯是易碎的并且限制了热管的尺寸和形状。我们已经通过使用火焰喷涂系统将铜或铝粉喷涂到铜基底上并充分降低颗粒速度和温度使得颗粒仅部分地彼此熔合来形成多孔芯。能够喷洒皮肤和多孔芯将彻底改变热管的制造，并将使它们变得非常薄，具有弯曲的表面，并覆盖非常大的面积。 本文是对用于换热器和热管的多孔介质中传热和流体流动的实验研究。该项目的长期目标是利用热喷涂技术开发紧凑型换热器和热管。这将大大降低制造成本，允许传热设备的新设计和形状，并促进能源效率和废热回收。 研究的短期目标是： 1)测量通过金属泡沫、穿孔板和金属丝网的对流传热。 2)具有复杂内部结构的激光烧结金属通道内对流换热的测量。 3)开发通过各种多孔介质的流动模型。 4)使用这些模型来优化热交换器的设计，并将其扩展到一系列应用。 5)开发制造不同形状和尺寸的热交换器的制造技术。 6)观察通过热喷涂铜或铝芯的毛细管驱动流体流动。 7)测量由于浸渍在热喷涂技术制成的多孔层中的液体的沸腾引起的热传递。 8)开发热喷涂金属热管的传热模型，并使用它们来优化设计。

The Centre for Advanced Coating Technology (CACT) at the University of Toronto has used thermal spray technology to developing high efficiency heat exchangers and heat pipes. Heat exchanger efficiency can be improved by bonding porous wire meshes, perforated sheets, or metal foams to the surface of heat exchanger tubes, increasing the area for heat transfer. CACT has developed a bonding technique, using a wire-arc spray coating method, to bond metal meshes, foams and perforated sheets to tubes. We will use high-efficiency heat exchangers for a variety of applications, including waste heat recovery, gas heaters and industrial ovens. Heat pipes are devices that are widely used for rapid transfer of heat from one location to another. A conventional heat pipe consists of a hollow copper tube that has a porous layer on its inner surface, usually made by sintering a layer of copper powder, which acts as a wick that is saturated with a volatile liquid. Sintered wicks are fragile and limit the size and shape of the heat pipe. We have formed porous wicks by spraying copper or aluminum powder using a flame spray system onto a copper substrate and decreasing particle velocity and temperature sufficiently so that the particles fuse only partially with each other. The abilty to spray both the skin and porous wick will revolutionize the manufacture of heat pipes and will allow them to be made very thin, with curved surfaces, and covering very large areas. This proposal is for an experimental study of heat transfer and fluid flow in porous media used for heat exchangers and heat pipes. The long term objective of this project is to develop compact heat exchangers and heat pipes using thermal spray technology. This will greatly reduce manufacturing costs, allow new designs and shapes for heat transfer equipment, and promote energy efficiency and waste heat recovery. The short term objectives of the study are: 1) Measure convective heat transfer through metal foams, perforated sheets and wire meshes. 2) Measure convective heat transfer in laser sintered metal channels with complex internal structures. 3) Develop models for flow through a variety of porous media. 4) Use the models to optimize design of heat exchangers and scale them for a range of applications. 5) Develop fabrication techniques for making different shapes and sizes of heat exchangers. 6) Observe capillary driven fluid flow through thermally sprayed copper or aluminum wicks. 7) Measure heat transfer due to boiling of liquids impregnated in porous layers made by thermal spray techniques. 8) Develop models for heat transfer in thermally sprayed metal heat pipes and use them to optimize designs.