Thermal spray fabrication of porous heat exchangers and heat pipes

多伦多大学先进涂层技术中心(CACT)已经使用热喷涂技术来开发高效热交换器和热管。通过将多孔金属丝网、穿孔板或金属泡沫粘接到换热管表面，增加换热面积，可以提高换热器的效率。CACT已经开发出一种粘接技术，使用丝弧喷涂方法将金属网、泡沫和穿孔薄板粘合到管子上。我们将在各种应用中使用高效热交换器，包括余热回收、气体加热器和工业烤箱。 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设备。传统的热管由一个中空的铜管组成，它的内表面有一层多孔层，通常是通过烧结一层铜粉制成的，铜粉的作用是一根被挥发性液体饱和的灯芯。烧结芯是易碎的，限制了热管的大小和形状。我们使用火焰喷涂系统将铜或铝粉喷洒到铜衬底上，并充分降低颗粒的速度和温度，使颗粒之间只部分融合，从而形成了多孔芯。同时喷皮和多孔芯的能力将彻底改变热管的制造，并将使其变得非常薄，具有曲面，覆盖非常大的区域。 本文对换热器和热管用多孔介质中的换热和流体流动进行了实验研究。该项目的长期目标是利用热喷涂技术开发紧凑型热交换器和热管。这将大大降低制造成本，允许新的换热设备设计和形状，并促进能源效率和余热回收。 这项研究的短期目标是： 1)测量金属泡沫、穿孔板和金属丝网的对流换热。 2)测量具有复杂内部结构的激光烧结金属通道内的对流换热。 3)建立了各种多孔介质的渗流模型。 4)使用这些模型来优化热交换器的设计，并根据不同的应用对其进行调整。 5)开发制造不同形状和尺寸的换热器的制造技术。 6)观察毛细管驱动的流体在热喷涂铜或铝芯中的流动。 7)测量由热喷涂技术制成的多孔层中浸渍的液体因沸腾而产生的热传递。 8)建立热喷涂金属热管的传热模型，并用于优化设计。

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.