Manufacture And Heat Transfer Performance Of Porous Micro/mini Cannel With Enhanced Heat Transfer Structure

To use forced convective heat transfer in the micro-channel has been already proven to be one of the most promising high efficient cooling solutions. Based on flow-solid enhanced heat transfer theory, mould pressing solid-phase sintering technology was used to fabricate the enhanced heat transfer structure of porous composite micro-channel. Due to huge influence of flow-solid surface structure to heat transfer in micro scale and complex structure of porous material, the heat transfer performances were also researched in detail. The major contents are as following:(1) Optimization design and manufacture of enhanced heat transfer structural based on solid-phase sintering technologyAccording to the forced convection heat transfer characteristics in micro-scale, four kinds of porous micro-channel structures were designed. The fabrication methods and technics processes of using molded compression solid-phase sintering to fabricate porous micro-channel heat transfer core were proposed. The processing parameters were optimized through experiments summarizations. Since it is difficult to manufacture high-porosity porous material by using the copper powder, copper fibers made through the multi-tooth cutting method were proposed to fabricate low-porosity porous sintered micro-channel heat exchanger core. It is proved by the experiment that porous channel structure manufacturing by solid state sintering is of high precision, controllable, and easy process, and so on. The copper fiber sintered porous materials is of wide porosity adjustment range, high thermal conductivity, very suitable used for micro-channel heat exchanger.(2) Heat transfer numerical simulation of flow-solid coupling in micro-channelFor the limitations of the channel heat transfer characteristics and fluid-solid contact surface tension, fluid viscosity and the channel diameter in micro scale, numerical simulation of single-phase and boiling part heat transfer characteristics in micro-channel was taken by synthetically using variable fluid properties, low Reynolds number k-e turbulence model and hybrid boiling phase change model. The results of the simulation show that: fluid properties strongly affect the convection and heat transfer characteristics in the micro-channel; at single-phase flow, numerical simulation of fluid entry development section, heat transfer coefficient, pressure drop characteristics can meet well with the experimental results; using mixed-phase transition model can effectively capture the gas-liquid phase distribution in the channel, which would be a good guide for design and manufacture of heat exchanger. ?(3) Heat transfer performance test of porous composite grooved micro-channel heat transfer coreIn the heat transfer structure of porous composite micro-channel, a layer of irregular copper powder was sintered in the channel bottom. Under the single-phase flow conditions, the heat transfer core with the largest size of porous layer particle has the best heat transfer performance, which was increased by about 30% relative to the heat transfer coefficient of smooth channel; friction coefficient of porous composite channel is higher than that of smooth channel. The correlation of these two friction coefficients were developed by using the existing data.In the boiling two-phase flow channel, the phenomenon of sharp fluctuations occurred in fluid, and multiple two-phase states were observed, of which the annular flow is the main flow. Porous layer is helpful to reduce the channel boiling superheat and improve the heat transfer performance when the dryness of the channel is small, but has no effect to enhance heat transfer in a strong boiling heat transfer channel.(4) Heat transfer performance test of porous micro-channel with different porosity and skeleton materialsTests were taken to compare four kinds of porosity sintered porous micro-channel heat transfer cores fabricated by copper powder and copper fibers. It was found in the experiment that at the same flow rates, copper powder channel with low porosity had the best heat transfer performance, but the pressure drop was greater. At the same pump power cost, copper fiber channel with the porosity rate of 70% had the highest heat transfer efficiency. No strong fluctuation phenomenon of pressure drop was observed in the porous micro-channel while boiling occurred.The heat transfer characteristics of porous composite grooved micro-channel heat transfer structure and porous micro-channel heat transfer structure were summarized. Porous composite grooved channel under lower pump power had higher heat transfer efficiency; while porous channel with low porosity under higher pump power had higher heat transfer efficiency, and is more suitable for boiling phase change heat transfer.