Multi-seale Miero Structure Surfaee To Improve Character Of Loop Heat Pipe

Traditional active cooling such as conduction or air convection cooling systems are no more efficient to transfer such sophisticated and advanced intensive technique equipment with high heat fluxes, and the extra energy consumption cannot accord to the idea of energy saving, environmental protection. Alternative cooling techniques have to be used, and among the available techniques, the passive two-phase heat transfer devices, are specially promising solution to this problem, due to the application of latent heat value. As the response to the challenge that more heat needs to be removed, the passive two-phase heat transfer devices require more efficient and more demanding in operational reliability and heat removing.In this context, the multi-scale micro structure surface was selected as one way to improve the performance of loop heat pipe. To study how the multi-scale micro structure improves the performance of loop heat pipe, we focused on the enhancing of heat transfer by various surface and the performance exhibited when applied to the loop heat pipe, which can be considered as an effective form of heat dissipation of high power LED.The multi-scale micro structure surface has two main functions, to increase the numbers of evaporation core(bubble nucleation), and to provide the capillary pressure for liquid supply, both of which could balance the heat exchanging of the surface, and adjust according to the value of heat exchange within a certain range. We sintered copper powder of three different mesh numbers,80,170,300, and nickel powder of three different mesh numbers150,300,1000, respectively, on the engraved grooves graphite in a furnace with vacuum atmosphere. From the observation of the test, we found that the one with mesh number of80provide better capillary pressure and stronger sintering neck with micro pores and macro grooves, which was sintered under1000℃in the hydrogen atmosphere for90-120minutes. It would be the best choice for subsequent experiments.The sintered multi-scale micro structure surface had two main feature, its own unique capillary pores, and the macro space controlled by graphite grooves, both of which can provide wide range scale of porosity, including the millimeter, from micron grade to nano one. The heat transfer effect of the six surfaces were tested though pool boiling experiments, under the pool temperature as38℃,48℃and55℃, developing acetone as the working fluid. The results showed that sintered multi-scaled micro structure surface with macro grooves exhibited desirable heat transfer characteristics, such as delaying the arrival of CHF.Addition, the loop heat pipe is designed with multi-scale micro structure surface made by the compressed commercialized metal foam, and its thermal performance is also tested. The result showed that this new type loop heat pipe can run well, however filling rate and placement angle are strongly coupled to impact during the operation. The increasing filling rate would increase the appearing power and adapt wider and higher ranges of high power supply. The highest point of the surface temperature could be controlled at50℃, with heat load of60W and placement angle of270°. And the maximum temperature of the heat sink is up about85℃, with the heat load equals to110W.