Investigation On LED Microgrooved Flat Heat Pipe

In recent years, because of the compactness and the miniaturization of LEDs, the heat flux of per unit increases rapidly which brings great threaten to the reliability of LEDs. It indicates that the invalid rate rises with the rule of index when the temperature exceeds a certain value. Therefore, it is one of the key technical problems to improve the heat sinking capability for the industrialization of high power LEDs. Currently, the flat heat pipe focused at home and abroad, has many unique advantages compared to the conventional tubular heat pipe. It takes strong control on temperature of discrete and partial heat source. And it can contact tightly with semiconductor apparatus because of its regular and slippery surface. Moreover, it can generate a unitary and isothermal surface which effectively extends the heat dissipation area and improves the dissipation efficiency. Due to all those superior thermal characteristics, the flat heat pipe has become the mainstream heat dissipation measure ofsemiconductor all over the world. In this paper, flat heat pipe used in LEDs is further studied and the main content is as follows:Firstly, the technology for LED cooling and the development of heat sink using flat heat pipe are summarized in this paper. And the operating principle of flat heat pipe is introduced briefly. The characteristics of microgrooved flat heat pipe such as its structure, heat transfer characteristics, heat transfer limit and thermal resistances are also included. Then a new type of microgrooved flat heat pipe radiator for cooling LED is adopted which has many advantages such as microgrooved structure, favorable intensity and rigidity, high heat dissipate efficiency and simple manufacture technique and so on.Secondly, a theoretical model for liquid wetting characteristics in the rectangular and microgrooves is found in the paper. Some programs are written and their feasibility and reliability are checked using two kinds of working fluid in literatures. Then the wetting length of acetone is calculated. Some factors which influence the capillary limit are also considered. The effects that the geometric parameters and inclination angle of microgrooves on wetting length of fluid in grooves are confirmed quantificational in theory.Thirdly, a horizontal microgrooved flat heat pipe is designed and the method of CFD numerical simulation is employed to simulate the exterior fluid field and temperature field of the new type of flat heat pipe. The predominant performance of microgrooved flat heat pipe is approved after the simulation of same structure radiators made in aluminum. The influence on the performance of microgrooved flat heat pipe in different heat flux distribution on soleplate, different structure of fins and different soleplate area are tested in this paper. An optimum structure is confirmed finally.Fourthly, according to the radiator limitation above in the fourth chapter, a vertical microgrooved flat heat pipe is designed after the simulation above in the paper. And the structure of fins is adjusted basing on the confirmation of exterior structure of radiator. Then the optimal model is put forward via choosing different distance and length of fins and the emissivity. Finally, it has fixed on 120W as the maximal cooling power through the calculation of thermal resistance and comparing the result of numerical simulation and experiment.