| Energy saving in the lighting area has leaded people to consider high power light emitting diodes (HP LEDs) as a strong alternative to traditional incandescent fluorescent lamps. HP LEDs are called to play an important contribution in global the energy consumption due to their superior efficiency, lifetime, reliability, and aesthetic light output. Along with this advancement comes the need of effective thermal management solution in order to preserve device performance and reliability. Heat pipe heat transfer technologies have proved to be good alternative to common used copper block heat sink heat spreader. Vapor Chamber (VC) is a specific kind of heat pipe characterized by a compact structure, good thermal conductivity, and excellent isothermal property. It possesses also the specificity to spread heat from one point to a two-dimensional large condensation area. In this paper water, acetone, and ethanol are used as working fluid theoretical analysis and heat transfer test performances have been carry out on two specific type of VC namely Type I VC and Type II VC respectively.For an efficient design of heat pipe, we presented heat pipe basic formulations and heat transfer limiting factors based on Cotter theory. Analyses done on the copper foam wicking material revealed that:with its high porosity copper foam ensures the use of larger wick thickness and help to decrease the two-phase flow circulation resistance in the vapor chamber. Working liquid, filling ratio and VC orientation were studied during the experiment. Heat transfer test performance conduced on our Type I VC showed that; water filled vapor chamber had the best thermal performance among the three working fluids. For most tested cases, the thermal resistances of the VC decreased when the heat load increased. The maximum heating power was170W for30%of filling ratio at horizontal orientation. This corresponds to heat flux of216W/cm2, for which the minimum thermal resistance was0.09K/W. Heat transfer conduced on our type Ⅱ VC which is an innovative multi artery VC revealed that; Temperature distribution in condenser block was uniform for a given heat input, and this characteristic was independent of the working liquid. For the four filling ratios used, our vapor chamber thermal resistance was decreased when the heat load was increased. Great filling ratios gave better heat transfer performance at great power input. For small filling ratio, orientation had a negligible effect on the thermal performance of our VC, but for great filling ration thermal performances were slightly and gradually affected by orientation at low heat load. Globally when the heat load was increased the thermal performances of our VC became independent of orientation. Heat transfer process was greatly affected without copper foam stick insert in arteries. Thermal resistance values of0.06℃/W and0.07℃/W were obtained for30%and40%of filling ratio respectively whereas values of0.1℃/W and0.09℃/W were given for20%and15%of filling ratio for160W of maximum input power. By considering that our novel VC is easy to assembly, cost effective, and made from materials that are abundant, these results obtained by simulating the density power of a high power LEDs chip with a copper block heater appear to be very good improvement when compared with literature best results. |
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