| Oscillating heat pipe(OHP)is a high efficient heat transfer device normally made of capillary tube and provides advantages of simple structure,low fabrication cost,fast response to high heat loads and good environmental adaptability.As a new member in the wickless heat pipe family,OHPs have received a continuing and growing interest in the past two decades and considered as a promising solution in many industrial and commercial fields,such as heat recovery,drying,solar energy collecting,and electronics cooling.But the two-phase system which embodies muti-disciplinary physics is so complicated that the investigation on OHPs is still at a primary stage,to further strengthen the thermal characteristics and application of OHP remains to be studied.In this paper,a compact three-dimensional oscillating heat pipe(3D-OHP)with flat plate evaporator is designed and fabricated,which combining the advantages of tubular OHP and plate OHP.The thermal performance of OHPs at different operating conditions was studied with different filling ratio and orientation.The main conclusions are as follows:(1)The heat transfer characteristics of 3D-OHP was experimentally investigated and at vertical,horizontal and side orientations.The starting and heat transfer performance of the heat pipe at different filling ratio were compared.Ethanol and deionized water was used as the working fluid at a volumetric filling ratio of 20%~70%.Experimental results show that 3D-OHP has good spatial applicability and starting characteristic.The start-up temperature decreases with the decrease of the filling ratio,the OHP has longer starting time,higher starting power and higher temperature at horizontal orientation than vertical orientation.The OHP also shows excellent heat transfer performance,which increases with the decrease of the filling ratio,the working fluid of OHP show more stable oscillating and better heat transfer performance,the difference of resistance between horizontal and vertical orientation rise with the increase of filling ratio.Better heat transfer characteristic,lower average temperature and better wall temperature uniformity was found on the OHP at working fluid of ethanol.However,the amplitude of temperature fluctuation both the condenser and evaporator is slightly higher than that in ethanol.(2)Copper powder sintering structure were prepared due to the worse thermal performance of OHPs at horizontal orientations,The wicking of copper powder sintering was processed inside parallel circular channel of the evaporator,The characteristics of starting and thermal resistance of the heat pipe under different conditions were studied and compared with those without copper powder sintering.The results show that the structure of sinter copper powder can obviously improve the starting characteristic,and the heat pipe has good heat transfer performance at both vertical and horizontal orientation,and has good anti-gravity property.(3)An experimental platform was constructed to apply the 3D-OHP in high-power LED cooling,the start-up characteristics,back temperature and lighting of the LED of the 3D-OHP was analyzed and discussed under different filling ratio,heating power,and inclination angle.As a result,it was found that the heat pipe had good performance for cooling LED,and the working fluid can quickly start and reach a stable operating station then maintain a stable oscillating motion.The heat transfer performance of the heat pipe increases as the filling ratio decreases.With the increase of inclination angle,the back temperature of the LED gradually decline and the light illumination gradually increases.The back temperature and the light illumination show the opposite trend.With the further rise of the heating power,the light illumination and the back temperature of the LED reveal greater change with the inclination angle,the more influence of the inclination angle on the light illumination and the temperature on the back of the LED. |
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