Research On The Heat Pipe Cooling Device For High-power LED Applied To Lighting

Light emitting diode (LED) is a kind of solid state semiconductor devices whichdirectly converts electrical energy into light. High power LED is keeping attractinginterests due to its significant impacts on solid-state illumination industry, and it is astrong candidate for the next generation of general illumination applications. LEDdemonstrates a number of benefits compared to traditional incandescent lamps andfluorescent lamp. However, at present the luminous efficiency of the LED is only at therange from10percent to20percent and the other energy of the input has is turned intothe heat energy whose accumulation will cause the ascending of the junctiontemperature of the LED’s chip. At present, the heat fluxes of LED chips are more than100W/cm2, and how to control thermal energy is still a key issue being dealt withduring device packing and application of high power LED. In order to guarantee the lifeof the device, currently, the junction temperature of LED should be controlled below the110℃. The methods used to resolve the thermal problem of LED system are mainly bychanging the LED substrate material, packaging structure and other auxiliary tools up tonow. However, when the high-power LED is applied to lighting and other occasions,the control of cost is also important, and the external heat sink size of LED is notallowed to be oversize; furthermore, fans are not permitted to be used for additionalcooling.The existing methods can not overcome the thermal problem of high-power LEDeffectively. Phase-change cooling is a promising method for cooling of high heat fluxdevices. Heat pipe is one kind of phase-change heat-transfer devices.The heat-release characteristics of high power LED package are analyzed and anovel flat heat pipe (FHP) cooling device for high power LED is developed in thisdissertation. The thermal performance, including the startup performance, thetemperature uniformity and the thermal resistance of high power LED package with aflat heat pipe heat sink has been investigated experimentally. By comparing with aordinary copper plate heat sink, the obtained results of the new device indicate that thejunction temperature of LED is about52℃and83℃for using the heat sink of the newflat heat pipe and the ordinary copper plate respectively; When the input power is3W,and correspondingly the total thermal resistance of LED system is8.8K/W and19K/Wrespectively. The thermal performance of flat heat pipe is more excellent than the cooper plate’s with increasing input power of high power LED.In this paper, a cooling device of high power LED for lighting with a ordinary loopheat pipe is also developed. The experimental results of the cooling system show thejunction temperature of the simulating LED’ chip could be controlled around60℃steadily for the heat flux of20W; and the thermal resistance of the heat pipe is nearly0.48K/W with the heat flux30W, which is obviously decreasing compared to theordinary cooling device of metal body.A novel flat evaporator loop heat pipe cooling device for high power LED isdeveloped. The thermal capabilities, including startup performance, temperatureuniformity and thermal resistance of loop heat pipe under different heat loads andincline angles have been investigated experimentally. The obtained results indicates thatthe thermal resistance of the heat pipe heat sink is in the range of0.19K/W~3.1K/W, thetemperature uniformity in the evaporator is controlled within1.5K, and the junctiontemperature of high power LED could be controlled steadily under100℃for the heatload of100W.