Research On Heat Dissipation Of Automotive Headlamp Based On LED

At present, LED(Light Emitting Diode) semiconductor lighting industry took its place in high-tech field. LED light source was become the light source in automotive lighting system replacing of incandescent lamps, halogen lamps and xenon lamps. LED source was mainly used in the instrument lights, tail lights and headlamps. However, due to the small chips, small location and closing to the engine, the heat dissipation was extremely important. If the heat could’t be dissipated, it could lead to many problems such as shorten life span and luminous decay, thus affecting the automotive headlamps application.Considering heat dissipation problem in LED automotive headlamps, this paper summarized development and research status in the field at home and abroad, and compared the different methods of advantages and disadvantages, such as natural convection, forced convectio, heat pipe, liquid cooling and semiconductor. At the same time, this paper conculted a large number of relevant literatures and found the key to solve the heat dissipation by analyzing the reasons and pathway of heat.In this paper, one LED automotive headlamp was selected as the reseach object. Firstly, we analyzed its thermal performance by combining to numerical simulation and experimental test. Secondly, according to dissipation requirement, this paper proposed an air cooling system which using wind to get heat away quickly when the car was moving, and verified by numerical simuation. What’s more, under the condition of no wind, air cooling system satisfied LED chips work normally by optimizing the sink parameter. Finally, took the system was open to the outside into consideration, it be optimized to wind tunnel in order to advoid dust and water droplets into the headlamp cacity. So, the main study content of this paper was as follows:(1) For one LED automotive headlamp, established physical model, meshed and set boundary condition, the temperature and flow pattern simulation of headlamp cavity could be obtioned by computational fluid dynamics: in the condition of 25℃ environment temperature and fans working, the temperature of high-beam was 58.54℃ and temperature of low-beam was 48.96℃,the temperature distribution of sink has obvious gradient feature and cooling effect was well. Simultaneously, the associated test was carried out to verify the accuracy of the numerical simulation by error calculation.(2) Considering small cavity and high-temperature environment, the structure of LED automotive headlamp should be improved. So, the new air cooling system was raised. The numerical simulation showed that the LED temperature of high-beam and low-beam was 126.91℃ and 118.48℃, the convective heat transfer coefficient of high-beam and low-beam was 2.36 and 2.50 W/(K·m2), the nusselt number Nu of high-beam and low-beam was 1.35 and 1.19 at 75℃ environment when there was no wind. This effect was not very well. But when wind velocity was 0.5m/s, the LED temperature of high-beam dropped to 90.51℃, the convective heat transfer coefficient and nusselt number Nu of high-beam were 10.42 W/(K·m2) and 5.95, which increase of 3.42 times and 3.41 times. The low-beam also was this trend and the cooling effect was more apparent as the wind velocity increases. Through orthogonal test to optimize the parameters of opening, sink of high-beam and low-beam, then determined the structure of air cooling system. In this structure, the LED temperature of high-beam and low-beam was 116.96℃ and 111.96℃, which less than LED junction temperature 120℃. The convective heat transfer coefficient of high-beam and low-beam was 2.97 W/(K·m2) and 2.72 W/(K·m2), which improved 25.85% and 8.09%.(3) Considering dust and water droplet may be entered headlamp cavity through air cooling system, so it was necessary to optimize wind tunnel to achieve waterproof and dustproof effect. This paper only researches the droplet flow because of the complexity of situation. It used gravity and inertia principle, designed T-junction and baffle to make droplet flow form a gas-liquid separation in the wind tunnel. Then the liquid guided outside through branch pipe and gas entered air cooling system to guarantee safety. By multiphase flow simulation analysis, in condition of better model, when inlet velocity was 5m/s, the proportion was 99.50% and when inlet velocity was 20m/s, the proportion was 52.29%.This paper raised a new vision which focuses on the thermal design of LED headlamps. It had a certain practical guiding significance for further application in the field of LED headlamps.