Research On The Numerical Simulation Of LED Heat Transfer Process And The Performance Optimization

The luminous system, which takes 20% of the total energy, is a big part of the whole energy dissipation. One of the important approach to decrease luminous power is to exploit new light sources. Light-emitting diodes (LED) featured advantages of high efficiency, long lifetime and low power dissipation contrasts to the contraditonal light sources. However, temperature over increasing is one of the most great challenges to LED system with influencing the luminous performance and the thermal failure. Thermal design is an efficiency way to gain a good thermal management of LED. Compared with the traditional chip cooling technology, the thermoelectric cooling method has gradually aroused attentiones for short response and easily achieving precise temperature control. However, researches on the performance of heat transfer processes integrated with LED package cooling was far to conclusion and further enough and further researches should be done.Based on widely review of the literatures, the operation principle, research progress and the existing issue were described in detail. Research on the heat transer process of LED thermoelectric coonling system combined theory analysis, test and numerical simulation methods were done. Also, the differences between the performance of the forced air convection cooling and the natural air convection cooling were discussed.The main work and conclusions were included as following:(1) A thermoelectric (TE) cooling analytical model, which includes the Peltier effect, Seebeck effect, Fourier effect and Joule effect, has been developed in order to analyse the refrigeration performance. And the exact equation of the refrigeration performance as a function of the Seebeck coefficient, resistance and thermal conductivity of TE material has been developed by using theoritical method. The resultes show that the driving current is an important factor influenced the refrigeration capacity and temperature difference between the cold side and hot side of thermoelectric cooler (TEC). We can obtain precise temperature control on the chip by adjusting the driving current of TEC. Based on the test result, the optimal current of TEC is from 2.5 A to 3.5 A.(2) The heat transfer model of chip integrated with TE cooling system was established and the heat transfer features were analysed based on the thermal resistance circle. The resultes show that the chip power, refrigeration performance of TEC, the structure of heatsink and the wind speed of fan are the main factors influenced the cooling performance of this system. By changing the chip power and the wind speed of fan resulted in different chip temperature. The general trend is the lower the chip power, the lower the chip temperature, and the higher the wind speed, the lower the chip temperature.(3) Evaluated the performance of the TE cooling system and the forced air convection cooling system and the resultes show that the cooling performance of TE cooling system is better than that of the forced air convection cooling system at the conditon of the wind speed on the heatsink surface is 3.6 m/s and the chip power is limited to 30 W.(4) The simulation model of the chip TE cooling system is established and the TEC refrigeration performance parameters includes the temperature difference, the refrigeration capacity, dissipation power and the coefficient of performance (COP) are evaluated by simulation at the condition of the chip power is 20 W and the TEC driving current is from 2.0 A to 3.0 A. The resultes show that the temperature difference between the two sides of TEC increases as its driving current increases, the refrigeration capacity, the dissipation thermal power of the hot side and the power increases as the driving current increases, COP decreases as the driving current increases, but the decline slows down as the driving current increases.(5) The cooling performance of the TE cooling system is better than the forced air convection cooling system at the condition of the fan surface wind speed limits to 3.6 m/s and the chip power limits to 30 W. However, the power disssipation of TEC is a big part of the tatal power dissipation of the LED system and it is needed to evaluate its economic performance. The resultes show that the LED integrated with TEC lamp saves more power of 24.67% and 41.78% than that of the fluorescent lamps at the condition of the LED chip power is 20 W and 30 W, but consumes more power of 1.51% than that of the fluorescent lamp at the condition of the LED chip power is 10 W.In this paper, we focused on the research of enhanced heat transfer and the application of LED integrated with TE cooling system, the chip thermal management theory and the heat dissipating performance. The optimal design for system constructure and TE material characteristics of the TE cooling system can be a reference for further researches. At last, a suggestion on how to gain a better performance of energy saving of TEC with the utilization of temperature feedback control driving currrent was proposed.