Design and thermal analysis of high efficiency LEDs for street illumination armatures in M1 and M2 categories

Light emitting diodes (LEDs) are solid state semiconductor devices that directly convert electrical energy into light energy. However, LEDs convert only about 20% of the applied electric energy to light energy. The remaining energy is converted into heat energy, causing high temperatures in the LED chips. High heat fluxes in the LEDs limit the reliability, stability and lifetime of them. Especially in high power LEDs, it is necessary to keep the junction temperature below the allowable limit. So, effective thermal management of the LED package is critical to improve LED performance. In this thesis, LED packages were designed to be used in street lighting. In order to remove the heat generated from the LEDs, a heat sink heat pipe geometry was designed and modeled. Thermal behavior of the heat sink heat pipe model with fins integrated into the LED packages are simulated using the ANSYS Fluent software. U-shaped cylindrical copper heat pipes are used in the design. Firstly, the optimum dimensions of the fins on the heat sink were determined. Secondly, thermal analyses were performed for different numbers, diameters and lengths of heat pipes and optimum values were obtained. Afterwards, suitable materials to be used as components of LED packages were determined. Finally, thermal analyses were performed using high power LED models with four different chip volumes to determine the effect of the LED chip volume on the maximum temperature. The effects of different turbulence models and wall approaches were evaluated by assumed continuous conditions and incompressible flow conditions for each LED model. An experimental set up was established for the verification of analyzes performed at ANSYS Fluent and temperature measurements were taken at certain points of the system. The experimental results were consistent with the numerical results.