Study On Natural Convection Heat Transfer In Metal Foam For LED Radiator

The energy consumption of lighting holds a fifth of the entire electric power consumption in the whole world. LED(Lighting Emitting Diode), having high luminous efficiency, low power consumption, long service life and being environmentally friendly, is of great significance when popularized and applied. However, with the increasing of power of every single LED, cooling problem has become a bottleneck restricting its development. As a sound member of the new function material family, metal foams have metallic struts connecting to each other and with open and interconnected void among them. Because of high specific surface area, high thermal conductivity and low density, the metal foam is a material of the compact heat sink which is small in size and light in quality, thus being potential solution to heat dissipation of LED.LED cooling includes two parts, the first one is the heat dissipation during packaging, and the other is heat dissipation to the environment. In this thesis, the natural convection of foam metal LED heat sink has been mainly discussed. On the basis of experimental research, the face-centered cubic(FCC) cell structure of the metal foam has been created. Then, use the CFD(Computational Fluid Dynamics) to figure out the permeability and the inertial coefficient of porous materials with different structure as the parameter of flow resistance in Fluent. And then, stimulate the natural-convection heat transfer process of the LED heat sink. At last, the effect of foam's structural parameters on LED cooling is analyzed.Experiments are carried out on performance of natural convection heat transfer in copper foams.An equivalent numerical simulation model that can describe the flow resistance performance of metal foam is constructed based on FCC cell structure. According to the numerical computing results, the effect of structural parameters of metal foam on flow resistance is analyzed. The results indicate that the place where pressure drop happens is mainly at the junction of voids and flow resistance increase significantly when the pores density increasing. By calculating the relationship between pressure gradient and velocity, the permeability and the inertial coefficient of porous materials with different structural parameters are obtained.The performance of natural convection in LED heat sink of metal foam has been studied by using porous medium model of software FLUENT. The calculated results are in good agreement with those acquired experiment, which verifies the model's applicability. Not only is the Nu increase when the Gr increases, but also it has the connection with porosity, cell density and dimensionless height of metal foam materials through the experiment. According to the numerical simulation results, the criterion equation of natural-convection heat transfer that is under conditions of the first and second boundary conditions are obtained. Besides, the heat dissipation of metal foams is simulated and analyzed. The results show that the Nu increases by 8.65% after slotted. The way to estimate LED junction temperature is also discussed and this can give some reference to the application and further study of the metal foam heat sink.