| dc.description.abstract | The high power LED possesses of high brightness, environmental protection, and energy saving. But owing to the heat effect, this LED would be reduced life time and efficiency, and result in the wavelength shift. The general heat sink cannot diffuse heat effectively for the small size LED. Therefore, using the main characteristic of two-phase changed of heat pipe can achieve the heat diffusion and reduce the junction temperature of LED. The cylinder heat pipe is not convenient for contacting with the flat heat source. Thus flat heat pipe is used to increase contact area and to decrease the contact resistance between heat source and heat pipe. The flat heat pipes not only increase the fill of working fluid, but also use more grooves to transport liquid back to hot point.
In this case, we fabricated different shape grooves flat heat pipes, radial grooves heat pipe and parallel grooves heat pipe, to observe the heat transportation of heat pipes. The heat transfer of radial heat pipe starts from the center to edge by vaporizing working fluid to enhance diffusing area. But the radial heat pipe has no significant effect in reducing the temperature of heat source. The main reason is that the temperature of heat pipe is controlled by cold point, thus the working fluid cannot boil. The heat transport of parallel heat pipe starts from edge to edge, so that the diffusion area of parallel heat pipe can be enlarged. In parallel case, the working fluid can boil under different liquid fills and incline angles, thus the thermal resistance is reduced effectively. The reducing thermal resistance of 30% fill is better than 63% fill, and 30% fill is no limited by gravity force. | en_US |