Research On Capillar Driving And Latent Heat Transfer On Silicon-based Micro Heat Pipe

A novel design of micro heat pipe (MHP) array with arteries that can limit the onset of the dry-out region is proposed. Additional pipes are inserted between adjacent MHP in order to improve liquid transportation ability from the condenser section to the evaporator section. These additional pipes have smaller cross-sectional dimensions than the MHP and serve as artery of MHP. Because of the liquid pressure difference in the meniscuses between the two ends of MHP. additional amount of working liquid can be effectively transported to the evaporator section through these arteries, which definitely improves the performance of the MHP. The working principle and optimal design of the arteries are numerically investigated with a1-D steady-state model of the artery MHP array. In order to verify the idea, a silicon based artery MHP array and traditional MHP sample with the same dimensional parameters are fabricated by lithography, micromachining and anodic bonding processes. In order to evaluate the thermal performance of this novel design of MHP array, its heat resistance in different working conditions is analyzed. An experimental setup is then used to generate the working circumstances of MHP heat spreader. The validation has been carried out by the comparison observation experiments of the novel MHP and the traditional MHP through a microscopic camera. Both the model's numerical solution and the observation results indicate that the artery MHP array can effectively extend thermal working range. The experimental data indicate that the MHP with arteries could extend its working temperature range by100percent.The main contents of this dissertation are briefly stated as the followings:(1) Build model for fluid transmission and vapor pressure distribution. According to the novel design of MHP implanted with artery, a one-dimensional model for fluid transmission based on the Young-Laplace equation, the existing model for vapor pressure distribution based on Clausius-Clapeyron equation is utilized here. It is proved that the micro heat pipe implanted with artery is able to enhance the fluid backflow by the numerical solutions of the models.(2) Optimal design of the MHP implanted with artery. Artery is used here to transfer additional amount of working liquid, the most important parameter for the artery is its width which determines the volume of the backflow liquid that flows through the artery. The model for fluid transimission is used to analyse the optimal design in order to let more and more liquid could be transfered to the hot end through the artery. And optimal fill charge of the MHP implanted with artery is also obtained to achieve better thermal performance.(3) Research on fabrication processes of MHP samples. In order to integrate the MHP with the IC equipment, the fabrication processes of MHP on the silicon wafer are discussed which includes wet etching, anodic bonding and filling and sealing. The detail parameters of these fabrication processes are obtained.(4) Temperature measuring and working condition observation of MHP implanted with artery. An experimental setup in vacuum chamber is used to measure the temperature distripution in the axial direction, and high speed camera is utilized to observe the working conditions of MHP implanted with artery. The experimental results are compared with the datas of the traditional MHP.