Fabrication of sintered wick in micro -grooved pipe
The sintering heat pipe is an ideal component in solving the heat dissipation of high heat flux chips. The heat pipe with sintered wick structure in micro-grooved pipe was featured with low heat resistance, high bond strength and hard to dryout. According to the sintering theory, the manufacturing process of sintered wick could be divided into four phases: reduction phase, sintering starting phase, sintering preservation phase and sintering cooling phase. The sintering temperature, sintering time and sintering atmosphere about fabrication of the innovative sintered wick were also inspected. The result was discoveried that 100 mesh spherical copper powders had high porosity and low radial shrinkage at the sintering temperature of 950°C for 3 hours and the mandrel could be easily pulled out. It was also found that the oxidation reduction process could manufacture new micro structure—the segmentation cracks structure on the surface of copper powders.
Fabrication and thermal performance of porous crack composite wick flattened heat pipe
Abstract A novel porous crack composite wick flattened heat pipe (short for PCHP) was developed for the cooling of micro chips. PCHP was fabricated from grooved-sintered wick cylindrical heat pipe (short for GSHP) by phase change flattening technology. Porous crack composite wick consisted of micro crack channels at the unbending section and porous sintered powder. Micro crack channels were mode I cracks formed during phase change flattening process. Thermal performance of PCHP such as start-up performance, isothermal performance, heat transfer limit and thermal resistance was investigated by experiments. It was found that PCHP was able to achieve its steady state in about 30 s. The maximum temperature difference between evaporation section and condensation section of PCHP was less than 0.5 °C when the input power was about 10 W. The heat transfer limit of PCHP was highest about 50 W at cooling water temperature of 50 °C compared with grooved wick flattened heat pipe (short for GHP) and sintered wick flattened heat pipe (short for SHP). The thermal resistance of PCHP was a medium value between GHP and SHP.
Metallic micro heat pipe heat spreader fabrication
Abstract Micro heat pipe heat spreaders (MHPHS) with three copper foil layers were designed to allow liquid and vapor flow separation to reduce viscous shear force. Two wick designs, one using 200 μm wide etched radial grooves and the other with 100-mesh copper screens were investigated. The foils were vacuum diffusion bonded to form 31 mm × 31 mm × 2.7 mm heat spreader. Thermal performance of the MHPHS was evaluated experimentally in a fan-heat sink CPU test apparatus with a heating area of 13.97 mm × 13.97 mm. The clamping pressure between the spreader and the heat sink was maintained at 13 kgf during the test. After evaluation, the MHPHS with 82% methanol fill rate, radial groove wicking structure showed the best performance compared to the other samples. The superior MHPHS had lower evaporator temperature with a 17 °C value, corresponding to a 30% decrease in thermal resistance at an actual input power of 35 W, compared to the system without MHPHS.