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.
Design and fabrication of sintered wick for miniature cylindrical heat pipe
Miniature cylindrical metal powder sintered wick heat pipe (sintered heat pipe) is an ideal component with super-high thermal efficiency for high heat flux electronics cooling. The sintering process for sintered wick is important for its quality. The sintering process was optimally designed based on the equation of the heat transfer limit of sintered heat pipe. Four-step sintering process was proposed to fabricate sintered wick. The sintering parameters including sintering temperature, sintering time, sintering atmosphere and sintering position were discussed. The experimental results showed that the proper sintering temperature was 950 °C for Cu powder of 159 μm and 900 °C for Cu powders of 81 and 38 μm, respectively, while the wick thickness was 0.45 mm and sintering time was 3 h. The optimized sintering time was 3 h for 0.45 and 0.6 mm wick thickness and 1 h for 0.75 mm wick thickness, respectively, when copper powder diameter was 159 μm and sintering temperature was 950 °C. Redox reduction reaction between H2 and CuO during sintering could produce segmentation cracks in Cu powders as a second structure. Sintering at vertical position can effectively avoid the generation of gap between wick and the inner wall of pipe.
Design of Miniature Loop Heat Pipe
In the present study, the loop heat pipe (LHP) was miniaturized for application to electronic cooling. According to the capillary limitation, the wick structure parameters that would affect the heat transfer capacity were analyzed theoretically. Among the various wick parameters, this study especially investigated the effect of wick thickness, which has rarely been mentioned in the literature. Here, various thicknesses were analyzed theoretically and then tested experimentally. The results showed that the temperature on the evaporator wall dropped with decreasing wick thickness. This effect would lead to the raising of heat transfer capacity and the descending of thermal resistance. According to the analysis and the practical demand for electronic cooling, a miniature LHP was fabricated with the evaporator outer diameter of 13 mm and the evaporator length of 50 mm. The testing results showed that, at the allowable working temperature of 80 °C, the maximum heat transfer capacity was up to 200 W and the thermal resistance was 0.17 °C/W. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(1): 42–52, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10133