Fabrication Process And Thermal Performance Analysis Of Ultra-thin Flattened Micro Heat Pipe Sintered With Composited Wick Structure

With the tendencies of high performance and high integration in micro-electronic and optoelectronic fields, more heat is urgent to be dissipated for electronic devices. Especially under the light and compact tendency of electronic devices, cooling problem has become an increasingly prominent issue that affecting the reliability and service life. As an efficient heat transfer device, micro heat pipes have been widely used in various fields to solve the thermal issue. To solve the heat dissipation issue in electronic devices with a limited space, a thinner ultra-thin micro heat pipe with good thermal properties is desired to be developed.The wick structure is one of the most critical factors to the thermal properties of micro heat pipes. This paper proposed three kinds of composited wick structures suitable for ultra-thin micro heat pipes, including single arced sintered-grooved structure, bi-arced sintered-grooved structure and mesh-grooved composited wick structure. The manufacturing process and parameters are designed for experiments.The samples with three kinds of composited wick structures are prepared under different filling ratios. The cross and longitudinal sections of the samples are observed by Scanning Electron Microscope(SEM), which in order to observe the composted sintered sate, powder layer pressing and powder layer tearing. Investigating the effect of compressing process on the composited wick final forming state. The effects of composited wick structure states on thermal performance are analyzed based on the experimental results.Based on the basic theories of heat pipe, the heat transport limitations of the ultra-thin heat pipes are analyzed and calculated based on the structure parameters of the composited wick structures and physical properties of the working fluid. Result shows that capillary limitation is the main limitation to the ultra-thin micro heat pipes. Under the condition of 55°C,the theoretical results of the heat pipes with three composited structures are 12.5 W, 15.4 W and 19.4 W.An experimental testing platform is set up to test the steady and dynamic thermal performance of ultra-thin micro heat pipe samples with different composited wick structure under different filling ratios. Investing the best filling ratio and comparing the thermal performance of each composited wick structure. Comparing the start-up performances of the ultra-thin heat pipes under different heat inputs. Infrared imaging method is applied to test the isothermal performance of the samples and the capillary performance of the composited structures. Result shows that the best filling ratio for single and bi-arced sintered-grooved structure is 70% and that for mesh-grooved composited wick structure is 80%. The heat transfer limit powers for each sample are 12 W,13 W and 14 W relatively. The evaporation thermal resistances of the samples decrease first, then increase. Relatively, the condensation thermal resistances maintain under 0.2 K/W. It takes about 100 s for an ultra-thin heat pipe to reach the equilibrium state under low input, but dry-out occurs at about 90 s under high input power. The isothermal properties of the ultra-thin heat pipes are much better than that of copper blocks. The capillary force for the bi-arced sintered-grooved structure is the best, while that for mesh-grooved composited wick structure is the worst.