Srinivas Parimi

The MEMS Loop Heat Pipe Based on Coherent Porous Silicon — The Modified System Test Structure

The previous papers presented at STAIF 2002 and STAIF 2003 discussed the design, fabrication and characterization of the evaporator section and the initial test cell of a planar MEMS loop heat pipe based upon coherent porous silicon or “CPS” technology. The potentially revolutionary advantage of CPS technology is that it is planar and allows for pores or capillaries of absolutely uniform diameter. Coherent porous silicon can be mass‐produced by various MEMS fabrication techniques. The preliminary experiments made with the original test structure exhibited the desired temperature and pressure differences, but these differences were extremely small and oscillatory. This paper describes modifications made to the initial test cell design, which were intended to improve its evacuated, closed loop performance. Included among these changes were the redesign of the compensation chamber and condenser, an increase in the porosity of the coherent porous silicon wick, the fabrication of silicon top “hot” plates with ...

Operating Ranges of the Planar Loop Heat Pipe Under Non-Vacuum Conditions

As the trend of high throughput in small packages continues, the heat dissipation becomes a very critical design issue in electronic devices and spacecrafts. The two phase loop heat pipe utilizes the latent heat of working fluid. It consists of an evaporator, compensation chamber, condenser, and liquid and vapor line. The primary wick used as a core part to circulate the working fluid is located in the evaporator. The planar loop heat pipe uses coherent porous silicon (CPS) wick as opposed to the conventional cylindrical configuration, which uses a sintered amorphous metal wick. The clear evaporator machined from Pyrex glass and transparent silicone tubes were utilized to monitor the complex phenomena which occur in the evaporator. Tests were conducted under the non-vacuum condition without a secondary wick. DI-water was used as a working fluid. Like an open loop test previously conducted, there was an operating range in which the liquid could be properly pumped from the compensation chamber to the vapor line under the pumping motion. In this device, more than 6 Watts could be convected from the evaporator to the ambient. Therefore circulation was not observed until powers greater than 6 Watts. There was a circulation of working fluid occurring due to energy transport within the loop when the input power was from 7.94 Watts to 17.6 Watts. The quantity of heat transportation to the loop was calculated by acquiring the empirical heat transfer coefficient. From this calculation it was found that, roughly, 12.1 Watts was transported to the loop and 5.51 Watts was convected to the ambient from the evaporator itself when the applied power was 15.27 Watts. This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.© 2005 ASME