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 an increased depth of the vapor reservoir and the integration of metal resistive heater elements onto the backside of the top plates to simulate the input heat. Some changes were made in the test sequence to produce more discernable differences in temperatures and pressures. The most recent results of the tests made with the modified system will be presented.
The focus of this work is the physical development and performance of an infinitely expandable planar non-standard MEMS loop heat pipe, targeted for electronic cooling. The composition is principally semiconductor grade silicon, with some glass components, requiring neither internal pumps nor external power, except the waste heat which causes its operation. In as much as modern microelectronics is of a planar configuration, the cooling device surfaces (unlike the classical cylindrical heat pipe) should ideally also be planar. Here the authors report such a compatible planar heat pipe, infinitely expandable in surface area, using inexpensive batch processing and glass (silicon dioxide) fiber as the wick. Preliminary results have demonstrated 42 and 65 W/Cm2 in closed and open loop configurations, respectively. These power dissipating levels greatly exceed that required for most emerging CPU's and other electronics.
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