Design and Operation of a Novel Capillary Pumped Two-Loop System for Cooling of Electronic Devices

Abstract

Heat pipes, loop heat pipes (LHP), and capillary pumped loops (CPL) have already proven their potential to remove high heat fluxes from a small electronic device and transport the heat to a heat sink that is large enough to transfer it into the ambient air. We introduce a novel two-loop system similar in design to CPLs but with an additional buoyancy-driven fluid loop. Non-degassed methanol is used as a working fluid. Key benefits compared to LHPs and CPLs are easy filling procedure, easy startup, and the tolerance toward noncondensable gases in the fluid. The amount of fluid in the system can be varied over a broad range without affecting the heat transfer performance. Three different inverted-meniscus-type evaporators have been employed in this study. A maximum evaporator heat transfer rate of 105 W has been obtained, which corresponds to a heat flux of 35 W/cm2 based on the projected surface area of the porous capillary structure (15 mm × 20 mm) inside the evaporators. A maximum heat transfer coefficient of 16.5 W/(cm2 K) has been achieved at a wall superheat as little as 0.45°C. Oscillations of pressure, temperature, and the liquid vapor interface occur for all experimental conditions. The analysis of different loop parameters indicates that the heat transfer coefficient is increased due to the periodical wetting/dewetting of the channel walls triggered by the interface oscillations.