Thermal Performance of a Capillary Pumped Loop for Automotive Cooling

The design and test results for a capillary pumped loop (CPL) for thermal management of up to 210 W at the source and heat transfer over a distance of 1 m are discussed. The design configuration of the CPL evaporator consists of an internally grooved aluminum evaporator, 31.70-mm outer diameter and 500-mm long, fitted with a porous ultra-high molecular weight polyethylene wick, 8- to 15-μm pore radius, and 38% porous volume. Heat was transferred using a stainless steel tube of 4.5-mm internal diameter for vapor and liquid lines. High-grade acetone (99.99% pure) was used as the heat transfer fluid inside the loop. In the tests, thermal characteristics of the CPL were specifically studied with respect to the temperature control capability using an active thermal device on the reservoir and to the start-up process through pressure priming of the capillary evaporator. The loop was able to start-up successfully at both low and high heat loads, although proper priming of the wick structure before start-up was necessary to attain low evaporator temperatures during steady-state operation. While maintaining constant reservoir temperature through active means, the loop was able to control evaporator temperature within 55 ± 3°C, even with changing input heat from 30 to 210 W. Total thermal resistance from the evaporator surface to the surroundings was 0.19° to 1.15° C/W with the minimum value achieved at the maximum heat load of 210 W. This study is intended to illustrate the thermal potential of the CPL as an effective temperature control device in automotive applications.