Heat Transfer Characteristics of a Loop Heat Pipe With Flat Evaporator Having a Bypass Line

Abstract

It is common for loop heat pipes to experience start-up problems under low thermal loads. The start-up characteristic of a loop heat pipe with flat evaporator was investigated experimentally in this study. A bypass line was attached to the evaporator to alleviate the difficulties associated with startup. Axial grooves were provided in the flat evaporator to serve as a vapor passage. The evaporator and condenser had dimensions of 40 mm (W) by 50 mm (L). Coolant paths were machined inside the condenser. The inner diameters of liquid and vapor transport lines were 2.0 mm and 4.0 mm, respectively and the length of the two lines was 0.5 m each. The thermal load range was up to 80 W using methanol as a working fluid with the condenser temperature of 10°C at horizontal position. The results showed that a minimum thermal load for the startup was lowered by 37% when the bypass line was employed. However, a periodical performance variation was observed once the startup was achieved under very low thermal loads.