Comparison tests of loop heat pipes with flat evaporators of different types

•Flat-oval and disk-shaped evaporators with the same active zone area were tested.•The evaporators were tested as parts of identical copper-water LHPs.•The flat-oval evaporator showed higher efficiency.•The disk-shaped evaporator was more compact.•The evaporators were designed for LHPs in high-power electronics cooling systems. Comparison tests have been conducted on a flat-oval evaporator with a longitudinal replenishment of the evaporation zone with a working fluid (ELR) measuring 110 × 50.5 × 10 mm3 and a flat disk-shaped evaporator with opposite replenishment (EOR) 50 mm in diameter and 19 mm in thickness. The evaporators have been tested as parts of copper-water loop heat pipes (LHPs) with identical design parameters, with a heat source of 40 × 40 mm2 at a heat sink temperature of 40 °C. It is shown that an LHP with an ELR has a significantly lower operating temperature in the whole range of heat loads. The maximum heat load of the device with an ELR was 800 W at an evaporator temperature of 109.5 °C and with an EOR it was 600 W at a temperature of 121.1 °C. The corresponding thermal resistances of the evaporators were 0.025 °C/W and 0.046 °C/W. At a nominal heat load of 300 W the ELR temperature was 70.2 °С and the EOR temperature 87.4 °С. The devices were designed for use in energy-efficient cooling systems for high-power electronics. A computer simulation of heat exchange processes in the evaporators was carried out taking into account parasitic heat flows into the compensation chamber.