Review: Loop heat pipes with flat evaporators

The paper contains an analytical review of developments, results of tests and simulation of loop heat pipes (LHPs) with disk-shaped, rectangular and flat-oval evaporators. Two main directions have been noted in the development of flat evaporators, which may be arbitrarily separated into evaporators with opposite replenishment (EORs) and evaporators with longitudinal replenishment (ELRs). The bodies of such evaporators are made of stainless steel, copper, aluminum. For making wicks use is made of sintered powders and mesh of stainless steel, nickel, titanium, copper, polytetrafluoroethylene (PTFE) and ceramics. Monoporous and biporous capillary structures are considered. Water, ammonia, methanol, ethanol, and acetone have been tested as working fluids. The best results were shown by the combination “copper–copper–water” at temperatures above 70 °C, when on trials an evaporator thermal resistance of less than 0.01 °C/W and a heat flux close to 1000 W/cm2 were achieved. For temperatures below 70 °C the most efficient combination is “stainless steel–nickel–ammonia”.