Numerical study of temperature oscillation in loop heat pipe

Loop heat pipes are high-efficient heat transfer devices. Many spacecraft have loop heat pipes to control the temperature of equipment precisely. Temperature oscillation, however, sometimes occurs in the loop heat pipe when the external conditions change. Temperature oscillation may impede the temperature-controlling ability of loop heat pipes. Nevertheless, the cause of temperature oscillation has not been understood yet. To understand the internal flow during temperature oscillation, we developed a transient model that can reproduce the fluid condition in the transport lines. In this study, the reservoir temperature, liquid line temperature, and condensation length were focused. Investigating the relation between each parameter, we found that the cause of temperature oscillation is the inflow of two-phase flow into the liquid line, which is caused by decreasing the reservoir temperature. In addition, as the amplitude of the condensation length becomes high, temperature amplitude also becomes high. When the sink temperature is low, the condensation length can barely oscillate, and thus, temperature oscillation is less likely to occur.