Visual investigation on startup characteristics of a novel loop heat pipe

•The driven force is composed of two parts in the novel LHP system.•Startup process is made up of seven stages, among which a breathing phenomenon is occurred.•A quicker startup accompanied with overheating problem is observed as heat load increased.•The loop starts up at a higher evaporator peak temperature as time difference increased.

In this experiment, visual investigations of pool boiling, redistribution of working fluid and temperature measurements were carried out to study the startup characteristics of a novel loop heat pipe in different conditions. The mechanisms behind were also explored. It is found that the driven force in this loop was composed of capillary force and the vapor pressure formed in the boiling pool, and the final startup could be obtained only when the vapor pressure ensured the subcooled liquid ingress into the compensation chamber and capillary force ensured the liquid supply from the compensation chamber to the boiling pool. The typical startup process was made up of seven stages, among which a peculiar breathing phenomenon occurred in the compensation chamber. With increasing heat load of boiling pool, a quicker startup was obtained and the peak temperature of evaporator was reduced significantly. However, it caused a quite serious overheating problem of boiling pool. With increasing time difference, a more violent boiling phenomenon appeared in compensation chamber. The loop started up at a higher peak temperature of evaporator, while that of boiling pool remained unchanged. Moreover, in the condition of an insufficient liquid charging and a loose fit, a pulsation operation mode of the loop system was observed.