The operating instability of a dual compensation chamber loop heat pipe (DCC-LHP) including temperature hysteresis, reverse flow and temperature oscillation is described and explained in this paper. Test results indicate that the steady state operating temperature under the variable conductance mode is not the same during the power cycle tests with the same heat load, and it is lower during the power reduction cycle than that during the power increase cycle. Orientation has an effect on the heat load range when temperature hysteresis occurs, and the effect of power variation amplitude can be ignored. Reverse flow tends to occur in some of the startups at low heat loads, even if vapor existed in the vapor grooves initially, which is caused by a higher pressure inside the wick due to evaporation in the evaporator core or vapor penetration into it. Temperature oscillation tends to occur in some of the startups at low head loads or some steady-state operations at high heat loads. Especially when the compensation chamber with the bayonet through is above the evaporator, the incidence rate of temperature oscillation is high.
