Abstract: Loop heat pipes are heat transfer devices based on the evaporation and condensation of a working fluid,and using capillary pumping forces to ensure the fluid circulation.A series of tests have been carried out with a miniature loop heat pipe(MLHP) with flat evaporator and a fin-and-tube type condenser.The loop was made of pure copper with stainless mesh wick and acetone was used as the working fluid.At low heat loads,temperature oscillations were observed throughout the loop.The characteristics of temperature oscillation of the flat MLHP at heat fluxes from 2W/cm2 to 3W/cm2were studied.The compensation chamber was considered as the most critical component of the MLHP and its hydrodynamic state dictated the extent and the characteristics of the temperature oscillations for the input heat load.The heat leaks from the evaporator to the compensation chamber,the heat loss to ambient and subcooled liquid temperature dictated the vapor condition inside the compensation chamber,and the rate of vapor growth or dissipation dictated the nature of the temperature oscillation.The effects of different liquid charging ratio and the tilt angle to the temperature oscillations were studied in detail.