Temperature Oscillation of mLHP with Flat Evaporator

Loop heat pipes (LHPs) are heat transfer devices whose operating principle is based on evaporation and condensation of a working fluid, and which use the capillary pumping forces to ensure fluid circulation. Temperature oscillations are a rather wide-spread phenomenon accompanying the operation of miniature loop heat pipes (mLHP), which depends on the charging ratio of the working fluid, the device orientation in the gravity field, and the conditions of the condenser cooling, and so on. Intense oscillation, whose amplitude may exceed tens of centigrade degrees and the period may be equal to tens of minutes, arises from the lack of a working fluid in a mLHP when a hot condensate or vapor bubbles periodically penetrate into the compensation chamber and act on the vapor phase in it, thus increasing its temperature and volume. Changes in the external conditions, for instance, the LHP arrangement in an unfavorable orientation or applied heat load with respect to the conditions for which the filling volume is optimal, also contribute to initiation of intense temperature oscillation. All in all, the heat leak from the evaporator to the compensation chamber, the heat loss to the ambient, and the temperature and rate of subcooled liquid dictate the vapor bubble condition inside the compensation chamber, and the rate of the vapor bubble growth or dissipation inside the compensation chamber dictates the nature of temperature oscillation. The effects of different liquid charging ratios and the tilt angles to the temperature oscillation are studied in detail.