Investigation of pulsations of the operating temperature in a miniature loop heat pipe

During the operation of miniature loop heat pipes (LHPs) one can observe pulsations of the operating temperature, which depend on the amount of the working fluid, the device orientation in the gravity field and the conditions of the condenser cooling. Intense pulsations, whose amplitude may exceed tens of degrees, arise from the lack of a working fluid in a LHP when a hot condensate or vapor bubbles periodically penetrate into the compensation chamber (CC) and act on the vapor phase in it, increasing its temperature and volume. Changes in the external conditions, for instance, the LHP arrangement in an unfavourable orientation or a more intensive cooling of the condenser with respect to the conditions for which the filling volume was optimal, also contribute to the initiation of intense pulsations of the operating temperature. In both cases one can observe redistribution of the working fluid between the condenser and the CC, as the result of which the liquid phase volume in the latter decreases and overshoots of vapor or a hot condensate there become possible.