What is going on in a critical thermosyphon?

Critically filled thermosyphons for heat transport differ in size and temperature distribution from critically filled testcells for property research. Consequently, the thermodynamic states within a thermosyphon are distributed more heterogeneously. In a glass thermosyphon, flows and phase distributions were observed. A break-down of the heat transport mechanism was found as a consequence of flooding the cooling region with liquid. Observed and explained — by use of a density/pressure diagram — were the effects of heating, of pressure and of fluid quantity on the distribution of the phases, the appearance of pulsations and the propagation of a heat pulse near the critical state.