Evaluation of the liquid charge for a closed two-phase thermosyphon

We present experimental results and a simplified theoretical model on the volume filled by the liquid-vapor mixture in the evaporator of a closed two-phase thermosyphon as a function of the power throughput. The volume filled by the mixture depends on its average density. Thus, we first correlate the mixture density to the vapor mass flow rate; then, we evaluate the density average value over the mixture volume. Finally, we derive an analytical correlation between the mixture volume, the liquid charge and the power throughput. Experimental results on the mixture volume agree well with the values calculated with the proposed correlation.