FLOW AND HEAT TRANSFER IN A TWO-PHASE DOUBLE-TUBE THERMOSYPHON

An investigation of flow and heat transfer characteristics in a two-phase double-tube thermosyphon was performed experimentally using water, ethanol, and Freon 113 (R113) as the working fluids. A theoretical study was also made on the circulation mass velocity. As the heat flux increased, the experimentally measured circulation mass velocity first increased and then decreased. After that, for ethanol and Freon 113, the mass velocity increased again at a certain heat flux, where the heat transfer coefficient also increased stepwise, and then decreased. It seems that this peculiar behavior was caused by a change in flow pattern. For water, the calculated circulation mass velocity agreed well with the experimental results. For ethanol and Freon 113, however, the agreement was not good enough because the change in the flow pattern was not taken into consideration in the theoretical calculation. The calculated mass velocity, however, did indicate the average line passing through the experimental data.