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 R113 as the working fluids. A theoretical study was also made on the circulation mass velocity. As the heat flux increased, the circulation mass velocity measured experimentally first increased and then decreased. After that, for ethanol and R113, the mass velocity increased again at a certain heat flux where the heat transfer coefficients also increased stepwise. It is considered that this particular behavior was caused by a change in the flow pattern. For water, the calculated circulation mass velocity agreed well with the experimental results. For ethanol and R113, however, the agreement was not good enough because the change in the flow pattern was not taken into consideration in the theoretical calculation. However, the calculated mass velocity indicated the average line passing through the experimental data.