The influence of the inclination angle on the performance of a closed two-phase thermosyphon

The effect of the inclination angle on the transport behavior of a closed two-phase thermosyphon is studied in a steel pipe containing the refrigerant R 115 as the working fluid. The pipe is electrically heated at the lower part ('heating zone') and cooled by water at a constant temperature along the upper part ('cooling zone'), while between these two zones there is a well insulated transport zone. The amount of fluid in the tube is chosen so that the critical specific volume is obtained. Results show that the maximum heat flow rate in the tube depends on the inclination, with the largest value of the heat flow rate being 2850 W at an inclination angle of 40 degrees. The effective thermal conductivity of the thermosyphon depends strongly on the inclination angle and the heat flow rate, so that the steeper the tube and the larger the heat flow rate, the higher is the effective conductivity. In addition, the condensation in the cooling zone exhibits the largest transport resistance, while the heat transfer with boiling in the heating zone shows large local differences and depends strongly on the inclination of the tube.