THEORETICAL AND EXPERIMENTAL ANALYSES OF THE THERMAL RESISTANCE OF A LOOP THERMOSYPHON FOR PASSIVE SOLAR HEATING OF BUILDINGS

This study presents experimental and theoretical analyses of the thermal performance of a two-phase copper-R141b loop thermosyphon, which was developed for solar heating of buildings. A prototype of the so-called wall thermosyphon was built and tested at the Heat Pipe Laboratory of the Federal University of Santa Catarina (Labtucal-UFSC). During the tests, three parameters were varied: purge method, power input levels, and inside wall evaporator roughness. The results show that both purge and vacuum pumps are equally effective in eliminating noncondensable gases from the system. Also, recent boiling heat transfer coefficient literature correlations are in good agreement with the experimental data from the prototype. However, the condensation thermal resistance calculated with the literature correlations do not represent the same trend found in the experiments. The effective thermal resistance of the wall thermosyphon prototype, which comprises the boiling resistance plus the condensation resistance, varies between 0.22 and 0.011 degrees C/W depending on the heat transfer rate from 2.5 to 200 W.