Experimental Studies on a Loop Thermosyphon for Solar Heating of Buildings

This study presents an experimental analysis of the thermal performance of a two-phase copper-R-141B loop thermosyphon for passive solar heating of buildings. A prototype was built and tested on a specially prepared test rig at the Heat Pipe Laboratory of the Federal University of Santa Catarina (LABTUCAL-UFSC).The boiling and condensation heat transfer coefficients were obtained experimentally as a function of the heat transfer rate for the range of temperatures of interest. The conditions for the correct start-up were studied and the maximum and the minimum heat transfer rates were measured. The results show that start-up of the tested prototype occurs when the evaporator reaches the temperature of approximately 37°C and the heat transfer rate is approximately 25 W. After start-up, the system works well at power levels less than 25 W. Even a heat transfer rates less than 5 W are sufficient to keep the loop-thermosyphon working properly. The prototype measured overall thermal resistance is approximately 0.03 K/W, which agrees with predictions from the literature. More studies are needed to minimize the start-up temperature so the device can operate in a wider range of evaporator temperatures.