Experimental and Theoretical Study of the Performance of Solar Water Heaters with Gravity-Assisted Heat Pipes

Abstract

The objective of this work is to study the performance of solar water heaters using heat pipes for heat transfer, from absorber plate to water tank, with two different types of working fluids (Ethanol and Acetone) and different numbers of heat pipes. Additionally, a theoretical investigation is conducted to predict the performance of the solar water heaters. These systems have been designed and fabricated with the same dimensions and materials. The hourly variation of the absorber plate temperature, the water storage tank temperature and solar radiation intensity are measured. Accordingly, the stored energy and the efficiency has been calculated. The results showed that, a good agreement has been achieved between the experimental and theoretical results. The operation point of the conventional system begins at the operating start while the operation point of the thermosyphon systems starts when the absorber plates temperatures reaches the boiling point of the working fluid. The maximum water temperatures gained of the forced convection system and thermosyphon system charged with ethanol and acetone were 66 C, 67.8 C, and 64.6 C, respectively while those of theoretical calculations were around 69.2 C, 69 C and 69.3 C, respectively. In addition, the maximum value of the actual efficiency of conventional system was ranged between 47~53% while that of theoretical calculation was between 50~53%. The experimental maximum efficiency of thermosyphon systems was around 55% at the case of installing 14 heat pipes charged with acetone and theoretical efficiency was 55% for same the case. The thermosyphon system gives better performance than forced convection system, because thermosyphon system does not consume electricity. Performance of the thermosyphon system using acetone as working fluid was better than the performance of the thermosyphon system using ethanol and the increase of the heat pipes number improves performance.