PERFORMANCE OF A WICKLESS HEAT-PIPE SOLAR COLLECTOR

The wickless heat pipe solar collector has the advantage of high effective thermal conductance due to its exploitation of phase-change phenomena, and the advantage of solving the problems of flat-plate solar water heaters such as scale formation (corrosion), cycle reversing (during the night), and freezing. The use of the heat pipe technology in solar collectors will not only solve these problems but also eliminate the effect of the daily and seasonal variation of the solar radiation on the collector performance. The purpose of this article is to obtain a comprehensive understanding of the thermal performance of a wickless heat pipe solar collector on the basis of heat-transfer analysis using R-11, acetone, or water as a working fluid at different charging pressures. Also the effect of angle of inclination and the effect of liquid fill on the performance of the wickless heat pipe solar collector were studied The experimental results show that the maximum efficiency occurs at 45-degrees tilt angle. The optimum liquid fill in the wickless heat pipe with solar applications is 0.7, where the temperature flattening phenomenon occurred in the collector. The most suitable working fluid for wider temperature flattening is R-11 compared with acetone or water. The predicted theoretical results, using R-11, were compared with the experimental data and proved the validity of the theoretical analysis.