Experimental analysis of a heat pipe operated solar collector using water–ethanol solution as the working fluid

In this paper heat pipes have been constructed and tested using solutions of ethanol and water as the working fluid at different tilt angles and concentrations. Tests were carried out to investigate the effects of ethanol concentration as well as the pipe evacuation and the use of a wick inside the pipe to ensure a continuous performance of the system. The tests indicate that ethanol in the solution enhances the heat pipe performance at low heat flux, and that concentrations of 50% and 75% show the best performance characteristics in transferring the heat. An efficiency of about 52% was obtained for the heat pipe operated solar collector in this case. It was concluded that the evacuation of a heat pipe or using a wick do not add much effect to the enhancement of a heat pipe performance, and that the collector had its highest heat transfer coefficient at a tilt angle of 35°. Using the results from testing the heat pipes, a thermo-syphon type solar water heater was developed, using the high efficiency heat pipe with evacuated glass cover tubes. The results of these experiments revealed that the collector water flow rate and evacuation of the glass cover tubes had little effect on the enhancement of the solar collector thermal performance.