Investigation on the Optimum Volume Filling Ratio of a Loop Thermosyphon Solar Water Heating System

Abstract

Volumefilling ratio of the working fluid has a predominant effect on the system performance of a closed twophase solar waterheating (SWH) system. To study this effect, a prototype of a loop thermosyphon SWH system, which uses remolded flatplate solar collector as the evaporator and the coil pipe in the water tank as the condenser, was set up. A set of longterm outdoor experiments under 10%, 20%, 30%, 50%, and 70% volumefilling ratios were conducted in this paper. R600a was used as working fluid. Loop thermosyphon solar collector thermal performance and system thermal performance under different volumefilling ratios, including the temperature distribution of loop thermosyphon evaporator, were presented. It is shown that the loop thermosyphon solar collector and the system had a better thermal performance than the conventional ones under 30% and 50% volumefilling ratio, and the loop thermosyphon evaporator had an even temperature distribution when the volumefilling ratio was higher than 30%. The optimum volume filing ratio lies in between 30% and 50% of the whole system volume.