Validated mathematical models of a solar water heater system with thermosyphon evacuated tube collectors

An evacuated tube solar water heater system using thermosyphon heat exchange was experimentally and theoretically investigated. Solar radiation and ambient temperature data from Chiang Mai Province were used as the modeling system by an Explicit Finite Difference Method (EFDM). The experimental setup consisted of 8 evacuated tube collectors (ETCs) with thermosyphon diameters of 15.88 mm for the evaporator and 22.22 mm for the condenser. Lengths of the evaporator, adiabatic, and condenser sections were 1700 mm, 150 mm and 100 mm, respectively. Mathematical model results of both thermal resistance method and EFDM were validated by experimental results. Theoretical results for temperature and thermal efficiency concurred with experimental results and previous research. Experimental result, thermal resistance method and EFDM results indicated that maximum temperature of hot water occurred at 4:00 p.m. as 65.25 °C, 71.19 °C, and 69.46 °C, respectively. Thermal efficiency of the solar water heater system was 58.28% of the experimental result, 55.97% of the thermal resistance method and 57.60% of the EFDM result. EFDM provided better accuracy than the thermal resistance method by 2.97%.