Experimental Study of the Thermal Performance for the Novel Flat Plate Solar Water Heater with Micro Heat Pipe Array Absorber

This paper presents a novel flat plate solar water heater (SWH) using micro heat pipe array (MHPA) sprayed solar selective coating and arranged closely as the absorber of collector. The collector has the advantage of resistance to freezing, high heat transfer ability, relatively low heat loss, elimination of welding, and prevention of leakage. The experiments were conducted first to investigate the thermal performance of the novel collector. The test results for the collector's instantaneous efficiency show that the slope and intercept of the instantaneous efficiency curve are 5.6 and 0.85 respectively. Then, the thermal performance monitoring analysis of the forced circulation SWH with 2 m2 novel collector under different weather conditions were carried out using trial installations in Beijing, China. The test data were analyzed from the aspects of water temperature, effective heat gain, and thermal efficiency. The test results show that the daily effective heat gains on the three typical days in different seasons are 13.43 MJ/m2, 11.05 MJ/m2, and 7.42 MJ/m2 respectively, corresponding to the solar irradiation of 18.9 MJ/m2, 17.2 MJ/m2, and 14.7 MJ/m2. The daily average thermal efficiencies are 71.05%, 64.25%, and 50.49%, respectively. These experimental results provide basis and reference for practical application of the novel SWH.