Effects of the pipe length of a solar collector on its heat collection performance
摘要
Flat plate solar collectors are one of the most commonly used solar thermal systems. The absorber plate is a crucial component of these systems, and researchers have attempted to enhance this component’s heat absorption capacity to increase system efficiency. The present study employed computational fluid dynamics software to investigate the effects of pipe length on outlet water temperature for a flat plate solar collector under varying solar radiation intensities, mass flow rates (for the working fluid), and inlet water temperatures. The simulation results indicated that outlet temperature increased with an increase in solar radiation intensity and pipe length and a decrease in mass flow rate. When the pipe length was 2000 mm and the mass flow rate was 0.00625 kg s−1, an increase in the solar radiation intensity from 300 to 1200 W m-2 resulted in a 17.8 K increase in outlet temperature. When the pipe length was 2000 mm and the solar radiation intensity was 1200 W m-2, a decrease in the mass flow rate from 0.025 to 0.00625 kg s−1 resulted in a 15.9 K increase in outlet temperature. Furthermore, under a solar radiation intensity of 1200 W m-2 and a mass flow rate of 0.00625 kg s−1, the outlet temperature rose by 9.1 K when the pipe length was increased from 1000 to 2000 mm. The effect of inlet water temperature on outlet temperature is found to be linear; that is, an increase of 5 K in inlet temperature results in a corresponding 5 K rise in outlet temperature. The thermal efficiency analysis further showed that, at a solar radiation intensity of 1200 W m-2, the maximum thermal efficiency of 47.0% was achieved at a pipe length of 1000 mm, a mass flow rate of 0.025 kg s−1, and an inlet water temperature of 303 K.