Influencing factors of resistance for evacuated tube solar air collecting systems

Through the analysis of internal flow process of the evacuated tube solar air collecting system, establishes a resistance calculation model for the heat collecting system, and analyses the resistance changes of evacuated tube solar air collectors and series heat collecting system under different design parameters. The results show that with the increase of heat collector temperature, the impedance decreases exponentially. Among the various influencing factors, the number of series collectors and the working fluid flow have the greatest impact on system resistance. The resistance of each group of collectors shows an increasing trend of decreasing growth rate with the increase of the number of series collectors. With the increase of mass flow, the system resistance increases exponentially, and the maximum resistance is 3.6 times the minimum value. With the increase of ambient temperature, solar radiation intensity and inlet temperature, the system resistance shows a positive proportional increase trend, and the influence of the ambient temperature on the system resistance is negligible. The resistance calculation model of the evacuated tube solar air collector system established by this research and the calculation table of the resistance per unit area of the collector can provide a convenient and reliable basis for the theoretical calculation of the resistance of the collector and collecting system.