Numerical study on the heat transfer characteristics of filled-type solar collector with U-tube

In this paper, the heat transfer characteristics of individual filled-type evacuated solar collector with U-tube is investigated by three-dimensional numerical method. The effect of thermal conductivity of the heat transmission component, mixed convection and the inlet velocity of working fluid on heat transfer characteristics of filled-type collector tube are analyzed. And the thermal performance comparisons between the filled-type collector tube and U-tube evacuated tube solar collector is also made. The results show that the temperature distribution and the heat transfer characteristics of the filled filled-type collector tube are affected remarkably by these factors. Under the action of buoyancy force, the temperature of the heat transmission component can be reduced compared with the pure forced convection, but the heat gain of working fluid is not increased. With increase of the thermal conductivity, the total heat gain of collector tube increases slightly when thermal conductivity of the heat transmission component is lower than 5 W/(m K), but the total heat gain of collector tube changes little once the thermal conductivity is above this value. The thermal efficiency of filled-type collector tube is 6% higher than that with copper fin. And the surface temperature of the absorber tube can reduce 40 °C, which indicates the filled-type collector tube has a favorable thermal performance.