Performance analysis of a new-design filled-type solar collector with double U-tubes

In order to eliminate the influence of thermal resistance between the absorber tube and the copper fin of the conventional evacuated solar collector, which would decrease the thermal performance of the evacuated tube collector, a filled-typed evacuated tube with single U-tube (SUFET) was presented in our previous work, in which the filled layer was used to transfer energy absorbed by the working fluid flowing in the U-tube. In this paper an improved filled-type evacuated tube with double U-tubes (DUFET) was presented by means of theoretical analysis and experimental study to increase the heat transfer area and then improve the heat transfer efficiency of collectors. The structure of filled-type evacuated tube with double U-tubes was given first, and then the thermal performance of filled-type evacuated tube with double U-tubes was studied in both theory and experiment. The experimental results showed the feasibility and validity of this design. Finally, a comparative study between SUFET and DUFET was given at the same working conditions.

► Gives the structure of filled-type evacuated tube with double U-tubes.
► The heat transfer efficiency of double U-tubes is higher than single U-tubes.
► The heat transfer model and the analytic solution of dimensionless model are given.
► The theoretical analysis results have been verified by the experimental studies.