A glass pipe and an absorbing black fluid were combined with a parabolic solar reflector into a solar collector. Thermal efficiencies for three different types of receivers with a parabolic trough solar reflector were compared: (1) single glass pipe with black fluid, (2) concentric annulus glass pipes with black fluid, and (3) black-painted copper tubing. The single glass pipe with a black working fluid performed best experimentally. The single glass pipe with a black fluid was better than the black painted copper tube by an average value of 5 percent absolute system efficiency or 14 percent on a total energy absorbed basis. Mass flow rate and wind speed were analytically found to be significant. The black fluid solar collector was found to have an optimum system efficiency for a blackening agent concentration of 15 ml per gallon of water. A numerical lumped heat capacity model was used to compare with the experimental data.

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