Experimental Investigation on the Vector Characteristics of Concentrated Solar Radiation Flux Map

It is difficult to measure the concentrated solar radiation flux (CSRF) inside a cavity receiver directly due to the complex geometry of cavity receivers. At present, most reports measure the CSRF at the aperture plane (generally coinciding with the focal plane of solar concentrators) of the cavity receiver instead of at the absorber wall, which would result in serious aberration because of the obvious difference in configuration between the aperture plane and the absorber wall. To obtain the CSRF at the absorber wall with complex geometry, the vector characteristics (consisting of both directional distributions and spatial distributions) of the CSRF at the focal plane were measured using developed double water-cooled Lambertian targets together with a CCD (charge-coupled device) camera. Then the CSRF images at the absorber wall of a hemisphere cavity receiver were carried out by applying MCRTM (Monte Carlo ray-tracing method) in combination with the measured vector results of the CSRF at the aperture plane. Results show that the directional distributions of the CSRF at the aperture plane are rather nonhomogeneous along the zenith angle and the circumferential angle. The directional distribution performance of the CSRF at the focal plane plays an equally important role in the CSRF images of the cavity receivers. In addition, the relative error of the peak CSRF value of the cavity receiver between the uniform and the measured directional distribution cases is up to 16%. The conclusions provide an important reference for the development of the CSRF measurement.