Optical characterization of a fixed focus Scheffler reflector for pressurized solar receiver testing

In this work, a method of focal region flux characterization of Scheffler fixed focus concentrator is presented. Being a fixed focus concentrator, Scheffler dish serves as an ideal focusing unit for on-Sun testing of scaled down high pressure receiver designs under actual boundary conditions. Flux characterization is performed numerically by tracing the ray trajectories from their inception till the focal region and experimentally using point-based heat flux sensors. A circular plate is mounted at the focal region with five water cooled heat flux sensors attached. Four of these sensors are positioned around a diameter of size corresponding to an existing cavity receiver aperture diameter and one sensor is located at the plate centre. These sensors help to obtain the point based flux measurements in the region. Since the dish is not parabolic, a non-Gaussian flux profile is obtained, and spatial averaging of the flux data is performed analytically to obtain an averaged heat flux value. This averaged flux density is then matched with the spatially resolved flux map average value obtained from the numerical analysis. Average thermal power intercepted on the target surface is also measured, which serves as a useful procedure for estimating the radiative power incident on the receiver aperture. Further, as a demonstration exercise of the present fixed focus dish characterization method, a receiver testing methodology with an existing hybrid cavity and tubular design using compressed air is presented.

Automated summary

This work presents a method for characterizing the focal region flux of a Scheffler fixed focus concentrator, utilizing both numerical and experimental approaches. The heat flux in the focal region is measured using heat flux sensors, and the results are compared with numerical analysis to obtain an averaged heat flux value.