Experimental investigations on thermal performance characteristics of a solar cavity receiver

The experimentation is carried out to examine the influence of receiver aperture/opening ratio (receiver's aperture diameter to the maximum diameter ratio, d/D), glass cover thickness and inclination angle of cavity receiver on its collection efficiency for various flow rates of ordinary water as a working fluid. Experimental tests have been conducted at lower incident energy, i.e., at lower cavity wall temperatures (less than 200 degrees C). The aperture ratio examined encompasses values as 0.46, 0.6, 0.7, and 0.93 for water flowing at flows of 0.8, 0.65, 0.5, and 0.4 LPM that corresponds to Reynolds numbers (Re) of 1880, 1525, 1175, and 938, respectively. The glazing thicknesses of 6, 4, and 2 mm were provided at an aperture. A modified cavity-type receiver is made inclined at angles 90 degrees, 60 degrees, 45 degrees, and 30 degrees (with 90 degrees as down-facing receiver opening and 30 degrees as close to sideway-facing of receiver opening). The tests have been conducted for cavity surface temperatures ranging from 90 degrees to 180 degrees C. It is observed that an aperture ratio of 0.6 demonstrates maximum receiver performance for the values of Reynolds number studied, while the receiver performance exhibited reducing trend with reduction in receiver tilting angle from 90 degrees to 30 degrees.