The influence of wind speed, aperture ratio and tilt angle on the heat losses from a finely controlled heated cavity for a solar receiver

The first systematic experimental study of the combined influences of wind speed (0–9 m/s), aperture ratio (0.33–1) and tilt angle (15°–45°) on the mixed (free and forced) convective heat losses from a heated cavity, is presented. The cylindrical cavity is heated by 16 individually temperature-controlled heating elements in the open section of a wind tunnel. Heat flux distribution and total heat losses from the cavity were measured. A complex inter-dependence was found between aperture ratio, wind speed and convective heat losses. In particular, the total heat losses can vary by up to ∼75% by varying the aperture ratio from 0.33 to 0.75, for no wind condition, but the effect of aperture ratio is decreased as wind speed is increased. The tilt angle was found to have a small effect on the heat losses relative to the aperture ratio and wind speed. Nevertheless, the average minimum mixed heat loss for various wind speeds occurs for a tilt angle of between 15° and 30° for a downward tilting solar tower system.