Effect of wind speed and direction on convective heat losses from solar parabolic dish modified cavity receiver

Abstract

The performance of solar parabolic dish collector is significantly influenced by heat losses due to wind speed and direction. In this article, investigation of convective heat losses from the modified cavity receiver of solar parabolic dish collector is carried out numerically by considering the wind direction, wind speed, receiver configuration and receiver orientation. The effect of wind on the receiver in various directions (φ=−90° to 90°), wide range of operating wind speeds (V=0–10m/s), receiver inclinations (β=0–90°) and varying surface temperature on convective heat loss from the receiver are studied. Velocity vectors, velocity contours, temperature contours are presented to show the effect of wind on the heat loss from the modified cavity receiver. The forced convection is found to have similar trend of free convection heat loss at lower wind speed. However at higher wind speed, such a pattern is not observed. At lower wind speeds say less than critical wind speed (<2.5m/s), the forced convection heat loss is lower than natural convection heat loss for lower receiver inclinations and wind direction ranging between −90° and 0°. The forced convection heat loss is more significant than free convection heat loss above 5m/s for all φ and β values. For side-on winds, at higher wind speeds above 5m/s, irrespective of receiver inclination, the variation of forced convection heat loss is marginal (less than 5%). The maximum forced convection heat loss occurs for partly open receivers (receiver aperture diameter ratio, RAD=0.4 and 0.6) at φ=0 (side-on wind) for all receiver inclinations and at φ=30° for RAD=0.8 and 1. The receiver inclination has less effect on heat loss from the receiver for V>2.5m/s due to side-on wind. The highest convection heat loss occurs for fully open (RAD=1) receiver as compared to partly open (RAD<1) modified cavity receiver. Nusselt number correlation is proposed to calculate combined convection heat losses from the receiver as a function of receiver inclination, wind direction, wind velocity and aperture diameter ratio.