Optical analysis and heat transfer modeling of a helically baffled cavity receiver under solar flux non-uniformity and windy conditions

Optical and thermal analyses of a parabolic dish collector (PDC) with spiral baffles embedded in the annular space of a cylindrical cavity receiver was studied in windy conditions under realistic non-uniform solar flux distribution. The asymmetric distribution of solar flux on the cavity walls was obtained by a nonsequential ray tracing and finite element (FEM) coupled simulation technique. The performance of the system was analyzed in windy conditions, for two different wind directions of inward and outward of the receiver aperture. The slope error of the dish surface has a significant effect on the distribution of reflected rays on the receiver walls. For higher slope errors, the dishes that are more concave and for smaller slope errors more flat dishes give higher thermal efficiency and have better performance. For a dish collector with a focal point of 1.5 m, when the slope error of the dish surface is only 10 mrad, about 13% of the total solar flux received by the dish is lost. When the slope error of the dish surface increases, the system thermal efficiency decreases, and this reduction is more severe for larger focal points and more flat dishes. The effect of wind direction on the system performance for inward aperture mode is more than that of outward mode, and by increasing the wind speed from 1 to 10 m/s, the system thermal efficiency is reduced up to 50%.