Numerical investigation of natural convection of cavity receiver for low power application

ABSTRACT

A parabolic dish/cavity receiver configuration is one of the solar thermal systems used for light-heat conversion at high temperature. Such systems are subject to continuous changes in ambient conditions such as wind, solar insolation, and ambient temperature. These environmental variations, as well as changes in receiver inclination angle, affect the overall receiver performance leading to energy loss. Natural convection contributes a significant fraction of the energy loss and hence a thorough understanding of its characteristics is essential to effectively minimize it in order to improve the system efficiency. A three-dimensional numerical investigation was conducted on a modified cavity receiver to quantify the convective components of the total heat loss and to determine the effects of the operating temperature, receiver inclination angle, and aperture size on the heat loss. The effects of the variation of air properties were accounted for by using polynomial relationships for density, specific heat capacity at constant pressure, dynamic viscosity, and thermal conductivity in the simulation. The calculated natural convection heat loss showed a nonlinear dependence on the inclination angle and aperture size. Visualization results such as temperature contours were also presented to gain an insight into the effects of natural convection.

KEYWORDS:

• Cavity receiver
• natural convection
• Nusselt number
• parabolic dish

Acknowledgments

The authors acknowledge the support of the Department of Mechanical and Aeronautical Engineering, University of Pretoria and the National Research Foundation.