A numerical study on optical and thermodynamic characteristics of a spherical cavity receiver

Abstract

In this paper, a 3D model is created to investigate optical and thermodynamic performance of the spherical cavity receiver. Spiral copper pipes placed in the cavity absorb radiation energy and achieve solar-thermal conversion. The reflected rays loss and optical efficiency is calculated by using Monte-Carlo ray-tracing method. The optical efficiency of spherical cavity receiver is 88.9%, slightly higher than other shape cavity receivers. When the spherical cavity receiver moves away from the focal plane either in positive location or negative location, the radiation flux distribution is more uniform. The reflected rays loss decreases with D/d increasing from 1.0 to 2.5, while optical efficiency maintains approximately 86.3%. The radiation flux resulted from Monte-Carlo method is used as boundary condition of the CFD model. On this basis, the temperature distribution and heat loss of the spherical cavity receiver are investigated. Convection heat loss of the receiver with different D/d is estimated by varying the inclination from 0° to 90°. For a certain D/d, the maximum convection heat loss is θ=0° and it decreases monotonously with inclination up to 90°. The temperature distribution with different D/d at θ=0° is investigated. The temperature differences between the heat transfer pipe and heat transfer fluid decreases with D/d increasing. An increase in the inlet temperature of heat transfer fluid leads to the radiation loss remaining unchanged, but convection loss and total heat loss increasing slightly. Three kinds of heat losses decrease as inlet velocity of heat transfer fluid increases, including total heat loss, radiation loss and convection loss. Based on the simulation results, solar thermal conversion efficiency of a concentrator-receiver system varies from 81.9% to 84.4%, and optimal aperture size is about 1.0–1.5.