The duct selective volumetric receiver: Potential for different selectivity strategies and stability issues

Recently much theoretical and experimental work has been conducted on volumetric receivers. However. not much attention has been paid to the possibilities of using different selectivity mechanisms to minimize radiation thermal losses, which an the main ones at high operating temperature. In this paper we present a duct volumetric receiver model and its results, which allow the evaluation of different selectivity strategies such as: conventional epsilon/alpha, geometry, frontal absorption and diffuse/specular reflection. We propose a new concept of selective volumetric receivers based on a solar-specular/infrared-diffuse radiative behaviour and evaluate its potential for efficiency improvement. In recent work on volumetric receivers based on simplified models, it has been concluded that the duct volumetric receiver is inherently unstable when working with high solar flux. We didn't find any unstable receiver behaviour even at very high solar fluxes, and conclude that a substantial potential fur efficiency improvement exists if selectivity mechanisms are properly combined. (C) 2000 Elsevier Science Ltd. All rights reserved.