Abstract :
Concentrating solar thermal systems offer a promising method for large scale solar energy collection. Although concentrating collectors
are generally thought of as large-scale stand-alone systems, there is a huge opportunity to use novel concentrating solar thermal
systems for rooftop applications such as domestic hot water, industrial process heat and solar air conditioning for commercial, industrial
and institutional buildings. This paper describes the thermal performance of a new low-cost solar thermal micro-concentrating collector
(MCT), which uses linear Fresnel reflectors, and is designed to operate at temperatures up to 220 C. The modules of this collector system
are approximately 3 m long by 1 m wide and 0.3 m high. The objective of the study is to optimise the design to maximise the overall
thermal efficiency. The absorber is contained in a sealed enclosure to minimise convective losses. The main heat losses are due to natural
convection inside the enclosure and radiation heat transfer from the absorber tube. In this paper we present the results of a computational
and experimental investigation of radiation and convection heat transfer in order to understand the heat loss mechanisms. A computational
model for the prototype collector has been developed using ANSYS–CFX, a commercial computational fluid dynamics
software package. The numerical results are compared to experimental measurements of the heat loss from the absorber, and flow visualisation
within the cavity. This paper also presents new correlations for the Nusselt number as a function of Rayleigh number.
2012 Elsevier Ltd. All rights reserved
