An experimental and computational study of a rooftop-mounted linear fresnel solar thermal concentrator

This research study describes the thermal performance of a new low-cost rooftop concentrating solar thermal collector (MCT), developed by Chromasun, which uses linear Fresnel reflectors, and is designed to operate at temperatures up to 200°C. The MCT collector provides thermal energy for domestic hot water, industrial process heat and solar air conditioning for commercial, industrial and institutional buildings. The objective of the study is to understand the heat transfer processes in order to help to maximise the overall thermal efficiency. In the MCT, the absorber is contained in a sealed enclosure to minimise convective losses. It was found that the main heat losses in the MCT are due to natural convection inside the enclosure and radiation heat transfer from the absorber tube. A computational model for the prototype collector has been developed using ANSYS-CFX .The numerical results are compared to experimental measurements of the heat loss from the absorber. In addition to measurements of overall heat loss, particle imaging velocimetry was used to visualize the flow field within the enclosure. Excellent qualitative and quantitative agreement of the flow field is achieved between the experiment and that predicted by the computational model. This research also presents new correlations for the Nusselt number as a function of Rayleigh number for MCT. Ray trace simulations using SolTRACE have been used to determine optical efficiency. Outdoor testing of the MCT collector was carried out to determine the heat loss coefficient and instantaneous efficiency of the MCT collector. Finally, the annual performance of this collector was evaluated using TRNSYS for domestic hot water and solar cooling applications under Australian conditions. From the results obtained in this study, it is found that the MCT collector has relatively small heat loss compared to flat plate and evacuated tube collectors at temperatures above 150oC and the efficiency can be increased by improving the design of current MCT. Suggestions are made such design in improvement