INCREASE IN CONCENTRATION RATIO OF A ROOFTOP PARABOLIC TROUGH USING A SECONDARY FLAT REFLECTOR
Secondary stage optics are an option to increase parabolic trough concentrators to enhance thermal efficiency. Increases of concentration up to 80 % were stated as possible with a flat secondary reflector in past work. In this work, a prototype of secondary flat reflector receiver was built and experimentally tested at RMIT's facilities in Melbourne, and its performance was compared with a conventional absorber. The
facility includes a closed loop hydraulic circuit to recirculate a heat transfer fluid which temperature is
controlled by an external heater and a cooling system.
In the case of the roof-top collector studied in this work, the use of a secondary flat reflector increased its concentration by 19.7 % while decreasing the incoming radiation by 3.5 % due to the shadow formed. In this work it is demonstrated how a smaller absorber can be used while maintaining the acceptance angle of the collector and increasing the uniformity of the flux, thus reducing the thermal stress on the absorber.
Additionally, a better tolerance to misalignments and optical aberrations is achieved with the flat secondary reflector, as it was proven during the experiments. Finally, the experimental results were compared with a 2D CFD model.