COMPARISON BETWEEN SIMULATION AND MEASURE-MENT FOR A TUBE RECEIVER FOR AIR HEATING

Kurzfassung

Using highly concentrated solar radiation for power generation with gas turbine cycles is a promising way for cost effective solar power production. In this application pressurized air must be heated to 800°C or higher. The easiest way to do this is using directly irradiated me-tallic tubes. A tube receiver was developed and tested together with a small gas turbine. The receiver consists of 16 helically bent tubes connected in parallel, arranged in a cavity behind a secondary concentrator. The receiver was successfully tested at the PSA, Almería, at tempera-tures up to about 600°C. Typical for this application is the strongly inhomogeneous heat load on the absorber tubes with high solar flux on the irradiated side. A receiver model was developed to simulate the thermal performance based on a 3-dimensional finite element (FE) model. Ray-tracing was used to obtain the solar flux distribu-tion on the FE grid. The heat transfer coefficients at the inner tube side are calculated with local Nusselt numbers and temperature dependent material properties. Radiation exchange is modelled by the enclosure method. The tool was used to calculate stationary operating condi-tions, e.g. the temperature distribution in the receiver, for a specific solar test condition. Based on air mass flow and inlet temperature the outlet temperatures and receiver efficiency were determined. Results from the model are compared to experimental results from solar tests for verification. Also, further development, both in modelling and hardware, for metallic tube receivers with temperatures of 800°C and higher is described.