An exergy analysis of tubular solar-thermal receivers with different working fluids

Tubular solar thermal receivers suitable for central towers are modelled using energy and exergy analysis, in a way that allows individual inspection of the the irreversibilities associated with the various receiver heat transfer processes occurring. The model was used to compare the behaviour of four working fluids: molten salt (NaNO3/KNO3), liquid sodium metal, supercritical carbon dioxide, and ideal air. In the working fluid temperature range 300550 °C, the model showed sodium and molten salt to be the best performers. At elevated temperature ranges, sodium and carbon dioxide become the preferred candidates. The biggest differences in exergy terms between the alternative fluids are in exergy loss by thermal emission, and in the exergy destruction associated with internal convection losses and wall conduction.