Optimal configuration of oblique air curtains for heat loss suppression from vertical solar-thermal receiver surfaces

An external solar-thermal receiver is critical to the operation of a solar-thermal power plant because it converts concentrated solar radiation into useful heat. However, as these receivers are surrounded by relatively cold air, they suffer from significant convective heat loss that is detrimental to their thermal performance. Air curtains, in the form of air jets directed obliquely from the top of the receiver surface, have been shown to provide significant local reductions in receiver heat loss. This study presents, for the first time, a rigorous optimisation of air curtain operation to increase the mitigation of overall convective heat loss. Two-dimensional computational fluid dynamics simulations in OpenFOAM were used to optimise jet speed, angle, position, and thickness. Performance was measured based on global effectiveness, with a maximum of over 18% achieved for a jet with speed Uac = 5.5 m s-1, angle a = 45 degrees, thickness b = 30 mm, and gap G = 30 mm. Increasing jet thickness yielded the greatest gains in overall effectiveness. An equivalent air curtain effectiveness was defined, with the optimal case having an effectiveness of around 14%. The effect of jet outlet temperatures on effectiveness was also examined, with effectiveness gradually decreasing with increasing jet outlet temperature.