A model of a solar cavity receiver with coiled tubes

Abstract

A model of a solar cavity receiver using helically coiled tubes as heat absorber is developed. The receiver geometry of the model mimics that of an experiment for a Cross Linear concentrating system, although the model has a potential for application to the same type of receivers. From solar flux distribution incident on the inner walls of the receiver, which is obtained from optical simulation, absorbed flux distribution is derived. Ignoring the convective heat loss from the cavity, temperature distribution of the heat transfer fluid and the coiled tubes in the steady state is calculated. The outlet temperature, the maximum temperature of the coiled tubes, the pressure drop, the heat losses, the receiver efficiency and the pumping power required for compressing the heat transfer fluid (air in this work) are assessed. The efficiency decreases when the receiver temperature is high or when the total incident energy is small for the receiver temperature. The conductive heat loss through insulators around the coiled tubes is negligible among the total incident energy for the present receiver configuration. The pumping power demand is sufficiently small compared with the expected electric power output. Finally, the absorptivity of the ceiling of the receiver could scarcely influence the outlet temperature as long as the difference of the absorptivity between visible and infrared light of the coiled tubes and the conductive heat loss are negligible.