Dynamic Performance Characteristics of a Porous Volumetric Solar Receiver Under Transient Flux Conditions

The solar flux incident on a volumetric receiver is inherently unsteady, resulting in high thermal stresses, fatigue failures and reduced component life. The knowledge of transient response characteristics of a porous volumetric receiver used in concentrating solar technologies is cardinal for its reliable and safe working. The dynamic controlling of the solar-to-thermal conversion process is also possible with the prior prediction of the output variations. The present study aims to investigate the transient behaviour of a porous volumetric receiver subjected to flux variations approximations occurring in real working scenarios with the help of a coupled transient model. The solid and fluid temperature fields, output fluid temperature and pressure drop variations are determined for transient flux conditions during start-up, shut-down, clear sky, and cloud passage. The results are used to analyze the thermal response of the receiver during various operating conditions. In addition, the effects of structural parameters of the porous absorber are also investigated. The results indicate that the receiver transient performance is comparatively more affected by the variation in porosity than in pore size for all conditions. Smaller porosities and pore sizes show slower thermal response to transient fluctuations and less temperature changes during cloud passage. Conversely, higher values help in the faster restoration of the steady-state output conditions without dynamic control.