Open Volumetric Air Receiver: Current Status, Challenges and Innovative Solutions

This paper deals with some of the practical and fundamentally relevant challenges that remain in the operation of open volumetric air receivers at high temperatures. These are the achievement of high thermal conversion efficiencies (over 90%), the minimization of thermal losses through volumetric effects, the generation of stable flow conditions in operation, and the analysis of how dust deposition affects all previous aspects. Experiments conducted with various square-channel monolithic honeycombs demonstrate stable flow conditions at air outlet temperatures in excess of 1000 K. The effects of absorber cross-sectional geometry on thermal conversion efficiencies are discussed, and it is generally concluded that a larger effect of the forced convection heat transfer mechanism with respect to the radiative mode is necessary to achieve the high efficiencies required for the widespread deployment of these components. Subsequently, numerical aerothermal simulations are presented, which both provide further insights into the aerodynamic stability of the flow field, and serve as the basis for the analysis of the detrimental effect of dust deposition on the absorber flow channels. Numerical results for dust-affected absorbers reveal a substantial temperature rise, of around 120 K, in the typical operating conditions of incident power per unit mass flow rate. Hence, the sustained operation of such receivers needs special provisions to address this aspect, which are discussed and expected to be helpful in the design of advanced open volumetric air receivers.