Homogeneous and Inhomogeneous Model for Flow and Heat Transfer in Porous Materials as High Temperature Solar Air Receivers

Kurzfassung

Results of calculations on flow and heat transfer in a porous Silicon Carbide honeycomb structure applied as a solar air receiver are presented. In this application porous materials are put in concentrated solar radiation. Flux densities of up to 1000 MW/m² are reached. Simultaneously, ambient air flows through the material to be heated up to temperatures of app. 800°C. This hot air is then used to feed the steam generator of a steam turbine to generate solar electricity (solar tower technology). The results are describing the resulting temperature field in the receiver. The main problem of the solar receiver is connected with the overheating and destruction of parts of the working surface. For the simulation material properties such as permeability, thermal conductivity and volumetric convective heat transfer are needed. These have been determined experimentally. The study has been carried out in 2 phases: 1. Simulation of the velocity distributions and temperature fields in a single channel of the honeycomb structure 2. Combined model with the honeycomb structure as a homogenized structure and the support structure taken with its real geometry. The obtained results of the numerical calculation for the mentioned cases are presented and discussed. The working temperatures, velocities and heat flux distributions which correspond to the used inlet parameters were found from the simulations. The results can be used as a base for the prediction of the working regimes. This approach can help to perform a safe operation and avoid overheating and damage of the receiver material.