Numerical simulation of convective heat transfer between air flow and ceramic foams to optimise volumetric solar air receiver performances

Porous ceramic foams are used to achieve high performance in solar heat recovery systems. Understanding the convective heat transfer between the air flow and the ceramic foam is of great importance when optimising the volumetric air receiver. In this work, the convective heat transfer was numerically studied. The present approach was designed to compute the local convective heat transfer coefficient between the air flow and a porous ceramic foam. For that purpose, the energy balance and the flow inside the porous ceramic foam were solved. In addition, a detailed geometry of the porous ceramic foam was considered. The ceramic foams were represented by idealised packed tetrakaidecahedron structures. The numerical simulations were based on the three dimensional Reynolds-averaged Navier-Stokes (RANS) equations. A sensitivity study on the heat transfer coefficient was conducted with the porosity, velocity and mean cell size as parameters. Based on the numerical simulation results, a correlation for the volumetric local convective heat transfer coefficient between air and ceramic foams was developed. The resulting correlation covers a wide range of porosities, velocities, cell sizes and temperatures. The correlation results were compared with experimental data from the literature, and the comparison shows good agreement. The correlation is intended to be used in the design of volumetric solar air receivers.