3D numerical simulation of upflow bubbling fluidized bed in opaque tube under high flux solar heating

Abstract

Current solar Heat Transfer Fluids (HTF) only work below 600°C. We proposed to use air-fluidized Dense Particle Suspensions (DPS), also called Upflow Bubbling Fluidized Bed (UBFB), in tubes as a new HTF and storage medium in the frame of the so-called CSP2 FP7 European project. UBFB can operate up to the solid sintering temperature (1400 °C for SiC particles), thus improving the plant efficiency and cost of produced kWh. The DPS capacity to extract heat from a tube absorber exposed to concentrated solar radiation was demonstrated and the first values of the tube wall-to-DPS heat transfer coefficient were measured. A stable outlet temperature of 750 °C was reached with a metallic tube, and a particle reflux in the near tube wall region was evidenced. In this paper, the UBFB behavior is studied using the multiphase flow code NEPTUNE_CFD. Hydrodynamics of SiC Geldart A-type particles and heat transfer imposed by a thermal flux at the wall are coupled in 3D numerical simulations. The convective/diffusive heat transfer between the gas and dispersed phase, and the inter-particle radiative transfer (Rosseland approximation) are accounted for. Simulations and experiments are compared. The temperature influence on the DPS flow is analyzed.