Effects of Preferential Concentration on Heat Transfer in Particle-Based Solar Receivers

Abstract

The working principle of particle-based solar receivers is to utilize the absorptivity of a dispersed particle phase in an otherwise optically transparent carrier fluid. In comparison to their traditional counterparts, which use a solid surface for radiation absorption, particle-based receivers offer a number of opportunities for improved efficiency and heat transfer uniformity. The physical phenomena at the core of such receivers involve coupling between particle transport, fluid turbulence, and radiative heat transfer. Previous analyses of particle-based solar receivers ignored delicate aspects associated with this three-way coupling. Namely, these investigations considered the flow fields only in the mean sense and ignored turbulent fluctuations and the consequent particle preferential concentration. In the present work, we have performed three-dimensional direct numerical simulations of turbulent flows coupled with radiative heating and particle transport over a range of particle Stokes numbers. Our study demonstrates that the particle preferential concentration has strong implications on the heat transfer statistics. We demonstrate that “for a typical setting” the preferential concentration of particles reduces the effective heat transfer between particles and the gas by as much as 25%. Therefore, we conclude that a regime with Stokes number of order unity is the least preferred for heat transfer to the carrier fluid. We also provide a 1D model to capture the effect of particle spatial distribution in heat transfer.

A correction scheme for two-way coupled point-particle simulations on anisotropic grids

“…This limited exposure of the computational cell to F (i) is not captured by the time-dependent term in Eq. (5) and must be accounted for separately. To show the need for this additional correction, consider a particle with high velocity that spends an infinitesimal time in each computational cell.…”

Accurate calculation of Stokes drag for point–particle tracking in two-way coupled flows

“…Other primary questions in particle-laden flows concern the nature of particle dispersion and concentration where the distribution of particles may influence other physical processes. For example, in particle-based solar collectors, non-uniform particle concentration can impact the overall system efficiency [9]. Another example concerns fluidized bed reactors where particles act as catalyzing agents lowering the activation energy necessary for reactants to reach activated complex.…”

Bi-fidelity approximation for uncertainty quantification and sensitivity analysis of irradiated particle-laden turbulence.

“…. , r, are identified from the permutation matrix P in (15) and indicate input samples ξ (i k ) corresponding to the LF realizations u (i k ) L (see Fig. 5, dark orange boxes, top row).…”

“…. , r, identified by the permutation matrix P in (15), are exactly the same as the corresponding columns of U L . Stated differently, an r × r sub-matrix of C L is a permutation of the identity matrix.…”

“…However, in regimes relevant to particle-based solar receivers, the background turbulence dominates over the buoyancy effects as the Froude number of the systems are typically very large. This problem was studied by Pouransari and Mani [15] by considering a convective flow of gas and particles subject to radiation and in the absence of buoyancy effects. In their study, it is shown how different particle concentration patterns, resulting from different Stokes numbers, have a strong influence on the heat transfer rates between particles and gas.…”