Particle Scale Investigation of Influencing Factors on Heat Transfer in Nonspherical Particle-Fluid System

Heat transfer characteristics of random suspensions of 0.25 aspect ratio (AR) cylinders are investigated for Reynolds numbers (Re) between 10 and 300 and solid fraction (phi) ranging from 0.1 to 0.3 using particle resolved simulations. The effect of particle inclination with respect to flow and particle clustering on heat transfer is investigated. The Nusselt number decreases with an increase in inclination angle and the dependence becomes stronger as phi and Re increase. On the other hand, while prolate ellipsoid suspensions of AR 2.5 follow the same trend, the Nusselt number increases with inclination angle as AR increases to 5 and 10 and as phi increases. Local particle clustering nominally decreases the Nusselt number because of the dominance of thermal wakes. At low phi, this effect is felt only at low Re, but as phi increases, the effect spreads to higher Re. Similar but weaker trends are also found in suspensions of prolate ellipsoids of AR 2.5, 5, and 10. High AR, low Re prolate ellipsoids exhibit the greatest dependence of Nusselt number on local solid fraction. Implementation of two independent definitions of reference length, i.e., volume equivalent sphere diameter d(eq) for ellipsoids and diameter d(p) of the cylindrical particle in the correlation of Tavassoli et al. (2015, "Direct Numerical Simulation of Fluid-Particle Heat Transfer in Fixed Random Arrays of Non-Spherical Particles," Chem. Eng. Sci., 129, pp. 42-48) provides good estimates of the respective suspension mean Nusselt numbers.