Convective heat transfer in suspensions of prolate ellipsoids

Abstract

Particle Resolved Simulations (PRS) using the Immersed Boundary Method (IBM) are performed for flow through suspensions of ellipsoids with aspect ratios of 2.5, 5, and 10 for solid volume fractions from 0.1 to 0.3 in the Reynolds number range from 10 to 200. The mean Nusselt number increases as Re1/2but shows only a weak dependence on the aspect ratio while increasing between 10-15% with an increase in solid fraction from 0.1 to 0.3. Two common practices of calculating Nusselt number in past literature are reconciled. It is shown that the suspension mean Nusselt number based on individual particles, by definition is always greater than or at the least equal to the Nusselt number based on the internal developing flow analogy. It is established that for Re≤50, the suspension heat transfer coefficient is very sensitive to the spatial distribution of particles or local-to-particle solid fractions. For the same mean solid fraction, suspensions dominated by particle clusters or high local solid fractions can exhibit Nusselt numbers which are lower than the minimum Nusselt number imposed by pure conduction on a single particle in isolation. This results from the dominant effect of thermal wakes at low Reynolds numbers. As the Reynolds number increases to 100 and beyond, the effect of particle clusters on heat transfer becomes less consequential. Unlike heat transfer, particle clustering has a less significant effect on mean fluid forces such as drag.