  We present results of interface-resolved simulations of heat transfer in
suspensions of finite-size neutrally-buoyant spherical particles for solid
volume fractions up to 35% and bulk Reynolds numbers from 500 to 5600. An
Immersed Boundary-Volume of Fluid method is used to solve the energy equation
in the fluid and solid phase. We relate the heat transfer to the regimes of
particle motion previously identified, i.e. a viscous regime at low volume
fractions and low Reynolds number, particle-laden turbulence at high Reynolds
and moderate volume fraction and particulate regime at high volume fractions.
We show that in the viscous dominated regime, the heat transfer is mainly due
to thermal diffusion with enhancement due to the particle-induced fluctuations.
In the turbulent-like regime, we observe the largest enhancement of the global
heat transfer, dominated by the turbulent heat flux. In the particulate
shear-thickening regime, however, the heat transfer enhancement decreases as
mixing is quenched by the particle migration towards the channel core. As a
result, a compact loosely-packed core region forms and the contribution of
thermal diffusion to the total heat transfer becomes significant once again.
The global heat transfer becomes, in these flows at volume fractions larger
than 25%, lower than in single-phase turbulence.
