The Effect of Particle Collisions on Heat Transfer in a Thermally Developing Mixing Layer in a Dilute Turbulent Particle-Laden Flow

We present a study on the influence of inter-particle collisions on the turbulent heat flux within a temporally developing thermal mixing layer between two homothermal regions in a homogeneous and isotropic turbulent velocity field. We carry out two-way thermally coupled Eulerian-Lagrangian Direct Numerical Simulations across a wide range of particle Stokes numbers, ranging from 0.2 to 3, at a Taylor microscale Reynolds number from 56 up to 124, while maintaining a thermal to kinetic relaxation times ratio of 4.43. The particle concentration in the dilute regime is set at 4x10^-4 volume fraction. The initial temperature difference between the two regions correlates temperature and velocity fluctuations in the mixing layer. However, scattering due to particle collisions tends to reduce these correlations. We quantitatively evaluate the overall impact on the average heat transfer and single point statistics of fluids and particles by comparing them with a collisionless regime. Remarkably, even at the highest simulated Stokes numbers, the effect remains minor. In addition, we present statistical data on the temperature difference between colliding particles under various flow conditions and collision rates. In particular, our results indicate that collisions do not significantly hinder the ability of particles to modulate fluid temperature fluctuations.