RANS modeling of flow structure and turbulent heat transfer in pulsed gas-droplet mist jet impingement

The turbulent flow structure and heat transfer of a pulsed gas-droplet impinging mist jet with low mass fraction of droplets (not more than 2%) are numerically carried out. A set of non-steady-state RANS equations for the two-phase flow is utilized. The dispersed phase is modeled by the Eulerian approach. Gas turbulence is computed with the Reynolds stress model for two-phase flow. The interaction between phases (two-way coupling) is considered by the addition of extra terms in equations for the mean and fluctuating motion. The effects of pulse frequencies, ratio of on time to total cycle time, distances between pipe outlet and impinging flat plate and Reynolds number on heat transfer are numerically studied. It is shown that both the increase (up to 45%) and the suppression (up to 25%) of heat transfer are characteristic of pulsed gas-droplet jet impingement, differently from the steady-state one. Reduced heat transfer in comparison with the steady-state impinging jet is typically in the low frequency range. The impingement heat transfer initially increases with distance from the pipe edge and target surface and the heat transfer decreases at distance from the pipe edge and flat plate.