Modeling of the droplets turbulent dispersion and deposition in a horizontal channel

Droplets dispersion and deposition in turbulent duct flows are important processes, occurring in numerous environmental and industrial applications. This work is devoted to the study of gas-droplets flows and, more particularly, the objective is to improve the droplets deposition modeling in horizontal flows. Droplets are supposed to be smaller than the Kolmogorov scale, with a density large compared to the density of the gas phase. Under these assumptions, the motion of a droplet is considered to be governed by the drag force, the buoyancy force, and the gravity. Dilute incompressible and isothermal gas-droplets flows are studied, so inter-particle collisions are neglected but two-way coupling is retained, which means that modulation of turbulence by the particles is accounted for. In horizontal flow, droplets reach the wall under the actions of the gravitational settling and the turbulent diffusion. Two approaches will be used in developing this deposition physics with a first study at the 3D local scale and a second one at the 1D scale, realized for an industrial need. For each case, a model is developed for the mean deposition velocity of the droplets, with is implemented in a numerical simulation tool and then validated by comparison to experimental data. The local deposition model is established under the assumptions that the liquid film is extremely thin and perfectly absorbing and is implemented in the Neptune-CFD code. The experience carried out by Namie and Ueda, which consist in small droplets deposition from a turbulent dispersed flow in a horizontal rectangular duct, is simulated. An analysis of the interphase transfer terms in the kinetic energy equations shows the interactions between the dispersed phase and the continuous one and the impact of these phenomena on the turbulence of the gas phase is pointed out. The 1D deposition model is developed for the CATHARE-3 code and experimental data from the REGARD facility of the CEA Grenoble are used for validation. (author)