Computing and results





 
 

    * Fluids
The fluid of the continuous phase is water. In the experiment at IMFT, the gas (discrete phase) is air. But FLUENT considers air only as reactant and not as an inert. So we have chosen nitrogen whose properties are really close to the properties of the air.

    * Inlet streams
Before injecting particles, we made Fluent run with the LES (Large Eddy Simulation) model to get an initial turbulent regime in the column. This calculation was done with an initial water velocity of 1 m/s. Then we injected 4 particles with a diameter of 0.5 mm and a velocity of 0.2 m/s. The injections were done from x = - 5 mm to x = 5 mm, as it is shown by the following contour:





     * Discrete Phase Model
We have chosen Coupled Discrete Phase Calculations, which means that every 10 iterations, FLUENT calculates a new Continuous Phase Flow Field from the results of the Discrete Phase Calculations. Besides, the model of tracking  is unsteady because of the use of the LES model.

 
 

2) Inlet at the bottom of the column
       The streams of water and nitrogen enter the column at the bottom. By the force balance, we can predict the behavior of the particles in the column. Indeed the velocity vector (U-Up) goes up and the rotational of the velocity (rot U) is oriented towards us. So rot U ^ U-Up goes to the walls.
Therefore we can guess that the particles will tend to go near the walls.

        The results are displayed in the following contour and are accorded to the theory.
 
 

           
 


 

 
3) Inlet at the top of the column
        Instead of changing the initial conditions to have the inlet streams coming down, the direction of the gravity was changed. In this case, the gravity goes up.

        With the same way as it was done for the previous case, the particles are likely to go to the middle of the column, which is what could observe on the following contour, presenting the particles presence rate.
 
 


 
 
 
 


 
 

4) Micro gravity case
        Without gravity, the gravity force is equal to zero, which means that the particles will not have a preferential place to go. The particles are likely to have a homogeneous presence rate in the column, which can be observed in the following contour.