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Two-Phase Flow Simulation

Material handling is one of the important parts of industrial processes. Nowadays, pneumatic conveying systems are widely used to transfer the powder material through the processing devices. The associated gasparticle flow should be studied carefully in order to optimize the design and operation efficiency of such industrial systems. This requires a careful choice and implementation of boundary conditions in numerical simulation. Especially, within confined flows such as pneumatic conveying lines, the movement of the solid particles is strongly affected by the wall-friction and wall-roughness of the confining walls.

Different state-of-the-art theories for the solid wall shear stresses as well as the flux of fluctuation energy at the wall were evaluated. Comparison of different models for wall-boundary conditions in particle-wall collisions demonstrated that the boundary conditions of Schneiderbauer et al. (2012) are the most developed one. (the solid colored line in best agreement with symbols).

Fig. 1: Normalized (a) shear stress and (b) flux of fluctuation energy over normalized slip, for different values of friction coefficient. The coloured solid lines are according to Schneiderbauer model (2012), the dashed lines stand for revisited Johnson-Jackson model (2011), dotted lines are based on Jenkins’ limit (1992) and the symbols indicate results of computer simulation of Louge (1994).

A new model for wall-roughness was introduced in the frame of two-fluid model based kinetic theory and implemented in the standard solver of OpenFOAM-2.2.x. This model is based on the virtual wall model of Sommerfeld (1992) implementation in the boundary conditions of Schneiderbauer et. al. (Fig. 2).

A turbulent model, accounting for gas-particle turbulence interaction and particles’ wake effect, was studied and implemented in the standard solver of OpenFOAM-2.2.x.

Fig. 2: The virtual wall model and shadow effect

The granular Eulerian solver, delivered with OpenFOAM (twoPhaseEulerFoam), was improved considerably by including wall-friction and wallroughness effects in boundary conditions as well as gas-particle turbulent model. The new model is able to predict particles velocity in fairly good agreement with the experiment. (Fig. 3 and Fig. 4 ).

Fig. 3: Particle’s velocity diagram for different roughness

Fig. 4: Particle’s velocity diagram for different particle’s diameter (black lines: experiment)

(Afsaneh Soleimani, Supervision: Simon Schneiderbauer)