ESEL Paper Review_20130509

By Hong Guo

Mail: hongguo@gist.ac.kr

Phone: (+82) (0)10 82276568

1, Title and Author

Title: CFD methodology for sedimentation tanks: The effect of secondary phase on fluid phase using DPM coupled calculation

Journal: Applied Mathematical Modelling

Authors:

Roza Tarpagkou* Asterios Pantokratoras

Laboratory of Hydraulics and Hydraulic Structures, Democritus university of Thrace, Department of Civil Engineering, V. Sofia 12, GR-67 100 Xanthi, Greece

2. Summary of Paper

? In this paper, Computational Fluid Dynamics (CFD) methods are employed in order to simulate the 3D hydrodynamics and flow behavior in a sedimentation tank. The momentum exchange between the primary and the secondary phase is taken in to account, using a Lagrangian method (discrete phase model) with two way couple calculations.

3. Results

? The flow pattern changes dramatically when the particle size and the volume fraction of the suspended particles increased.

? When the water depth increases (Run B) {Fig. 10a, single-phase flow}, no vortices have been appeared. In the two-phase flow (d = 50 lm) two vortices appeared near the entrance. As the particle size increases (d = 500 lm) the previous two vortices increase and reach the center of the tank, and in addition a new small vortex appears near the outlet corner

? In Fig. 7 (case 1, two-phase flow d = 50 lm) the particle diameter is small, the corresponding Stokes number is 0.0091 << 1, the particles follow the flow and two almost symmetrical vortices appear. In case 2 (d = 500 lm) the particles diameter is now higher, the Stokes number is also higher (1.2 > 1) and the flow tends to lose symmetry. Finally in case 3 (d = 500 lm, volume fraction 10%) the particles diameter is the same as in case 2, but the volume fraction is much higher and this means that the particles influence is much higher and the symmetry is lost.

? Run A:

? As it can be seen particles with small diameters (d = 50 lm) are still on suspension and follow the flow passively, whereas particles with bigger diameters (d = 500 lm) deposit at the bottom after a short distance from the tank inlet(approximately 1 m).

? the larger the Stokes number for any dispersed phase, the greater is the tendency to behave independent of the carrier phase.

? RunB:

? The large concentration of heavy particles near the tank inlet

influences the path of the fluid phase and as a consequence the fluid

velocity increases

? The large concentration of heavy particles near the tank inlet

influences the path of the fluid phase and as a consequence the fluid

velocity increases

? The turbulent intensity attenuates when particles are introduced

in the flow field

? As the particle diameter increases, the attenuation of the

turbulent intensity tends to be greater.

? Fluid turbulence attenuates by the addition of particles and the degree

of attenuation increases with particle Stokes number. Small particles

do not affect turbulence, up to a certain mass loading; the most

massive particles have a greater effect and reduce the turbulence

intensity and this is also observed in the present paper (Fig 15).

4. Contribution:

Unlike other research, in this paper, the author study about influence among the

primary and secondary phase, in the present work numerical simulation are

performed for several particle sizes and volume fractions.

5: Contact: rozatarpagou@hotmail.com