[AnthonyBowers]

ANSYS FLUENT: COUNTER-FLOW BUBBLE COLUMN BY ADDITION OF SECONDARY PHASE SOURCE TERM
Hi all,

I need some advice or understanding in my simulation. The details on the selection of models can be seen at the end. First, I want to explain the intent of this simulation.

I am attempting to simulate a stripping column in which bubbles are injected at the bottom of the pipe Z = 200cm (from Z=0). The injection, computationally, occurs by adding a source term, continuity and z-momentum, for the second phase. This is accomplished by patching a few cells to contain the bubbles exclusively. The source terms values of continuity and momentum are M_dot_bubble/V_patched (units of kg/m3-s) and M_dot_bubble*Uz_bubble/V_patched (units of kg/m2-s), respectively. The method by which I implement the source terms couples momentum and mass flow rate through the volumetric flow rate being the area of the cell's face, which is patched to contain the secondary phase, multiplied into velocity (Uz_bubble).



Information of current simulations

I seem to only be able to stabilize the residual curves if the simulation is conducted under transient conditions. Moreover, I seem to have to run a Non-Iterative Time Advancement for a while so that the degassing boundary condition iterates. If I switch back to an iterative time advancement the residuals plateau (primarily the tritium in the tritium-helium phase residual).

Once the flow time reaches a certain time and I switch back to an iterative time advancement method the simulations converge on each time step.

Question to users of the CFD community?

I ideally want to simulate the counter-current bubble column under a steady state, but I believe this is not possible for the addition of source terms and the inherently transient environment I am trying to simulate, is this correct?

I am getting reversed flow during transient and steady-state simulations. Additionally, for the steady-state simulations (they don't run long due to divergence) turbulent viscosity ratio is above 1e+05 for "x" amount of cells.



General Model:

Eulerian-Eulerian (Number of Phases =2 )

Implicit Volume Fraction Formulation

Constant Bubble Diameter = .508 mm

Mass transfer included

Interfacial Area

ia-particle

Phase Interactions

Ishii-Zuber (Drag Force)

Tomiyama (Lift Force)

Antal-et-al (Wall Lubrication )

Troshko-Hassan (Turbulence Interaction )

Constant Virtual mass of 0.5 ( D_pipe <0.15m)

Turbulence Model:

RNG k-e

Scalable Wall Fn

Dispersed Turbulence Multiphase Model (Default Parameters)

Species Transport Model:

Included for two-phase Tritium-Fuelsalt (Liquid) ; Tritium-Helium (Gas)

Boundary Conditions:

Top-pipe = Degassing

Liquid-inlet (in pipe 1) = Velocity (V1) [0.279659 m/s]

*V2=A1/A2*V1 equates to a velocity, V2 , of [0.083898 m/s]**

Bottom-pipe= Outlet-pressure

Operating conditions :

Atmospheric Conditions

Source Terms conditions :

Uz_bubbles = 0.0071 m/s (7mm/s)

M_dot_bubbles= 3.752E-06 kg/s





r/CFD - ANSYS FLUENT: COUNTER-FLOW BUBBLE COLUMN BY ADDITION OF SECONDARY PHASE SOURCE TERM


r/CFD - ANSYS FLUENT: COUNTER-FLOW BUBBLE COLUMN BY ADDITION OF SECONDARY PHASE SOURCE TERM