Multiphase Flow - Science topic

Hi Sina Mirzaei ,

You can use transport of dilute species (TDS) module in COMSOL, when your fluid mixture is homogeneous in nature in order to have an effective mixing index, while in the case of heterogeneous mix it's good to use any of multiphase model/module in COMSOL (Laminar flow or Creeping flow based on the Reynold's number).

When it comes to the physics to be added for numerical computation, I prefer Phase field over Level Set as the diffusion part dominates in the case of Level Set and few a times based on case to case the results varies a lot when tried with different cases. Phase Field is a better option.

If you are using the explicit VOF model, you should choose your time step in a way that Courant number is less than 1.

In my simulations I used 1e-8 s, and I did not face any problem.

In the context of multiphase flows, the terms sharp interface model and diffused interface model refer to how the interface between two immiscible phases (e.g., liquid and gas) is represented.

Famous Methods in this Category:

Famous Methods in this Category:

The choice depends on application requirements:

Practical Preference:

Choosing the best model also depends on the available computational resources and the physics of the problem being simulated.

In the context of multiphase flow modeling, interface tracking and interface capturing methods are two distinct approaches to handling the evolution of interfaces between different phases (e.g., liquid-liquid, liquid-gas). Here's an explanation of each and where methods like the phase-field model and level-set method fit in:

Hello Mohammed Mansour Meky ,

The negative cell volume in ANSYS Fluent is related to dynamic mesh whether the flow is single phase or multiphase. You have to double-check the dynamic mesh model and settings and try to reduce the time step size. If there is a boundary layer adjacent to the moving wall (object) you have to check the option that excludes the boundary layer from remeshing.

Kind regards,

Ashkan

Hi, I wonder why you do not define the coarsing criterion in Fig. 4?

Modeling and simulation of the electrospinning process

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Dear Sarabjeet Kaur ，For more details please visit the conference website:

Thanks Suresh Ahuja

Hope these files are helpful to you.

Hi,

I guess you could chose one of the two fluid inter solvers. They are based on Volume of Fluid and easy to apply. But you should really take care about cell resolution for good results of course. To take account for natural convection just apply boussinesq or polynomial thermophysicalProps. For polynomials you need to fit function coefficients according to your const. Pressure and temperature range. Unfortunately it can happen, that property calculation is not that precise.

On the other hand it is possible to chose euler solvers instead of inter solvers of course. But in my opinion you need really deep knowledge about all those empirical coefficients.

Hope that helps.

Regards David

This may help you:

For mixtures of differing composition you can follow the procedure near the end of this:

For elements of "similar" Z, the attenuation coeff is similar, so the values will scale roughly with density so it seems that telling one salinity from another might be quite difficult.

Hi

It may say that you do the simulation with your own code, or with Fluent or CFX?

Yes, you have to define a multi-phase model, e.g., VOF or Euler-Euler.

Dear Salman,

This is very much appreciated.

Many thanks.

The difference is in the morphology of the flow:

bubbly flow - gaseous and liquid phase are NOT mixed on a molecular level, but the gaseous phase forms bubbles as macroscopic inclusions into a continuous liquid phase. E.g. Air bubbles of 2mm size in water.

flow of a mixture - the gaseous and liquid phase are mixed on a molecular level. No macroscopic inclusions of either of the two phases can be observed. E.g. dissolved CO2 in water.

Bubble nucleation - the process of forming first macroscopic bubbles from a continuously dissolved gaseous phase. E.g. you open a pressurized bottle of mineral water with gas. In the first moment, there is only clear water visible. But after some miliseconds first bubbles appear and this process (e.g. if you shake the bottle) can become pretty "violent". This is called nucleation and bubble growth by depressurization. Other mechanisms of nucleation are possible.

Regards,

Dr. Th. Frank.

If the size t is less than 8-12 distances to the bottom surface, the drag force will be determined, among other things, by the added masses of the liquid reflected from the bottom surface. If this is not important, then in the model you need to specify a distance of more than 12.

The number of wall layers is enough 5.

From above on a free surface, the wind has a speed and direction?

Yes, and it does not show good precision.

Ziyi Wu, Thank you, I know what you said. But my question is about how to simulate dynamic contact angle instead of static contact angle.

THE ENHANCEMENT OF HEAT TRANSFER BY TWO PHASE OR MULTIPLE IS MORE THAN SINGLE PHASE

Without more details, I only may speak about the phenomenological aspects that may be verified. (i) When one applies User Defined Function (UDF) this should not contradict the mass conservation of the dispersed phase (ii) the initial diameter would depend on many factors: surface tension, turbulence, injection device...References on dispersed turbulent flows are available on the following research projects: https://www.researchgate.net/project/Single-Phase-and-Multiphase-Turbulent-Flows-SMTF-in-Nature-and-Engineering-Applications https://www.researchgate.net/project/Interfacial-Transfer-Closure-for-Eulerian-Eulerian-Two-Fluid-Modeling https://www.researchgate.net/project/Turbulence-Closure-for-Eulerian-Eulerian-Two-Fluid-Models

Hi Armin Hajighasem Kashani

I have three suggestions for you:

1- Check the below link:

As this topic is popular in our country, I am sure you can find different Ph.D. and M.Sc. theses in Iranian universities.

2- Ask your question in CFD online forums:

3- If you could not find your answer about bridge piers, search for other hydraulic structures (for example, spur dikes) and use their information.

Good luck,

Maryam

More information is needed to answer this question. Basically, even in single-phase flows, the normal gradient of the pressure is almost zero only in parallel or almost-parallel vertical laminar flows. The average pressure is "permeated" by turbulence even in 2D parallel flows. When it comes to two-phase flows and within the framework of RANS modeling using Eulerian-Eulerian two-fluid models closure is needed in order to express the pressure in one phase as a function of that of the second phase. The simplest considers that the two pressures are equal in the absence of surface tension. See references within the research projects: https://www.researchgate.net/project/Single-Phase-and-Multiphase-Turbulent-Flows-SMTF-in-Nature-and-Engineering-Applications https://www.researchgate.net/project/Interfacial-Transfer-Closure-for-Eulerian-Eulerian-Two-Fluid-Modeling https://www.researchgate.net/project/Turbulence-Closure-for-Eulerian-Eulerian-Two-Fluid-Models

Noted professor Stam Nicolis , I will keep that in mind. Thanks for your time and help!

Yes you can, First you have to specify the type of material in the fluid part and then select the flow type again with the Multiphase (Volume of Fluid)

We have tried AMR for multiphase flow with phase-field in the past. Usually, refinement is dependent on the phase-field parameter and you can control the number of refinements in a given time scale of simulations. You can refer to the following articles for more information on the implementation of AMR in the Comsol phase field.

1) Yue, P., Zhou, C., Feng, J. J., Ollivier-Gooch, C. F. and Hu, H. H., "Phase-field simulations of interfacial dynamics in viscoelastic fluids using finite elements with adaptive meshing," Journal of Computational Physics, 2006, v. 219, n. 1, pp. 47-67.

2) Zhou, C., Yue, P., Feng, J. J., Ollivier-Gooch, C. F. and Hu, H. H., "3D phase-field simulations of interfacial dynamics in Newtonian and viscoelastic fluids," Journal of Computational Physics, 2010, v. 229, n. 2, pp. 498-511.

3) Yue, P., Feng, J. J., Liu, C. and Shen, J., "A diffuse-interface method for simulating two-phase flows of complex fluids," Journal of Fluid Mechanics, 2004, v. 515, pp. 293-317.

4) Yue, P., Zhou, C. and Feng, J. J., "Spontaneous shrinkage of drops and mass conservation in phase-field simulations," Journal of Computational Physics, 2007, v. 223, n. 1, pp. 1-9.

5) Yue, P., Zhou, C. and Feng, J. J., "Sharp-interface limit of the Cahn–Hilliard model for moving contact lines," Journal of Fluid Mechanics, 2010, v. 645, pp. 279-294.

6) https://www.emerald.com/insight/content/doi/10.1108/HFF-01-2020-0001/full/html

I doubt you gonna get reliable results studying droplet deformation in liquid-liquid dispersed flow by means of simulations with commercial codes. The phenomena involved is too complex. Droplets break and coalesce under simultaneous population and wall effects, also depending on the interfacial tension between phases as well as on the local pressure (assuming constant temperature). For a given pair of fluids, the relative velocity between droplets and continuous phase depends on size and shape of droplets. The relative velocity also induces pairs of vortices rotating in opposite directions inside droplets (conservation of angular momentum). These may cooperate for the droplet breakage.

Even though it may be well outside your research scope, experiments are required if you want reliable data.

I guess a little craft hability is required. Build a mechanical device where small parallel glass plates (same width and thickness as those used in microscopy) are pulled along in opposite directions, similar to your Couette rheometer. Clearly the experiment will be 2D. The small gap between plates would be filled with the liquid-liquid dispersion. Some sort of rail system will be required for guiding the sliding plates. The plates could be pulled with the help of an electrical DC electrical motor with variable rpm and a system of pulleys. Make photograph/film from above. Ah, include my name on the Patent application (laugh).

Resources and academic tools on turbulent single-phase and multiphase flows in industrial facilities and in natural environments

SINGLE PHASE AND MULTIPHASE TURBULENT FLOWS (SMTF) IN NATURE AND ENGINEERING APPLICATIONS | Jamel Chahed | 3 publications | Research Project (researchgate.net)

I refer you to two discussions which bear on the two problems of Eulerian two-fluid models closures: Turbulence and momentum interfacial transfer:

(6) Turbulence Closure for Two-Fluid RANS Modeling (researchgate.net)

(6) Interfacial Transfer Closure for Two-Fluid RANS Modeling (researchgate.net)

I refer you to two discussions which bear on the two problems of Eulerian two-fluid models closures: Turbulence and momentum interfacial transfer:

(6) Turbulence Closure for Two-Fluid RANS Modeling (researchgate.net)

(6) Interfacial Transfer Closure for Two-Fluid RANS Modeling (researchgate.net)

Look forward to exchanges on these topics

Almost a year later, but anyways:

I wrote together with someone else an article that probably suits your needs:

Preprint is on researchgate.

Giuseppe Altieri thanks very much for your answer

In my limited understanding, i utilized a steady state model to calculate the permeability of certain structures (resembling metallic foam). The simple way that I used to adopt was to apply a known pressure difference at the inlet and outlet, and obtain volume flow rate through post processing. This would simply give you the permeability. Ofcourse, the higher the volume flow rate, the more permeable the porous medium shall be. However, under transient conditions and using variable viscosity, the problem gets much more complicated. Nonetheless, steady state isothermal condition can be a good starting point and may give you a reasonably accurate ball park value.

Go for Ansys CFX or COMSOL.

Dear Shilpa,

the source of the problem can be varied from one model to another. However, overall, coupling process of solute transport with the phase flow behavior can cause such issue. The associated factors, however, can be changed from traditional factors (i.e. grid size and time step) to non-conventional factors ( e.g. Effective concentration and the shape of rel perms). Also the solution type of the numerical scheme can be another source of such issue (e.g. fully coupled schems causes convergence issue more than decoupled scheme). See SPE-192074-MS and

Al-Ibadi, H., Stephen, K., & Mackay, E. (2020). Pulse Generation and Propagation in the Numerical Solution of Low Salinity Water Flooding. Journal of Petroleum Science and Engineering, 108151.

Hasan

Dear Ziqiang Cui,

Within the classical framework, one can minimize the error between measurements and calculated values, in function of the multiphase electrical properties. There are different optimization algorithms which deal with non-linearity, with the most popular being Gauss-Newton, Simulated Annealing and Kalman filtering. Of these three, Simulated Annealing requires a large processing time and Kalman filtering may be suitable for real time (depending on other aspects).

Right click 'Setup' and press reset. This will force you to start everything after the updated mesh from scratch. Don't bother looking for the error.

Well did you got the answer ?

Don't know with fluent but with Hypermesh mesh refinement can be achieved.

These videos will help to learn 2D and 3D mesh transition techniques.

It is better to approach Eularian-Lagrangian Model in this regard. Most of the comparative research articles shows better fit with this model than any other models.

Leonardo Henao; Use the HRIC Scheme and refine the mesh in the z-direction (the wave elevation direction).

I think that the "species transport model" is the most suitable for your simulations, it's more suitable for the mixing of miscible fluids but you must be careful because you need to disable the reaction process.

For the colleagues who recommended the VOF model, I inform them that it is suitable for multiphase flows where fluids are immiscible, and for the others like mixture and Eulerian models the problem arises that you can't introduce the diffusivity coefficient particularly to validate with previous work.

Good luck.

A good starting point is the book of Krüger et al. as well as the open source code OpenLB and the LBM spring school, see www.openlb.net .

Thank you very much Swapnil! I

Please mention the direction of motion of both phases i.e., water and air and tracer inlet position.

Guangpu Zhu

Hi, I was able to to it. Thanks for your reply. It was really helpful.

You also need to consider contact angle; so the corrected version is as follows based on Franken's model:

Pe = -2*B*sigma*cos (theta)/ R_max

where B depends on the pore geometry shape: 1 for cylindrical pores and 0<B<1 for non-cylindrical ones. Note that for B =1, the equation converts to well-known Young-Laplace equation.

Dears Somnath Rangrej , Purushottam More

Please write your considering sources as formulas here. Maybe I could help.

Thank you.

You can also use the C_VOF. It works for both models.

For example, you can just simply write: v1=C_VOF(cell,liq1);

Thanks for your answer very much. I have no plans to use the Shan Chen model although it can simulate this issue with good results. I also noted that there are several related works, such as [Taehun Lee, Physical Review E 2006, Journal of Computational Physics 2016] , that can eliminate the parasitic currents. However, I still want to know about some other technologies that can be employed on non-uniform meshes. Can you recommend some related literatures?

Okay I made a systematic study recently with OpenFOAM about the issue that you were talking about. And it seems not surprisingly, you will over all lose mass/vol. while you track the whole mass in the system. And the reason for this is that the equation which is solved for the interface (alpha advection) is of hyperbolic type and once you try to solve it with a dissipative discritization (Upwinding) it'll make minor errors in your alpha field resulting in overall misbalance of mass/vol. in your enclosed medium. Of course this is not noticed once you try to simulate an open case. Anyways, what is important is that you cannot avoid this dissipation in the solution of alpha because it has also a good side and that is "stabilization". The good news is refining the cells at the interface would make this effect less vibrant.

BTW check the implementation of VOF in OF as well (interFoam solver) regarding the interface compression...

Sorry for the late reply, I didn't receive a notification for your last reply for some reason.

How can I set a pressure drop exactly?

Gravity is on.

For the geometry, it's a 2D rectangular tube 20 mm long and 0.7 mm wide placed vertically, I patched the whole tube with powder.

DPM is working fine but the eulerian granular model is more interesting for me.

Yes Ofcourse

I would have a look at the newly introduced expression language capabilities in ANSYS Fluent 2019 R1 and R2. I could imagine, that using expressions, you do not have to write a UDF anymore? In an expression, the defined wall flux could be just multiplied with an expression value, which is always 1 for the primary phase of your multiphase flow and always zero for all other phases. I have not yet tried this by myself in ANSYS Fluent, since usage of expressions in this solver is rather new, but that is how I would implement it in e.g. ANSYS CFX using CCL language. New expressions in ANSYS Fluent should allow to do that at some point as well.

Regards,

Dr. Th. Frank.

I would suggest trying to define wall slip in the wall boundary condition and see where that leads you.

Simply plug and play the (ijes) or parasolid model into the ansys workbanch and then try to resolve it

The Knudsen number is defined via the mean free path l_fp. In liquids the mean free path hardly can be introduced. Though liquids differ greatly from the solids, the marked molecule in liquid actually is moving under the impact of the self-consistent-field caused by the other molecules. Introducing the concept of the quasi-particles we can introduce the mean free path for those quasi-particles. The last is of the order of the mean distance between the molecules. Knudsen number as Kn_p=l_fp/D, where D is the nanoparticle diameter formally can be introduced, but how can it be used for the continuous model justification? The Knudsen number arises as a dimensionless parameter in the kinetic equation. Small Knudsen numbers correspond to the continuous model, even taking into account, that for the dense gas, all the more for the liquids, much more complicated kinetic equation compared to the Boltzmann equation should be used. That parameter has no practical use without considering of any type of the kinetic equation. For the nanoparticles Kn_p may not be small, so I see no application field for such parameter, specially taking into consideration the long-range interaction of the particles via the liquid.

Hi Weijia Lu,

Great point. Machine learning uses algorithms to parse data, learn from that data, and make informed decisions based on what it has learned. Deep learning structures algorithms in layers to create an “artificial neural network” that can learn and make intelligent decisions on its own.

Best,

Moh.

Well,

q=kA (P1- P2)/ µL---------------------- (Equation ) where

q = Volume flow rate

k = Permeability

A = Core area perpendicular to flow direction

P1 = Upstream pressure at location 1

P2 = Downstream pressure at location 2

µ = Dynamic viscosity of flowing fluid

L = Distance over which pressure drop (P1- P2) occurs.

Hi Ankita

Interfacial tension is the work (J or N.m) that is required to increase the surface area of an interface between two phases, expressed per unit surface area (m2). The units of interfacial tension is therefore J/m2, or N/m.

Given two immiscible liquids in a thin tube, capillary pressure is the difference in pressure accross the boundary between the two phases. It results from the interfacial tension between the two phases.

All the best

Johan

Thanks a lot Ricardo

Its calculated based on effective mixture properties.

I think you should check mesh independency for your solution, changing the solver, will result in change in the mesh dependency criteria.

hi

used for non Newtonian flow

You can check below mentioned article:

Article A LBM-DEM solver for fast discrete particle simulation of pa...

Hi Saptarshi,

Granular Viscosity in a Eulerian-Eulerian mixture model indicates the sum of kinetic, collisional and frictional viscosity components for the solid particles.

In general, kinetic viscosity is calculated using an expression given by Syamlal et.al from [1] or Gidaspow et. al [2] depending upon the particle volume fraction and particle diameter used.

Collisional viscosity is modelling by an expression given by Gidaspow et.al [2]

Frictional viscosity is calculated by an expression given by D.G.Schaeffer [3]. This frictional velocity is significant only when the volume fraction is closer to the packing limit (63%). In nanofluids, we generally consider a volume fraction less than 5% due to practical constraints. Hence, frictional viscosity component is generally ignored for nanofluids.

Solid pressure indicates the pressure gradient term in the fluid-solid momentum equation. It is generally estimated by a model proosed by Lun et. al [4]

In order understand more about these concepts, you can read on kinetic theory of granular flow.

[1] M. Syamlal, W. Rogers and T. J. O’Brien. MFIX Documentation: Volume1, Theory Guide>. National Technical Information Service, Springfield, VA. DOE/METC-9411004, NTIS/DE9400087, 1993.

[2] D. Gidaspow, R. Bezburuah, and J. Ding. "Hydrodynamics of Circulating Fluidized Beds, Kinetic Theory Approach". In Fluidization VII, Proceedings of the 7th Engineering Foundation Conference on Fluidization. 75–82. 1992.

[3] D. G. Schaeffer. "Instability in the Evolution Equations Describing Incompressible Granular Flow". J. Diff. Eq. 66. 19–50. 1987.

[4] C. K. K. Lun, S. B. Savage, D. J. Jeffrey, and N. Chepurniy. "Kinetic Theories for Granular Flow: Inelastic Particles in Couette Flow and Slightly Inelastic Particles in a General Flow Field". J. Fluid Mech. 140. 223–256. 1984.

Tristan Davenne is entirely right. Essentially what you mentioned about your current solution points in the same direction. It seems to me, like ANSYS support has recommended to you to switch from a disperse multiphase flow formuölation to a VOF-like (VOF = volume-of-fluid) formulation. VOF exists in the ANSYS software in two flavours - homogeneous and inhomogeneous. The homogeneous model with just 1 set of momentum equations follows the assumption, that both phases move with the same velocity field. In that case no assumptions or knowledge about interfacial momentum transfer is needed. ANSYS has implemented an inhomogeneous VOF model as well. In that case from the local ratio in volume fractions of both phases an inherent drag term is deduced, but in that case you don not have to specify it yourself. It assumes, that separatign interfaces between the two phases are rather macroscopic and resolved by the simulation like typically done in free surface flows.

Regards,

Thomas Frank.

Dear Professor Suresh,

Thank you for your reply.

Much appreciated.

If I understand correctly, it is an elongated tube that can serve as a waveguide. The electromagnetic waves can not penetrate the wall of the pipe, even at very high power. You have to couple the energy on one side of the wet diaphragm and measure the electromagnetic energy on the other side with a similar probe. Suitable coupling elements can be found here:

Thanks Ricardo Vicente de Paula Rezende .

What would you say about the 'Bulk mass flow rate' available for Outlet boundary condition.

For that, no volume fraction information is asked in CFX-Pre.

Should I conclude that, if I use that option: the liquid+vapor=bulk; it would mean that it is necessarily kept constant (0.3kg/s both for inlet and outlet)?

If so, is it Physically possible as well?

P.S.: my fluids are liquid water and water vapor (wall boiling case).

Dear Sir,

For multiphase flow inside porous media, you can use the mathematical formulation of TPMM along FVM instead of VOF. For further information, please see my articles in my page and also you can contact with me at any time.

best regards

I fully agree with previous answers. But your question is not clear enough.

the distribution of fluids (previous history) and wettability (if the viscosities are similiar) are the controlling factors for the pressure needed to flow. involving capillary pressure muddles the issue.

For example, if your water saturation is 40 % and all the other variables are the same. Not all the pores have 40%! some will have 100% and others 20%. Therefore, the pressure drop will be different for different pore size distributions, mainly if they are not unimodal.

Also, during imbibition and drainage at the same saturation you will have different fluid distributions and as a consequence different pressures.

by P. Vorobieff, C. A. Brebbia

Publisher: WIT Press / Computational Mechanics (April 18, 2018)

Efstathios Michaelides, Clayton T. Crowe, John D. Schwarzkopf

September 1, 2016 by CRC Press

Thanks a lot for your kind references.

Deewakar

As long as you have low mixing, a sufficiently high water column and volume (to provide buffer against liquid/gas phase contact) and a membrane/module which can inject the gas (smaller pores work better; "pore-free" silicone is also effective), and you can control the gas input pressure/flow, you should be able to inject high amounts before the liquid phase becomes fully saturated and bubbles start to form. The Henry's constant and mass transfer characteristics (which would severely limit the amount of H2 you could inject (i.e. 1.6mg/L) if the liquid phase is open to atmosphere) are then not limiting in this case. In a similar vein, if you have high H2 partial pressures in the gas phase and your reactor is well-sealed, you can dissolve more as well.

https://www.cfd-online.com/Forums/cfx/90063-ansys-cfx-solver-exited-return-code-1-a.html

http://www.cfd-online.com/Forums/ansys-meshing/79815-proper-way-name-boundaries-2d-model-use-cfx.html

https://www.researchgate.net/post/Problem_with_CFX_solver

https://studentcommunity.ansys.com/thread/cfx-solver-error/