Question

Asked 17th Apr, 2019

Tianjin University

I need some help regrading numerical simulation modeling??

Hello Sir / Ma'am

I am currently doing research on Numerical simulation and modeling on hydrodynamic vortex separator, and using a research paper as reference model. When i go along the research and run the case file in the fluent.15.0 use the same geometry and my mesh quality is also good i apply same method & conditions but could n't get similar values of results and also same trends of graphs of the reference paper. I tried many times change different methods and boundary parameters, but could not succeed. Could some one help me asap. reply back

21st Apr, 2019

Port Said University

When you do C.F.D for any problem , do not trust in the paper you get you should depend on your self and make sure you do the best. Suppose you do not have any reference. I mean that you search for another method to check out.

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Salwa Yammine

Lebanese University

Nidhal Kamel Taha El-Omari

The World Islamic Science and Education University (WISE)

د. الاء حمزة شناوة دويلي

University of Baghdad

Ljubomir Jacić

Technical College Požarevac

Hazim Hashim Tahir

Ministry of Science and Technology, Iraq

18th Apr, 2019

Muneer Ismael

University of Basrah

Dear Mahaveer,

If you got the same trend of curves, then you should:

1- Check again the domain, the researchers sometimes solve for symmetry domain.

2- carefully check the boundary conditions.

3- If the problem is time dependent, try to vary the initial time and the time step.

4- Try another cases of the same paper.

5- If you do not get a consistency with these checks, you can try another paper, another cases, etc.

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1 Recommendation

18th Apr, 2019

Thomas Frank

Ingenieurbüro Dr. Frank – CFD Consulting –

You potentially should consider the possibility, that the published result in the reference paper is simply wrong, in particular if the underlying research is published in a conference proceedings volume or in a scientific journal with not 100% well known excellence of there scientific paper review procedure.

In addition I would like to encourage you to:

a) Use a contemporary version of ANSYS Fluent, i.e. not a 6 years old version of ANSYS Fluent, but version 2019.R1. In the meanwhile dozens of known errors have been corrected in ANSYS Fluent over that period of time.

b) Vortex separators are known to be sensitive to the results of turbulence models. Which turbulence model are you using? If the flow has strong streamline curvature and swirl, use a k-omega-based BSL RSM turbulence model. If you can afford, try to do scale-resolving simulation using SAS-SST or SBES model for comparison with your first result. Are the results still the same (in time-averaged data with sufficient statistical reliability)?

c) Give it a trial and run the model in a different CFD code for verification. With only a little effort that can be done in ANSYS CFX. With a bit more effort in e.g. OpenFoam. Are the results the same? Trends the same? Is either one of the solvers giving an answer which corresponds with the reference publication?

By that you could try to narrow down the issue to its source.

Regards,

Dr. Th. Frank.

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1 Recommendation

18th Apr, 2019

Saad Najeeb Shehab

Mustansiriyah University

Mr. Muneer Ismael.. Right, I agree with your answer.

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20th Apr, 2019

Naveed Ahmed

National University of Sciences and Technology

For the modeling of hydrodynamic vortex separator you need to try different turbulent models. With different turbulent model sometimes convergence issue also happens but if your results are getting the general trend as presented in the paper, then for accuracy you need to double verify the boundary conditions and suppositions. But the if the simulation cases are very well converged with all same mentioned conditions, then you need to consider trying on some other CFD tool as suggested by Thomas Frank

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21st Apr, 2019

Ahmed Abdelhameed

Port Said University

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How to model a volumetric reaction rate inside porous media with variable porosity?

Question

14 answers

Asked 28th Jun, 2018

Soumendu Dasgupta

Hydrodesulfurization in packed beds takes place according to the following general reaction:

Sulfur Compound (ArS) + 2H2 --- H2S + Aromatic (Ar)

The kinetic rate is given by:

rHDS = (−KHDS) [ArS]^1.6 * [H2]^0.56 / (1+kad * [H2S]) [kmol/(kgs • s)]

The adsorption coefficient (kad = 50, 000 [m3/kmol]) does not depend on the temperature.

KHDS = 2.5•10^12 • exp(-19.384/Ta) [(m3)^2.16/(kg •(kmol)^1.16 • s)]

The geometry is a 3D cylinder and assembly meshing gives me a minimum orthogonal quality of 0.92, which is a desirable mesh. I have activated the Eulerian 2 phase and species transport models, and selected the mixture template for both the phases in the species transport model. Next in the materials section, all four materials (ArS, H2, Ar, and H2S) are defined inside the mixture template. The porous media is selected in the cell zone conditions and the appropriate UDF is loaded for the same.

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#include "udf.h"

#include "mem.h"

#define KHDS 0.005083992078

DEFINE_VR_RATE(vol_reac_rate,c,t,r,mole_weight,species_mf,rate,rr_t)

{

begin_c_loop(c,t)

{

real X_ars=C_YI(c,t,3)*C_R(c,t);

real X_h2=C_YI(c,t,1)*C_R(c,t);

real X_h2s=C_YI(c,t,0)*C_R(c,t);

if (FLUID_THREAD_P(t) && THREAD_VAR(t).fluid.porous)

*rate=((-KHDS)*(pow(X_ars,1.6))*(pow(X_h2,0.56)))/(1+(kad*X_h2s));

2. Selecting two different templates to define the materials and following the remaining steps as it was in point no. 1.

I am using ANSYS Fluent for the simulations and maintaining a time step size of 1e-08, but there is no change in the mass fraction of the reactants. In other words the mass fractions of ArS and H2 are 1.0 throughout the simulation and mass fractions of Ar and H2S are 0.

Any kind of support regarding this would be reallyhelpful.

Thanks.

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