We are studying, using CFD Fluent software, fluid flow in rectangular channels with two inlets and 5 outlets at constant temperature and pressure. At the two inlets, there will be mixture of two liquids. So, how to define a mixture of two liquids in Fluent and how to setup the boundary conditions for this problem?
In my opinion you go with VOF model although you can use multiphase but VOF is much better for your problem.
Since there is no chemical reactions and phase changes (i.e. constant temperature, constant presure, mixing of two liquids), we plan to use species transport model in Fluent. Later, we will compare with other models.
Multiphase model is the best. VOF used for fluid-fluid interface only
Do I still need to use a multiphase model for mixing of two liquids during a laminar flow inside a nanochannel at room temperature and pressure?
Anybody has compared using different liquid mixing (at constant temperature and pressure) models in Fluent software? VOF vs. Multiphase vs. Species? Got different results?
I did few cases but i didn't validated with any paper they were just for learning purpose so i can not guarantee but i think for you it will be better to use both and first do a 2d analysis and then you can save your time as well and comparison will also be there.
Since you have used both models; I am curious to know whether they give different results?
For fluid flow in rectangular channels with two inlets and 5 outlets at constant temperature and pressure, should I use "pressure-outlet" or "outflow" for outlet boundary conditions?
hi Ahmad
if you are not aware of the pressure situation in your domain then you can use outflow as it works with zero diffusion flux while for pressure outlet it might produce good result if there is recirculation in your outlet. so choose wisely.
The other problem when choosing "outflow" is we need to specify whether the flowrates at different outlets are equal or not. What to do if we are not sure of the flowrates?
And if we use "pressure-outlet" condition, we still need to specify the mass faction of the mixtures at the outlets. So, I guess we need to do theoretical calculations for either the mass fraction or flowrates at the outlets?
Yes you are right but first try by using default flow rate i.e. 1 in fluent and compare the results and meanwhile you can calculate your flow rate.
The default flow rate of 1 implies that the flow will be equally distributed among the outlets, which is NOt the case of nanochannels with 5 outlets.
I have tried both outlet conditions. The "pressure-outlet" gives much better results and it converges much faster.
Steady state results look great. How can we simulate the transient initial stage of the flow?
That is easy go to unstedy part and then in your solution animation section you can define which quantity you want to see and make a plane where you want to observe the changes. And then define a small time step size and depending upon your time requirement i.e. For how long you want to make simulation you can define the no of time steps.
Will the results of "steady" and "unsteady/transient" be identical at long time?
Thanks Wang; what models did you use? Which one gave the best results?
If you want to define the efficient of the pure mixing due only to the trasport phenomena due to momentum gradient, why you don't use injection in order to follow the "particles" during the mixing?
Dear Simone Ripandelli,
Very good suggestion! Can you elaborate more? We are interested in injecting continuosly two different liquids at two inlets.
Sure. Can I suggest you to read my only publication? I think that it can be interesting for your job. Anyway, if you want more information I will be happy to help you.
Best
Dear Ahmad, i hope you got solution for your problem, i am also facing same problem in my work, can you help me, i want to define two fluids at one inlet (dispersed phase) at another inlet continuous phase, dispersed phase have two fluids like dye and water. i am using VOF and species method. i have all physical properties of fluids. i want to know to define mixture in dispersed phase and i want to define diffusivity aslo in dispersed phase .
If you have any idea, please help ..thanks in Advance
I hope following paper will be helpful to you.
http://onlinelibrary.wiley.com/doi/10.1002/srin.201500210/abstract
For my situation which is similar to this I am dealing with Oil+Ethanol mixing and how should i define the mass diffusivity of ethanol into oil using VOF model ? I am trying to use UDS scalar to define diffusiivity ..?
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