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mass flowrate is non conserved

Posted 20 mars 2014, 10:59 UTC−4 5 Replies

Antonio Ficuciello
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Dear all,

I was trying to simulate the water flow into a system with two inlets and three outlets and I used the ''surface integration'' io order to compute the total mass flow rate and I found that the total outgoing mass flow rate is higher (around 5%) than the incoming mass flow rate.
Thus, I decided to do a simpler case, a cylinder representing an injector, and comparing the numerical results in terms of outlet velocity with the experimental ones. Numerical results agree with the experimental but I still found that the mass flowrate through the exit surface is higher (around 1.5%) than the inlet mass flow rate.

Could it be due to the mesh resolution or not?

Thank you in advance for your help.

Antonio
5 Replies Last Post 25 mars 2014, 09:57 UTC−4
Niklas Rom COMSOL Employee

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Posted: 1 decade ago 21 mars 2014, 08:36 UTC−4
Hello Antonio,
We recommend an upgrade to the current version, 4.4, in which several mass conservation issues have been addressed.
kind regards
Niklas

Dear all,

I was trying to simulate the water flow into a system with two inlets and three outlets and I used the ''surface integration'' io order to compute the total mass flow rate and I found that the total outgoing mass flow rate is higher (around 5%) than the incoming mass flow rate.
Thus, I decided to do a simpler case, a cylinder representing an injector, and comparing the numerical results in terms of outlet velocity with the experimental ones. Numerical results agree with the experimental but I still found that the mass flowrate through the exit surface is higher (around 1.5%) than the inlet mass flow rate.

Could it be due to the mesh resolution or not?

Thank you in advance for your help.

Antonio


Hello Antonio, We recommend an upgrade to the current version, 4.4, in which several mass conservation issues have been addressed. kind regards Niklas [QUOTE] Dear all, I was trying to simulate the water flow into a system with two inlets and three outlets and I used the ''surface integration'' io order to compute the total mass flow rate and I found that the total outgoing mass flow rate is higher (around 5%) than the incoming mass flow rate. Thus, I decided to do a simpler case, a cylinder representing an injector, and comparing the numerical results in terms of outlet velocity with the experimental ones. Numerical results agree with the experimental but I still found that the mass flowrate through the exit surface is higher (around 1.5%) than the inlet mass flow rate. Could it be due to the mesh resolution or not? Thank you in advance for your help. Antonio [/QUOTE]
Marino Miccio
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Posted: 1 decade ago 21 mars 2014, 09:37 UTC−4
Dear Antonio,

is the mass flowrate not conserved even if you increase the mesh resolution?
Does the error change with the mesh or is constant?

Regards.

--
Marino Miccio
Chemical Engineer
marinomiccio.wix.com/home
Dear Antonio, is the mass flowrate not conserved even if you increase the mesh resolution? Does the error change with the mesh or is constant? Regards. -- Marino Miccio Chemical Engineer http://marinomiccio.wix.com/home
Antonio Ficuciello
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Posted: 1 decade ago 24 mars 2014, 10:26 UTC−4
Hello Niklas,

unfortunately I have not the possibility to use the new version for the moment and I would like to understand which kind of improvements have been done in regarding.

Best regards.

Antonio
Hello Niklas, unfortunately I have not the possibility to use the new version for the moment and I would like to understand which kind of improvements have been done in regarding. Best regards. Antonio
Antonio Ficuciello
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Posted: 1 decade ago 24 mars 2014, 10:42 UTC−4
Dear Marino,

in the case of the cylinder, considering the Physics controlled mesh provided by COMSOL, varying from the extremely coarse to the coarse mesh, the percentage difference decreases.
Which is not true in the case of the real geometry.

The problem is that I can not obtain a very fine mesh because of the power of the actual machine on which I am using COMSOL and I would like to understand if this difference in mass flowrate is due to the mesh limit I have or to a COMSOL issue (or both) and how it affects the quality of the simulation in order to well interpret the results I obtained.

Thank you.
Best regads.

Antonio
Dear Marino, in the case of the cylinder, considering the Physics controlled mesh provided by COMSOL, varying from the extremely coarse to the coarse mesh, the percentage difference decreases. Which is not true in the case of the real geometry. The problem is that I can not obtain a very fine mesh because of the power of the actual machine on which I am using COMSOL and I would like to understand if this difference in mass flowrate is due to the mesh limit I have or to a COMSOL issue (or both) and how it affects the quality of the simulation in order to well interpret the results I obtained. Thank you. Best regads. Antonio
Hans Parmentier
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Posted: 1 decade ago 25 mars 2014, 09:57 UTC−4
First of all try to get the latest version this helps a lot for mass flow calculations.

Next to that try to make your tube longer and plot streamlines sometimes they are re-entering the surface (when a object is disturbing the flow) maybe this can have an influence on the mass flow calculation?
First of all try to get the latest version this helps a lot for mass flow calculations. Next to that try to make your tube longer and plot streamlines sometimes they are re-entering the surface (when a object is disturbing the flow) maybe this can have an influence on the mass flow calculation?

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