Excuse me it's not my profile

Yes, COMSOL can solve for compressible fluid flow.  You probably also need the CFD module to be able to do this though.  You can also have gas mixtures and solve the diffusion equation simultaneously.

I'm very thankful to you Derek, somehow you are mentionning what I'm intending to do with Comsol.

The idea is to study the transient flow of a gas mixture through a pipeline coupling with the diffusion equation (diffusion gas into gas and if possible gas into the pipline wall).

I'm not well familiar with Comsol, I was thinking to use both the pipe flow module and the two phase darcy's Law module.

Several problem in coupling arise !!

How to take in consideration the varying density of gas when defining the material for pipe flow module (same problem with the water hammer module when assigning a celerity of pressure waves which's not constant in case of gas flow)?

Is Darcy'law suitable for gas flow to couple it with pipeflow module ?

Also, to my knowledge, Darcy's law is valid for laminar flow (low Reynold number), how it can be formulated for gas flow that may reach turbulence?

A lot of questions and any idea from any researcher will be very helpful.

Darcy's law is for for flow through a porous medium, where the pores are much much smaller than the dimensions that you are concerned with.  It allows you to calculate a mean velocity through the porous medium without having to literally model the flow through each of the pores.  In such a case it is almost inconceivable that the flow through the pores would be anything but laminar, even for gases.

Thanks again Derek, so without considering the porous medium, the two Phase Darcy's Law module will be useless for me and I have maybe to look for another module to couple with pipe flow to solve simultaneously the diffusion equation also ?

The standard Fick's law is included in the basic COMSOL multiphysics, but that's really only valid for dilute species.  If you are looking diffusion of concentrated species, you need the chemical reaction engineering module, I think.

Really, what you need is to talk to COMSOL.  They can answer all these questions about the capability of their own software better than I can.  Also you can get a free 2-week trial license to see if it can really do what you want to.

Your comments and suggestions are well appreciated and you have clarified some points to me.

Thanks a lot Derek

Hallo Zahreddine,

I have some experience with what you are saying. So for the compressible flow, it is just another setting in the main fluid interfrace under "Physical model" (version 5.0 and higher) or as a check box in the older versions (as far as my memory serve).

For the transport equation, it depends on the concentration of the material. So as a rule of thumb, you can use transport in diluted species with a gas concentration

Thanks Zaid,

As I don't have a long experience with Comsol, based on your suggestions, (Zaid and Derek), I will go step by step starting by one gas flow in a single duct and then see.

Please allow me to be back to you for any query.

Thanks for you both Zaid and Derek.

hi 

based on my experience on Comsol, I can say that comsol can model compressible gas flows well. but if you have a liquid in you problem comsol can not treat the liquid as compressible as the gas so you may get wrong solution.

hamid 

Hi Hamid,

Thanks for you answer. Just I want to ask, based on your experience, which is the suitable module to use to model a gas mixture flow in a pipe (steady and transient analysis).

Again, thanks a lot.

Zahreddine

what do you mean by gas mixture flow ? Do you mean a flow containing mixture of different gases? 

Exactly, I intend to simulate hydrogen natural gas mixture flow in a pipe.

Well, we can assume that the mixing leads to an homognous gas.

my question is about the suitable Comsol module to simulate transient gas flow in a pipe.

Thanks.

Zahreddine