Transient Species Transport
 

Hello everyone.

I am a college student trying to model the flow of acid through a porous rock sample. I am currently in the process of simply modeling the species transport through a cylinder before adding in the complex mechanisms. Below I've included my geometry and mesh:

http://i.imgur.com/amllaLp.png

http://i.imgur.com/BvSAyG0.png

My Fluent setup is as follows:

• Solver is Pressure Based and Transient
• Species Transport is enabled
• Diffusion Energy Source is disabled
• Flow is laminar
• Fluid domain is a mixture of water and HCl
• Inlet velocity is 1.65e-05 m/s
• Inlet HCl mass fraction is 0.0155
• Outlet pressure is 0 Pa
• Time stepping is fixed

I've encountered two main issues:

1. I am unable to disable the energy equation with species transport enabled. Is there a way to forcefully disable/neglect the effects of the energy equation/temperature on my solution?
2. With a time step of 0.01 all of the equations (continuity, velocity, etc) return 0 for the first 4 time steps and seem fine after that. Is this normal or is there an error in my setup/model? Below is the graph of the residuals.http://i.imgur.com/KmZ2c6X.png

Any help would be greatly appreciated!

I know there are a lot of questions asked on this forum, but any insight would be very helpful.

The issue of not being able to turn off the energy equation is most probably caused by the fact that something in your setup needs the result of the energy equation as an input. For example, check your materials if there are some material properties that depend on temperature. Then Fluent won't let you turn off the energy equation.

Thank you for your response. I've determined that it is caused by the density calculation method of my species mixture, which by default is set to incompressible-ideal-gas. Which option should I select instead to allow me to disable the energy equation and not interfere with the rest of my simulation?

Depends on your system. You can set the density as constant if you know it beforehand. Or volume-weighted-mixing-law should do as well. You need to choose the definition that satisfies your physics.

Alright. Thank you for the explanation.

Hello Baden, currently i am doing a simulation by using species transport...however, i have found that if i change the setting from steady to transient model, the concentration of one of the species at the outlet became relatively small (10^-250)...i was wondering is it species transport model cannot be applied in transient case?Do u encounter the same problem before? The settings of my case is shown as below:

Inlet 1: fluid A
Inlet 2: fluid B (Bulk species)

Output results (mass fraction of A) at the outlet:
Steady case: 0.5-0.6
Transient case: 0