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Changing the diffusion coefficient has no effect
Posted Dec 1, 2015, 3:59 a.m. EST Fluid & Heat, Chemical Reaction Engineering Version 5.1 1 Reply
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Hello everyone,
I tried to model the residence time distribution of a (dye) tracer in a static mixer.
I first computed a stationary laminar flow field and then conducted a time-dependent study using the 'transport of diluted species' module with a time-dependent inlet concentration.
In principle this worked fine, but the distribution curve that i got was much steeper than in the experiment, i.e. too little diffusive.
I tried to change the diffusion coefficient (from the default 1e-9m²/s to 5e-9m²/s) but this did not have any effect. The tracer propagation is convection dominated (I think), but i still find it curious that the diffusion coefficient has no effect whatsoever.
Any ideas why that is or what I could try?
I also should mention that the default BDF solver did not converge and I had to use the generalized alpha solver. Not sure if this is relevant.
Any suggestions would be highly appreciated!
I tried to model the residence time distribution of a (dye) tracer in a static mixer.
I first computed a stationary laminar flow field and then conducted a time-dependent study using the 'transport of diluted species' module with a time-dependent inlet concentration.
In principle this worked fine, but the distribution curve that i got was much steeper than in the experiment, i.e. too little diffusive.
I tried to change the diffusion coefficient (from the default 1e-9m²/s to 5e-9m²/s) but this did not have any effect. The tracer propagation is convection dominated (I think), but i still find it curious that the diffusion coefficient has no effect whatsoever.
Any ideas why that is or what I could try?
I also should mention that the default BDF solver did not converge and I had to use the generalized alpha solver. Not sure if this is relevant.
Any suggestions would be highly appreciated!
1 Reply Last Post Dec 1, 2015, 5:12 a.m. EST
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Posted:
9 years ago
Consider the Peclet number of your system. If Pe >> 1 diffusion has no significance.
BR
Lasse
BR
Lasse