Learning Forum

[albertocaracuta]

Hi, i'm a beginner to ansys fluent, i'm trying to simulate the following system:

i have a titanium nanotube in which there is a solution of water + sodium naproxene, at the exit of the nanotube i have just water.

what i want to simulate is the mass diffusion of this molecule outside the nanotube and in the water.

 

the problem is that i'm not able to set the concentration of the molecule in the nanotube at a fixed value at time=0, in this way i'll be able to appreciate the elution of the molecule from the nanotube in the water. Actually i'm only able to set a constant value of the concentration at the wall or in a area by using a patch, by this way the concentration is kept constant for all the simulation and doesn't change in the nanotube, even if the diffusion and elution occurs.

[Rob]

Nano-scale will be pushing the solver as it's not designed to work at that scale - you may want to read up on the continuum assumption and Knudsen Number limits. 

Do directly answer the question, the word you're looking for is "Patch". 

[albertocaracuta]

Thank you for your answer, i know that on this scale is more correct to use a molecular dinamics simulation, but i want to try first a cfd, anyway i tried to set a patch but it defines the concentration i set in the patch in every surface of my model, not just on the area i'm interested to.

Could this problem related to the dimension of the simulation?

 

[Rob]

If the region you want to patch is different to the whole fluid then you may need a register (under adaption) to create a smaller zone. 

[albertocaracuta]

Hi, sorry to bother you again.

I actually tried to scale up my system in order to understand if the problem with my simulation was just related to dìthe dimensio of the system, but actually is not.

i'll try to explain better my problem, as you can see in the image, i have a surface in which i put a mixture of water+sodium, and after the interface there is another surface with just pure water, what i want to do is to configure the system in order to have at time=0 a defined mass fraction of sodium only on the left part of my system, and pure water on the right part.

I tried by using a patch (also on the macroscopic system), defining the mass fraction of sodium i want just in the left surface of my system, but when i check what the patch has done the sodium is spread in all the system and not just in the left section, could be a problem of the mixture? or i'm using in a wrong way the patch function?

Thank you

[Rob]

Did you initialise as "Standard" or "Hybrid"? Then patch the sodium to the left section. 

[albertocaracuta]

I initialize as standard, and patch the left section, but still doesn't work

[Rob]

Please post what you're doing.