 ## Fluids

• Ionatan
Subscriber

I would like to ask a question about the modeling of my problem.

I want to simulate the dispersion of decomposing tracer gas in a cold storage chamber. I already have the boundary conditions for the mass flow rate of the tracer gas and the air circulation, as well as kinetic data for the gas. The problem arises in modeling this air recycle, which must have conservation of the tracer gas, not being able to set only the mass flow inlet condition in the diffusers and the pressure outlet condition in the fan. I would like to be able to simplify this region where the recycling occurs, between the fan and diffuser, but I do not know how to do this, is it possible through a UDF? Or do I have to model this recycle region, then I get into the problem of how to find the fan's characteristic curve since the only information I have about it is the air mass flow rate. Below are some figures to better visualize the problem. Any ideas or guidance are welcome.

• Karthik R
Hello:
It depends on your modeling objectives. If the recycle region is important, then I'm afraid you will need to include this as part of your simulation. If you know the type of fan, you may be able to get the fan curve from the manufacturer (something to look into). If you are trying to set up as a first pass, you may wish to remove this region and use a simple mass flow inlet.
Karthik
• Ionatan
Subscriber
The recycle region is not of great interest, I just want to conserve the species, where all the gas that comes out of the fan goes back into the diffuser, how could I simplify this part to get this result?
• Rob
Ansys Employee
If you use an expression you can calculate the mass fraction of tracer on the way out and then set that value on the way into the domain. As an aside, given then inlet never quite equals the outlet how are you stopping the solver reaching either infinite pressure or perfect vacuum?
• Ionatan
Subscriber
I found a UDF, but it's for water humidity, how could I convert it to my trace gas? I'm still trying to decipher it, looking at its parts and the UDF user manual.

#include "udf.h"
#define OUTLET_ID 11

{
face_t inlet_face_index, outlet_face_index;
real water_mass_fraction=0;
real n = 0.;
real H_AVG = 0.;
Domain *domain;

domain=Get_Domain(1);

{
water_mass_fraction = water_mass_fraction + F_YI(outlet_face_index,outlet_thread,variable_inde x);
n = n + 1;
} 