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tichaona February 24, 2012 07:47

tracer gas
greetings from South Africa to all collegues.

I want to include a tracer gas in the domain and then monitor its decay in concentration with time. I will monitor the concentration at specific points so that I can calculate mean age of air and air change effectiveness. How can I do that.

Any help is welcome.

Thank you in advance.

shk12345 February 25, 2012 10:23

i am nit sure what you wanna achieve

make a function in fluent as the concentration in define custom function
then the approach may change depending upon weather your mesh is 2d or 3d.

for 2 d make a line along the flow domain and see the variation of conectration on that line
in 3 d make a plane and so the samee

hope that will help you

hiddenbunny February 27, 2012 13:32

tracer decay
I assume you are referring to replicating a tracer decay test in CFD so you can find out the air exchange rate, etc in an indoor environment.

In fluent you need to turn species on, then setup your tracer gas. You can then turn the whole room volume into a source then run a steady state simulation, while monitor the concentration. Since you used the room volume as source, the concentration should be pretty even, emulating a well-mixed room.

When you get a concentration high enough, switch to unsteady state simulation and have your openings boundary conditions set (inlets and outlets), then run the unsteady case until the concentration does down.

To make calculations, output your concentration (make monitor points at the locations of your interest) per time step, then you will have a file of concentration decay, which you can then turn into air exchange rate or age of air via post processing.

tichaona February 28, 2012 03:17

tracer decay
Thanks to your replies hiddenbunny and shk12345. I have opened the species in Fluent. Which option do I use species transport/ composition pdf transport, the other options include combustion thats why I did not mention them. Under pdf transport, should I use langrangian or Euler what values are for the particles/cell etc. May you please shed more light.

Thank you once again.


tichaona February 28, 2012 03:33

tracer gas decay
Thank you shk12345 for reply. I want to enter the concentration function C(t) = C(0)e^-It under the custom field functions. under select operand field functions which do I choose? Can you please explain to me in detail if possible. I will appreciate the help.

where C(t) is concentration of tracer gas at time t
C(0) = initial concentration of tracer
I is the Air chnage rate per hour
t is time.

Best regards

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