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June 12, 2008, 00:03 
Particle residence time!!

#1 
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Hello there,
I want to calculate the age of air in a volume. will, calculating the particle residence time give me a solution on this. if so can you please tell me how i can do it. Please let me know. Thanks Kind Regards Kandy 

June 12, 2008, 00:35 
Re: Particle residence time!!

#2 
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Try pathlines colored by particle residence time. I have used this to visually get an estimate of residence time without any text summary statistics.


June 12, 2008, 04:55 
Re: Particle residence time!!

#3 
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Hi,
I think you have to define particle injections using Discrete Phase Model. Using DPM u can define particle injections from a surface(for ex: from inlet). best regards 

June 12, 2008, 17:07 
Re: Particle residence time!!

#4 
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you need not use DPM. You can use a user defined scalar that is seeded into the domain. Just solve your steady case then setup the UDS and solve a few iterations (say 5 or 10) for the UDS. Your support group can provide details of this UDS approach or I can if you cannot obtain.


June 12, 2008, 20:17 
Re: Particle residence time!!

#5 
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Thanks Guys!!
We din't purchase support in the package. Please type me in the details in your spare time. i will be highly obliged. With Kind Regards Kandy 

June 13, 2008, 04:18 
Re: Particle residence time!!

#6 
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Hi Red lemon,
Can u please send me the procedure u worte. It will be interesting for me how to do this task using a udf. Regards 

June 13, 2008, 04:31 
Re: Particle residence time!!

#7 
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dear sir,
yes, pls tell us the procedure for the EulerianEulerian model. I mailed Fluent.Inc many times, but without any reply from them. They refer to Solution No. 619. However, this method is not suitable for RTD measurement of multiple dispersed phases. (if anyone requires the solution 619, i can paste the same here) redlemon,we are all hoping for your reply. thanks and regards. 

June 13, 2008, 08:32 
Re: Particle residence time!!

#8 
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ok I will post use of uds for residence time. It is the same method employed in Airpak that uses Fluent but in this case it is done in the GUI in a simpler format and Fluent's method is a bit confusing. Bear with me as I recover details.


June 17, 2008, 13:51 
Re: Particle residence time!!

#9 
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OK here you go.
Convert this text to a *.c file then compile as usual and follow notes to hook in. Then solve for scalar only and post process. /* Diffusivity for mean age of air is solved using a userdefined scalar. This calculation can be performed after the normal problem has already been solved ... just turn off all of the previous equations being solved for and activate solution of the userdefined scalar0 equation. Make sure to select  mean_age_diff as the uds diffusivity in the materials panel  mass flow rate as the uds flux function  mean_age_source as the uds volumetric source term in all fluid regions Use a journal like this to do that in F63 : def bc fluid fluid1 n y 0 0 0 0 0 0 0 1 n y "mean_age_source" n y 0 0 0 0 0 0 n n n def bc fluid fluid2 n y 0 0 0 0 0 0 0 1 n y "mean_age_source" n y 0 0 0 0 0 0 n n n def bc fluid fluid3 n y 0 0 0 0 0 0 0 1 n y "mean_age_source" n y 0 0 0 0 0 0 n n n etc  set uds0 scalar values = 0.0 at all inlets and outlets mean age of air calculations do not require any energy, radiation, or species transport calculations to have been performed */ /************************************************** *****/ #include "udf.h" #include "prop.h" DEFINE_DIFFUSIVITY(mean_age_diff, c, t, i) { return C_R(c,t)*2.88e05+C_MU_EFF(c,t)/0.7; } DEFINE_SOURCE(mean_age_source, c, t, dS, eqn) { dS[eqn]=0; return C_R(c,t); } 

June 25, 2008, 11:03 
Re: Particle residence time!!

#10 
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Hi red lemon,
This is for a singlephase flow..but what should we do if we have multiphase flow and need to claculate the residence time of the dispersed phases only ? Thank you. 

June 25, 2008, 21:13 
Re: Particle residence time!!

#11 
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Hi red Lemon,
Thank you very much. I was on holidays. will try this. Thank you one again. Regards Kandy 

October 20, 2011, 06:39 
Hi to every one...I want know How to post process the Mean age of air in fluent.. Ple

#12  
New Member
Hanumanth
Join Date: Aug 2009
Posts: 6
Rep Power: 10 
Hi to every one...I want know How to post process the Mean age of air in fluent.. Please any one can help regarding this...Thanks in advance ....
Quote:


January 26, 2016, 05:51 

#13 
Senior Member
James
Join Date: May 2013
Posts: 111
Rep Power: 6 
Hi everyone,
In your diffusivity formula: return C_R(c,t)*2.88e05+C_MU_EFF(c,t)/0.7 Which values should I choose for a water system? Also, I am finding several difference on maximum residence time when I increase mesh size. I guess this is just an issue of the faces that the UDF is taken into account, and if element size tends to zero, then this maximum residence time will converge for a constant value...Am I right? Thanks in advance!And special thanks for sharing this useful tool! 

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