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October 19, 2010, 21:19 |
Problems Calculating Residence Time [trace]
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#1 |
New Member
Vitor de Miranda Henrique
Join Date: Sep 2010
Posts: 6
Rep Power: 16 |
Hello,
I'm trying to calculate the residence time of a Plug Flow reactor, this is my steps: 1: Create a Variable: Tracer, Specific, with no units; 2: Enable the variable in the reactor domain; 3: Create a TracerInjection with the units kg/s My equation is step((t - 1[s])/1[s])*1[kg s^-1]*step((2[s] - t)/1[s]) this equation give a step between the times of 1 to 2 seconds; 4: Create a monitor equation TracerOut = areaAve(Tracer)@outlet; 5: Put all inicial conditions; The problem is when I solve the simulation, the CFX-solver give me a wrong chart of de DTR (including up to negative times) I am attaching a picture of the graph i get. The green curve is the step, and the others are of the DRT. http://img403.imageshack.us/i/tracer.jpg/ I do not know what I'm doing wrong. I would be grateful if someone could help me Vitor Henrique Last edited by wyldckat; September 3, 2015 at 18:01. Reason: disabled embedded images |
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October 19, 2010, 22:13 |
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#2 |
Senior Member
Michael P. Owen
Join Date: Mar 2009
Posts: 196
Rep Power: 17 |
How is this supposed to calculate the residence time?
There are two methods you could use. Either use an additional variable with dimensions of time initialized to 0[s] and with the inlet boundary value set to zero and use an AV source to increment it at a rate of 1s/s, or skip the source and set the inlet value equal to the current simulation time, so each parcel of fluid knows when it was "born." |
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October 19, 2010, 23:25 |
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#3 | |
New Member
Vitor de Miranda Henrique
Join Date: Sep 2010
Posts: 6
Rep Power: 16 |
Quote:
I followed this "tutorial": http://www.cfd-online.com/Forums/cfx...lysis-cfx.html how can I do this other method? i create a variable, with unitis of [s] then I set transport equation? How can i create this AV source? Sorry about the questions, but i'm new in CFD. Tanks, Vitor Henrique |
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October 21, 2010, 10:28 |
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#4 |
Senior Member
Michael P. Owen
Join Date: Mar 2009
Posts: 196
Rep Power: 17 |
Vitor,
That thread is about injecting a tracer into the flow. That isn't what you want to do; you're trying to calculate residence time. Essentially that thread has absolutely nothing to do with what you want, as far as I can tell. You should use one of the two methods I described. You could also just plot the time on streamlines in Post, but for transient simulations the interpretation of this is tricky and may not yield what you want. |
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October 21, 2010, 15:57 |
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#5 | |
New Member
Vitor de Miranda Henrique
Join Date: Sep 2010
Posts: 6
Rep Power: 16 |
Quote:
Michael I know how to create a variable, and how to set the units.But how can i use an AV source to increment it at a rate of 1s/s ? What is a AV source? Thank you Vitor Henrique |
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October 21, 2010, 16:39 |
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#6 |
Senior Member
Michael P. Owen
Join Date: Mar 2009
Posts: 196
Rep Power: 17 |
Insert a subdomain scoped to the entire domain. On the Sources tab, check sources, and then input a source for your additional variable.
All of this is in the documentation. |
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June 24, 2012, 01:49 |
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#7 |
New Member
sepideh
Join Date: Jul 2011
Posts: 21
Rep Power: 15 |
Hi
If the situation is steady state can I still use streamline and plot time?because I dont have time variable! I have a rectagular box with a slot at the top of the box,that is inlet,I dont have any outlet and the approach is E-E. Regards, Sepi |
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June 24, 2012, 07:13 |
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#8 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,828
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Time is a variabel on streamlines, not a general simulation variable.
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June 24, 2012, 18:39 |
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#9 |
New Member
sepideh
Join Date: Jul 2011
Posts: 21
Rep Power: 15 |
Thank you so much for reply.
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November 8, 2014, 22:46 |
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#10 |
Senior Member
Ashkan Javadzadegan
Join Date: Sep 2010
Posts: 255
Rep Power: 17 |
Dear all,
I am trying to use the suggested method for calculating residance time. The only problem is the unit of source term for AV. the unit is kg/m^3; however, as it is mentioned here, the unit of source term should be [s/s]. Does any body know how to make the unit of source term [s/s]? Thanks |
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September 27, 2016, 11:13 |
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#11 | |
New Member
Prashanth
Join Date: Jun 2016
Posts: 20
Rep Power: 10 |
Quote:
i have to calculate particle residence time and mass concentration in the cell. am feeding steady particles in the transient flow using DPM method. How can i come up with this. Thank you |
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Tags |
problem, residence, rtd, time, tracer |
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