CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

tracer flow

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 18, 2003, 13:25
Default tracer flow
  #1
uma
Guest
 
Posts: n/a
Hello All, I need help with the flow of a tracer in a fluid. I am using the multispecies model. I am trying to give a step input of the tracer( with a udf of step input with a velocity of 3.145 m/sec) and the other fluid flows with a velocity of 0.153m/sec at constant flow rate.Both the fluids have similar viscosities and densities. When you give a step input to a system, you have to find a bell curve concentration profile at the outlet( trying to plot the concentration of the tracer with flow time). But I am getting the profile of the tracer just as the input, I mean a perect square. Can anyone help me to know if there is some mistake in my idea. Or, is it that you can not get a bell curve, when you give a step input. I thought that when I use the model above, it may be that there is nothing much going on in the system, and so I am getting a square profile of the concentration at the outlet. So, i tried to give to give few other inlets, through which the fluid enters and then find the concentration profile of the tracer. But even then, the profile is a square. can anyone help me! Thanks a lot for taking your time. Best regards, Uma
  Reply With Quote

Old   October 18, 2003, 17:48
Default Re: tracer flow
  #2
thomas
Guest
 
Posts: n/a
Hi, I do not think you made a mistake in your setting. However according to your flow parameter I am not really surprise of your result. You have a Fluid 1 flowing at 0.153 m/s. The aim of a tracer is to roughly charaterize the behaviour of this fluid 1 in a finite domain ( residence time, local mixing capability ect ect ). If I follow what you say you inject a tracer (Fluid 2) at 3,145 m/s which has the same density. With such a velocity, don't you think it is this Fluid 2 which is gonna 'dominate' the flow in the domain. Therefore I am not surprise that you found such a result at the outlet if you intiate a step of Fluid 2 using this velcotiy. Have done some previous experiments using those velocities ? what are the results ? If those velocities are those you have to study, what I could suggest is to maybe just introduce your tracer not using a step, but just a Dirac impulse. What do you think about all that ?

cheers thomas ( anti-psg )
  Reply With Quote

Old   October 19, 2003, 20:56
Default Re: tracer flow
  #3
uma
Guest
 
Posts: n/a
Hello Thomas! Thanks a lot for taking your time. I did not do any experiments for this yet. I am trying to see if the model works and then do the experiment. As you said, the velocity of the tracer must be dominating the system, so I will try to give smaller value and do the simulation. Also, by Dirac impulse, do you mean a high input value for a very less time. I usually give the tracer input as the unsteady state input and plot it as the surface integral of the concentration vs flow time at the outlet. In that case, what amount of flow time should I use for the dirac impulse at the inlet(0.2 or 1 or what is the value).I hope I am clear. Once again thanks a lot for taking you time. Best Regards, Uma
  Reply With Quote

Old   October 20, 2003, 05:35
Default Re: tracer flow
  #4
thomas
Guest
 
Posts: n/a
Hello, The signal you set at the inlet of your domain depends on what information your looking for ! For example you can be searching if you reactor closer than a slug reactor or than a CSTR. Personnaly, i am sorry I cannot bring you real futher information wihtout having the problem under my eyes. Just let me know what are your results using smaller tracer velocity, or shorter time injection at the inlet.

Cheers thomas

  Reply With Quote

Old   October 21, 2003, 22:47
Default Re: tracer flow
  #5
uma
Guest
 
Posts: n/a
Hello Thomas, I am able to get a curve instead of the step concentration profile for lower velocities. Thanks a lot for all the guidance and help. Best regards, Uma
  Reply With Quote

Old   October 22, 2003, 11:02
Default Re: tracer flow
  #6
thomas
Guest
 
Posts: n/a
Just for personal interest, can you describe me a little bit the type of reactor, process , or whatever thing you are trying to simulate ???? thanks. thomas
  Reply With Quote

Old   October 22, 2003, 15:13
Default Re: tracer flow
  #7
uma
Guest
 
Posts: n/a
Hello Thomas, I am actually doing study of the contrast in the veins. This, I guess is similar to the injection of a tracer in a vessel. I hope I have answered your question. Best Regards, Uma
  Reply With Quote

Old   October 23, 2003, 15:16
Default Re: tracer flow
  #8
thomas
Guest
 
Posts: n/a
HI, Your problem made me wonder about what kinda of information you could get by using a step impulse for the tracer. I am just more familiar with normal injection or dirac impulse. thomas
  Reply With Quote

Old   October 28, 2003, 13:13
Default Re: tracer flow
  #9
uma
Guest
 
Posts: n/a
Hello Thomas, I apologise for getting back late. I am very sorry about this. Regarding the question, in the Clinical cases, usually the contrast material is given as a step input,not an exact step(more like a trapezoidal but with very less inclination and tends to look more like a square) and not as a dirac impulse. I hope I have answered your questions. Best Regards, Uma
  Reply With Quote

Old   October 28, 2003, 18:11
Default Re: tracer flow
  #10
zwdi
Guest
 
Posts: n/a
Hello Uma, I am trying to simulate the traceflow also. In my case, no energy is involved. I want to use multispeices model as you did also. But I could not find this model in Fluent. I only can find SPEICES model in Fluent. Could you please give me some help? Did you use UDF for scalar transportation? Thank you very much. Best regards, Zwdi
  Reply With Quote

Old   October 29, 2003, 11:54
Default Re: tracer flow
  #11
uma
Guest
 
Posts: n/a
Hello Zwdi, I think if your problem is similar to mine, then you can work with the species model. This model is going to solve for all the species that u specify.so this is infact the multispecies model i think. You have to define the materials that you want to use in the model. Even I dont need the energy equation, I do not know how to eliminate it. But one way where I can get the residuals very very low, I mean a straight line with a very low value in the residuals plot. For this, after u select the species model in fluent, go to materials panel. In the mixture-type box, scroll and select mixture. Then go to Cp in the column below and change its value as constant and make the value zero. I dont know if this will help you. But you can give a try. I hope I am clear, else please let me know. And i did not use any UDF for scalar transportation. Good luck! Best Regards, Uma
  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Seeding the Flow - Tracer gases? Carlos FLUENT 2 August 23, 2007 12:15
reversed flow at velocity inlet / mass flow inlet ib FLUENT 1 March 26, 2007 14:11
How to change from mass flow to volume flow rate stanley FLUENT 1 February 2, 2007 07:44
potential flow vs. Euler flow curious ... Main CFD Forum 23 July 21, 2006 08:40
Plug Flow Franck Main CFD Forum 3 September 4, 2003 06:57


All times are GMT -4. The time now is 00:52.