CFD Online Discussion Forums

CFD Online Discussion Forums (
-   FLUENT (
-   -   Flow of tracer in a tube (

uma September 29, 2003 18:55

Flow of tracer in a tube
Hello All, I am trying to model a tracer introduced from a small tube into a main straight tube.I will have a steady flow of the main fluid in the straight tube. After a little distance, I have the tracer introduced through a small tube at an inclination to the main tube. I need to measure the tracer output velocity at the end of the tube. I know the velocity of the fluid in the main tube and also I am using the UDF to have different velocity profiles for the tracer. I need to use laminar flow in the tubes. Can someone suggest me which multiphase model can I use and any suggestions about what kind of output should I take(a pressure outlet or outflow).Thankyou so much for taking your time. Best Regards, Uma

thomas September 30, 2003 04:10

Re: Flow of tracer in a tube
Hey, First of you are not really in a multiphase simulation case, you have a multispecies flow. You tracer represents the other species and has its own transport equation. To do that either you declare a UDS in a UDF to transport the volume fraction of your tracer for example, either you use Fluent default species transport set-up (see fluent users documentation to use it). For the oultlet boundary condition, it depends on what is going on at the outlet. Outflow will not work if backflow happen at the outlet. I would that pressure outlet will work in any case.

hope this help, thomas.

zwdi September 30, 2003 10:43

Re: Flow of tracer in a tube
Hi thomas, I tries to use species transport model.

By clicking Species Transport, Fluent will automatively active Energy option. I don't need to calculate energy for my case.

By using text command, define--->model--->species--->species transport--->material, I checked the Species Transport option, it acturally didn't active. I don't know why. Moreover, for materials, could I define my own materials,not using database, in Fluent?

Thanks a lot.


uma September 30, 2003 10:44

Re: Flow of tracer in a tube
Hello Thomas, Thanks a lot! I will work with ur suggestions and see if it works!!Once again thanks a lot for the help!! Best Regards, Uma

thomas October 1, 2003 07:19

Re: Flow of tracer in a tube
Hey, You can effectively define your own component in the data-base in terms of density and viscosity. For the rest I am surprise that the energy is enable by default. You should check again, otherwise you can implement that by UDS which pretty simple to do.

cheers thomas

rey October 1, 2003 10:30

Re: Flow of tracer in a tube
Hello Thomas, I am in a situation similar to the above case. I do modelling of blood flow in a vein(which is a straight long tube) and inject a contrast material (through a small tube connectd to the main tube after a little distance from the main tube) into the vein and try to find the concentration or velocity profile for the contrast material at the end of the vein. Do you think even I have to use species transport here? Because I thought that my flow was a multiphase model and I am trying to use the mixture model in multiphase.Please let me know if I am wrong so that I can correct it. thanks! best wishes rey

thomas October 2, 2003 04:03

Re: Flow of tracer in a tube
Hey, First off in exchange of some information you got to tell from which country are you (means what courntry is ? it is just for personal culture :). Okay concerning your case I would effectively say you are injected a tracer. It means your second fluid is not a second phase but a second species. So I would say you have to define a multispecies case and not a multiphase case. However I do not know the particular properties of Blood so maybe your tracer will be flowing under the droplet or particle shape. Therefore you are gonna have to define a particle diameter which in that case can be done using the mixture model.

Hope this is what you were expected! Do not forget to answer my question :) regards thomas

rey October 2, 2003 10:23

Re: Flow of tracer in a tube
Hello Thomas! I am actually from India but residing in U.S.A. this is my pen name i use at times.. and implies... this answers ur questions :) Regarding the problem, i know the density and viscosity of blood and contrast and they are density-blood (1060 kg/m3),contrast(1330 kg/m3) viscosity-blood(0.0032 kg/m-sec) and contrast(0.0095 kg/m-sec). I assume the diameter of contrast as 8e-09m. And all I want is that these two mix very well and then find the concentration of the contrast at the outlet.So, can I still use multiphase(but when I am using the multiphase, I am getting the velocity profile of the contrast as same as that of the mixture and blood..(so i am not sure if this is right). I hope I am clear.thanks a lot for taking ur time.. its a huge help for me! Best Regards, Rey

thomas October 3, 2003 04:10

Re: Flow of tracer in a tube
Hey, Well the fact you get the same velcotiy profile (means same profile but not same intensity of velocity) is normal i guess in your case. Both fluid have slightly the same properties so the interaction between themselves will be mininum -> this is the characteristic of a tracer/contrast method. So you are assumming a certain diameter for your contrast. Are you doing that because the physical properties of your tracer involves that your contrast is flowing under bubble shape or are you doing that because the mixture model needs to enter a diameter for the second phase. In the second case do not declare anymore a second phase (=need a diameter ) but a second spece (= an additional scalar with its own transport equation).

hope this is what you were expected. thomas

rey October 3, 2003 14:53

Re: Flow of tracer in a tube
Hello Thomas, Thanks a lot! I think this is pretty much what I wanted. I am mentioning the diameter of the contrast(just because the model is asking for it). So, I guess I must get started with the species model now. Thanks a million for all ur advice!! Best Regards, Rey

All times are GMT -4. The time now is 14:12.