Menu

Discussion Forum

New Discussion
Filtra

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Continuity in transport of diluted species

Posted 27 giu 2017, 07:58 GMT-4 5 Replies

Daniel Hernández
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi:

I´m working in a 3D model of a pipe cross junction with different velocity conditions, about chlorine distribution throught de cross section (see attached image please). My model only consist of 2 inlets, 1 with clean water an 1 with a constant concentration of 250mol/m^3, and two outlets. When I run the simulation, I check the two outlets, resulting this:

Concentrations

inlet 1 = 0 mol/m3
inlet 2 = 250 mol/m3
outlet 1= 58.7643 mol/m3
outlet 2= 247.905551 mol/m3

A wanto to know if this is correct. I supose that the concentration sum of two inlets must be 250mol/m3, but the two outlets reach 360.66981 mol/m3. There exists other form to verify the continuity of species?

Thank you for reading.

Attachments:

5 Replies Last Post 29 giu 2017, 06:14 GMT-4
Lasse Murtomäki
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 7 years ago 28 giu 2017, 02:53 GMT-4
How about the mass balance, i.e. what are the flow rates? I experienced troubles with mass balance until I used a denser mesh.

BR
Lasse
How about the mass balance, i.e. what are the flow rates? I experienced troubles with mass balance until I used a denser mesh. BR Lasse
Daniel Hernández
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 7 years ago 28 giu 2017, 08:39 GMT-4

How about the mass balance, i.e. what are the flow rates? I experienced troubles with mass balance until I used a denser mesh.

BR
Lasse


Thanks for answer:

The flow rates for this example are these:

**INLETS**
inlet 1 = 6.553 lt/s
inlet 2 = 12.432 lt/s

inlet 1 + inlet 2 = 18.9851 lt/s

**OUTLETS**
outlet 1 = 8.473
outlet 2 = 10.492

outlet 1 + outlet 2 = 18.9647 lt/s

**difference between inlets, outlets = 0.0204 lt/s (0.107% error)

About flowrates, the continuity is reached with very slow error, this happens in all different flow conditions that I am simulating. The mesh in all cases is fine, predefined by comsol for turbulent conditions and the y+ = 11.1, at the same way, this is for turbulent flow conditions.

But I don´t know why the concentration continuity is not developed like this.

Thanks BR Lasse
[QUOTE] How about the mass balance, i.e. what are the flow rates? I experienced troubles with mass balance until I used a denser mesh. BR Lasse [/QUOTE] Thanks for answer: The flow rates for this example are these: **INLETS** inlet 1 = 6.553 lt/s inlet 2 = 12.432 lt/s inlet 1 + inlet 2 = 18.9851 lt/s **OUTLETS** outlet 1 = 8.473 outlet 2 = 10.492 outlet 1 + outlet 2 = 18.9647 lt/s **difference between inlets, outlets = 0.0204 lt/s (0.107% error) About flowrates, the continuity is reached with very slow error, this happens in all different flow conditions that I am simulating. The mesh in all cases is fine, predefined by comsol for turbulent conditions and the y+ = 11.1, at the same way, this is for turbulent flow conditions. But I don´t know why the concentration continuity is not developed like this. Thanks BR Lasse
Lasse Murtomäki
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 7 years ago 29 giu 2017, 01:42 GMT-4
Your picture looks laminar flow. What is the Reynolds number? What are the dimensions of the picture?

Lasse
Your picture looks laminar flow. What is the Reynolds number? What are the dimensions of the picture? Lasse
Lasse Murtomäki
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 7 years ago 29 giu 2017, 02:54 GMT-4
Actually your mass balance is quite good:

Inflow = (0.25 mol/L)*(12.432 L/s) = 3.108 mol/s

Outflow1 = (0.0587643 mol/L)*(8.473 L/s) = 0.481 mol/s
Outflow2 = (0.2479 mol/L)*(10.492 L/s) = 2.601 mol/s

Total outflow = 3.082 mol/s

Error is thus only 0.8%.
Actually your mass balance is quite good: Inflow = (0.25 mol/L)*(12.432 L/s) = 3.108 mol/s Outflow1 = (0.0587643 mol/L)*(8.473 L/s) = 0.481 mol/s Outflow2 = (0.2479 mol/L)*(10.492 L/s) = 2.601 mol/s Total outflow = 3.082 mol/s Error is thus only 0.8%.
Daniel Hernández
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 7 years ago 29 giu 2017, 06:14 GMT-4

Actually your mass balance is quite good:

Inflow = (0.25 mol/L)*(12.432 L/s) = 3.108 mol/s

Outflow1 = (0.0587643 mol/L)*(8.473 L/s) = 0.481 mol/s
Outflow2 = (0.2479 mol/L)*(10.492 L/s) = 2.601 mol/s

Total outflow = 3.082 mol/s

Error is thus only 0.8%.


THANKS VERY MUCH LASSE MUTOMÄKI!!!

This is what i'm talking about, I didn't know the correct way to see my mass balance. I only maked simple sums of concentration, buy what I need to verify is a particle flow depending time, like you did.

Thanks again!

Daniel Hernández Cervantes
[QUOTE] Actually your mass balance is quite good: Inflow = (0.25 mol/L)*(12.432 L/s) = 3.108 mol/s Outflow1 = (0.0587643 mol/L)*(8.473 L/s) = 0.481 mol/s Outflow2 = (0.2479 mol/L)*(10.492 L/s) = 2.601 mol/s Total outflow = 3.082 mol/s Error is thus only 0.8%. [/QUOTE] THANKS VERY MUCH LASSE MUTOMÄKI!!! This is what i'm talking about, I didn't know the correct way to see my mass balance. I only maked simple sums of concentration, buy what I need to verify is a particle flow depending time, like you did. Thanks again! Daniel Hernández Cervantes

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content