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Old   January 27, 2010, 06:15
Post Multiphase Problem
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I'm working on senior project about the evaporation of gasohol, We do the experiment on a real fuel-tank with E0,E10,E20 and E85 I've search on this forum and found the same topic, but no reply those topic is 2006 I hope someone can help me here.
My teacher suggest me to do a simulation of fuel-tank model by fluent to compare the data we got from experiment, I'm using auto-cad to draw a model then export to STEP file import it to GAMBIT the model separated to 2 part the upper part is air and lower part is C8H18.
In GAMBIT i combine the face of upper part and lower part together and set it to interior. another face is all wall.
My model have some problem when i use mesh as HEX/WEDGE fluent can't read the file. so I use TET/HYBRID instead and its work well.

And now for fluent I want to set a condition like fuel-tank have 2 part air and c8h18 then all wall have a temperature change with time, but i found that if i want to vary value with time I've to write C language or something else so, my teacher said just iterate and change temperature every time step this should be work.
At first we gonna put a pressure relief valve on the model and let it be Outlet and try to show how volume of c8h18 change, but now the time is not enough so he want me to show how temperature flow in the tank.
then I try this

- activate Energy Equation and Multiphase as Volume of Fluid
- change primary phase to c8h18
- add temperature for all wall = 313.15K(40C) (air and c8h18 start at reference at 298.15K(25C)
- initialize the temperature of all zone = 313.1508

I'm just notice that when activate Multiphase it will automatic change to Unsteady isn't it?

then I'm iterate it by 1sec and 10 and this happening

Updating solution at time level N... done.
iter continuity x-velocity y-velocity z-velocity energy time/iter
! 1 solution is converged
1 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 2.9206e-08 0:00:19 19
Flow time = 1, time step = 1
9 more time steps

I didn't familiar to this output it's not like this with my previous work, so I search a word about 'solution is converged' and it seems to be a bad sign.
I don't know what's wrong with my model or my setting.

My work here is now just an extra to my project, so if it not work i have to drop it, but I'm not give up yet.

Thank for reading and apologies for my poor English.
Attached Images
File Type: jpg Fuel-tank.JPG (20.9 KB, 12 views)
File Type: jpg Fuel-tank-mesh.JPG (88.3 KB, 11 views)
File Type: jpg Result.JPG (31.0 KB, 13 views)
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Old   January 28, 2010, 02:42
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'solution is converged' implied that there is nothing to compute.

I think the problem lies within the case setup. It is because you 'initialize the temperature of all zone = 313.1508', and the wall is also set to 313.15. Hence no heat transfer.
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Old   January 28, 2010, 03:24
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i agree with Mas comment. There is too less changes for the time u set.

Initialization is the method u set intial condition of every zone in the simulation.
For example, u set the fluid inside tank as 500 celcius, then once u start simulate, u will get whole tank fluid is 500 celcius. It just like u pouring 500 celcius of fluid into tank.

make sure u set the initialization carefully and same with the real situation.

initialization is totally useless in steady simulation (unless u meet divergence)
but it very very important in unsteady simulation.

Add Reputation if I am right
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Old   January 28, 2010, 03:43
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Hi again.
Thank for reply. I was thinking initialize is only appear to the origin of model. what a shame. Maybe i should read more manual.
I'll work on this again tonight. Hope it's work.

anyways thank you
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