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-   -   creating model for pipe system???? (http://www.cfd-online.com/Forums/ansys-meshing/92376-creating-model-pipe-system.html)

 keng September 13, 2011 01:57

creating model for pipe system????

i'm using gambit to create pipe system in the water tank with the airflow inside the pipe.

do i have to create volume of pipe and tank or just create two volume of fluid(air and H2O) and set the pipe as wall boundary condition

 -mAx- September 13, 2011 04:39

can you post a sketch of your geometry?

 keng September 13, 2011 06:03

http://image.free.in.th/z/tp/gmpic.jpg

here is my problem
air flow in pipe system in water with the heater on bottom face of tank

 -mAx- September 13, 2011 06:56

where is water? (outside pipes?)
I assume you have solid conduction between air and water, right?

 keng September 13, 2011 08:17

yes,water is outside

in the picture is two fluid zone of air and water and i set all air-volume's face except inlet and outlet to be wall

do i have to create solid volume of pipe and tank

 -mAx- September 13, 2011 08:35

ok, I am not experienced with this kind of calculations, but I would take a look at the online help >> two sided walls with thermal conditions (http://my.fit.edu/itresources/manual...e253.htm#32911)
In this optic, you need to define the surfaces separation between air & water as wall.
If you don't do this (and if your splits are correct) then fluent will interpret those surfaces as internal.
Then you have two separated domain on which you can set separated fluid domain (fluid1 & fluid2) http://my.fit.edu/itresources/manual...zone_cont_type

But be sure your fluid domain are correct (if your delete water domain, it remains air), and if you delete air domain, it remains water domain (with hollow instead of pipes >> enable render option in gambit)

 keng September 13, 2011 10:26

so fluents will create wall-shadow for my pipe-wall right???

 -mAx- September 14, 2011 01:33

it is mentionned in the online-help, yes:

"If the wall zone has a fluid or solid region on each side, it is called a "two-sided wall''. When you read a grid with this type of wall zone into FLUENT, a "shadow'' zone will automatically be created so that each side of the wall is a distinct wall zone. In the Wall panel, the shadow zone's name will be shown in the Shadow Face Zone field. You can choose to specify different thermal conditions on each zone, or to couple the two zones"

 keng September 14, 2011 06:51

thank you very much for ur advice,-mAx-
now i'm running it on fluents6.3.26

i set inlet face as pressure_inlet and outlet face as preesure as pressure_outlet for air domain with std k-e solver

but some problem is appear in water domain

my tank has 1 m height in z-axis and i set the gravity of -9.81m/s2 in z
total pressure at bottom of the tank should be density*gravity*height=998.2*9.81*1= 9792.342 Pa or near by right?
but my result show aroud 5100 Pa at bottom of the tank and -4500 Pa on top. i set all tank wall to be copper 0.002m-thickness with shell conduction
i try to turn on laminar zone in water fluid panel but the result is worst,total pressure is around e+18 Pa
how can i fix it?
thank you very much again for ur advice

 -mAx- September 15, 2011 03:18

very quick 'cause I am in vacation... :)
Your pressure difference between inlet and outlet seems to be ok:
5100 - (-4500) = 9600 Pa which are in accordance with hydrostatic.
You can also set an operating pressure which is in fact an offset.

 keng September 15, 2011 05:49

hi max,
im try to patch pressure in solve>initialize>patch to be 4900 Pa which around half of hydrostatic before iteration and the result come good,is that right way to fix it???

Quote:
 You can also set an operating pressure which is in fact an offset.
if i change the operating pressure, is it effect to air domain, i set air-density as ideal-gas and water as piecewiese-linear with temp

THX

 Kamu November 14, 2011 11:10

For a two sided wall when you want to specify different thermal conditions it looks like there is no heat transfer between the walls. How can you enable heat exchange between a wall and its shadow??

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