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 ritmat July 16, 2007 04:24

set up boundary

hi everybody. I would like some advice about my problem. I have lets say one cube full of air without velocity and one of his faces is at 1800 C . This face is heating this volume by radiation. Then i want to set up a cooling system around that, in order to decrease the temperature at faces of the cube. So i had two plates around the cube where a flow of water is flowing between the two plates. The water inside is at 2 bara. But i have problem to set up the boundary conditions. i set up temperature of walls for the face of the cube which causes radiation , then i use velocity inlet for inlet of water and then pressure outlet to set up my pressure in the water. But should I and can I set up teh pressure in the inlet cos i get reversed flow in my outlet?

I hope i am clear in my question and i would be grateful if anyone can help me... thanks

 ritmat July 18, 2007 03:09

Re: set up boundary

ok i see that my question is not that clear.... My problem is that i never used fluent with two fluids so i am not sure about the set up. what i am doing now is that i have one inlet for the air without speed on one face of my cube and one outlet at the opposite face (outflow). The other face of my cube are surrounded by a layer of steel and then water which has one inlet (velocity inlet) and one outlet (outflow). it is not converging and i got reverse flow. Anybody has an idea. One of my problem is to set the pressure of the water at 2 bara inside the cooling plate. How can I do . Thnak you

 ritmat July 19, 2007 09:11

Re: set up boundary

 ritmat July 20, 2007 04:45

Re: set up boundary

now i am there: i have one velocity inlet with 0 velocity at 1800 deg C for the face which radiate the volume of air. The outlet is at pressure atm. The inlet of water is at 20 m/s with T of 60 degC and the pressure outlet of water at 2bara. What should be the boundary conditions for the solid plates between water and air. Cos my water doesnt even become hot...

 red lemon July 23, 2007 18:23

Re: set up boundary

check heat balance using report>fluxes. Ensure energy is being transferred if mesh is conformal or using non conformal interfaces. Solid plates can be thin or thick walls. For former (coupled walls with shell conduction) just define 1D heat conduction materials otherwise define solid material properties for 3D heat conduction. For conjugate cases use double precision solver due to vastly different thermal conductivities.

 ritmat July 24, 2007 03:38

Re: set up boundary

thanks for advice. I altough found few problems. One was due to my geometry. My interface air/steel and steel/water had not connected faces. But in my case i have to use couple for the boundary conditions of my wall interface cos i dont know temperature and convection coefficient at the interface. So if you get a shadow face after connected faces at interface you can then coupled the BC and just require to set up internal emission ( iam using solid plate define by solid material properties) I succeed to get a convergence for a pressure atm of water with velocity of 0.1m/s. But now i just put the outlet pressure at Pgauge 100000 to fix 2 bara of water, and now i got again this reverse flow???? the pressure at the inlet should increase automaticallly,isnt it? One last thing, i am not clear as well with how in the tutorial of radiation they adjust the value for gravity. I would like to know exactly why, cos i saw as well that i had problem to converge my problem with a value of 9.81m/s2 for gravity. It was ok when i disabled it. Put in my problem i need to input that into my equations cos outlet of water is higher than inlet. thanks for help

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