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-   -   how to set if the domain in vacuum condition (http://www.cfd-online.com/Forums/cfx/22593-how-set-if-domain-vacuum-condition.html)

jasonchang May 22, 2006 22:33

how to set if the domain in vacuum condition
 
Hi,all

I am simulate at such condition,there is only the inlet and wall boundary condition,without outlet. It is in vacuum in the domain,with the pressure 0 Pa.How should I set in cfx .Any suggestion will be appreciated.

If the pressure is 1000Pa, with water to fill the domain, is it a single phase ?

Thanks a lot.

with regards,


Robin May 23, 2006 14:06

Re: how to set if the domain in vacuum condition
 
Hi Jason,

There will always be some pressure, even in a vacuum. You could use Air Ideal Gas as the gas phase in the vacuum and set the pressure to be very low, but not zero.

If you are interested in how the water fills the domain you will need to solve this as a 2 phase problem. Homogeneous multiphase with free surface would do. Some of the water would evaporate, since liquid water will not remain liquid in a vacuum, but assuming your water fills the vessel quickly this may not be an issue. Otherwise, you will also need to account for the phase change.

Regards, Robin

jasonchang May 23, 2006 20:40

Re: how to set if the domain in vacuum condition
 
Dear Robin,

Thanks for your advice. It's very useful to me.

By the way, This vessel has no outlet,only with all and inlet at the bottom.The wall is made of sand ,only allow the air flowing out.Indeed it is use for foundry.

How should I setting the boundry condition? Best wishes.

Jason

Robin May 25, 2006 13:16

Re: how to set if the domain in vacuum condition
 
Hi Jason,

Investment cast moulding is a challenging thing to simulate. Two approaches may be possible:

1. Add a mass sink at the wall to draw air out.

2. Add a porous domain around your part to simulate the sand. You can add appropriate resistances to the movement of air and a higher resistance for the liquid.

Regards, Robin

jasonchang May 26, 2006 01:34

Re: how to set if the domain in vacuum condition
 
Dear Robin,

Thank you.I will try it as what you suggest.

Another problem confuses me: How to set the inlet boundary condition in transient flow ,for example,the inlet pressure.

I try to set it use static pressure and total pressure,but it didn't success,because the fluid I used was multiphase,which is compressive.But just as showed in the CFX_POST ,the Pressure only can be used for incompressive fluid. Regards,Jason

jasonchang May 26, 2006 03:43

Re: how to set if the domain in vacuum condition
 
Hi,Robin,

Can you tell me how to set the mass sink or porosity mdomain in detail? I have never use it before.

Regards,

Jason

jasonchang May 26, 2006 08:31

Re: how to set if the domain in vacuum condition
 
Hi, I browsed the "HELP" of CFX10.0,and found that mass sink can only be used in multicomponent flow. My simulation use water,or alminium at last,for the fluid, so perhaps mass sink doesn't fit my simulation.Maybe I should consider porous model just as what you suggest.But haven't use it before.I'm not sure if I can do it successfully.

Robin May 26, 2006 15:45

Re: how to set if the domain in vacuum condition
 
Sorry, too much detail for me to get into here. I suggest contacting support or reviewing the user documentation.

-Robin


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