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Munggang March 7, 2012 02:37

How to create smaller pipe inside bigger pipe?

I want to model a flash tank. It is basically a cylindrical tank in which the inlet comes from the side, the outlet 1 at the bottom and the outlet 2 at the top. The size of inlet and outlet pipe are much smaller than the vessel.

The inlet is a hot water, the outlet 1 is colder water and the outlet 2 is the vapour.

I did my geometry using design modeller as follow:
- create the cylindrical tank using skin
- create inlet using extrude
- create outlet 1 and outlet 2 using extrude

The DM automatically create the whole parts as one body. I did simulation in fluent using this single body, and it was good.

The problem is, in actual condition, the outlet 2 is basically a pipe that goes through few centimeters into the vessel. Hence, there has to be steel separation between the vapor inside the tank and the vapor that goes out into outlet 2.

When I try to freeze the outlet 2 at DM (so that there are 2 bodies), the software assume it as it is not connected with the tank so that there's no vapor coming out when I simulate it.

Does anyone know, how to connect these 2 bodies but still treat them as different bodies? I need to do so because I want to define the wall heat flux of the outlet 2 in fluent.

Any help will be appreciated.

Thanks in advance.

PSYMN March 7, 2012 10:14

I think your problem was the first step...

Instead of modeling the tank as a skin, start with a solid cylinder for the outer dimensions... Then subtract a cylinder for the inner dimensions, then create your inlet, outlets, etc...

Munggang March 7, 2012 15:01


Thanks a lot for your help. This is my general design

Actually, when applying skin function, I define it as "add material" and set the property as fluid. The problem arises when I tried to define my "outlet 2" as different body because its wall properties is different from the cylindrical vessel. I did that by freezing the "outlet 2", so that I have 2 bodies 2 parts at the moment.

When I use the geometry in fluent, the software seems to assume the "outlet 2" is not a part of the cylindrical tank. Thus, there's no fluid coming out of it. This condition is different from when I just combine the "outlet 2" body with the cylindrical body into single body (in which worked perfectly fine). Seems like the surface between the bodies are not in contact.

Do you know how to solve this problem? How to create a contact surface between the "outlet 2" pipe with the main cylindrical tank but still treat them as separate entity?

Thanks before.

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