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-   -   how to set inlet and outlet? (https://www.cfd-online.com/Forums/phoenics/51760-how-set-inlet-outlet.html)

 green May 17, 2004 23:44

how to set inlet and outlet?

Air is export from a pipe having special shape with a fun, the pipe is in a room. The volume rate of the fan is given. I want to konw the velocity and pressure in the pipe, how I should set the inlet and outlet? I have tried different ways. First, I set the velocity at outlet, but the pressure in the pipe is positive, but this is not right. Then I set the outlet to default, and before the outlet I set a fan with given volume rate, but it seems difficult to converge. Do you have any good idea? Thanks.

 leon mills May 17, 2004 23:53

Re: how to set inlet and outlet?

Green,

If you are trying to look at the properties in the pipe only, then I suggest setting up the problem as follows.

Define the pipe, maybe using BFC. Define the fan as an inlet with a fixed m3/sec Define the outlet as an opening, with the correct coefficient. Check POLIS for this as it has some good examples.

Hope this helps.

Leon

 green May 18, 2004 00:54

Re: how to set inlet and outlet?

I have done it in the way you told. But I also want to know if there is a smoke source at the inlet of the pipe, all the smoke will be export through the pipe or there will be some s,oke going into the room space. So I can't set an inlet at one end of the pipe, do you have any good idea? Thanks

 leon mills May 18, 2004 01:36

Re: how to set inlet and outlet?

The big question is, does the pressure profile in the pipe matter.

If not, just model the smoke entering the room from the pipe.

You could work out from a 'pipe only' model the flow accross the outlet and ake the intel into the room, seperate model, be the same.

There maybe be a way of linking the two but I do not know how.

Otherwise to get suffcient resolution in the pipe region look at fine grid embedding.

 green May 18, 2004 23:41

Re: how to set inlet and outlet?

The pressure in the pipe is what I want to know. I only know the velocity at the fan and the pressure at the room which is 1.0e5. I want to know the pressure and velocity in the pipe. I have tried to do it in such a way. Just before the outlet, I set a fan with the given velocity, but I don't know how to set the pressure in the outlet, because I don't know the pressure drop in the pipe. In fact, the pressure drop is what I want to konw.

 leon mills May 18, 2004 23:52

Re: how to set inlet and outlet?

Green,

If all you are after is the pressure drop in the pipe.

Set up the geometry of the pipe. If there are bends or the like i recomend using BFC.

I find that with fans it is better to set the inlet pressure, to induce a velocity, or a flow rate. I have found this method to be more reliable when I want to find out velocities and pressures.

If you are talking about friction losses, have a look through POLIS and CHAM website, for examples on wall friction and surface roughness.

I would set the oulet pressure to be the ambien tpressure of the room. For this type of example it would seem fair.

Leon

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