# how to set inlet and outlet?

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 May 17, 2004, 23:44 how to set inlet and outlet? #1 green Guest   Posts: n/a 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.

 May 17, 2004, 23:53 Re: how to set inlet and outlet? #2 leon mills Guest   Posts: n/a 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

 May 18, 2004, 00:54 Re: how to set inlet and outlet? #3 green Guest   Posts: n/a 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

 May 18, 2004, 01:36 Re: how to set inlet and outlet? #4 leon mills Guest   Posts: n/a 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.

 May 18, 2004, 23:41 Re: how to set inlet and outlet? #5 green Guest   Posts: n/a 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.

 May 18, 2004, 23:52 Re: how to set inlet and outlet? #6 leon mills Guest   Posts: n/a 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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