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Problems in pressure when using mass flow rate outlet |
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May 30, 2011, 18:12 |
Problems in pressure when using mass flow rate outlet
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#1 |
New Member
rafik
Join Date: Jan 2011
Posts: 16
Rep Power: 15 |
hi all,
i faced a problem in the pressure along car park simulation , when i use the exhust fans as outlet with mass flow rate the pressure gradient is increasing by getting closer to the outlet which is unacceptable solution i used the supply fans as opening with pressure of 0 [pa] i think i miss some physical inputs to have the correct solution. what is the correct setup of the outlet and inlet to have more realistic pressure solution note: fluid is Air at 25 ref pressure at 1 [atm] thnx for your time and help |
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May 30, 2011, 18:49 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,830
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You use a boundary condition setup which matches what you are trying to model. The documentation has some comments about boundary condition choice which is worth reading as well.
And what do you mean by "the pressure gradient is increasing by getting closer to the outlet which is unacceptable"? |
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May 30, 2011, 19:18 |
problems with the pressure
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#3 |
New Member
rafik
Join Date: Jan 2011
Posts: 16
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i mean that the pressure before the outlet is greater than the pressure after the inlet
which i think its not realistc because the flow moves from the high pressure to the lower pressure not vice versa my condition is to maintain only the outlet (Mass Flow Rate value) thnx |
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June 1, 2011, 05:03 |
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#4 |
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rafik
Join Date: Jan 2011
Posts: 16
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hi all
i want to ask if i use for outlet with mass flow rate if i chose Shift Pressure option would it help me to have a -ve pressure befor the outlet and what about pressure profile blend value thnx for help |
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June 1, 2011, 07:04 |
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#5 |
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Glenn Horrocks
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Location: Sydney, Australia
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Can you post an image of what you are seeing, which you think is not realistic?
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June 1, 2011, 07:13 |
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#6 |
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Redddy
Join Date: Sep 2010
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hiii,
Usually, i am using mass flow rate as outlet and TP = 0 as inlet for fans. Does your fan is at open atmosphere? I means to say no pressure drop at in let and outlet. if it is so, you can use inlet Bcs as TP=0 and outlet as SP=0, then frm these you will get mass flow rate. still it is not your cup of tea, if possible try to explain your problems in more details? Glenn Horrocks feedback is more helpful... |
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June 1, 2011, 07:47 |
sorry for lack of details
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#7 |
New Member
rafik
Join Date: Jan 2011
Posts: 16
Rep Power: 15 |
sorry for lack of details
and thanx for trying to help i attached the car park i am working with the openings are [ 0 pa] the outlets are 11 [kg/s] each the domain is air with pres ref of [0 pa] in my opinion the pressure before the outlet has to be lower than the pressure after the inlet (opening) acording to flow direction sorry for mis understanding of me and thank you for your help and time |
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June 1, 2011, 08:25 |
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#8 |
New Member
Redddy
Join Date: Sep 2010
Posts: 25
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Check with Total pressure at both sides.
Apply Bernoulli equation on both sides and check it. I think what every measuring is static pressure. it was same as flow through diffuser or diverging channel. |
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June 1, 2011, 18:26 |
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#9 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,830
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Also your reference pressure should be atmospheric pressure, not zero pressure. Unless this is a car park in space that is.
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June 2, 2011, 05:04 |
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#10 |
New Member
rafik
Join Date: Jan 2011
Posts: 16
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i am sorry
the domain Reference pressure is [1 atm] air @ 25 [C] the opening boundry pressure is [0 pa] thnx |
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January 2, 2014, 09:14 |
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#11 |
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Abdul Afoo Parkar
Join Date: Oct 2012
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I would have suggested making the Inlets as massFlow specified and outlet as Average Static Pressure of 0 or -1.
Probably your problem is solved by now. Did you manage to figure out what was wrong? |
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January 2, 2014, 17:21 |
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#12 |
Senior Member
hamed
Join Date: Apr 2009
Posts: 148
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I think you need to define a pressure inlet rather than opening.using mass flow BC and an opening sometimes leads to diverged results
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