Intake-Fan BC/velocity to pressure jump correlation

ahmad_xjtu · March 19, 2019, 22:59

Hi all,
I am trying to find heat losses from a flat plate. The plate is located 1m away from the fans as shown in the picture below. The wind velocity at fans exit is 3m/s. However, I don't know how to input the velocity in terms of pressure jump.
Any help/reference/ book would be highly appreciated.

Thank you

gartz89 · March 20, 2019, 00:57

There is an option for define the polynomial function of normal velocity and static pressure, but unfortunately you have to know the characteristic of the system and I'm not quite sure, but that is not very easy way.

ahmad_xjtu · March 20, 2019, 02:48

thank you for your response
I have checked the option but I don't have required parameters. The only known parameter is velocity. If you come across any tutorial please share. I am searching for the same as well.

thanks again.

LuckyTran · March 20, 2019, 09:32

You need the fan curve. It is a performance spec of the fan. Ask the manufacturer of the fan for this curve.

All fans have a rated volumetric flowrate (usually in CFM if you are in the US) and a pressure head.

You can also crudely backcalculate this pressure head if you know the flowrate (from velocity) and power input needed to run the fan (Wattage). The Wattage either goes into doing work on the air or is dissipated into heat. Electric motors are quite efficient and don't produce that much heat relative to the flow work that the fan does. The pumping power is equal to the volumetric flowrate (velocity x area) multiplied by the static pressure rise.

gartz89 · March 20, 2019, 11:44

Ok but I'm wondering when we know this air - ventilator curve for
(velocity x flow area) and the static pressure how can we define this curve in fluent. For example I've got experimental data and I've got many measure points for pressure and mass flow. If I want to validation this experiment with the simulation, then fluent gives me absurd results. My question is when I've got these parameteres where can I set them, because the pressure and velocity is quite independent. Regards!

LuckyTran · March 20, 2019, 14:34

It's in the Fan boundary conditions settings. It should be pretty obvious how to get there if you have Fluent open. Just choose the fan type and click edit.

ahmad_xjtu · March 20, 2019, 22:23

Thanks guys.
Thanks Luckytran. got it. Thanks for time and effort. I hope I will get it solved now.

Cheers,

gartz89 · March 22, 2019, 07:17

Sorry for disturb you again, but If I define the Fan boundary condition like a interior, after that I define my curve like a polynomial function and solve the problem... and how ansys determinate the balance between losses in the system and this fan curve. Could you explain this, because if I change my interior like a only fan I don't know how to set the losses in the system. Regards!

March 20, 2019, 14:34		#6
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,750 Rep Power: 66	It's in the Fan boundary conditions settings. It should be pretty obvious how to get there if you have Fluent open. Just choose the fan type and click edit. gartz89 likes this.

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March 20, 2019, 00:57		#2
gartz89 Member Angel Penev Join Date: Apr 2016 Location: Bulgaria Posts: 47 Rep Power: 10	There is an option for define the polynomial function of normal velocity and static pressure, but unfortunately you have to know the characteristic of the system and I'm not quite sure, but that is not very easy way.

March 20, 2019, 02:48		#3
ahmad_xjtu New Member ahmad Join Date: Mar 2018 Posts: 21 Rep Power: 8	thank you for your response I have checked the option but I don't have required parameters. The only known parameter is velocity. If you come across any tutorial please share. I am searching for the same as well. thanks again.

March 20, 2019, 09:32		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,750 Rep Power: 66	You need the fan curve. It is a performance spec of the fan. Ask the manufacturer of the fan for this curve. All fans have a rated volumetric flowrate (usually in CFM if you are in the US) and a pressure head. You can also crudely backcalculate this pressure head if you know the flowrate (from velocity) and power input needed to run the fan (Wattage). The Wattage either goes into doing work on the air or is dissipated into heat. Electric motors are quite efficient and don't produce that much heat relative to the flow work that the fan does. The pumping power is equal to the volumetric flowrate (velocity x area) multiplied by the static pressure rise.

March 20, 2019, 11:44		#5
gartz89 Member Angel Penev Join Date: Apr 2016 Location: Bulgaria Posts: 47 Rep Power: 10	Ok but I'm wondering when we know this air - ventilator curve for (velocity x flow area) and the static pressure how can we define this curve in fluent. For example I've got experimental data and I've got many measure points for pressure and mass flow. If I want to validation this experiment with the simulation, then fluent gives me absurd results. My question is when I've got these parameteres where can I set them, because the pressure and velocity is quite independent. Regards!

March 20, 2019, 22:23		#7
ahmad_xjtu New Member ahmad Join Date: Mar 2018 Posts: 21 Rep Power: 8	Thanks guys. Thanks Luckytran. got it. Thanks for time and effort. I hope I will get it solved now. Cheers,

March 22, 2019, 07:17		#8
gartz89 Member Angel Penev Join Date: Apr 2016 Location: Bulgaria Posts: 47 Rep Power: 10	Sorry for disturb you again, but If I define the Fan boundary condition like a interior, after that I define my curve like a polynomial function and solve the problem... and how ansys determinate the balance between losses in the system and this fan curve. Could you explain this, because if I change my interior like a only fan I don't know how to set the losses in the system. Regards!