Inlet vent and Pressure outlet

Ramesh_21M · May 20, 2022, 01:14

Hi all,

I'm working on a problem where I have to find the pressure at the inlet to get the desired pressure at the outlet of the pipe. I tried using Inlet vent type at the inlet and mass flow outlet, but I don't think the values I'm getting are right. I tried using pressure outlet with Target mass flow turned on, but the continuity equation keeps on increasing, Since the default mass flow rate is 1 Kg/s, when I put the required gauge pressure as the desired pressure (4 bar - converted to gauge pressure and entered), the continuity keeps on increasing.

I don't know what I'm not understanding, Kindly help me with this, Thanks in advance for your time!

I'm new here, please excuse any mistakes if made.

LuckyTran · May 20, 2022, 11:09

Continuity rises means nothing.

What exactly are you trying to do? What are the constraints and what are you trying to retrieve? What is known?

Ramesh_21M · May 20, 2022, 11:54

Hi, Thanks for your reply.

I need to find how much pressure the inlet should be in, to get the desired pressure at the outlet (Absolute pressure: 4 bar).

The fluid is steam.

LuckyTran · May 21, 2022, 03:44

So use a pressure outlet with outlet pressure equal to 4 bar and mass flow inlet or velocity inlet depending on whatever is your operating condition. Then whatever pressure you get in the solution is the pressure you are looking for.

Ramesh_21M · May 21, 2022, 04:00

Thanks for your suggestion, I will try that.

can you please explain, can inlet-vent with pressure-outlet be used to solve this?

Again, thanks for your help!

LuckyTran · May 21, 2022, 09:01

If you absolutely must use an inlet-vent, then there are two ways to proceed and both require iterating at the outlet level on your part.

1) Use an inlet vent and pressure outlet with outlet pressure set to 4 bar. Guess an inlet pressure. Run the case until convergence. Check the massflow. If the massflow is too low/high, increase/decrease the inlet pressure, run it again. Check it again. Repeat. Repeat. Repeat until you match the desired flowrate. Once that is done, possibly some 1000 iterations later, then retrieve the inlet pressure.

2) Use an inlet vent and pressure outlet with targeted mass flow rate setting. Set the flow rate. Set an inlet pressure. Run the case until convergence. Check the outlet pressure if it matches 4 bar or not. If it is too low/high, then increase/decrease the inlet pressure. Run the case again. And again. And again until the outlet pressure reaches 4 bar. Once it reaches 4 bar, get the inlet pressure.

Ramesh_21M · May 22, 2022, 00:32

Thanks a lot, I will try that.

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May 20, 2022, 11:09		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	Continuity rises means nothing. What exactly are you trying to do? What are the constraints and what are you trying to retrieve? What is known?

May 20, 2022, 11:54		#3
Ramesh_21M New Member Ramesh M Join Date: May 2022 Posts: 4 Rep Power: 3	Hi, Thanks for your reply. I need to find how much pressure the inlet should be in, to get the desired pressure at the outlet (Absolute pressure: 4 bar). The fluid is steam.

May 21, 2022, 03:44		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	So use a pressure outlet with outlet pressure equal to 4 bar and mass flow inlet or velocity inlet depending on whatever is your operating condition. Then whatever pressure you get in the solution is the pressure you are looking for.

May 21, 2022, 04:00		#5
Ramesh_21M New Member Ramesh M Join Date: May 2022 Posts: 4 Rep Power: 3	Thanks for your suggestion, I will try that. can you please explain, can inlet-vent with pressure-outlet be used to solve this? Again, thanks for your help!

May 21, 2022, 09:01		#6
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	If you absolutely must use an inlet-vent, then there are two ways to proceed and both require iterating at the outlet level on your part. 1) Use an inlet vent and pressure outlet with outlet pressure set to 4 bar. Guess an inlet pressure. Run the case until convergence. Check the massflow. If the massflow is too low/high, increase/decrease the inlet pressure, run it again. Check it again. Repeat. Repeat. Repeat until you match the desired flowrate. Once that is done, possibly some 1000 iterations later, then retrieve the inlet pressure. 2) Use an inlet vent and pressure outlet with targeted mass flow rate setting. Set the flow rate. Set an inlet pressure. Run the case until convergence. Check the outlet pressure if it matches 4 bar or not. If it is too low/high, then increase/decrease the inlet pressure. Run the case again. And again. And again until the outlet pressure reaches 4 bar. Once it reaches 4 bar, get the inlet pressure.

May 22, 2022, 00:32		#7
Ramesh_21M New Member Ramesh M Join Date: May 2022 Posts: 4 Rep Power: 3	Thanks a lot, I will try that.