Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Pressure driven flow through a pipe with a Y split
Posted Aug 1, 2017, 2:52 p.m. EDT 2 Replies
Please login with a confirmed email address before reporting spam
Hello,
I am trying to model flow through a pipe that splits into two different outlets. The pipe sections after the split are smaller in diameter than the starting section of pipe and are not equal to each other. The flow in the pipe is driven by fluctuating pressure as a function of time in the input. The model is supposed to describe a section of a larger system, but the outlet flow from the pipe has no pressure, where in the actual system there should still be pressure.
To solve this I have tried to use another pressure function of time for the outlet, but COMSOL fails to solve even though the time-dependent function for inlet pressure worked. I have also tried tried modifying the outlet pressure according to Poiseuille's law as a function of p (pressure variable) and the diameters of each section of tube. What I have found to work, though it is inaccurate, is using a constant pressure for the outlet, using a fraction of p (e.g. outlet = p*.95), or using a constant velocity in the outlet.
Thank you
I am trying to model flow through a pipe that splits into two different outlets. The pipe sections after the split are smaller in diameter than the starting section of pipe and are not equal to each other. The flow in the pipe is driven by fluctuating pressure as a function of time in the input. The model is supposed to describe a section of a larger system, but the outlet flow from the pipe has no pressure, where in the actual system there should still be pressure.
To solve this I have tried to use another pressure function of time for the outlet, but COMSOL fails to solve even though the time-dependent function for inlet pressure worked. I have also tried tried modifying the outlet pressure according to Poiseuille's law as a function of p (pressure variable) and the diameters of each section of tube. What I have found to work, though it is inaccurate, is using a constant pressure for the outlet, using a fraction of p (e.g. outlet = p*.95), or using a constant velocity in the outlet.
Thank you
2 Replies Last Post Aug 2, 2017, 10:59 a.m. EDT
Please login with a confirmed email address before reporting spam
Posted:
7 years ago
Hi Evan:
Can you share the dimensions of your model and the flowrate? What is the error that COMSOL throws when it doesn't solve.
Sri.
Can you share the dimensions of your model and the flowrate? What is the error that COMSOL throws when it doesn't solve.
Sri.
Please login with a confirmed email address before reporting spam
Posted:
7 years ago
Updated:
7 years ago
I'm trying to design the model so that the dimensions can be varied. The diameter of the pipes will be between a millimeter and a micrometer, right now the largest pipe diameter is about 100 micrometers. I am not sure what the flow rate should be through the model, I am still trying to find that, so I was hoping to use pressure driven inlet and outlets. The flow should also vary with time so it needs to be pulsating or oscillating.
Here is the error code from trying to run the model with the outlet being a function of time. Boundaries 18 and 20 are the outlets for the two ends of the model after the split. I am using the same function as the inlet, but multiplied by 95% (Inlet Pressure = F(t), Outlet Pressure = F(t) * .95) and using the function for the inlet works fine.
Undefined variable.
- Variable: t
- Geometry: geom1
- Boundaries: 18, 20
Failed to evaluate variable.
- Variable: comp1.spf.p0
- Defined as: unit_Pa_cf*(Pressure_Pa(t/unit_second_cf)*0.94999999999999996)
Failed to evaluate variable.
- Variable: comp1.spf.f0
- Defined as: comp1.spf.p0
Failed to evaluate expression.
- Expression: dvol*((-comp1.spf.f0)*comp1.spf.nxmesh)
Failed to evaluate Jacobian of expression.
- Expression: (-comp1.spf.f0*(test(comp1.u)*comp1.spf.nxmesh+test(comp1.v)*comp1.spf.nymesh+test(comp1.w)*comp1.spf.nzmesh))*(dvol)
Here is the error code from trying to run the model with the outlet being a function of time. Boundaries 18 and 20 are the outlets for the two ends of the model after the split. I am using the same function as the inlet, but multiplied by 95% (Inlet Pressure = F(t), Outlet Pressure = F(t) * .95) and using the function for the inlet works fine.
Undefined variable.
- Variable: t
- Geometry: geom1
- Boundaries: 18, 20
Failed to evaluate variable.
- Variable: comp1.spf.p0
- Defined as: unit_Pa_cf*(Pressure_Pa(t/unit_second_cf)*0.94999999999999996)
Failed to evaluate variable.
- Variable: comp1.spf.f0
- Defined as: comp1.spf.p0
Failed to evaluate expression.
- Expression: dvol*((-comp1.spf.f0)*comp1.spf.nxmesh)
Failed to evaluate Jacobian of expression.
- Expression: (-comp1.spf.f0*(test(comp1.u)*comp1.spf.nxmesh+test(comp1.v)*comp1.spf.nymesh+test(comp1.w)*comp1.spf.nzmesh))*(dvol)