Simscape Fluids - 2 resevours, 1 flow rate source model results in pressure below allowed minimum.

Hello,

I am trying to create a simple (IL) flow model where the flow from the inlet splits into two routes with different resistence, to see how the flow rate in each route if affected.

I want to fix the inlet boundary pressure and the outlet flow rate, my understanding is that I have to have two reservours so I have also placed a resevour after the flow rate source.

When I try to run the model I get an error saying that the pressure at the flow rate source outlet is below the minimum allowed pressure, but I cant figure out why, would someone be able to tell me what I am doing wrong?

Thank you

Answer 1

[Yifeng Tang]

Looks like a parametrization issue to me.

In your model, the pressure at the inlet (point 1) is fixed by the upstream reservoir. The pressure at the outlet, because of the flow rate source block, will be whatever pressure needed to drive the specified amount of liquid through the pipe network. If the specified flow is too large OR the pipe network is too restrictive (too narrow, too long, resistance too high, etc.), the required pressure difference will be large. Will the pressure at the inlet fixed, the outlet pressure will be lowered and if the required difference leads to an outlet pressure level below the minimum working pressure set by the liquid property block, you get an error.

Things to check:

1. Are the pipes parametrized properly? Can you check the pressure drop using a different (lower) flowrate and compare to any reference data you have? Based on the flowrate split between the two branches (simulated at 10% of the original flowrate), the upper branch is the more restrictive one right now.
2. Is it reasonable to assume that the inlet is always at a fixed pressure? It's more common to see outlet being fixed. Meaning you move the flowrate source to the upstream of the network and pushes flow from left to right.