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Fluid Dynamics Downstream of Valve

Fluid Dynamics Downstream of Valve

Fluid Dynamics Downstream of Valve

(OP)
Hi, I've gotten valuable info here for a number of years, but this is my first post.

I have a situation where a pressurized reservoir of liquid is connected to the inlet of a solenoid valve. The outlet is connected to a length of plastic tubing, which discharges to the atmosphere. With the valve closed, there is liquid in the line downstream (at atmospheric pressure). The valve opens for a short time (min 20msec, max 1sec) and closes, dispensing an amount of liquid out the end of the tubing. I'm interested in modeling the pressure/flow in the tube downstream. I know there are dynamic effects as the pressure builds & decays, but don't know what equations to apply to analyze it.

The steady-state flow in the tubing is laminar, and the liquid is low viscosity (solvent-based, ~0.5cP). The tubing downstream of the valve is .020"ID, 48" lg. The inlet to the valve can be assumed to be at constant pressure.

If I had CFD software available, I would use it, but sadly I don't. :( So I'm looking to do it the old-school way. Let me know if I've left out anything important. Thanks!

RE: Fluid Dynamics Downstream of Valve

plastic tubing has a low value of E ( youngs modulus) so some of the energy of the pressure pulsations will be absorbed by the flexibility of the plastic tubing.

If the plastic tubing rises more than 25' above the valve then it is possible that some water will flash before it exits the tubing.

"Whom the gods would destroy, they first make mad "

RE: Fluid Dynamics Downstream of Valve

your question is a bit generic and lite on specifics, but in a sense you have already modeled the flow in stating that it is laminar, you don't need cfd for that get a copy of the crane flow manual/software if you can't lay you hands on a text book

RE: Fluid Dynamics Downstream of Valve

There is no "old school" approach to a dynamic problem. Even if its not CFD a 1D flow analyser is not a simple thing. I would suggest that you either find some software that can di the tric or hire a consultant if its a one-shot job.

Best regards, Morten

RE: Fluid Dynamics Downstream of Valve

What is it that you're really interested in?. I guess flow as it is an open ended tube.

The old school way was simply to do a series of tests and see if the results were repeatable then create a table or graph of time of opening pulse vs flow or volume. Then if you change one thing at a time such as type of tube you'll know what the effect is.

There are far too many variables and transitory events going on here to even guess at flows and pressure.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

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