Actual Liquid Velocity Calculation
Actual Liquid Velocity Calculation
(OP)
How to calculate the actual liquid velocity from the superficial liquid velocity of a multiphase flow ?
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Actual Liquid Velocity Calculation
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RE: Actual Liquid Velocity Calculation
First you need to know the flow regime and second the actual volume fraction in the pipe at the point where you are looking at. Both normally come from the transient flow analysis tool you are using. They may also give you the answer directly.
Slug flow or very wavy flow, the actual velocity will vary wildly and change constantly.
Stratified and wavy in a flat pipe you might get less variation, everything else, huge variation.
Why do you need to know?
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RE: Actual Liquid Velocity Calculation
RE: Actual Liquid Velocity Calculation
This is all great on paper, but the reality is somewhat more complex. If you can place a bet that your actual liquid flowrate in any section of the line is as someone claims to be, then the calculation is again simple and straightforward. More often, you will find that actual velocities will vary so much along the line that it is impossible to confirm the actual velocity/flowrate unless you actually measure it. Gas and Liquid move with different velocities. Slugging is one consequence of this phenomenon. Depending on many parameters, your actual velocity can be anywhere between zero and the velocity at fully dispersed flow.
Dejan IVANOVIC
Process Engineer, MSChE
RE: Actual Liquid Velocity Calculation
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Actual Liquid Velocity Calculation
As you and zdas04 also note, even the average liquid velocity will change along the line as pressure changes, gradually increasing if the overall flow is steady state. I think "superficial" velocity is just the standard liquid flowrate at some fixed volume fraction. Actual is actual and will vary a lot along the line.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Actual Liquid Velocity Calculation
All of the places I know of where superficial velocity is useful re-calculates it at each point in the line (I don't know of anywhere that the average over the line in multi-phase flow would be useful). I don't show gas superficial velocity in the graphic above (it isn't important to that particular segment of the class), but in the left hand example the gas superficial velocity at the bottom is around 4 ft/s and at the top it is closer to 30 ft/s. At 30 ft/s a drag model like Souder-Brown or Turner says it will drag small droplets along with the bulk flow. At 2 ft/s all the drag models say it won't.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Actual Liquid Velocity Calculation
Dejan IVANOVIC
Process Engineer, MSChE
RE: Actual Liquid Velocity Calculation
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.