Full pipe min flow calculation 2

[NCENG78]

How do you calculate the min. flow needed to keep full pipe flow

 

[dcasto]

You need to explain that one. Why would a pipe not be full?

 

[djack77494]

dcasto,
I believe what dearman is referring to is the transition point wherein a partially full gravity flow line is asked to handle additional flows until the point where it becomes totally full. There is a name for this point, which I have forgotten, and there is a formula for determining the associated flowrate. Hopefully a fellow reader can supply this missing information.
Doug

 

[pleckner]

10.2 * (I.D.^2.5)

This will keep a horizontally orientated pipe (with no pockets or change in the vertical direction) full of liquid all the way to discharge.

I know someone will ask me where this comes from and I do have the reference, but not with me at this time. I'll have to post the reference tomorrow (East Coast, USA) unless someone else has it posted by then.

 

[dcasto]

A self venting drain? try this.

http://www.freecalc.com/selffram.htm

 

[pleckner]

By the way, the equation I give above yields the flow in gpm. Sorry for not stating that before.

 

[katmar]

For a sloped pipe you can use the Manning equation. For a flow less than the critical value the pipe will run part full. The critical flow will vary with the angle of slope.

For a vertical (or near vertical) pipe you should use Darcy-Weisbach with a pressure drop gradient equal to the static height. For a given height the static head is density x gravity x height and if the friction head exactly matches this the pipe will remain full and there will be a zero net pressure gradient. If the flow is such that the friction head is less than the static height the pipe will partially drain, and if the flow is such that the friction head exceeds the static head the pipe will over flow. This analysis will apply if the pipe entrance is "open" like a drain. If the pipe entrance is always flooded then you should look for the syphon point, which will be at a slightly lower flow rate than the zero pressure gradient analysis gives.

For a truly horizontal pipe I would expect the critical value to depend on the length of the pipe. I cannot recall the equation suggested by pleckner, but it looks like it could be a useful rule of thumb. Presumably those gpm are USgpm and the ID is inches and the fluid is water?

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[pleckner]

Here are the references for the equation I gave above:

Druand, A.A & M. Marquez-Lucero, "Degermining Sealing Flowrates in Horizontal Run Pipes", Chemical Engineering, March 1998.

Another source is:

Sandler, H.J. & E.T. Luckie-wicz, "Practical Process Engineering", McGraw Hill, 1987

And as katmar stated, the diameter is in inches and the flow is in USgpm.

 

[STYMIEDPIPER]

pleckner
Thanks for following up
Good effort

 

[djack77494]

Yes, sealing flowrate is what it's called. Thanks, Phil.

 

[pleckner]

Glad to be of help!

 

[sailoday28]

Consider a pipe sloped in the upward direction that has a liquid containing air or other gases. As the gas comes out of solution (in the flow direction) other factors shoud be accouted for to determine when the pipe is not flowing full. For example, use of Henry's Law, etc.

Regards

 

[JStephen]

To add to Katmar's post, if the pipe is vertical, you run into a couple of issues. If the friction is less than the gravitional force, then applying Bernouli's equation from start to finish will give you a flow rate, but it is based on a negative pressure in the vertical run. Depending on the length of the run, this could be a partial vacuum or a negative absolute pressure (IE, not possible, would lead to cavitation). In the partical-vacuum case, if air can get back up in the pipe (not running full), then the flow rate will drop.

 

[BigInch]

For ANY pipe orientation, minimum steady state flowrate is that flowrate which yields an internal pressure equal to the vapor pressure of the fluid inside, at some point anywhere inside the length of the pipe segment, thus it depends on fluid density (if there is an elevation difference), vapor pressure, viscosity and pipe roughness. You can use any appropriate head loss equation to find the distance from a point of known internal pressure (Po) to the point where the internal pressure P1 = vapor pressure. Generally speaking, that will also yield the minimum differential pressure between those same points required to maintain full flow.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[sailoday28]

BigInch (Petroleum)
Per my previous post, what if a non-condensible gas comes out of solution?
Regards

 

[BigInch]

Sailo,

I assumed the OP was interested in a typical scenario, since no further details were given by him, other than he wanted to avoid 2-phase flow. The thread managed to stay within those parameters, until you brought up the gas leaving solution in your post, however, since 2-phase flow was to be avoided and the OP did not mention any particular problem with that phenomenon, I didn't think it relevant to address it further.



BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[sailoday28]

BigInch
The orig question was --How do you calculate the min. flow needed to keep full pipe flow.

Can a typical liquid have dissolved gases? Does a gas coming out of solution not apply?--or perhaps my question is to complicated?

Regards

 

[BigInch]

I think your question is applicable when it is applicable, however since it didn't form part of of the original post, it must not have been of any concern to the OP, and as such, was no concern of mine.

Certainly there are many typical liquids that could have that flow characteristic you describe, oil with 5% air for example, or heating water to steam in a long pipe, but I didn't see where any of those conditions formed part of the problem as proposed by the OP.

My advice is, "don't make a problem's solution more complicated than it has to be solve the question at hand".

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[mfelzien]

This is the design equation I use:

If {Q/d}^2.5 >= 10.2 The pipe is running full.
If {Q/d}^2.5 < 10.2 The pipe is partially filled.

where,

Q [volumetric flow rate 'gpm']
d [pipe diameter 'in']

This is located in C. Brannans handbook.

M. Felzien

 

[katmar]

M. Felzien,

The equation you have given here looks similar to that presented earlier by pleckner, but would give very different results to his because in your equation the Q is raised to the power of 2.5, but it was not in pleckenr's. Does Brannan give references, and are they the same as those pleckner gave?

pleckner do you have any comment on this? It is a useful looking equation that I would like to add to my list of tools, but this discrepancy worries me and I do not have the original references.

regards, Harvey

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com