7 replies to this topic

[stacgre]

I am looking for guidence on calculating fluid volumetric partial flow through a pipe. I will need a certain amount of covereage (undetermined) at the base of the pipe, but essentially there will be minimum flow. I am not looking for sollutions, just a formula that will give me a start. I have been doing some research online and there are so many different formulas available and I am not sure which one would be appropriate in this case, as well as which assumptions I can make and which ones can absolutely not be made.

Thank you in advance,
GS

[katmar]

If a circular pipe is running only partially full then it is effectively an open channel. The most commonly used formula (in my experience) for open channel flow is the Manning equation. You will find plenty of references to Manning on this forum, or over at Eng-Tips.

A useful document that is downloadable from the internet is
http://www.efm.leeds...Hydraulics2.pdf

[srfish]

Assuming this is a horizontal pipe, The flow pattern should be stratified where the liquid flows along the bottom of the tube and the gas flows along the top.

The superficial liquid velocity needs to be under 0.5 ft/sec and the superficial gas velocity to be under 50 ft/sec.

[kkala]

1. It might be useful to distinguish when an horizontal pipe has a full or a partial flow, though this is not the main subject. http://www.globalspe...ontal-run-pipes suggests a calculational method for it, also reported in C R Branan's "Pocket Guide to Chemical Engineering", Gulf, 1999, Chapter 1, flow in partially full horizontal pipes. Original source is "Chemical Engineering", March 1998, p.129, "Determining sealing flow rates in horizontal run pipes", by A A Durant and M Marquez-Lucero.
2. Civil engineers have written a lot about flow in open channels, being generally more complex than full flow in pipes. A concise guide is Chapter 10 of Schaum's Theory and problems of Fluid Mechanics and hydraulics, McGraw-Hill (1977), SI edition. The brief theory (4 pages) is completed through application problems (25 pages). Manning coefficient for steady uniform flow is indeed "preferable" to coefficients by Kutter, Bazin, Powel. Unfortunately I have not been involved in the design of such systems, only in measuring their flow rate.

[ankur2061]

stacgre,

The concept of "hydraulic radius" comes into picture when dealing with partially filled flow conduits or channels.. The hydraulic radius is the function of the filing depth or the fill percentage of the conduit or channel. A very nice online calculator for calculating hydraulic radius of a cirucular conduit (pipe) is available at:

http://www.ajdesigne...us_equation.php

As mentioned by Katmar the Manning equation deals with flow through partially filled open channels. Even the Hazen-Williams equation used for calculating frictional losses in water systems incoroporates the concept of hydraulic radius to account for partially filled pipes. A very instructive article related to the Hazen-Williams equation for calculating frictional losses in water network is available at:

http://webwormcpt.bl...al-loss-in.html

http://webwormcpt.bl...loss-in_07.html

Hope this helps.

Regards,
Ankur.

[kkala]

Attached "openchan.xls" tries to give an elementary example of flow calculation in a partially full pipe. Doing so, I understood the last sentence of the post by stacgre. For the beginner (like me) the task looks complex. Probably a way out is to make a spreadsheet specific to your need (e.g. pipe diameter for a given flow) by applying Manning formula, play with the parameters to have a feeling of results, then give it to some hydraulic engineer for advice and improvement. Remarks are noted on the attachment, hopefully it is useful. The whole spreadsheet is based on Chapter 10 of Schaum's "Theory and problems of Fluid Mechanics and hydraulics", mentioned before.

Attached Files

•  openchan.xls   32KB   92 downloads

Edited by kkala, 26 December 2011 - 06:07 PM.

[ankur2061]

Dear All,

I had forgotten that a post relating to calculation of hydraulic radius for partially filled pipes was posted by me in which 2 spreadsheets are available for calcualting hydraulic radius. Refer the link below:

http://www.cheresour...5621#entry35621

Regards,
Ankur.

[hbengts41]

See the blog article at: www.engineeringexcelspreadsheets.com/?p=185, for information about using a spreadsheet for partially full pipe flow calculations. Equations and spreadheet screenshots are included. This artcle is about calculations for using the Manning Equation for partially full flow in a pipe with a slope so that flow is by gravity.