Finding the flow rate through an open-end pipe

[Mech_Engineer]

Well the Darcy friction factor is 4x the fanning friction factor, so you decide.

Great catch, I got sloppy with my friction factors and wasn't distinguishing between Fanning and Darcy.

Here's the updated equation set:

And the results:

Looks like this is about as accurate a calculation as I can provide given the parameters known? Thanks @Chestermiller and @JBA , I learned a good deal in this thread!

 

[Mech_Engineer]

I thought of one more possible error- the water main's pressure will probably be specified at gauge pressure, meaning the discharge pressure P2 would be zero, not 1 atm (gauge pressure of zero).

That increases the flow a bit, see here:

I also tried a quick check by comparing calculated flow rates against a hose discharge chart here: http://www.engineeringtoolbox.com/water-discharge-hose-d_1524.html. The flow rates calculated by my sheet appear to be right in-line with the values from this chart.

Calculated values from my sheet (100 ft length for all):

• 1/8" hose, 100 psi: 0.25 gpm
• 1/2" hose, 40 psi: 6.38 gpm
• 1/2" hose, 100 psi: 10.75 gpm
• 3/4" hose, 40 psi: 19.02 gpm
• 3/4" hose, 100 psi: 32.03 gpm
• 6" hose, 10psi: 1965 gpm
• 6" hose, 60 psi: 5202 gpm

Compare to chart from EngineeringToolBox.com: