Isothermal Tail Gas Calc - Darcy Friction Factor?
Isothermal Tail Gas Calc - Darcy Friction Factor?
(OP)
I am using Jan 07 API 521 isothermal equation (25) pg 105 for tail gas calcs. The std state friction factor = Moody, but doesn't state whether Darcy or Fanning. The std states another method uses Fanning.
I am assuming Darcy for isothermal, but am not 100% sure this is correct. Does anyone know which to use?
I am assuming Darcy for isothermal, but am not 100% sure this is correct. Does anyone know which to use?





RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
So Fanning:
dP=4*f*L/D*den*(V^2)/2
Darcy
dP=f*L/D*den*(V^2)/2
Of the two, the Darcy factor is more commonly used by civil and mechanical engineers, and the Fanning factor by chemical engineers, but care should be taken to identify the correct factor regardless of the source of the chart or formula.
Best regards
Morten
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
I2I
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
The method presented is a "suggestion" it was not haded down to Moses with burning bushes and everything
Best regards Morten
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
K = fDarcyL/D = 4fFanningL/D
Sound reasonable?
Good luck,
Latexman
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
So you can use a formula for Darcy if you got a Darcy and a fanning if you got a Fanning map. if you got a Fanning map and no other fomula - then i go for Latexman: Its Darcy
Best regards
Morten
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
Bill - why don't you test it out based on an example out of Crane (Chapter 4) or another source or create a ficticious, easy problem, like 100 feet of 2", Sch. 40 pipe with enough flow of 60 F and 100 psig air to have about a 10% pressure drop (from Table B-15 in Crane that's 166.6 cfm at 60 F and 100 psig for a 10.1 psi drop). Which friction factor gives you about the right answer? That's the one!
Good luck,
Latexman
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
skearse, I appreciate your confirmation on this.
API is confusing, however, because the alternate tail gas methodology (the shortcut Lapple calc) calls for Fanning. That fact is what led me to be cautious about this.
Thanks to all for your input!!!
Bill
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
You are not limited to what is printed in API521 - as long as you can argue that its just as good or better! And its even printed in the API. A standard is not an excuse for not thinking imo! I have had clients that though the other way around
Best regards
Morten
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
RE: Isothermal Tail Gas Calc - Darcy Friction Factor?
Best regards
Morten