Talk:Darcy–Weisbach equation

message: I am trying to compare the head lost due to friction value by using the Darcy-Weisbach Equation and the Hazen-Williams Equation,however, I can`t get equivalence, the 2 values differ allot, 1 is 1.2 bar (Darcy-Weisbach Equation), the other is 0.5 bar! How could this happened? Which will be more correct? Or are there any rules that stated which equation is suitable for which situation?— Preceding unsigned comment added by 60.49.7.1 (talk • contribs) 08:15, May 24, 2006‎ (UTC)
::It appears to me that the Hazen-Williams equation is not dimensionally correct, unlike the Darcy-Weisbach equation. This means two things:
# the coefficient in the Hazen-Williams equation has units and cannot be directly compared to the dimensionless Darcy friction factor; and,
# the Hazen-Williams equation is probably only useful for a particular range of Reynolds numbers.—Miguel (talk) 13:44, 15 March 2008 (UTC)
replies: text: You may check the drop in pressure coefficient for an equation to find out if one is absolute pressure and others dynamic. I use the formula of Hencky to compare deformations of small volumes.
\ln \left(\frac{p \inf {2 }}{p\inf { 1}}\right)
I suspect one pressure to lead to a out of the real space, infinity
and second one to
\ln \left(\frac{p \inf{ 2}}{p\inf {1}}\right)=\ln (\frac{\delta\cdot{p}}{1.013})=\ln \delta \cdot{p} - \ln 1.013\cdot {f(dB)}
, where patm is the pressure in air, 1.013atm
, and f(dB) must be one for any EPS
188.25.48.61 (talk) 14:41, 1 August 2011 (UTC)
thread_title:  Equivalence to Hazen-Williams equation 

message: From the navier-stolkes equation there is the energz conservation:
\frac{d{r}}{dt} +U \frac{du}{dt} +V \frac{dv}{dt} = \frac{p}{\rho} + f + 4\mu \nabla \frac{v^2}{2}
so f is force and none f-factor. I tagged f as unknown, hope to prove it as head looss in pressuse in the darcy eq. Since then please leave f to disambuation—188.25.48.61 (talk) 14:23, 1 August 2011 (UTC)
replies: text: Anonymous butter-fingered typist, your <math> expressions are malformed gobbledygook, making it impossible to discern what point you were trying to make. — QuicksilverT @ 01:15, 27 May 2015 (UTC)
thread_title: Quote for ''f''

message: Seems like a reasonable merge to me. +mwtoews 22:42, 1 July 2007 (UTC)
replies: text: Seems reasonable to me, too.Mas-wiki 20:52, 30 July 2007 (UTC)

text: Now merged. No discussion to merge. Miguel (talk) 12:19, 15 March 2008 (UTC)
thread_title: Merge [[Darcy friction factor]]

message: The previous Confusion with the Fanning friction factor section said: "... the slope of the linear relation between the friction factor and the inverse of the Reynolds number in the limit of small Reynolds numbers. If the slope is 16/Re, ..."
*The first sentence seemed convoluted: "linear relation between the ... and the inverse".  Saying "inversely proportional" would be more compact, but there is also:
*The "slopes" are 16 or 64.  But "16/Re" is the entire right-hand side of a formula.
-Ac44ck (talk) 20:12, 7 April 2008 (UTC)
thread_title:  Formula instead of slope 

message: Some good info in the last few edits.  The placement for some of it might be better elsewhere.
The given Blasius formula is for the Fanning friction factor.  The Darcy friction factor would be a better fit in this article.  But friction factor formulae are compiled elsewhere.  And the formula given seems to use slightly different values from the one here.
The section which focuses on distinguishing between the Darcy and Fanning friction factors assumes that the reader is familiar enough with at least one of them (Darcy or Fanning) to identify the laminar friction factor line in a Moody diagram.
Discussing the limiting Reynolds number for laminar flow, and the distinctions between various friction factors may be more fitting here.
The procedure in the "Confusion with ..." section works for any location on the laminar friction factor line where the Reynolds number is an integral power of ten.  The line is usually plotted only in the laminar flow region, but it can be extrapolated to any convenient Reynolds number and the given procedure still works.
Moved the content of these sentences from the "Confusion with ..." a new section in the Fanning friction factor article:
It should be noted that f=16/Re is the friction factor for flow in round tubes. For a square channel this becomes 14.227/Re for example.
A Moody diagram assumes (round) pipe flow.  That the friction factor is defined for round conduits might be stressed in a section other than the one which is intended to heighten awareness about the distinction between the Darcy and Fanning friction factors.
The square-channel friction factor is interesting.  It appears to be a Fanning friction factor.  I moved it to a new section of the article on the Fanning friction factor.
:The Moody diagram is not only applicable to round conduits, it can be used for any arbitrarily shaped cross section. The difference in its use is that in the calculation of the Reynolds number and the relative roughness parameters one needs to use in place of diameter the quantity 4 times the hydraulic radius of the cross section where the hydraulic radius is defined as the cross sectional area divided by the wetted perimeter.  —Preceding unsigned comment added by 64.126.190.120 (talk) 03:11, 5 January 2009 (UTC)
thread_title:  Removed Blasius, etc. 

message: Should be Darcy–Weisbach (with en-dash), not Darcy-Weisbach (with hyphen).  See WP:DASH.
—DIV (128.250.80.15 (talk) 10:10, 20 August 2008 (UTC)
thread_title:  Title 

message: I think that darcy-weisbach is better termed a "semi-empirical" equation than a phenomenological equation for two reasons.  It contains a part that is solidly grounded in theory (the v^2/2g term, and to a lesser extent the L/D term) and the term "semi-empirical equation" is in more common use than "phenomenological equation"Mikejens (talk) 16:06, 12 November 2008 (UTC)
replies: text: The Darcy–Weisbach equation is exact for laminar flow and can be derived theoretically. The formula may be extended to turbulent flow by varying the friction factor. The Colebrook-White equation for the turbulent friction factor has bases in experiment. Reading the article on Phenomenology_(science) confused me a bit. At this point, I am not sure that it is proper to call the Darcy–Weisbach equation itself either phenomenological or semi-empirical. Its application may yield a well-founded exact value or a less-well-founded approximation, depending on the how the friction factor was determined. -Ac44ck (talk) 19:23, 12 November 2008 (UTC)
thread_title:  Phenomenological versus semi-empirical 

message: In this section (right at the end), an alternative expression for hf based on volumetric flow rate rather than velocity is derived. If my algebra is correct, the friction factor corresponding to the other coefficients in the formula would be the D-W one, but the symbol used is f rather than fD. I leave it to better experts to fix if it is wrong (given the dire warnings about confusing the two).  — Preceding unsigned comment added by 83.67.40.215 (talk) 07:49, 29 May 2012 (UTC)
thread_title:  Practical applications 

message: Figure 4 is mentioned twice in the text, but is not visible.  — Preceding unsigned comment added by Aubrey Jaffer (talk • contribs) 21:15, 16 February 2017 (UTC)
replies: text: The text should have referred to "Figure 3"; I corrected it. ArthurOgawa (talk) 08:27, 15 November 2017 (UTC)
thread_title:  Where is Figure 4?