Is the Fanning Friction Factor Calculation Affected by Unit Usage?

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Discussion Overview

The discussion revolves around the calculation of the Fanning friction factor and whether the choice of units, specifically English versus SI units, affects this calculation. Participants explore the implications of dimensional analysis in the context of fluid mechanics equations.

Discussion Character

  • Technical explanation, Debate/contested, Conceptual clarification

Main Points Raised

  • One participant questions if English units must be used for calculating the Fanning friction factor, noting a potential confusion regarding the dimensional analysis of the equation for head friction.
  • Another participant asserts that the Fanning friction factor is non-dimensional and challenges the correctness of the initial formula presented for head loss due to friction.
  • A participant seeks clarification on the inclusion of gravitational acceleration (g) in the equations, expressing uncertainty about when to incorporate it based on unit systems.
  • Another participant confirms that g is always included, regardless of the unit system used, and suggests performing a dimensional analysis to verify this.
  • A participant expresses confusion stemming from lecture materials that may have contributed to misunderstandings about the topic.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the necessity of using specific units for the Fanning friction factor calculation, and there is ongoing confusion regarding the application of gravitational acceleration in different unit systems.

Contextual Notes

Limitations include potential misunderstandings in dimensional analysis and the impact of unit choice on the interpretation of fluid mechanics equations. The discussion does not resolve these ambiguities.

gfd43tg
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Hello,

I was wondering if when calculating the fanning friction factor, do english units need to be used?

The equation for the head friction is

h_f = 4f(L/D)V^2/2

where L is the length, D is the diameter of the pipe, and f is the fanning friction factor. This ends up having units of length squared/time squared, but I think it should be power/mass
 
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Is the g included whether you use english units or not? I get confused when I need to divide by g or not these days since we keep going back and forth with english and SI units
 
Yes, the g is always there, even in SI or furlongs per fortnight units. Do a dimensional analysis and confirm.
 
You can see why I was confused, this is directly and repeatedly on the lecture slides
 

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