Is the Fanning Friction Factor Calculation Affected by Unit Usage?

In summary, the conversation is about the use of English or SI units when calculating the fanning friction factor. The equation for head friction is discussed, with the correct formula being h_f = 4f(L/D)V^2/(2g). It is clarified that the fanning friction factor is non-dimensional and that the g value should always be included in the calculation, regardless of the unit system being used. The importance of dimensional analysis is emphasized and it is noted that the lecture slides contain the correct formula.
  • #1
gfd43tg
Gold Member
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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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  • #2
  • #3
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
 
  • #4
Yes, the g is always there, even in SI or furlongs per fortnight units. Do a dimensional analysis and confirm.
 
  • #5
You can see why I was confused, this is directly and repeatedly on the lecture slides
 

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1. What is the definition of fanning friction factor?

Fanning friction factor, also known as the Darcy-Weisbach friction factor, is a dimensionless parameter used in fluid mechanics to describe the resistance of a fluid flow in a pipe or duct. It is a measure of the frictional losses in the flow due to the roughness of the pipe walls.

2. How is the fanning friction factor calculated?

The fanning friction factor is calculated using the Colebrook-White equation, which takes into account the fluid properties, pipe dimensions, and roughness of the pipe walls. It is a complex equation that is typically solved iteratively using numerical methods.

3. What factors affect the value of the fanning friction factor?

Several factors can affect the value of the fanning friction factor, including the roughness of the pipe walls, the viscosity of the fluid, the Reynolds number (a measure of the flow regime), and the pipe diameter. Additionally, the fanning friction factor may vary along the length of a pipe or duct due to changes in flow conditions.

4. Why is the fanning friction factor important in fluid mechanics?

The fanning friction factor is important because it is used in various equations and calculations to determine the pressure drop in a pipe or duct due to frictional losses. This information is crucial for designing and analyzing fluid flow systems in various industries, such as plumbing, HVAC, and oil and gas.

5. How does the fanning friction factor differ from the Moody friction factor?

The fanning friction factor and the Moody friction factor are often used interchangeably, but they are not exactly the same. The Moody friction factor is four times the fanning friction factor, and it is used in the Moody chart, a graphical representation of the Colebrook-White equation. However, in most practical applications, the two terms are used synonymously.

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