Why is the Darcy friction factor used in mechanical engineering calculations?

Click For Summary
SUMMARY

The Darcy friction factor is essential in mechanical engineering calculations, particularly in the Darcy-Weisbach equation, which is expressed as f(L)(v^2) / 2gD. The confusion arises when comparing it to the Fanning friction factor, which is represented as 4fF. The relationship between these factors is defined as fD = 4fF, indicating that both equations are valid depending on the chosen friction factor. Misapplication of these factors is a common error in fluid dynamics problems.

PREREQUISITES
  • Understanding of the Darcy-Weisbach equation
  • Familiarity with the concept of friction factors in fluid dynamics
  • Knowledge of mechanical engineering principles
  • Basic grasp of fluid flow calculations
NEXT STEPS
  • Study the derivation and application of the Darcy-Weisbach equation
  • Learn the differences between the Darcy and Fanning friction factors
  • Explore fluid dynamics textbooks that cover common mistakes in calculations
  • Investigate practical applications of friction factors in engineering projects
USEFUL FOR

Mechanical engineers, fluid dynamics students, and professionals involved in calculations related to pipe flow and friction losses will benefit from this discussion.

foo9008
Messages
676
Reaction score
4

Homework Statement


the major loss in the fluid due to pipe friction is f(L)(v^2) / 2gD , (darcy weisbech equation)

why the author use 4fL(V^2) / 2gD ? in the equation ? is it wrong ?

Homework Equations

The Attempt at a Solution

 

Attachments

  • 209.PNG
    209.PNG
    49.5 KB · Views: 484
Physics news on Phys.org
Hi! The Darcy-Weisbach equation is written in terms of the Darcy friction factor (fD), whereas the second equation you posted is probably written in terms of the Fanning friction factor (fF), which is weird, because the problem provides the Darcy factor. The relationship between them is fD = 4fF, so both equations are correct depending on the friction factor you use. However, in your example, they just plugged in the 0.008, so yeah, there is something wrong with the calculation or the problem statement. This is actually a pretty common mistake. Is that from a textbook?

As a generalization, the Darcy friction factor is commonly used in mechanical engineering calculations, while the Fanning factor is used in chemical engineering calculations.
 
Last edited:

Similar threads

Understanding the Formulas for Major Head Loss in Pipes
  • · Replies 3 ·
Replies
3
Views
2K
What is the pressure at the tap due to Darcy losses?
  • · Replies 8 ·
Replies
8
Views
1K
Calculating Major Head Loss Due to Pipe Friction
  • · Replies 18 ·
Replies
18
Views
4K
Friction loss is significant in short pipe
  • · Replies 9 ·
Replies
9
Views
2K
Pressure drop through volumes of compressible fluid
  • · Replies 1 ·
Replies
1
Views
1K
Fluid Mechanics: Head Loss Question (Conceptual)
  • · Replies 3 ·
Replies
3
Views
2K
Fluid Mechanics: Fluid Transfer Between Two Reservoirs at Different Heights
  • · Replies 7 ·
Replies
7
Views
3K
How Do You Calculate Fluid Velocities in Diverging Pipes?
  • · Replies 1 ·
Replies
1
Views
2K
Friction loss due to exit pipe to reservoir
  • · Replies 5 ·
Replies
5
Views
3K
Fluid Dynamics in Pipe Lines Problem
  • · Replies 1 ·
Replies
1
Views
1K