Calculates the Moody friction factor and then the head loss and pressure drop per classic equations.  

 Enter temperature, pressure, pipe diameter, and PPS, lbs per second flow rates, has mass to volume relationships.  

Uses VBA for an iterative solution to the friction factor, twice, once in a subroutine with button click and then ported to function for excel auto updating.

In English units with Metric conversion for verification, and various references on separate sheets.  Note the interpolation routine in the viscosity pages, this isn't mine but is very nice, note also this workbook uses named cells, useful and clear.  

Calculation Reference

Air Flow Calculations

Moody Friction Factor

Air Flow in Pipes

To calculate the Moody friction factor, head loss, and pressure drop in a pipe, you need to follow these steps:

  1. Calculate the Reynolds number (Re): Re = (ρ * v * D) / μ


  • ρ = fluid density (kg/m³)
  • v = fluid velocity (m/s)
  • D = pipe diameter (m)
  • μ = dynamic viscosity (Pa·s)
  1. Determine the relative roughness (ε/D): ε/D = ε / D


  • ε = pipe roughness (m)
  • D = pipe diameter (m)
  1. Use the Moody chart or an approximation formula (like the Colebrook-White equation) to find the friction factor (f) based on the Reynolds number (Re) and the relative roughness (ε/D).

For turbulent flow (Re > 4000), you can use the Colebrook-White equation, which requires an iterative method to solve:

1 / √f = -2 * log10[(ε/D) / 3.7 + 2.51 / (Re * √f)]

  1. Calculate the head loss (h_L) using the Darcy-Weisbach equation: h_L = (f * L * v²) / (2 * g * D)


  • f = friction factor
  • L = pipe length (m)
  • v = fluid velocity (m/s)
  • g = acceleration due to gravity (approximately 9.81 m/s²)
  • D = pipe diameter (m)
  1. Calculate the pressure drop (ΔP) in the pipe: ΔP = ρ * g * h_L


  • ρ = fluid density (kg/m³)
  • g = acceleration due to gravity (approximately 9.81 m/s²)
  • h_L = head loss (m)

By following these steps, you can determine the Moody friction factor, head loss, and pressure drop in a pipe. These calculations are essential for designing and analyzing fluid transport systems, such as water distribution networks, HVAC systems, or industrial processes.

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25 Apr 2023
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johndoyle[admin] 11 years ago
I have extended your XLC Pro subscription by 3 months by way of thanks.
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