Pressure Drop Through Pipe Calculation

Pressure Drop Through Pipe Calculation

  • Darcy–Weisbach equation is an empirical equation to determine the head loss, or pressure loss, due to friction for a given length of pipe to the average velocity of the fluid flow for an incompressible fluid
  • This formula is directly proportional to the square of the average velocity

Darcy-Weisbach formula

Steps to determine the Pressure Drop through the duct

  • Known Quantities:
    • Density of the fluid, ρ
    • Dynamic viscosity of the fluid, μ
    • Hydraulic diameter of the duct,  D = 2* a* b / (a + b)
    • Average fluid velocity, ⟨v⟩
  • Determine Reynolds Number: Re = ρ*⟨v⟩* D/μ
    • Laminar flow: Re < 2100
    • Turbulent Flow: Re >  4000
  • Determine the friction factors  (Fd) as a function of friction factor and Reynolds number
    • Refer to the fluid Mechanics books to get different correlations for friction factor

Friction factor for Reynolds number

    • Commonly used the Swamee-Jain Equation for turbulent flow 

Swamee-Jain Equation

  • Determine Pressure drop per unit length of pipe (ΔP/L) in wg/ft

Pressure Drop Calculator 

  • Enter values in the column
  • For hydraulic diameter:
    • Enter the sectional sizes (a x b) for non-circular ducts
    • Enter a diameter (D) directly  for circular pipe
  • Understand  the type of flow: laminar or turbulent, however, the turbulent formula has been used
  • Note SI or Imperial units