Pressure Drop Calculator
Calculate pipe friction losses using the Darcy-Weisbach equation with automatic friction factor calculation via Colebrook-White.
Pressure Drop Calculator
Darcy-Weisbach equation for pipe flow
Pressure Drop
87.189
kPa
(87.189 kPa per 100 m)
Flow Parameters
Reynolds Number
99,601
Flow Regime
Turbulent
Friction Factor (f)
0.0218
Head Loss
8.906 m
Relative Roughness (ε/D)
9.000e-4
Velocity Head
0.204 m
Darcy-Weisbach Equation
How to Use This Calculator
Select pipe material to automatically set the surface roughness, or choose "Custom" to enter your own value. Different materials have significantly different roughness values.
Enter pipe dimensions (inner diameter and length) and flow conditions (velocity). Use the fluid presets for common fluids or enter custom density and viscosity values.
Results show pressure drop (in kPa or psi), head loss (in m or ft), Reynolds number, flow regime, and the calculated Darcy friction factor.
Understanding Pressure Drop
Pressure Drop (ΔP) - The decrease in pressure as fluid flows through the pipe due to friction. Measured in kPa or psi.
Head Loss (h_f) - Pressure drop expressed as height of fluid column. Used for pump sizing. 1 bar ≈ 10.2 m of water head.
Friction Factor (f) - Dimensionless number representing friction resistance. Depends on Reynolds number and relative roughness (ε/D).
Velocity Head - The kinetic energy term v²/2g. Multiple velocity heads are lost through fittings (valves, elbows, tees).
Frequently Asked Questions
What is the Darcy-Weisbach equation?
The Darcy-Weisbach equation calculates pressure drop due to friction: ΔP = f × (L/D) × (ρv²/2), where f is the friction factor, L is pipe length, D is diameter, ρ is density, and v is velocity. It's the most accurate method for pressure drop calculation.
How is the friction factor calculated?
For laminar flow (Re < 2300), f = 64/Re. For turbulent flow, this calculator uses the Colebrook-White equation solved iteratively, which accounts for both pipe roughness and Reynolds number.
What is pipe roughness and why does it matter?
Pipe roughness (ε) is the average height of surface irregularities inside the pipe. Rougher pipes have higher friction factors and more pressure drop. New steel pipe has ε ≈ 0.045mm; corroded pipes can have ε > 1mm.
How do I convert pressure drop to head loss?
Head loss (h) = ΔP / (ρg), where ρ is fluid density and g is gravity (9.81 m/s²). Head loss is useful for pump sizing as pumps are typically rated in meters or feet of head.
Why does the calculator show different friction factors for different materials?
Different pipe materials have different surface roughness. Smooth materials like PVC (ε ≈ 0.0015mm) have lower friction than rough materials like concrete (ε ≈ 1mm). This significantly affects pressure drop, especially in turbulent flow.
What pressure drop is acceptable for piping systems?
Typical design limits: 0.5-2 kPa/100m for water, 0.1-0.5 kPa/100m for gases. Total pressure drop should allow pumps/compressors to operate efficiently. Balance capital cost (larger pipes) vs operating cost (pumping energy).
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