How To Calculate Pressure Drop In A Tube

Darcy-Weisbach Equation:

\[ \Delta P = f \cdot \frac{L}{D} \cdot \frac{\rho V^2}{2} \]

Friction Factor (f):

dimensionless

Length (L):

Diameter (D):

Density (ρ):

kg/m³

Velocity (V):

m/s

Pressure Drop (ΔP):

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1. What Is The Darcy-Weisbach Equation?

The Darcy-Weisbach equation is a fundamental formula in fluid mechanics used to calculate the pressure drop due to friction along a given length of pipe or tube. It provides a more accurate assessment of pressure loss in fluid systems than simpler empirical equations.

2. How Does The Calculator Work?

The calculator uses the Darcy-Weisbach equation:

\[ \Delta P = f \cdot \frac{L}{D} \cdot \frac{\rho V^2}{2} \]

Where:

\( \Delta P \) — Pressure drop (Pa)
\( f \) — Friction factor (dimensionless)
\( L \) — Length of tube (m)
\( D \) — Diameter of tube (m)
\( \rho \) — Fluid density (kg/m³)
\( V \) — Fluid velocity (m/s)

Explanation: The equation accounts for frictional losses in pipe flow, with the friction factor depending on the Reynolds number and pipe roughness.

3. Importance Of Pressure Drop Calculation

Details: Accurate pressure drop calculation is crucial for designing fluid transport systems, selecting appropriate pumps, optimizing energy consumption, and ensuring proper system operation.

4. Using The Calculator

Tips: Enter friction factor (dimensionless), tube length (m), tube diameter (m), fluid density (kg/m³), and fluid velocity (m/s). All values must be positive and valid.

5. Frequently Asked Questions (FAQ)

Q1: How do I determine the friction factor?
A: The friction factor depends on flow regime (laminar or turbulent) and pipe roughness. It can be found using Moody charts or calculated from Reynolds number and relative roughness.

Q2: What are typical friction factor values?
A: For laminar flow (Re < 2300), f = 64/Re. For turbulent flow, values typically range from 0.008 to 0.08 depending on pipe material and flow conditions.

Q3: When is this equation applicable?
A: The Darcy-Weisbach equation applies to steady, incompressible flow in straight pipes of constant cross-section. It works for both laminar and turbulent flow regimes.

Q4: Are there limitations to this equation?
A: The equation doesn't account for minor losses from fittings, valves, or changes in direction. These must be calculated separately and added to the total pressure drop.

Q5: Can this be used for non-circular ducts?
A: Yes, but you must use the hydraulic diameter (4 × cross-sectional area / wetted perimeter) instead of the actual diameter.