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Mechanical EngineeringP0

Hydraulic Diameter Calculator

Calculate hydraulic diameter for non-circular ducts and pipes used in Reynolds number and pressure drop.

Inputs
Enter your values below
Result
Hydraulic Diameter
—
Enter values and click Calculate
Formula
4 × (width × height) ÷ (2 × (width + height)) × 1000
Result unit: mm

Dh = 4A/P. For rectangular duct: A = W×H, P = 2(W+H). ×1000 converts m to mm.

Introduction

Hydraulic diameter (Dh = 4A/P) allows using pipe flow equations (Reynolds number, Darcy-Weisbach) for non-circular ducts. For a circular pipe, Dh equals the actual inner diameter.

Calculation Example

400×200mm rectangular duct: Dh = 267mm, allowing pipe flow equations to be used.

Inputs: width=400, height=200
Result: 266.7 mm

Engineering Applications

  • •HVAC duct design
  • •Shell-and-tube exchangers
  • •Rectangular channels
  • •Annular flow

Frequently Asked Questions

Why use hydraulic diameter?

Dh lets engineers apply circular pipe correlations (Re, f, Nu) to non-circular geometries like rectangular ducts and annuli.

What about annular flow?

For an annulus between outer diameter D_o and inner D_i: Dh = D_o − D_i. This calculator handles rectangular ducts.

Related Calculators

Reynolds Number CalculatorDarcy-Weisbach Pressure Drop Calculator

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Disclaimer: Calculations are for reference and educational purposes only. Always verify results independently for engineering design. See full disclaimer.