Equivalent Diameter Calculator

This calculator determines the equivalent circular diameter for non-circular ducts and channels, which is essential for fluid flow calculations in HVAC, ventilation, and hydraulic systems.

Calculation Settings

Duct/Channel Type Rectangular Oval/Elliptical Triangular Annular (Ring) Custom (Hydraulic Diameter)

Unit System Metric (mm) Imperial (inches)

Rectangular Duct Dimensions

Width

mm

Height

mm

Oval/Elliptical Duct Dimensions

Major Axis

mm

Minor Axis

mm

Triangular Duct Dimensions

Triangle Type Equilateral Isosceles Right-angled Scalene (General)

Side Length

mm

Base

mm

Leg

mm

Base

mm

Height

mm

Side A

mm

Side B

mm

Side C

mm

Annular (Ring) Duct Dimensions

Outer Diameter

mm

Inner Diameter

mm

Custom Shape (Hydraulic Diameter)

Cross-sectional Area

mm²

Wetted Perimeter

mm

Calculate

Reset

What is Equivalent Diameter?

The equivalent diameter is a concept used in fluid mechanics and HVAC engineering to represent a non-circular duct or channel as an equivalent circular duct that would have the same pressure drop or flow characteristics. This allows engineers to use circular duct formulas for non-circular ducts.

Calculation Methods

There are several methods to calculate equivalent diameter:

• Equal Friction Method: The equivalent diameter that gives the same friction loss per unit length as the non-circular duct.
• Equal Velocity Method: The equivalent diameter that gives the same average velocity as the non-circular duct.
• Hydraulic Diameter Method: Defined as 4 times the cross-sectional area divided by the wetted perimeter.

Applications

Equivalent diameter calculations are essential in:

• HVAC system design and ductwork sizing
• Ventilation system engineering
• Fluid flow calculations in non-circular pipes
• Heat exchanger design and analysis
• Industrial exhaust systems

Formulas Used

For rectangular ducts, the equivalent diameter is calculated as:

Where a and b are the width and height of the rectangular duct.

The hydraulic diameter is calculated as:

Considerations

When using equivalent diameter calculations:

• The equivalent diameter is most accurate for fully developed flow conditions.
• Different calculation methods may be more appropriate depending on the specific application.
• For highly non-circular ducts, the accuracy of equivalent diameter calculations may decrease.
• The aspect ratio (ratio of width to height) affects the accuracy of the equivalent diameter calculation.