What is Hydraulic Diameter?
The hydraulic diameter (Dh) is a commonly used term in fluid mechanics and heat transfer when dealing with flow in non-circular tubes and channels. It allows engineers to use the same Reynolds number correlations developed for circular pipes to predict flow behavior and pressure drops in non-circular sections, such as square ducts or rectangular HVAC vents.
The Formula Behind the Calculator
The standard definition of hydraulic diameter is four times the cross-sectional area of the flow divided by the wetted perimeter of the cross-section. The formula is expressed as:
Dh = 4A / P
Where A is the area of the flow and P is the wetted perimeter (the perimeter of the cross-section that is in contact with the fluid).
Why is it Important?
Most engineering calculations for friction factors and Reynolds numbers are based on circular cross-sections. However, in reality, ducts are often rectangular or annular. By converting these shapes into an equivalent "Hydraulic Diameter," we can apply circular-pipe empirical data to complex industrial systems, ensuring accurate cooling and ventilation designs.
How to Use This Calculator
1. Select the shape of your duct or pipe from the dropdown menu (Rectangular, Circular, or Annulus).
2. Enter the required dimensions (Width, Height, or Diameters).
3. The calculator will automatically compute the hydraulic diameter in real-time.
4. Ensure all units (e.g., mm, cm, inches) are consistent across all input fields for an accurate result.
Frequently Asked Questions
Is hydraulic diameter the same as geometric diameter?
No. For a standard circular pipe filled with fluid, the hydraulic diameter is equal to the geometric diameter. However, for any other shape, they differ significantly.
What is wetted perimeter?
Wetted perimeter is the total length of the surface that is in direct contact with the flowing fluid. If a pipe is only half-full, the wetted perimeter only includes the bottom half of the circle's circumference.