Hydraulic Diameter

Hydraulic diameter, abbreviated as \(d_h\), is normally used when the flow is in non-circular pipe or tubes and channels.  Circular pipe has the same pressure drop of a rectangular channel but a greater average velocity.  Square or rectangular pipes have a greater weight and a greater pressure drop compared with a circular pipe with the same section.

The hydraulic diameter is a useful concept because it allows for the comparison of flow characteristics between conduits of different shapes, such as circular, rectangular, or triangular.  By using the hydraulic diameter, engineers and researchers can analyze and predict fluid flow rates, pressure drops, and heat transfer rates in various types of channels or pipes.  In circular conduits, the hydraulic diameter is equal to the actual diameter of the pipe.  However, for non-circular conduits, the hydraulic diameter provides an equivalent measure that simplifies calculations and analysis.

 

Hydraulic Diameter Formula
\( d_h \;=\; \dfrac{ 4 \cdot A_c }{ P }\)     (Hydraulic Diameter) \( A_c \;=\; \dfrac{ d_h \cdot P }{ 4 }\)  \( P \;=\;  \dfrac{ 4 \cdot A_c }{ d_h }\)
Units	English	Metric
\( d_h \) = Hydraulic Diameter	\( ft \)	\( m \)
\( A_c \) = Flow Area Cross-section	\( ft^2 \)	\( m^2 \)
\( P \) = Wetting Perimeter Cross-section	\( ft \)	\( m \)