This term is commonly used in hydraulic engineering and represents the kinetic energy of a fluid flow within a given streamtube. It has the physical dimension of length (hence the term "head"), and corresponds to an energy per unit weight. If u is the velocity and g the acceleration due to gravity, the velocity head is defined by u2/2g. If the flow within a pipe, channel, or duct is uniform over a given cross-section, this definition of the velocity head applies to the entire cross-section. However, if the flow is nonuniform, the variation in kinetic energy from one streamtube to another is accounted for by a correction factor α. In this case the velocity head appropriate to the section is:
where A is the cross-sectional area and ū is the mean velocity. In terms of a traditional energy level approach, the velocity head represents the distance between the hydraulic gradient line (defined by the static head), and the total energy line or total head line.
Heat & Mass Transfer, and Fluids Engineering