What is a head coefficient and what is it used for?
The head coefficient characterizes the head generated by a pump under certain operating conditions. It is a dimensionless coefficient which is assumed to be constant for pumps with similar flow conditions. The rotational speed can be determined at which a geometrically similar pump should operate, in order to generate an equal amount of head while maintaining similar flow conditions.
Following from the similarity considerations and the flow coefficient, similar velocity distributions between pumpsyield similar force distributions, only if the forces have the same relation to the fluid velocities at all corresponding points of the considered pumps. This is only the case when inertia forces are the only forces acting on the fluid. Following this assumption, a relation between head and the fluid velocity under similar flow conditions can be established. As velocities change proportionally to one another, only one velocity needs to be considered which is representative for the general state of the flow.
The head H is proportional to the square of fluid velocities u2 with g the gravitational constant for dimensional consistency. Velocity u is proportional to the rotational speed N multiplied with the rotor diameter. This relation is therefore rewritten, such that the head coefficient is obtained.
