Critical velocity is the velocity of a liquid flow upto which its flow is streamlined and after which its flow becomes turbulent. The critical velocity depends on coefficient of viscosity 'h', density of the liquid 'r', and radius of the tube (r). Using the methods of dimensions, one can show that where k is constant of proportionality
The Reynolds number is a pure number that determines the nature of flow through a pipe. The critical velocity 'VC' is given by
