A nozzle is a local flow resistance with a gradual cross-section constriction (e.g. rounded inlet edge) on which the smallest flow cross-section - unlike on the orifice - is within the geometric cross-section constriction. The pressure losses due to fluid friction are generally no longer negligible. The flow rate through the nozzle is, as on orifices, defined with the aid of Bernoulli's equation. The loses due to fluid friction and the surge losses are taken into account by the pressure loss factor or the flow coefficients.
Fluidlexikon