According to the configuration of a real nozzle bubble

the author proposes a physical model which describes the nozzle bubble as a tadpole structure. Unlike a spherical bubble

the long tail part of a tadpole bubble has great influence on the inertia force and the drag force acting on the bubble. Thereupon

the author discusses the bouyancy force

the inertia force

the drag force and the surface tension force acting on a nozzle bubble in equilibrium before detachment takes place. An iteration equation for calculating bubble detachment diameter is estableshed which contains all the important factors of the liquid phase physical properties

the nozzle diameter and the gas rate. The calculated detachment diameter is in good agreement with experimental observations in almost all ranges of the above mentioned parameters. Various individual cases are calculated with high accuracy by this iteration equation as compared with equations of other investigations

and the causes of deviation oi the latter ones are discussed.