6.1 Principle of operation g ()O0-P0)d 18 When separation of an oil globule in water is taking place,Fs F will equal Fr and the above equations can be worked to express the relationship of the terminal (or in this case rising velocity of the globule with viscosity, relative density and particle size6.1 Principle of operation • When separation of an oil g1obule in water is taking p1ace, Fs will equal Fr and the above equations can be worked to express the relationship of the terminal (or in this case rising) velocity of the globule with viscosity, relative density and particle size: 2 0 )( ) 18 ( d g u    =  −