The change of atomization mechanismat the edge of a rotating disk was studied based on theoretical consideration and various experimental data. The flow rate at the transition was determined by seeing directly the transition phenomenawith a stroboscope. Four kinds of liquids and five kinds of disks were used in this experiment, and the rotational number was varied from 500 to 4C00 rpm. As a result, it was seen that the transition accompanied a kind of hysteresis phenomenon. The flow rate at the transition from direct drop to ligament formation was a little more than that at the reverse transition, as given by Eqs.( 27) and ( 28), respectively. Also, for the transition from ligament to film formation and the reverse transition, a similar hysteresis was obtained. Hinzeand Milborn's equation can be used for liquid of less than a few poises in viscosity for prediction of the flow rate at the transition from ligament to film formation, and the equation by Tanasawa et aU is applicable to more viscous liquids.

Various theoretical solutions including the author's for the thickness of a viscous liquid film on a rotating disk are presented in terms of two dimensionless parameters and are compared with experimental results. The film thickness on the disk was measured by a micrometer which is movable with a needle used as a surface detector. The numerical solution of the equations as simplified by von Karman's method and Bruin's solution agree well with the experimental results in a wide range of operating conditions. Polynomial approximation with orders up to fourth and fifth degree is usable to predict the film thickness.