FILM COOLING ON A ROTATING-DISK

The unsteady flow of a liquid film on a cold rotating disk is analysed by means of matched asymptotic expansion under the assumptions of radially uniform film thickness that varies with time. The velocity, the temperature and the rate of heat transfer are determined. It is shown how the uniform film thins with time for fixed values of the cooling or heat dissipating parameter β, and the Prandtl number σ. When either β increases or σ decreases, the film thickness increases, which implies that a relative resistance to film thinning is developed inside the film- A zone S, bounded by a curve in the r-z plane, may be delineated such that the temperature is minimum on this curve. Thus, heat flows from the disk to the fluid, inside the zone S, and in the opposite direction outside S. © 1990.