Boiling Incipience in Plane Rotating Water Films

Abstract

Knowledge of heat transfer in rotating liquid films is of paramount importance for evaluating the thermal efficiency of gas turbines with water-cooled blades. Centrifugal forces constitute the primary driving forces for liquids flowing in radial rotating channels. Coriolis forces, on the other hand, tend to thin out the flow in the form of a film that covers one side of the channel. Fully developed motion of the film is determined by a balance between centrifugal and shear forces. Thus, rotating film motion resembles that of a free-falling gravity-driven film since both are characterized by a balance between shear and body forces. However, Coriolis forces can strongly influence interfacial waves and turbulent velocity fluctuations of rotating films. This is evident from the results of Kirkpatrick (1980), who compared film thickness measurements for the cases of free-falling and rotating films. His data indicate profound waviness at higher Reynolds numbers for the case of gravity-driven films. On the other hand, interfacial waves in rotating films were found to stabilize at Reynolds numbers in excess of 8,000. This paper focuses on the effects of Coriolis forces and wall roughness on the convective heat transfer coefficient and the incipient boiling heat flux in thin rotatingmore » films.« less