Development of Crisis Phenomena in Falling Wavy Liquid Films at Nonstationary Heat Release

Abstract

This paper deals with investigation results on crisis phenomena for nonstationary heat release in falling liquid films. According to the experimental results, in the studied range of irrigation degree alteration (Re in = 60–1,690), parameters, characterizing decay of the falling liquid film with stepped heat release (distribution of time of boiling incipience along the liquid film, velocities of movable boundaries in the boiling-up and drying fronts), depend complexly on the Reynolds number, wave characteristics and heat flux density. The time of boiling incipience at stepwise heat release was simulated numerically with consideration of intensive evaporation development from the free surface of a laminar-wave film, transportation of large wave crests at typical process times and influence of the convective component of heat transfer. It is shown that the convective component of heat transfer in the wave liquid films and film thinning because of intensive evaporation provide a significant increase in the time of boiling incipience for the given heat fluxes under the conditions of nonstationary heat release. It is also revealed that for low densities of the heat flux at decay of a laminar-wave liquid film occurs with formation of metastable regular structures with liquid rivulets and large-scale dry zones between them. When loading thermal impulses of high intensity, film decay is determined by dynamic characteristics of propagation of the self-maintained front of liquid boiling-up and the shape of structures, formed during its development.