Heat transfer from turbulent falling films of water and non-Newtonian solutions, on smooth and on ridged plates

Abstract

Theoretical relations are derived for heat transfer into or from turbulent falling films of liquid, flowing both over smooth and over very rough surfaces. Heat transfer from turbulent falling films over smooth plates and ridged plates has been measured, for pure water. The enhancement of h L by the ridges can exceed two times, with suitable dimensions of the ridges. Our results are compared with those of previous workers. Our theory predicts heat transfers in fair accord with our experiments. The addition of ‘Separan’ to render the water non-Newtonian decreases h L for both the smooth and the rough plates. But the enhancing effect of the roughness remains about the same as for pure water. The addition of a surface-active agent to the water usually decreases h L somewhat, though very low concentrations of agent at low angles of inclination can increase h L .