ABSTRACT
Falling film evaporation is used in the chemical industry for vaporization of both single component and multi-component liquids. This process is a special case of single component boiling, wherein bulk flow is induced by gravitational body force and the liquid flows as a thin film on vertical heat transfer surfaces. With appropriate wall superheats, bubble nucleation and boiling occurs on the heat transfer surface within the flowing film. The critical heat flux (CHF) is governed by quite different mechanisms than those commonly found for either pool boiling or convective boiling in channels.
An experimental investigation was conducted to measure the critical heat flux at approximately atmospheric pressure using three test fluids: F-113, water, and aqueous isopropanol. The new experimental data and observations supported Ueda et al. (1981) findings regarding the existence of more than one breakdown region in films undergoing nucleate boiling. The dry patch model failed to predict CHF data because it required unrealistic contact angles.
