A Simple Model for Rewetting of Hot Tubes Limited by Flooding

Abstract

A study of the cooling of a hot vertical tube by a falling liquid film in the presence of countercurrent flow of rising hot air is presented. Vapour generated during tube quenching mixes with the injected air to form an air-vapour mixture flow opposite to the falling liquid film. This upward mixture flow resists the downward penetration of the liquid film and may cause flooding of the injected liquid. The objective of this study is to estimate the quenching rate of the hot tube in terms of The initial tube temperature, countercurrent air flow rate and tube dimensions. A simple model is developed starting from the momentum equation of the falling liquid film. The energy equation was applied to calculate the vapour generation rate during the quenching process. A one-dimensional conduction-controlled model was used to find the rewetting velocity in the absence of the countercurrent flow of rising gases. Correlations for the liquid penetration rate and interfacial friction factor, based on experimental data, was incorporated in the model. The resulting governing equations were solved iteratively and the results were compared with available experimental results. Good agreement was obtained.