Distribution characteristics of falling film thickness around a horizontal corrugated tube

Abstract

Falling-film evaporation has an essential method for desalination. The heat transfer tube is the core component of falling film evaporator. Liquid film thickness is one of the most important parameters for predicting heat and mass transfer coefficient of falling film evaporation. In this paper, a set of experimental apparatus for measuring the film thickness of a horizontal tube is set up. The experiments have been undertaken under different parameters, i.e. the tube diameter varying from 25 to 45 mm, the tube spacing ranging from 10 to 60 mm, the corrugated radius varying from 0.25 to 1 mm, and the film Reynolds number ranging from 150 to 1000. The liquid film falling around a horizontal tube is performed to explore the distribution characteristics of the film thickness. The liquid film thickness is measured by the conductance probe measurement method. The experimental results showed that the film thickness of the corrugated tube increases with the increasing of the film Reynolds number, which is the thinnest from 90° to 120°. It decreases as the tube spacing increases and increases with the tube diameter and corrugated radius. The liquid in the wave troughs can be replenished to the wave crests at any time because of the corrugated structure. The falling film thickness was thinner at the wave crests and thicker at the wave troughs. The phenomenon of dryout hardly appears in the falling film flow of the corrugated tube. Based on the experimental data, a new correlation has been given to predict the film thickness of the corrugated tube.