Vapor/Liquid Interaction and Entrainment in Falling Film Evaporators

Abstract

The problem of vapor/liquid interaction and entrainment in falling film evaporators is analyzed. Attention is focused primarily on horizontal tube falling film evaporators where liquid falls from one tube to the next in either a droplet or column mode. A criterion is presented for the onset of column formation, and equations are derived for the deflection of droplets and columns due to vapor crossflow. Based on an experimental study of drop detachment and breakup, a correlation is established for the resulting droplet sizes. For high vapor crossflow velocities, a criterion is presented for the inception of liquid entrainment by a process known as stripping. Based on the foregoing models, conditions are defined under which vapor/liquid interaction and entrainment are important for falling film evaporators.

Flow Structures of a Liquid Film Falling on Horizontal Tubes

“…(19) and (20) is occurring in either direction without hysteresis. It should be noted in this context that Yung et al [25] gave an equation for the mass flow rate at the transition from the droplet to column mode on a plane tube which can be rearranged to give:…”

A study of the coupled heat and mass transfer during absorption process in a spiral tubular absorber

“…The diameter (d i ) is generally deduced from empirical relation as suggested by Yung et al [15]; while in this study we have deduced (d i ) directly from the equation traducing the equilibrium of forces of a detached falling droplet taking into account the superficial tension effect:…”

Falling-film evaporation on horizontal tubes—a critical review

“…It can also promote either the formation of dry patches or better liquid distribution [46]. Thus, the effects of a vapor flow can either increase or decrease the bundle average heat transfer coefficient.…”

“…The pattern is referred to as falling-film mode and may play an important role in the heat transfer process. Yung et al [46] correlated the flow rate for a transition from the droplet mode to the jet mode with the droplet production frequency set equal to the capillary wave oscillation frequency. Yung and his co-workers based their studies on results from a single tube with a single liquid detachment site in quiescent vapor.…”