Analyzing wall adhesion effects on falling film hydrodynamics for aqueous lithium bromide application

Abstract

Over the past decade, there has been a concentrated effort to accurately characterize the film thickness in horizontal tube falling film evaporators (HFFEs). Despite the experimental challenges in measuring thickness across the entire tube, researchers have made advances using adaptable operational settings, such as numerical modeling, to analyze falling films. One such condition is to analyze film hydrodynamics for different wall adhesion contact angles. In this study, a 2-D computational fluid dynamics (CFD) model is developed to quantify film thickness and wetting time and to analyze hydrodynamics for aqueous lithium bromide (LiBr) applications. The variation of liquid load (Γ1/2) from 0.01–0.05 kg/(m·s) and contact angle from 0–45° are studied for LiBr concentrations (C) of 0.45 and 0.65. Results indicate that the impact of contact angle diminishes at higher liquid loads and LiBr concentrations. At C = 0.45, the film thickens by 13.8 % for Γ1/2 = 0.05 kg/(m·s). Moreover, the effects of contact angle on wetting time are more pronounced than the average film thickness. With a higher contact angle, heat transfer may deteriorate due to the poor thermal resistance caused by higher average film thickness.