A Review of Computational Models for Falling Liquid Films

In this chapter, a comprehensive review of numerical studies for falling liquid films over plain flat surfaces and horizontal tubes have been presented in terms of flow hydrodynamics and coupled heat and mass transfer. The early studies on the falling film transport models were based on simplified assumptions, and the reduced equations yielded approximate solutions. Developments in Computational Fluid Dynamics (CFD) led by Professor Spalding at Imperial College since the 1960s have enabled the solution of the full set of equations, and space- and time-accurate solutions. The present review primarily discusses recent studies that are based on the solution of the full set of coupled liquid–gas flow equations and highlights some key observations based on these studies. For liquid film flow over plain flat surfaces, the review highlights the important role of interfacial waves and the associated enhancement in the sensible heat transfer rates. However, the impact of these interfacial waves on coupled heat and mass transfer and the potential interaction of these waves with the gas medium is not fully understood. For film flow over horizontal tubes, the recent literature has made significant progress through full-scale models and employing sharp interface capturing techniques. Time- and space-resolved calculations for falling film evaporation over horizontal tubes are currently limited in the literature, but could reveal key underlying mechanisms and/or assist in developing underlying models related to dry-out conditions.