The effect of gas streams on the hydrodynamics, heat and mass transfer in falling film evaporation, absorption, cooling and dehumidification: A comprehensive review

Falling film heat and mass transfer, representatives of advanced and low-carbon heat and mass transfer technologies, has been applied in a variety of thermal processes due to its great prospect for heat and mass transfer enhancement. However, the hydrodynamics, heat and mass transfer are significantly influenced by the gas (vapor or air) streams during the operation of falling film heat exchangers. To acquire the detailed profiles of flow, temperature and concentration and to explore the influence mechanism of gas stream shearing on the falling film hydrodynamics and heat and mass transfer, researchers have adopted experimental, analytical and numerical methods for different attempts. This paper presents a comprehensive summarization of the relevant work concerning the hydrodynamic, heat and mass transfer characteristics of falling film components, including the evaporator, absorber, evaporative cooler and dehumidifier. Considering the specific applications, the cocurrent, countercurrent, and cross gas streams shearing on the liquid film on a horizontal tube and bundle, a vertical tube and a vertical plate are reviewed. The objective of this review is to cover sufficient knowledge of the results, findings and insights of gas stream impacts on the hydrodynamics, heat and mass transfer in building utilized heat exchangers to provide guidance on how to maximize the positive effect or at least minimize the negative impact of gas shearing on the falling film heat and mass transfer. Schematics of gas stream models encountered in various applications. • Provide the first review of the gas stream effect on falling liquid film flow. • Clarified mechanisms of gas effect on liquid film flow, heat and mass transfer. • Summarized studies of gas stream effect on falling film flow, heat and mass transfer. • Concerned film thickness, heat and mass transfer prediction under gas shearing. • Proposed some recommendations and improvements for future research.