This study presents a rigorous three-dimensional (3D) computational fluid dynamics (CFD) investigation into the complex hydrodynamic characteristics of an external falling liquid film flowing over horizontal tubes, focusing on a representative unit of the shell-side of a spiral-wound heat exchanger (SWHE). The primary objective is to quantitatively analyze the synergistic influence of key operating and structural parameters─namely, Reynolds number (Re), tube outer diameter (D), and tube spacing (S)─on the liquid film profile, coverage uniformity, and flow regime transition. A volume of fluid (VOF) model was established and validated to accurately track the gas–liquid interface. The analysis reveals three major findings: (1) Increasing the Reynolds number from Re = 300 to Re = 2000 drives a critical flow regime transition from a stable columnar flow dominated by viscous and gravitational forces to a highly dynamic fan flow. This transition significantly intensifies interfacial wave activity, which is quantified by a positive correlation between wave amplitude and Re. (2) An increase in tube diameter (D) promotes the concentration of the liquid film into distinct columns, decreasing film coverage uniformity and increasing local film thickness, as surface tension and inertia compete for liquid distribution across the larger surface. (3) The tube spacing (S) critically governs the hydrodynamics in the intertube region; an optimal spacing (S = 6 mm in this study) is identified where liquid columns effectively merge and redistribute, maximizing coverage while minimizing flow restriction. This quantitative analysis provides crucial, mechanistically grounded hydrodynamic data essential for the optimized structural design of industrial SWHEs, aiming to enhance overall heat and mass transfer efficiency.
Dong et al. (Tue,) studied this question.