TY  - EJOU
AU  - Zheng, Lishuang 
AU  - Chen, Fengjun 

TI  - Swirl-Induced Flow Instabilities and Heat Transfer Enhancement in Vertical Falling Films at High Reynolds Numbers
T2  - Fluid Dynamics \& Materials Processing

PY  - 2026
VL  - 22
IS  - 7
SN  - 1555-2578

AB  - A computational fluid dynamic (CFD) numerical framework is established in this article to comprehensively uncover the flow evolution laws and gas-liquid phase-change heat transfer mechanisms of vertical falling film with high Reynolds numbers (<i>Re</i>). Systematic numerical analysis are carried out to characterize the liquid film spatial distribution, flow velocity field, internal turbulent vortex structures and comprehensive heat transfer behaviors. The swirl-induced coherent structures are identified using velocity vectors and vortex-detection criteria, and the influences of swirl angle, channel width, and platform height on film thickness distribution and thermal performance are examined. Model validation is performed through comparison with published numerical and experimental data, showing good agreement. The results indicate that, under high Re conditions, swirling motion significantly disrupts the liquid film and intensifies interfacial turbulence, thereby enhancing heat transfer. The inlet region exhibits the highest thermal performance, driven by strong vortex activity. Increasing the swirl angle leads to a reduction in liquid film thickness and an overall enhancement of heat transfer. However, turbulent kinetic energy and dissipation rate exhibit nonlinear responses to changes in swirl angle. An optimal configuration is identified at a swirl angle of 60°, where the average film thickness is approximately 4.03 mm and interfacial fluctuations remain most stable. In addition, a coupled optimal range is observed for channel width and platform height, highlighting their combined influence on flow stability and thermal efficiency. The underlying two-phase transport mechanisms are interpreted in terms of vortex dynamics and energy transfer processes. Based on the simulation results, a heat transfer correlation valid for high Re conditions is developed. The maximum heat transfer coefficient reaches approximately 700 W/m<sup>2</sup>·K. Furthermore, fitting of the dimensionless heat transfer coefficient (h<sup>+</sup>) demonstrates excellent predictive capability for heat transfer trends in gas–liquid two-phase internal flows, with a coefficient of determination (R<sup>2</sup>) of 0.999.
KW  - Swirl falling film; fluid dynamic; liquid film thickness; turbulent flow; phase change heat transfer; HTC

DO  - 10.32604/fdmp.2026.083363