Experimental and Numerical Hydrodynamic Analysis of a Waterfall Humidifier

This study experimentally and numerically investigates the hydrodynamic performance of a waterfall-type direct humidification system under crossflow air conditions. A transient, three-dimensional, multiphase Computational Fluid Dynamics (CFD) model based on the Volume of Fluid (VOF) method was developed to simulate the interaction between the horizontal air stream and a vertical water column. Experiments were conducted in a 90x90 mm test section, and an image processing algorithm was utilized to compare physical and numerical flow profiles. The effects were evaluated at a constant water flow rate (0.021 kg/s) across Reynolds numbers corresponding to three different air velocities (10,340, 13,787, and 18,958). The results demonstrate that increasing air velocity causes aerodynamic deformation, bending, and ultimately the fragmentation of the water column into multiple thin streams. This structural transition leads to a non-linear behavior in the two dimensional (2D) projected wetted area and a significant reduction in the three dimensional (3D) wetted surface area. The developed VOF model successfully captures the overall flow physics, providing a valuable framework for optimizing free-surface humidification systems.