Experimental and numerical study of falling-film hydrodynamics and droplet flow regimes over horizontal tubes

Gravity-driven horizontal falling-film flow phenomenon is a ground-breaking technology that has been actively used in a wide range of industrial applications, including desalination, petroleum refineries, food processing industries, and refrigeration, among others. A series of experiments and a 2-D two-phase model were developed to investigate falling-film flow regimes, microscopic flow mechanism, and finer flow parameter details. The experiments focused primarily on axial inter-tube flow modes, and circumferential flow parameters were evaluated using numerical simulations. A high-speed digital photographic device was used to capture and visualize the flow pattern. The VOF method is used to capture the liquid-gas interface. The Reynolds number ranged from 41 to 1000, the tube spacing was 10/20/30/40 mm, and the contact angle was 0 degrees. According to the findings, droplet flow has three important phases, detached spherical flow pattern, discrete spherical flow pattern, full neck formation by linked droplets, and droplet flow before reaching column flow. The Reynolds numbers 166, 208, and 250 have departure-site spacing values of approximately 23.84 mm, 18.16 mm, and 14.52 mm, respectively. The flow parameters such as radial film thickness and vortices beneath the tube increase with increasing Reynolds number. As Reynolds number increases, the departure-site spacing and liquid film inter-tube propagation time decrease. The thinnest film zone appeared between 90 degrees and 140 degrees. The velocity magnitude of the liquid film over the test tube is greater than that of the stabilizing tube, despite being close to the distributor. Furthermore, the film velocity on the lower half of the tube wall is slightly higher than that on the upper half of the tube wall.

Automated summary

Gravity-driven horizontal falling-film flow is an innovative technology widely used in various industries. Through experiments and numerical simulations, the flow regimes, flow mechanisms, and parameter details were investigated. The study found that droplet flow has three important phases and increasing Reynolds number leads to increased film thickness and vortices formation.