The hydrodynamic behavior of the liquid film has great significance in horizontal tube falling-film flow. The flow patterns between the horizontal tubes can be used to mathematically model the heat transfer analysis. Basic flow modes between inline horizontal tubes include droplet flow, column flow, sheet flow, and intermediate flow modes such as droplet-column and column-sheet mode. The flow patterns between the tubes can be adjusted by flow rate, fluid properties, distributor type, tube spacing, and spraying width. Droplet flow is one of the fundamental flow modes, which is commonly found in industrial heat exchangers. In the present study, a high-speed digital camera is used to visualize the complete progression of droplet flow phenomena between the tubes at different inter tube spacing. To illuminate the test section 100W LED lamp is used, resulting in high-definition images with clear boundaries for further image processing. Phantom V440L high-speed camera is used to capture the hydrodynamic behavior of the falling liquid over the tubes. A series of experiments were performed to examine the droplet flow behavior at 1500 frames per second, with a resolution of 1920x1080 pixels. The test liquid was circulated through the system for 30 to 40 minutes to ensure that the tubes were fully wetted and the piping system was free of air. Adjust the focal length of the high-speed camera to capture the center portion of the test rig. The middle part of the test rig area is chosen to prevent the "edge effect" and to take the videos. It should be noted that there are at least two to three dropping sites in the test area. Finally, convert videos to a number of frames. The Sobel edge detection algorithm with gradient function is adopted in this work to quantify the flow parameters and spreading of droplets in the axial direction. The Sobel edge detection technique was implemented in MATLAB, and the results were obtained using it. The results indicated that the droplet flow phenomena between the tubes can be broadly divided into the following phases; wavy droplet formation, droplet evolution, droplet elongation, droplet impact, and distribution of a droplet over the tubes. The development of detached spherical droplet pattern is observed with increased tube spacing. The droplet neck formation and retraction stages were clearly observed with the increasing inter tube spacing. It is found that the droplet falling velocity increases with the increases in tube spacing. The findings are useful for modeling a heat transfer analysis in droplets.Keywords: Droplet flow, Falling-film, High-speed camera, Horizontal tubes, Sobel edge detection.

Experimental Investigation on Falling-Film Droplet Flow Behavior on Varied Horizontal Tube Spacing

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.