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

Abstract

The hydrodynamic behavior of the liquid film has a great significance in horizontal tube falling-film flow. 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, the complete progression of droplet flow phenomena between the inline horizontal tubes for tube spacing of 10/20/30/40 mm is visualized with the aid of high-speed photography. The Sobel edge detection algorithm with gradient function is adopted in this analysis to detect the edges. The results indicated that the droplet flow phenomena between the tubes can be broadly classified 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, neck formation and retraction stages were observed with increased tube spacing. For the same Reynolds number and different tube spacing, the difference in droplet impacting modes were observed. It is found that the droplet velocity increases with the increases in inter tube distance. The findings are useful for modeling a heat transfer analysis in droplets.