Liquid film dispersion on horizontal circular tubes under spray impingement

The evaporative cooling equipment using spray films can improve the thermal and anti-scaling characteristics owing to the advantages of simple structure, effective removal of the blockage and expanded liquid coverage. This paper explores the liquid dispersion and film phenomena over the horizontal circular tubes under spray impingement at varied water flow rates and positions. In the experimental study, a high-speed camera is used to capture the optical images of spray film flows for viewing the impingement of ejected fan-shaped liquid sheets, development of falling spray films exhibiting three basic fluid modes as well as formation and distribution of liquid films over the tubes. To simulate the moving interface progression, the theoretical analysis implements the unsteady three-dimensional volume of fluid (VOF) method and continuous surface force (CSF) scheme with the stress transport (SST) k-ω turbulent model for turbulence closure. The liquid film flows are predicted and compared with the measured liquid film thickness distributions around the tubes to validate the computational model. Both the experimental measurements and CFD simulations are then extended to investigate the film flow patterns and liquid film thickness distributions of falling sprays on the tubes at varying water flow rates and locations. At a low water flow rate of 3 l/min, the reduced ejection velocities develop a lesser spreading coverage over the horizontal tubes, causing the completely dryout results on the tube surfaces at a distance of 95 mm from the centerline. The scenarios at high water flow rates of 5 and 7 l/min can cover broader, more uniform spray areas, with the film thicknesses ranging 0.28–0.85 mm and 0.22–0.75 mm, respectively.