No abstract

The collision of two successive water droplets with a hot solid was investigated. Experiments were carried out on water droplets with a diameter of approximately 0.6 mm and an impact velocity of 3.5 m/s at various droplet spacing and time intervals. The temperature of the solid surface was set at 120, 300, and 500°C. The Weber number, based on the pre-impact diameter of droplet and the impact velocity, is approximately 100. At low surface temperature (120°C), the coalesced liquid is deformed into the shape of a crown with its height increasing with droplet spacing. The hydrodynamics of the formation process of the crown is also studied in detail by numerical simulations under isothermal conditions. For the cases of 300 and 500°C, the coalesced liquid breaks up into small droplets as boiling occurs at the liquid-solid interface. The time evolution of droplet shape is dependent on the surface temperature as well as the spacing between two droplets.KEY WORDS: successive collision of droplets; photographic observation; numerical simulation; spray cooling; Weber number.

This study is concerned with the deformation behaviors of two droplets impinging successively onto a solid. Photographic means is used to understand the physics of the interaction phenomena between the two droplets. Water droplets of diameters between 0.39 mm and 0.65 mm with impact velocities ranging from 2.0 to 5.0 m/s are examined. The temperature of the solid surface is set at 25, 300 and 500 °C. The effects of varying solid surface temperatures, impact velocities of droplets and time intervals between the successive discharges on the collision behavior of the two impinging droplets are studied.

This study is concerned with the collision behavior of water droplets impacting onto a solid. Three-dimensional computer simulations are performed to understand the physics of phenomena. The Navier-Stokes equations for unsteady, incompressible, viscous fluid in a three-dimensional Cartesian coordinate system are approximated and solved by a finite difference method. The VOF (Volume-of-Fluid) technique is used to track free liquid surface. The effects of liquid viscosity, surface tension, gravity, and wettability between liquid and solid are taken into account. Normal and oblique collisions of droplets with the substrate are simulated at relatively low impact inertia of droplets. Experiments are also carried out in order to validate the numerical results. The numerical results agree reasonably well with experiments. The physics of phenomena is discussed in detail from theoretical aspects.