Ice growth and interface oscillation of water droplets impinged on a cooling surface

We focused on the attenuation of air-water interface oscillation for impinged water droplets freezing on a cooling surface. We carried out not only experiments but also two-dimensional numerical simulation on the droplets using a Phase-field method and an immersed boundary method. The Reynolds number and Weber number were in the range of 35-129 and 1.6-22, respectively. The experimental and computational results showed that the height of the impinged droplets on the symmetrical axis started to oscillate as a result of the impact of the collision of droplets with the surfaces in all the cases that we investigated. The measured frequency of the oscillations in the case of the adiabatic droplets was equal to the frequency estimated from the equation for the capillary-gravity waves on sessile droplets (Temperton, 2013) [30]. The oscillations converged rapidly in all impinged water droplets that froze on the cooling surface. This is due partly to the growth of ice shells along the air-water interface and partly to decreases in water volume as a result of the ice growth mainly on the cooling surface. In addition, the thermal field was disturbed not only by the latent heat transfer but also by the upward component of recirculating flow induced by the droplet impingement.