Observations of droplet impingement on a ceramic porous surface

The dynamic aspects of droplet impingement on a porous ceramic surface were studied experimentally. Single-shot flash photography was used to photographically record the deformation and spreading on the surface. The observations were made with ambient pressure (0.10 MPa), ambient temperature (cu. 22”C), initial droplet diameter (1.5 mm), and the impact Weber number (43) fixed. The primary parameter was the surface temperature, which ranged from 22 to 200°C. The liquid was n-heptane. The spreading rate of a droplet on a porous surface at 22°C was measured to be lower than that on a stainless steel surface. No transition to film boiling was observed with the porous surface at a surface temperature of 2OO”C, unlike that seen with a stainless steel surface. The evolution of wetted area and spreading rate, both of a droplet on a porous surface as well as on a stainless steel surface, were found to be independent of surface temperature during the early period of impact. This result was attributed to negligible surface tension and viscous effects. The maximum value of the diameter of liquid which spreads on the surface was found to be lower on the ceramic surface than it was on the stainless steel surface at the same temperature.