Motion analysis of drop impaction on a strawberry surface

Abstract

A drop-generating and videographic system was developed and used to study the processes of drop impaction on a strawberry surface. Uniform drops, 0.5 to 4 mm in diameter, were produced using a drop generator with either a piezoelectric crystal or a miniature metering pump. Drops were released from heights of 25, 50, 75, 100, 125 and 150 cm above a strawberry fruit target. Five impact angles, 0, 15, 30, 45 and 60° from horizontal were tested for each size-height combination. Impact and splash events were recorded using a high resolution video camera. Splash droplets were also collected on water sensitive paper. Specialized computer software was used to calculate size, number, position, and velocity of incident drops and splash droplets. Diameter and release height of incident drops significantly affected number, mass, travel distance, velocity, splash angle and kinetic energy of splash droplets. Total mass and kinetic energy reflected by splash droplets were linearly related to the kinetic energy of incident drops on a log-log scale. The reflective factors of mass and kinetic energy (ratio of reflection to incidence), however, were found to increase with impact velocity at lower ranges of impact velocity and approached maximum constants of 0.68 and 0.09, respectively, as impact velocity increased. The reflection angle of the resultant trajectory vector was found to be close, and linearly related, to the incident angle. The initial velocity of individual droplets was significantly correlated to both splash angle and diameter. The Weibull cumulative distribution function provided an excellent fit to data of droplet diameter, velocity, kinetic energy, and travel distance.