Spray Impact on and Carry-Over from Complex Shaped Surfaces

Personal care products are pervasive. A common mechanism for transporting products to the desired target is via spray application, a method capable of efficiently breaking the product into droplets and creating coverage of a surface. The work presented in this thesis focuses on (i) experimentally investigating sprays generated from deodorant-type aerosol cans and (ii) generating a validated numerical model to aid in both understanding the mechanisms and predicting the fate of the generated droplets.

To do this, spray generation from nine different aerosol cans, with varying formulation and nozzle type, are investigated using three experimental setups: high-speed schlieren imaging; particle size measurement using laser diffractometry; and a thermocouple array. Schlieren imaging gives insight into the two-phase nature of the spray and allows the spray angle to be measured, with measurements varying from 16.3° - 22.2°. Particle size measurements show that a log-normal distribution is able to represent the initial sizes generated by an aerosol can. Centreline temperature measurements reveal that temperatures can drop as low as -41 °C due to the evaporation of the alkane-based propellants used to carry the product. The formulation and the nozzle type have a strong influence on these parameters.

A carrier-jet CFD model is created, finding that the realizable k-epsilon turbulence model performs best at predicting momentum decay and propellant dispersion. One-way coupling modelling is used to capture the movement of droplets as they approach a surface and the resulting capture efficiency is determined. The surface is parameterised in terms of standoff distance and degree of curvature. Model predictions show that flatter surfaces result in a reduced capture efficiency and that the release position of the droplets significantly impacts their efficiency. An extension of the model to two-way coupling of droplets with the carrier-jet shows that incorporating droplet latent heat due to vaporisation is important for capturing the spray temperature.

Both the developed methods and the results give new insights into the complex behaviours of aerosol sprays which remains a relatively unstudied area.