Shear-Atomization of Paraffin Wax in a Heated Fuel Slab Experiment

This study investigates shear-driven atomization of paraffin wax droplets within a heated slab configuration representative of melt-layer entrainment in hybrid rocket systems. Hot-flow experiments were conducted using a High-Speed Slab Burner where a paraffin wax fuel slab was exposed to preheated air, producing a recirculation region and liquid shear layer responsible for droplet entrainment. High-speed imaging combined with particle tracking velocimetry (PTV) was used to measure droplet diameter, velocity, and height, with statistical analysis performed using LaVision and MATLAB. Results show a transition in atomization behavior between low and high oxidizer mass flux conditions. Below approximately 200, droplet counts are limited and probability density functions exhibit increased variability due to incomplete ligament breakup. At higher mass flux, droplet counts increase substantially and size distributions converge, indicating more stable and consistent entrainment behavior. Conditional averaging reveals that droplet velocity decreases systematically with increasing diameter, while droplet height shows weaker and more variable dependence on diameter. These results demonstrate that oxidizer mass flux strongly influences droplet formation and transport dynamics, providing experimental insight into shear-driven entrainment mechanisms governing regression behavior in liquefying hybrid rocket fuels.