Regime maps of collisions of fuel oil/water emulsion droplets with solid heated surface

Abstract

The paper presents the experimental research findings for the characteristics of secondary atomization of fuel oil/water emulsion droplets colliding with a solid substrate. This reproduces the interaction of fuel droplets with heated walls of combustion chambers, reactors, mixing units and swirlers. Conditions were identified, when two regimes of the interaction of a substrate with a parent droplet occur consistently and lead to its atomization or sticking. To approximate the experimental conditions to the gas–vapor-droplet technologies, the main parameters were varied in wide ranges: relative water and fuel oil concentrations, droplet sizes (0.1–2.5 mm), droplet velocities (0–8 m/s), temperatures of the fuel (20–90 °C) and substrate (20–300 °C). The key characteristics were recorded: collision regimes, critical Weber, Reynolds and Ohnesorge numbers, child droplet number and sizes, liquid surface area. Interaction regime maps were drawn up. Equations describing the transition boundaries between the interaction regimes were derived. The surface areas of fuel oil/water emulsion droplets after and before the fragmentation were calculated. Guidelines were provided for applying the research findings to the development of secondary atomization technologies of fuel oil/water emulsion droplets.