Parametric study of the micro-explosion occurrence of W/O emulsions

Abstract

When a water-in-oil (W/O) emulsion droplet is heated, a phenomenon called micro-explosion (μ-exp) may occur. Micro-explosion can be defined as the burst of the continuous phase (i.e. oil) by the energy of evaporation of dispersed droplets (i.e. water) and the volume expansion that goes with it. In the paper are presented results that show a strong correlation between size average value (and distribution size) of water droplets and micro-explosion occurrence rate. Emulsion dispersed phase size, when using micro-channel techniques, depends highly on the emulsion composition and the energy provided to the system (Oil flow rate). A (3–18) μm diameter range was measured in the tests discussed in the paper. Micro-explosion occurrence can reach 70% for larger droplet sizes (about 20 μm). It declines to less than 20% for small sizes (between 5 and 10 μm). Influence of other parameters on micro-explosion occurrence like temperature heating or physical properties is also studied. Ohnesorge number seems to be an adequate parameter to study micro-explosion occurrence because of its direct relation with the relevant emulsion properties: droplet size, oil viscosity and interface tension. Micro-explosion rate achieves its maximum rate (60%) for Oh = 0.12, in other words, for emulsion where dispersed droplets move easily (low viscosity) with a great ability to coalesce (larger droplets and no surfactant).