| Summary: | Experimental studies have revealed that the introduction of a small amount (0.5% by volume) of permanent and chemically inert gas bubbles leads to the intensification of droplets disintegration in a liquid–liquid system (emulsification) in a pulsating flow type apparatus. The liquids used were water (continuous phase) and oil (dispersed phase) at room temperature, and nitrogen was used as a gas. The gas hold-up <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi mathvariant="sans-serif">φ</mi><mrow><mi>i</mi><mi>n</mi></mrow></msub></mrow></semantics></math></inline-formula> was varied in the range of 0% to 4%. The volume fraction of the dispersed phase (oil) was 1% with respect to the continuous phase. The size of the oil droplets was determined by microphotographs; at least 600 drops were photographed in each experiment. The optimal gas hold-up in terms of the highest interfacial area (for the studied conditions) was found to be 0.5%, at which value the droplets’ Sauter mean diameter <i>d</i><sub>32</sub> decreased 1.88 times, and the maximum droplet size decreased 1.3 times, compared with the case without gas input. The effect of decreasing the average droplet size <i>d</i><sub>32</sub> upon the injection of an inert gas in the continuous phase disappears at φ<i><sub>in</sub></i> ≈ 2%. The pressure loss at φ<i><sub>in</sub></i> ≤ 2% within the measurement error remained constant, while at 4%, it increases by only 5.4%. The role of an inert gas is explained by several factors: (i) a redistribution of momentum over the volume of liquid; (ii) the occurrence of microflows near bubbles and drops, which leads to an increase in shear stresses on the surface of the drops; and (iii) gas bubbles act as pseudocavitation bubbles, whereby when they collapse, they break up adjacent droplets.
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