Transport of emulsion‐encapsulated compound droplets in rigid and deformable constricted microchannels

Abstract Transport of compound droplets in confined geometries is relevant to emulsification processes, multiphase transport, and microstructured flow systems. This study presents an experimental investigation of oil‐in‐water‐in‐oil, (O/W)/O, emulsion‐encapsulated compound droplets flowing through a constricted microchannel, with emphasis on the effects of flow‐rate ratio, internal droplet size, and channel wall compliance on droplet transport behaviour. A multiple emulsion was formulated using xanthan gum (0.16–0.2% w/v) to obtain stable and optically clear compound droplets suitable for micro‐scale visualization. The influence of flow‐rate ratio (3 ≤ ≤5), internal droplet confinement, and channel compliance on droplet size and total transit time was examined. The results indicate that both droplet size and transit time increase with increasing flow‐rate ratio within the investigated range. Droplets containing larger internal inclusions exhibited approximately 8% higher mean transit times compared to those with smaller inclusions, indicating the influence of internal structure on transport resistance. Channel wall compliance was observed to affect droplet behaviour by modifying the effective flow geometry, resulting in earlier droplet formation and increased transit times relative to rigid channels. A maximum increase of approximately 35% in total transit time was observed under compliant conditions. These observations highlight the combined role of internal droplet structure and channel compliance in determining compound droplet transport in confined systems. The results provide experimentally derived trends that may be useful for the design and operation of processes involving structured emulsions in confined or microstructured flow environments.