A Review of Transport Mechanisms and Interfacial Physics of Gas–Liquid Flow in Microchannels

In a microchannel, a gas bubble can occupy much of the available cross-section. Its shape and motion then depend closely on the channel walls and the thin liquid layer between them. This review examines how such confinement governs gas–liquid flow and its momentum, mass, and heat transport. It first considers the forces and flow regimes that arise in different channel geometries, then examines how surface tension and wettability affect bubble formation, deformation, breakup, and coalescence. It focuses on squeezing, dripping, and jetting in T-junction and flow-focusing devices. The review connects these interfacial processes to pressure drop and to transport through bubble caps, liquid films, and recirculating slugs. It also assesses what experimental measurements and numerical methods can reveal about these processes. Across the studies considered, bubble size, void fraction, film thickness, and wall conditions help explain why similar flow rates can produce different hydraulic and transport responses. Progress in prediction will require more complete measurements of interface behavior and models tested across multiple fluids, geometries, and flow regimes.