The hydrodynamic characteristics of liquid-liquid flows in a micro-mixing plate with a ‘heart/spade’ geometry and a hydraulic diameter of \(\sim\) 0.36 mm at the contraction point are studied experimentally in the Reynolds number range of \(250 - 1,000\) . Localised optical observations of the two-phase flow within the micro-mixing device units are performed using a high-speed camera in combination with an LED-induced fluorescence imaging technique. A qualitative interpretation of the instantaneous images enabled the development of a regime map with three stable flow patterns, each with a metastable transitional state. The formation of secondary flows and recirculation zones resulted in the breakup of interfaces and fragmentation of droplets. The droplet size distribution of an MTBE-water dispersion is studied across a broad range of the dispersed phase (water) ratios, \(\phi _{\textrm{d}} = 0.091 - 0.714\) . The resulting Sauter mean diameter of water droplets is used to evaluate the improvement in the specific surface area and was correlated as a function of the energy dissipation rate and the Reynolds and Weber numbers.
