Among numerous microfluidic setups the droplet based devices have a significant role due to their various potential applications.  In such devices microfluidic processing is performed on unit volumes of fluid which are transported, stored, mixed, or analyzed in a discrete manner. Efficient design of the micro-devices based on droplet-laden flows requires comprehension of various issues affecting their performance, such as motion of droplets within the imposed confined flow, interface heat/mass transport, droplet breakup and coalescence, and other.    

Currently there is no reliable tool for modeling of these systems - the conventional "sharp interface" methods are difficult to apply when the droplet breakup or coalescence is concerned. In the present work the "interface capturing" approach combined with volume-of-fluid (VOF) method is applied to numerically simulate droplet-laden flows in microchannels. The steady motion of spherical and slender droplets in a pressure-driven laminar flow in a microchannel is considered first. The calculated velocity of the droplet drift is in a very good agreement with asymptotic approximations. Forced heat convection in a droplet-laden flow in a microchannel is modeled next. The numerically determined effective heat transfer rates are higher than those for a single-phase laminar flow and the enhancement is shown to be a result of the augmented convective mixing due to moving drops. Finally, some "unit operations" involving topological change of a droplet shape are modeled, such as droplet breakup and coalescence. The results of the numerical simulations corresponding to droplet breakup at the microchannel T-junction show a good agreement with previously reported experimental results. The adequate physical mechanism of the droplet breakup is discussed.