for all these applications, it is crucial to control and predict flow behaviors, such as flow pattern, bubble or slug size and
their velocity, which are function of parameters such as the geometry and size of microfluidic devices, gas and liquid flow rates and fluid properties. Unlike in conventional devices, bubbles or droplets rarely coalesce with each other in microfluidic systems. So the flow behaviors are mainly located in the region where various phases meet. In other words, all the important phenomena occur in the region of the formation of bubbles and droplets.