For mass transfer limited liquid-liquid reactions,  as o called `slug flow` capillary microreactor has already been suggested. Internal circulations inside the slugs lead to increased mass transfer. The knowledge on the development of circulations and effects of operating parameters is crucial. The present work shows the state of art to predict the internal circulation inside the liquid slugs using computational fluid dynamics (CFD) simulations and visualization with the help of developed CFD particle tracing alorithm. Each slug was considered as separate domain and solved for individual slug as single phase flow. The effect of flow velocity and slug length on the velocity profile, stagnant region and internal circulations for slug without and with film is discussed. The internal cirulations were qualitatively predicted with the help of particle tracing algorithm.