In continuous casting process, tundish operates as a refining finisher. Different flow modifiers can be used in order to optimize cleanliness of liquid steel. To study the effect of various flow modifiers such as dam, weir, inlet shroud and etc., a three dimensional mathematical model was developed to simulate turbulent flow inside the tundish. The computed flow field was further used to model the transient mass transfer in the melt flowing in the tundish. The residence time distribution (RTD) of particles was determined by mass transfer model. The performance of the model was evaluated by experimental data obtained by a physical model. The verified model was used to evaluate the effect of location and size of different flow modifiers on flow pattern and particles residence time and consequently on tundish performance.