Residence time distribution is an important concept in reactor engineering. In this project, you will study the residence time distribution in a narrow channel using COMSOL. Multiphysics. You do this in three steps: (1) solve the fluid field of a narrow channel. The geometry is your choice. (2) Freeze the fluid field and introduce a tracer of constant concentration at the inlet. Solve the transient mass transfer. Record the outlet concentration as a function of time. (3) Calculate the cumulative residence time distribution based on the inlet and outlet concentrations