A model for the residence time distribution of bubble-train flow in a square mini-channel based on direct numerical simulation results

This paper presents an original method for evaluating the liquid phase residence time distribution in bubble-train flow using data from direct numerical simulations (DNS). The method is a particle method and relies on the uniform introduction of virtual particles in the volume occupied by the liquid phase within a single flow unit cell. The residence time distribution is obtained by statistical evaluation of the time needed by any particle to travel an axial distance equivalent to the length of the flow unit cell. Residence time curves are evaluated from DNS data of bubble-train flow in a square mini-channel for different lengths of the flow unit cell. The curves obtained are well fitted by an exponential relationship, which has been developed on basis of a two-tanks-in-series compartment model, where the first tank is a plug flow reactor and the second is a continuous stirred tank reactor.