Residence time distributions in microchannels with assistant flow inlets and assistant flow outlets

Abstract

Residence time distributions (RTD) have been extensively employed to characterize the flow behavior in reactors, which significantly impact reaction conversion and selectivity. RTDs are investigated in microchannels with assistant flow methods by computational fluid dynamics, including assistant flow outlets (AFO), assistant flow inlets (AFI), and assistant flow inlets and outlets (AFIO). The inlet velocity ranges from 0.01 to 1 m/s, with flow rate weights ranging from 0.4 to 0.8 for the central flow outlet and from 5/8 to 1/13 for the central flow inlet. For AFO, as the decreasing flow rate weight of the central flow outlet, the peak of RTDs occurs closer to mean residence time, i.e., dimensionless mean residence time (θ) θ = 1. Meanwhile, the peak value grows higher, and the RTDs of tracking particles become narrower. There is a reduction of the dimensionless variance (σθ2) of particle residence time by tens of times compared with straight channels. For AFI, the central flow is further encapsulated in the center, leading to better RTDs and smaller σθ2 at a low velocity, but it is excessively disturbed at a high velocity, resulting in the increasing σθ2. AFIO not only achieves better RTDs but also diverts assistant flow to guarantee the weighting of central flow at the central outlet. This method using assistant flows can be extended to various size ranges and structure designs to promote the RTDs in continuous flow systems despite still laminar conditions.