Numerical and experimental studies of mixing characteristics in a T-junction microchannel using residence-time distribution

The mixing behavior in laminar flow in microchannels is investigated using numerical and experimental approaches. The concept of residence-time distribution (RTD) was applied to indirectly characterize flow and mixing in a T-junction microchannel chosen as a model microchannel mixer/reactor. The residence-time distribution used in this study, although a well-known method for characterizing mixing behavior in conventional macro mixers/reactors, is still a novel measure for the characterization of mixing in microchannels. The standard T-junction microchannel and one of its modifications were studied for their mixing characteristics by performing computational fluid dynamics (CFD) simulations of pulse tracer experiments. Experimentally, RTD measure in conjunction with a UV–vis absorption spectroscopy detection technique was used to characterize flow and mixing quality in the microchannels studied. The moments of the RTD and coefficient of variation were used to quantify the mixing behavior. Two flow models, namely the well-known axial dispersion model (ADM) and a semi-empirical model (SEM), were used to obtain model descriptions for the RTD of the microchannel. As expected, the SEM fits better the experimental data than the ADM since the SEM with its characteristic asymmetric distribution predicts better the strong laminar flow behavior in the microchannels than the ADM. The results from the simulations and experiments are in very good agreement thus establishing the validity of the mathematical model and the associated solution algorithm implemented in the CFD simulations. The CFD code in conjunction with the RTD measure can then be used as a predictive tool in the design, evaluation, and optimization of microscale flow systems.