Following the fast development of microfluidics over the last decade, the need for methods for mixing two gases in flow at an overall flow rate ranging from 1 to 100 NmL·min-1 with programmable mixing ratios has been quickly increasing in many fields of application, especially in the calibration of analytical devices such as air pollution sensors. This work investigates numerically the mixing of pure gas pulses at flow rates in the range 1⁻100 NmL·min-1 in a newly designed multi-stage and modular micromixer composed of 4 buffer tanks of 300 µL each per stage. Results indicate that, for a 1 s pulse of pure gas (formaldehyde) followed by a 9 s pulse of pure carrier gas (air), that is a pulses ratio of 1/10, an effective mixing up to 94⁻96% can be readily obtained at the exit of the micromixer. This is achieved in less than 20 s for any flow rate ranging from 1 to 100 NmL·min-1 simply by adjusting the number of stages, 1 to 16 respectively. By using an already diluted gas bottle containing 100 ppm of a given compound in an inert gas same as the carrier gas, concentrations ranging from 10 to 90 ppm should be obtained by adjusting the pulses ratio between 1/10 and 9/10 respectively.
Keywords: gas mixing; modelling; modular micromixer; multi-stage micromixer; pulsed flow.