Enhanced Laminar Mixing in Multifluid Droplets via Multiphase Flow in a Microchannel

Abstract

Laminar flow mixing remains an active area of research within the microfluidics community. Traditional mixing methods often rely upon turbulent flow, which is generally not present on the micro-scale and so alternative approaches must be sought. This work studies enhanced laminar mixing for use in a proposed monopropellant microthruster based upon homogeneous catalysis in a flow with Re < 10. The enhancement is realized through the introduction of an inert gas at a channel junction, which can lead to the formation of discrete liquid slugs. These slugs contain the monopropellant and the catalyst and have an internal recirculation that is found to enhance mixing. The focus of this study is on the numerical investigation of this process with the goal of minimizing the mixing length and characterizing the dependence of mixing on inlet conditions. The slug formation process is found to decrease the minimum mixing length by a factor of up to 7.2, with much of the benefit of the multiphase flow occurring shortly after slug formation. As minimizing the dimensions of the microthruster is a key design consideration, this reduction in mixing length demonstrates the value of the enhanced laminar mixing for the proposed micropropulsion application.