Gas Dissolution in Microscale Segmented Gas-Liquid Flow

We investigate the scalar transport of gas molecules from uniformly and equally spaced bubbles across the gas-liquid interface and the liquid plugs that separate them (segmented gas-liquid flow). The saturation time, i.e., the time that is required for a gas molecule to achieve a uniform concentration of the gas in the liquid is measured experimentally and validated by a two-dimensional numerical model.

We investigated the dependence of the saturation time while varying the Peclet number, Pe, between 2,500 and 30,000, utilizing an image-based control strategy in combination with an automated microfluidic platform. The experimental results confirmed the analytical prediction of the saturation time that scales with a quarter of the microchannel width as the characteristic length scale for the diffusive transport during gas dissolution. We found that at low capillary numbers (Ca < 0.01), the saturation time varies with Pe to the power -0.67.  In a serpentine microchannel we assessed the effect of chaotic advection in reducing the saturation time and length, and in increasing the dissolution rate. We found that 5 microchannel turns increased the dissolution rate by 30% and decreased the saturation length by 17%. No additional enhancement was observed in configurations with a larger number of turns.