09. Heat and Mass Transfer

This study presents a determination method of spatially varying diffusion coefficients of acids, bases, and salts during the acid−base reaction, based on near-infrared imaging and advection-diffusion-reaction modeling. In this paper, the concentration profiles of HCl, KOH, and KCl, when the aqueous solutions of HCl and KOH flowed side by side in a microfluidic channel, are shown and analyzed. Each concentration profile was approximated by a Gaussian or error function, to calculate the advection, diffusion, and reaction terms analytically and robustly. The diffusion coefficients differed significantly within the channel, increasing toward the reaction interface. These values were larger than the literature values measured under non-reactive conditions. The validity of the determination method and areas for improvement are discussed.