Abstract Summary (Max 250 words)
The mechanism of turbulent mixing in liquid-phase neutralization reactions in a continuous-feed semi-batch stirred-tank reactor, where the base solution was fed with a jet in an acid solution, was investigated. The overall rate constant of the neutralization reaction, k_aV, was experimentally quantified using pH visualization images, a pseudo-first-order reaction model, and a material-balance equation for the base. The effects of the impeller rotational speed N, base feed flow rate Q, base inflow nozzle diameter din, and nozzle location on k_aV were investigated. Mathematical relationships between k_aV and Q, din, and N were derived based on micro- (engulfment) and meso- (shedding) mixing models. Two neutralization experiments were conducted: (i) continuous base injection without stirring (jet mixing only) and (ii) continuous base injection with stirring (jet and stirring mixing). In jet mixing only, k_aV was determined by the turbulent dissipation rate ε, indicating that the reaction rate is governed by the turbulent eddies elongating and entraining the surrounding unreacted fluid owing to viscous deformation (micro-mixing). For jet and stirring mixing with the nozzle set at the impeller tip, k_aV was determined by stirring-induced micro- or meso-mixing, depending on the strength of ε and the turbulent energy k in the discharge flow from the impeller. When the nozzle was positioned far from the impeller tip, k_aV was affected by both jet and stirring mixing. This effect depends on the injection and circulating flows in the reaction zone, which vary with the nozzle position.
