Abstract The hydrodynamic characteristics of pump-mixers have been studied in the present work. The effect of different geometrical parameters on the head–flow characteristics of the system has been investigated. The effects of (i) different types of impellers, (ii) impeller location in the suction box and mixer, (iii) size of suction chamber and (iv) impeller diameter, etc. have been studied. Computational fluid dynamics (CFD) model has been developed to predict the head–flow characteristics. The model has been validated with the help of experimental data for two different types of the impellers used in the work. This work has enabled developing geometries that can produce higher head and flow than those reported in the previous literature. Based on the CFD simulations, stator–rotor type of system has been proposed. From the experimental results and the understanding from CFD simulations, optimum pump-mix mixer geometry has been proposed.