Properties of gas-liquid dispersion and mixing of seven types of impellers were studied and compared in a stirred vessel with aeration. New correlations for the properties including critical dispersion impeller speed, dispersion regime, power consumption, gas hold-up, discharge flow number and discharge efficiency have been developed. The fluid/wall heat transfer was also studied with several types of dual impeller combinations. There is a critical impeller speed which determines how aeration changes the heat transfer coefficient. Operating conditions influence heat transfer interactively by three factors, which can be expressed by proper dimensionless variables.