An electrical resistance tomography (ERT) system retrofitted to a 2.3 m(3) vessel has been used to image the vessel volume for single feed semibatch operation. Images reconstructed from the raw ERT measurements may be represented as time incremented 3-D iso-surface representations of the fluid mixing. ERT derived mixing curves have been evaluated against a network of zones (NOZ) mixing model, which is able to compute the time evolving concentration fields. Like the ERT system, the NOZ model is also able to visualise the evolving feed plume and has the power to predict the corresponding time-wise reaction behaviour in space for a simple A + B → products reaction.