A transient modelling framework for a vanadium redox-flow battery (RFB) is developed and experiments covering a range of vanadium concentration and electrolyte flow rate are conducted. The two-dimensional model is based on a comprehensive description of mass, charge and momentum transport and conservation, and is combined with a global kinetic model for reactions involving vanadium species. The model is validated against the experimental data and is used to study the effects of variations in concentration, electrolyte flow rate and electrode porosity. Extensions to the model and future work are suggested.