Crystallization modelling is limited by the availability of methods to reliably predict mixing, temperature and concentration distributions, supersaturation, nucleation and growth kinetics for crystallization systems of industrial size. A new software environment for modelling batch cooling crystallization has been developed integrating crystallization and fluid dynamics. The mathematical model can reliably predict mixing in stirred vessels of a given geometry and its effect on the crystallization kinetics and crystal product properties thus reducing the cost and time required for the design and scale-up of industrial crystallizers. The paper describes the development and application of crystSim for modelling industrial crystallization in stirred tanks. The software is developed in Visual C# making full use of Object Oriented Programming (OOP) and multithreading. (C) 2011 Elsevier Ltd. All rights reserved.