In this thesis a novel computer based model is developed which accurately simulates the operation of a plate heat exchanger (PHE). The model allows for the variation of all relevant fluid properties as the temperatures of the fluids vary through the PHE. It is set up in a spreadsheet in such a way that one can observe the variation of fluid properties and heat transfer parameters through the PHE during steady state operation. Although the model could be used for general purpose analysis of PHE's, it is intended to be used in an educational environment, where students can run "virtual lab sessions" with the model and so gain a better understanding of the overall and detailed operation of plate heat exchangers. The model is validated using experimental data representing a range of different PHE sizes, flow configurations, fluid types and flow conditions. Instructions have been provided on how it can be used in an educational environment to assist student to discover more about the general and detailed operation of a PHE.