A general computer code for all types of evaporation and flashing processes has been developed and is currently being used by a number of Scandinavian industries and UAE University. Its advanced graphic capabilities enable the user to construct process flow sheets on the screen. The results can be displayed either graphically, as text file, or in any other form chosen by the user, and can be studied both for the whole plant such as concentration, temperature, and pressure profiles, and for a particular piece of equipment. The program is modular in structure and includes a number of modules for evaporators, heat exchangers, condensers, flash chambers, compressors, steam jet ejectors, etc. Each module has its own mathematical model. The program also includes a comprehensive database for the physical properties of seawater as well as other liquors. There is a library containing correlations for the heat transfer coefficient of different heat transfer surfaces and flow regimes. Account is made to all thermodynamic losses in the process such as boiling point elevation, non-equilibrium allowance inside the evaporators and flash chambers, temperature drops due to pressure drops in demisters, transmission lines, and condensers. Designed to be very flexible, the program can be used as an excellent tool for the simulation, rating and optimisation of all types of thermal desalination processes. Currently, it is being tested for on-line monitoring of process performance in a major food industry.