ASPEN is a process simulation software package widely used in industry today. Given a process design and an appropriate selection of thermodynamic models, ASPEN uses mathematical models to predict the performance of the process. This information can then be used in an iterative fashion to optimize the design. This accurate modeling of thermodynamic properties is particularly important in the separation of non-ideal mixtures, and ASPEN has a large data bases of regressed parameters. ASPEN can handle very complex processes, including multiple-column separation systems, chemical reactors, distillation of chemically reactive compounds, and even electrolyte solutions like mineral acids and sodium hydroxide solutions.
ASEM is comprised of a large number of basic systems, all of which need to work in order for the basic machine to function. As any user needs to understand how these things work in order to understand how their actions (or lack of them) can affect their results (or basic functionality of the SEM), then this is the best place to start.