Operating speed versus time
Material transfer - Methodology

Modeling a unit operation in chemical engineering ultimately consists of expressing quantities - material or heat flows, concentrations or temperature, etc. - using functions of either spatial (x, y, z) or discrete (floor number) variables, on the one hand, and of time, on the other. Clearly, the most convenient models are the simplest ones, i.e. those that depend on a minimum number of parameters. In this section, we'll outline the conditions required for a model to be time-independent.

Models based on the flows defined in para-graph 3