General Model

In this analysis, in order to obtain the essence of the process, some simplified assumptions are made. It simplest model of such process is when a piston is displacing the gas though a long tube. It assumed that no chemical reaction (or condensation/evaporation) occur in the piston or the tube ^12.1. It is further assumed that the process is relatively fast. The last assumption is a appropriate assumption in process such as die casting.

Two extreme possibilities again suggest themselves: rapid and slow processes. The two different connections, direct and through reduced area are combined in this analysis.