Energy engineering

Industrial operations are generally continuous, with each component (turbine, pump, valve, etc.) constantly receiving and discharging material. When, as is often the case, their operating conditions are stabilized, possibly periodically, they are referred to as "steady state" or "stationary". Under these conditions, industrial processes must be considered as open systems in the sense of thermodynamics.

Even when real evolutions take place in a closed system, as for example in a positive displacement compressor, we are generally less interested in what happens inside the closed enclosure than in the mean stationary state obtained upstream and downstream of the machine, which can then be studied as an open system...