A compressor is used to obtain a pressure increase for gaseous fluids. A compressor has one inlet and one outlet. As for pump, either pressure increase or an absolute outlet pressure is specified. Alternatively a compression ration can be specified, either as the ratio between inlet and outlet pressure, or as the ratio between outlet and inlet volume.
Furthermore, either an isentropic efficiency or the actual work required has to be specified.
The compressor efficiency is commonly defined by the ratio between the work needed for an isentropic (adiabatic) pressure change, WΔS=0, and the actual work, W.
If efficiency is specified, we therefore obtain the following relation:
Using a pS equilibrium calculation to determine the conditions at ΔS=0, enthalpy for the outlet is calculated.
Enthalpy can also be specified directly, or as an energy inlet stream.
The remaining outlet conditions of the compressor are determined by an enthalpy flash. An iteration over product pressure is required in case a volume ratio is specified.
If enthalpy is not specified via an energy inlet stream, an energy outlet stream can be connected that will receive a value for the work consumed by the compressor.
For a liquid flow, use a pump unit operation.