Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles27Irreversibilities are the factors that cause a process to be irreversible. They include
friction, unrestrained expansion, mixing of two gases, heat transfer across a finite
temperature difference, electric resistance, inelastic deformation of solids, and chemical
reactions.
Irreversibility I is any difference between the reversible work Wrev and the useful work
Wu due to the irreversibilities present during the process. Irreversibility can be viewed as
the wasted work potential or the lost opportunity to do work.
Isentropic efficiency of a compressor is defined as the ratio of the work input required
to raise the pressure of a gas to a specified value in an isentropic manner to the actual
work input.
Isentropic efficiency of a nozzle is defined as the ratio of the actual kinetic energy of the
fluid at the nozzle exit to the kinetic energy value at the exit of an isentropic nozzle for
the same inlet state and exit pressure.
Isentropic efficiency of a turbine is defined as the ratio of the actual work output of the
turbine to the work output that would be achieved if the process between the inlet state
and the exit pressure were isentropic.
Isentropic process is an internally reversible and adiabatic process. In such a process
the entropy remains constant.
Isentropic stagnation state is the stagnation state when the stagnation process is
reversible as well as adiabatic (i.e., isentropic). The entropy of a fluid remains constant
during an isentropic stagnation process.
Iso- prefix is often used to designate a process for which a particular property remains
constant.
Isobaric process is a process during which the pressure P remains constant.
Isochoric process (isometric process) is a process during which the specific volume v
remains constant.
Isolated system is a closed system in which energy is not allowed to cross the boundary.
Isometric process (see isochoric process).
Isothermal compressibility relates how volume changes when pressure changes as
temperature is held constant.