Isentropisia

Isentropisia is a term used in thermodynamics to denote a condition in which entropy remains constant during a process. In many texts the more common English term is isentropy or isentropic process, while isentropia may appear in some languages or older literature. The concept refers to the idea that the system’s disorder, as measured by entropy, does not change as the process unfolds.

In practice, an isentropic process is typically associated with a reversible adiabatic change, where there is no heat exchange with the surroundings (dQ = 0 for the reversible path), and the entropy change is zero (dS = 0). For a simple compressible system, this condition leads to characteristic relations for an ideal gas, such as PV^γ = constant and TV^(γ-1) = constant, where γ is the heat capacity ratio Cp/Cv.

Applications of the isentropic idealization appear in engineering and atmospheric science. In turbines, compressors, and nozzles, designers use isentropic relations to estimate performance under idealized conditions. In meteorology, parcels of air are often treated as isentropic during rapid, adiabatic lifting or sinking, though real processes involve irreversibilities that cause entropy to increase.

Limitations exist because real processes exhibit irreversibilities, friction, and heat transfer, which raise entropy. Consequently, the isentropic model provides a useful approximation and a basis for defining isentropic efficiency, which measures how closely a real process approaches the ideal isentropic limit. See also isentropy, reversible processes, and adiabatic processes.