Isentropic process
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In thermodynamics, an isentropic process (a combination of the Greek word "iso" -same- and entropy) is one during which the entropy of the working fluid remains constant. By the second law of thermodynamics we may write
- <math>\delta Q \le TdS</math>
where <math>\delta Q</math> is the amount of energy the system gains by heating, <math>T</math> is the temperature of the system, and <math>dS</math> is the change in entropy. The equal sign will hold for a reversible process. For a reversible isentropic process, there is no transfer of heat energy and therefore the process is also adiabatic. For an irreversible adiabatic process, the entropy will increase. Hence removal of heat from the system (cooling of the system) is necessary to maintain a constant entropy (within the system) for an irreversible process. Thus irreversible isentropic process is not adiabatic.
For reversible processes then, an isentropic transformation is carried out by thermally insulating the system from its surroundings. Temperature is the thermodynamic variable conjugate to entropy, and so the conjugate process would be an isothermal process in which the system is thermally connected to a constant-temperature heat bath.es:Proceso isentrópico fr:Isentropique
