What is the difference between adiabatic compression and isentropic compression?
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My understanding is unclear. What is the difference between adiabatic compression and isentropic compression? Is there isobaric compression? Generally, compressors perform adiabatic compression; the temperature rises after each stage of compression, but there is no energy exchange with the outside environment. This post was last edited by “Endless Scenery on Dangerous Peaks” on March 27, 2009, at 14:14.]
The isentropic compression of a compressor refers to the fact that this compression process is an adiabatic and reversible compression.
I’ve heard of throttling expansion, which is an isenthalpic process, but I’ve never heard of isenthalpic compression. Compressed liquid?
Compression requires work to be done on the gas, causing its enthalpy to increase; therefore, there is no isenthalpic compression.
An isentropic process is an adiabatic reversible process; isn’t there such a thing as isenthalpic compression?
The compression process of a gas without any heat exchange with the surroundings is called adiabatic compression. In thermodynamics, reversible adiabatic compression is a isentropic process. At this point, the work done in compressing the system is equal to the increase in the system’s internal energy. There is a cooler at the outlet of the compressor after compression; it serves for heat exchange, removing the heat from the compressed gas promptly! There are isenthalpic processes. But there is no isenthalpic compression. When a system changes from state 1 to state 2 with an unchanged enthalpy, it is called an isenthalpic process.
Why wasn’t isenthalpic compression used? The device does work on the system while also exchanging heat with the surroundings; according to H = Q – W, isobaric compression is possible. Only, this process is very inefficient; all the work is converted into heat energy and lost, and it is difficult to implement in actual devices.
U=Q-W, H=U+PV; isn’t adiabatic compression an isenthalpic process?
The Clausius inequality shows that an isentropic process is an adiabatic reversible process
Isentropic compression is an adiabatic reversible process; an adiabatic process is not necessarily reversible, so it is not necessarily isentropic! There is isothermal compression, but no isenthalpic compression
To clarify, an adiabatic process refers to one in which there is no heat exchange with the outside world； Isentropy, on the other hand, involves the concept of reversibility, that is, adiabatic reversibility. In practice, isentropy does not exist.
Theoretically, there exist compression processes with constant enthalpy, but such processes are of no practical significance for research. Typically, two processes are studied: adiabatic compression and isothermal compression. The practical significance of these two processes is: (1) The single-stage compression process can generally be regarded as an adiabatic compression, and in theoretical calculations it can further be considered as an adiabatic reversible compression, that is, an isentropic compression ； (2) Infinite-stage intercooling compression can be regarded as an isothermal compression process, representing the theoretical limit of polytropic compression; the work done in isothermal compression is thus the minimum theoretical compression work.
Isentropic compression is a process of adiabatic reversibility; therefore, adiabatic compression is not necessarily isentropic compression