3. Compression / Expansion of Gas and vapors¶
In applications of thermodynamics to thermal machines, compressions and expansions of gases is of fundamental importance. These transformations occur in compressor, turbines, internal combustion engines, etc. Transformations in such machines are irreversibles, and the calculs are always performed thanks to associated reversible transformation and corresponding efficiencies often obtained thanks to manufacturer’s data.
In this section:
We make a review on the different kind of compressions and expansions of gases (isothermal, polytropic, isentropic) and their impact on the technical work.
We study the way of optimisation of such transformations.
We present the a brief description of the main elements that can perform compressions or expansions of a compressible fluid:
Volumetric compressors: including reciprocating compressors (present in refrigerators or heat pumps) and rotating compressors.
Dynamic compressors: contains a rotary mechanical device (rotor) that increase fluid pressure continuously. This is the case of ventillators, centrifugal compressors or axial compressors.
Turbines: also contains a rotor that provide a work from decresing the fluid pressure continuously. We talk about impulse turbine or reaction turbine.