BeginnerTopic 12 of 105Thermodynamics & Fluids
Thermodynamic processes
Isothermal, isobaric, isochoric and adiabatic describe constant property paths.
In depth
Special cases: isobaric (P const), isochoric (V const, W=0), isothermal (T const, PV=const), adiabatic (Q=0, PVᵞ=const) and polytropic (PVⁿ=const). Work for polytropic: W=(P₂V₂-P₁V₁)/(1-n). Quasi-equilibrium assumed.
Key points
- Reversible vs irreversible
- Process paths on diagrams
- Isentropic = reversible adiabatic
ExampleIsothermal compression of an ideal gas requires heat rejection equal to work input.
What is Thermodynamic processes?
Isothermal, isobaric, isochoric and adiabatic describe constant property paths.
Why is it important to understand thermodynamic processes?
The named processes describe common idealised paths, and they allow quick calculations of work and heat for gases.
What is an adiabatic process?
A process with no heat transfer across the boundary, which is approximated by fast compressions and expansions in engines.
What is an isochoric process?
A process at constant volume, in which no boundary work is done and all heat goes into internal energy.
How is Thermodynamic processes used in practice?
Typical applications include modelling a slow compression in a piston as isothermal, describing a fast compression in an engine as nearly adiabatic and analysing a heating process at constant volume in a sealed tank.
What should I learn before Thermodynamic processes?
Study "Ideal gas law" first (topic 11 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Thermodynamic processes?
Reversible vs irreversible. Process paths on diagrams. Isentropic = reversible adiabatic.
Can you give an example of Thermodynamic processes?
Isothermal compression of an ideal gas requires heat rejection equal to work input.
What comes after Thermodynamic processes?
The next topic is "P-V diagrams", which builds directly on this one.
How difficult is Thermodynamic processes?
It is classed as Beginner in Thermodynamics & Fluids (topic 12 of 105). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.