Isotherm
Definition
... a process at constant temperature, denoted by a reciprocal function on a pV diagram and a horizontal line on a Ts diagram.
Where it occurs.
In the theoretical Carnot and Sterling Cycles, heat is added and rejected at constant temperature.
Special features
For an ideal gas, heat addition and work output are equal.
How to draw it
Locate the POI and press the isotherm button.
The theory
We assume an ideal gasLet 1 be the start state (at the POI). At the start condition the derived expression for the entropy of an ideal gas follows integration of the Gibbs Equation. The Gibbs Equation is rearranged to yield:
$$ p = 1.013 \, bar \times exp(- s/R) (T/273.)^{\gamma/(\gamma-1)} $$
The calculations of ideal gas internal energy, enthalpy and specific volume are explained in conjunction with
the point of interest.
Exercises
Click on the graph to get a POI and plot an isotherm through it. Click along the isotherm to set new POIs and note how - within the constraints of setting POIs by eye - temperature and internal energy are constant.
Links
... to follow.