Deduction process:

Based on van der Waals equation, it is proved that the temperature, pressure and volume of gas in critical state are

(Hint: The cubic equation written by Van der Waals equation, for the critical point, is substituted to get the triple solution. )

The working medium absorbs heat from the high-temperature heat source, and part of it is transferred to the low-temperature heat source, while the working medium does work externally.

The working medium absorbs heat from the low-temperature heat source, accepts the work done by the outside world on the working medium, and transfers the heat to the high-temperature heat source.

Example: Try to prove that two insulated wires on the drawing cannot intersect.

Deduction: