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Reversing the operation of an electric pump

In an electric pump, the electric process drives the hydraulic one. At the same time, heat is generated. The system can be reversed, except for the production of heat. A system of turbine and generator reverses the electric and hydraulic processes (Fig. 1). However, heat is not destroyed, it is again produced.

Interpretation

Physical processes can be reversed, with one exception. This is the production of heat. If we had to reverse all processes of a heat producing system, we would have to destroy heat. This does not happen. Instead, heat is again produced. We conclude that heat is a quantity that can be produced but not destroyed (watch Movie 1…).

Heat, caloric, entropy. The quantity we have been calling heat in our interpretations of thermal processes was called caloric by Sadi Carnot and his contemporaries. This easily visualized and intuitively understood quantity best fits what after 1850 was called entropy in physics, chemistry, and engineering. Therefore, the concept of entropy which, in standard presentations of thermodynamics is considered to be a completely abstract quantity, has simple and intuitive roots. It is analogous to volume and to charge in fluids and electricity, respectively.