CONCEPTS OF THERMAL PROCESSES (3)

See Concept Map

Refer to the Chapter of Processes and Energy

When entropy flows from a point of higher to a point of lower temperature (thermal potential), energy is released at a rate proportional to the flow of entropy and to the temperature difference (thermal power). The energy released is used in follow-up processes, for example in motors or pumps, or to produce more entropy in irreversible processes.

In involuntary thermal processes, we need energy to drive a flow of entropy from a lower to a higher temperature. Devices that let us do this are heat pumps (refrigerators). When we do this, we create potential differences (temperature differences).

If entropy is added to a body (in conductive transfer), energy is added at a rate proportional to the flow of entropy and to the temperature of the body.

Energy can be stored together with entropy in bodies. The energy stored depends upon the entropy (and therefore upon the temperature) of the body, and upon the properties and size of the body.

If entropy is produced, energy is needed. The energy needed is said to be dissipated; the dissipation rate depends upon the rate of production of entropy and the temperatue of the material in which dissipation takes place.

Principle of optimization: Energy needed to produce entropy is not available for other (more desirable) processes. Therefore, processes are optimized if entropy production can be minimized.

1  |  2  |  3