Thermodynamic operation

A thermodynamic operation is an externally imposed manipulation that affects a thermodynamic system. The change can be either in the connection or wall between a thermodynamic system and its surroundings, or in the value of some variable in the surroundings that is in contact with a wall of the system that allows transfer of the extensive quantity belonging that variable.^[1][2][3][4] It is assumed in thermodynamics that the operation is conducted in ignorance of any pertinent microscopic information.

A thermodynamic operation requires a contribution from an independent external agency, that does not come from the passive properties of the systems. Perhaps the first expression of the distinction between a thermodynamic operation and a thermodynamic process is in Kelvin's statement of the second law of thermodynamics: "It is impossible, by means of inanimate material agency, to derive mechanical effect from any portion of matter by cooling it below the temperature of the surrounding objects." A sequence of events that occurred other than "by means of inanimate material agency" would entail an action by an animate agency, or at least an independent external agency. Such an agency could impose some thermodynamic operations. For example, those operations might create a heat pump, which of course would comply with the second law. A Maxwell's demon conducts an extremely idealized and naturally unrealizable kind of thermodynamic operation.^[5]

Another commonly used term that indicates a thermodynamic operation is 'change of constraint', for example referring to the removal of a wall between two otherwise isolated compartments.

An ordinary language expression for a thermodynamic operation is used by Edward A. Guggenheim: "tampering" with the bodies.^[6]