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Phenomenological Thermodynamics of Irreversible Processes have its roots in the 19th century with N.L.S Carnot and his general statement in 1824 [1,2] that mechanical work can be gained from heat. J.R. Mayer in 1842 [3] formulated the equivalence principle of convertibility into heat and vice versa. He may have been the first to formulate the “First Law” of thermodynamics. It was R.E. Clausius who established the “Second Law” of thermodynamics in 1850 [4]. He phrased it in terms of the concept of “entropy” in 1865 [5] and, therefore, brought the structure of thermodynamics to a provisional closure. Nearly simultaneously, W. Thomson (Lord Kelvin) [6] had presented a different form of the Second Law in 1851. This expressed the observationally suggested and unanimously verified “principle of irreversibility” of all physical processes. The period, approximately from the mid-19th century up to the 1940s, was characterized by acquiring a deeper understanding of the principles. By introducing the concept of the absolute temperature by Lord Kelvin in 1857 [6] as a measure of coldness of a body point, the meaning of entropy as an additive monotonic quantity of a thermostatic system under adiabatic conditions (see Caratheodory 1909 [7]) demonstrates the irreversibility principle for the impossibility of “perpetua mobile”.

This article belongs to the Special Issue Phenomenological Thermodynamics of Irreversible Processes