Question concerning the usefulness of phenomenological thermomechanics (in order of discussion)

It is possible to state the following three heat concepts (from phenomenological thermomechanics): the Carnot theory of thermal processes or the substantive caloric theory for which constant entropy is characteristic; the Clausius theory of thermal processes (phenomenological thermomechanics in which entropy is varied); and the Ulybin theory of thermal processes (phenomenological thermomechanics with zero entropy). Some of the Clausius and Ulybin concepts are examined in greater detail