Meaning and Handling of Entropy
In the previous Chap. 12 the caloric equations of state have been introduced and derived thermodynamically. A new state value, the specific entropy s has been introduced. However, at that point it was not clear how to utilise entropy in order to evaluate thermodynamic systems. This chapter focuses on clarifying why entropy is beneficial. First, a comparison is made with the first law of thermodynamics, so that entropy balancing is comprehensible: In contrast to energy, entropy is not a conservation value, since entropy can be generated within a system. Nevertheless, entropy can be balanced. A distinction is made between closed/open systems and thermodynamic cycles. Furthermore, a new state diagram, i.e. the T, s-diagram, is derived. Such a state diagram visualises the process values specific heat q and specific dissipation \(\psi \). Obviously, together with the p, v-diagram, that illustrates the other process value, i.e. the specific work, it is an important diagram in thermodynamics. Finally, two new changes of state, namely the isentropic and polytropic change of state are treated in this chapter.