Applications to Thermodynamics, Chemistry and Biology

Entropy often appears as a mysterious concept yet it is really quite simple: Entropy flow is the thermal flow variable in the sense of Bondgraphs (Table 2.1) and entropy itself is accumulated entropy flow (Thoma 1970B). Hence the fundamental point to know is that thermal power in conduction, usually called heat flux, is absolute temperature times entropy flow. This fundamental equation appears in Fig. 7.1. Some important observations: The fundamental equation is strictly valid for conduction of thermal power (heat flux) without mass flow.With mass or convection there is a correction to the fundamental equation, which remains approximately valid. It is expressed by the convection factor of sec. 7.2.We have to take the absolute temperature (expressed in Kelvins) in the fundamental equation.Entropy is often associated with disorder. This is true but not necessary for most practical engineering including Bondgraphs.