There are several examples of heuristic rules first proposed from empirical observation, which eventually earned physicochemical validity after the fundamental derivation of a posteriori. This may be the case of Sherwood’s plot – for which a sound rationalization from first principles, entailing enthalpy and mass balances, is provided here; it applies to (fine) chemicals undergoing concentr...

written for a particular gain. Then KGH = −1 so that a) when the amplitude of KGH is 1 or 0 dB and b) phase is 180o then we have the system just become unstable. Both the conditions have to be fulfilled. Hence, if we ask the question: How far is the system from instability ? We get two answers. The gain increment required at the frequency where phase is 180o and the phase increment required at ...