Carnot Controls to Unify Traditional and Work-Assisted Operations with Heat & Mass Transfer

Year 2003, Volume: 6 Issue: 2, 59 - 67, 01.06.2003

Stanislaw Sieniutycz

Abstract

This work is a synthesizing approach in which a new methodology is analyzed in the thermodynamic modelling of thermal machines and traditional heat and mass exchangers, where certain special control variables called the Carnot controls are suitable. With these controls, expressions describing the lost work and entropy production assume the same form in endoreversible thermal machines and in traditional processes of purely dissipative transport. Mathematical models of thermal machines and characteristics of endoreversible operations are particularly simple in terms of the Carnot controls. The efficiency decrease caused by the exergy dissipation and finite rate limits on mechanical energy yield or consumption are estimated in terms of maximum work released from an engine or minimum work added to a heat pump. Remarkable simplification in analysis of complex thermal machines is achieved when Carnot controls are applied. Generalized analyses include mass transfer and lead to finite time counterparts of classical available energy (exergy). For sequential-type equipment of a finite size, enhanced limits are obtained for the energy production or consumption. Progress in the theory and its applications in the energy generation problems is achieved; examples of applications are discussed.

Keywords

thermodynamic optimization, efficiency, endoreversible engines, heat pumps