tailieunhanh - EXERGY ANALYSIS AND ENTROPY GENERATION MINIMIZATION

In this chapter, we review two important methods that account for much of the newer work in engineering thermodynamics and thermal design and optimization. The method of exergy analysis rests on thermodynamics alone. | CHAPTER 42 EXERGY ANALYSIS AND ENTROPY GENERATION MINIMIZATION Adrian Bejan Department of Mechanical Engineering and Materials Science Duke University Durham North Carolina INTRODUCTION 1351 HEAT TRANSFER 1359 PHYSICAL EXERGY 1353 STORAGE SYSTEMS 1361 CHEMICAL EXERGY 1355 SOLAR ENERGY CONVERSION 1362 ENTROPY GENERATION MINIMIZATION 1357 POWER PLANTS 1362 CRYOGENICS 1358 INTRODUCTION In this chapter we review two important methods that account for much of the newer work in engineering thermodynamics and thermal design and optimization. The method of exergy analysis rests on thermodynamics alone. The first law the second law and the environment are used simultaneously in order to determine i the theoretical operating conditions of the system in the reversible limit and ii the entropy generated or exergy destroyed by the actual system that is the departure from the reversible limit. The focus is on analysis. Applied to the system components individually exergy analysis shows us quantitatively how much each component contributes to the overall irreversibility of the Entropy generation minimization EGM is a method of modeling and optimization. The entropy generated by the system is first developed as a function of the physical characteristics of the system dimensions materials shapes constraints . An important preliminary step is the construction of a system model that incorporates not only the traditional building blocks of engineering thermodynamics systems laws cycles processes interactions but also the fundamental principles of fluid mechanics heat transfer mass transfer and other transport phenomena. This combination makes the model realistic by accounting for the inherent irreversibility of the actual device. Finally the minimum entropy generation design Sgen min is determined for the model and the approach of any other design Sgen to the limit of realistic ideality represented by Sgen mi is monitored in