tailieunhanh - Ebook Introduction to chemical engineering thermodynamics (7th edition): Part 2

The chapters are written in a clear, logically organized manner, and contain an abundance of realistic problems, examples, and illustrations to help students understand complex concepts. New ideas, terms, and symbols constantly challenge the readers to think and encourage them to apply this fundamental body of knowledge to the solution of practical problems. The comprehensive nature of this book makes it a useful reference both in graduate courses and for professional practice. The seventh edition continues to be an excellent tool for teaching the subject of chemical engineering thermodynamics to undergraduate. | Chapter 10 Vapor Liquid Equilibrium Introduction Preceding chapters have dealt largely with purr or with constant-composition mixtures. eg. air. However composition changes are the desired outcome not only of chemical reactions but of a number of industrially important mass-transfer operations. Thus composition becomes a primary variable in the remaining chapters of this text. Processes such as distillation absorption and extraction bring phases of different composition into contact and when the phases are not in equilibrium mass transfer between the phases alters their compositions. Both the extent of change and the rate of transfer depend on be departure of the system from equilibrium. Thus for quantitative treatment of mass transfer the equilibrium T. p. and phase compositions must be known. The most commonly encountered coexisting phases in industrial practice are vapor and liquid although liquid liquid vapor solid and iiquid soild systems are also found. In this chapter we first discuss the nature of equilibrium and then consider two rules that give the number of independent variables required to determine equilibrium states. There follows in Sec. a qualitative discussion of vapor ỉĩquid phase behavior. In Sec. we introduce the two simplest formulations that allow calculation of temperatures pressures and phase compositions for systems in vapocfliqttid equilibrium. The tirst. known as Raouli s law is valid only for systems at low to moderate pressures and in general only for systems comprised of chemically similar species. The secund known as Henry law. is valid for any species present al low concentration but as presented here is also Limited to systems at low to moderate pressures. A modification of Rao Lil Is law that removes the restriction to chemically similar specie is treated in Sec. . Finally in Sec. calculations based on equilibrium ratios or AT-values are considered. The treatment rtf vapor liquid equilibrium is .