unsw ceic3001 lecture w1 advance thermo

unsw ceic3001 lecture w1 advance thermo - SCHOOL OF...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
1 SCHOOL OF CHEMICAL ENGINEERING CEIC3001 Advanced Thermodynamics and Separation VAPOUR/LIQUID EQUILIBRIA: INTRODUCTION (Text: Smith et al., Chapter 10) CONTENTS Vapour-Liquid Equilibrium for Pure Substance. ................................................................................. 2 The Phase Rule . ................................................................................................................................... 3 Phase Diagrams for Binary Systems. ................................................................................................... 4 The Txy Diagram. ............................................................................................................................ 4 The Pxy Diagram . ............................................................................................................................ 5 The PT Diagram. .............................................................................................................................. 5 The PTxy Diagrams . ........................................................................................................................ 6 Azeotropes . .......................................................................................................................................... 7 Raoult's Law. ........................................................................................................................................ 8 Dewpoint and Bubblepoint Calculations with Raoult's Law. .............................................................. 9 Henry's Law . ...................................................................................................................................... 11 Dewpoint & Bubblepoint Calculations from K -Value Correlations. ................................................. 12
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Vapour-Liquid Equilibrium for Pure Substance refers to the state of coexistence between liquid and vapour phases concerned with the conditions of T and P at which the phases coexist and the distribution of components between the phases at equilibrium phase transitions are represented by phase diagrams consider the phase diagram for a pure substance (see figure 1) vapour pressure: the pressure exerted by a vapour at equilibrium with a solid or liquid phase the vapour pressure of a pure substance is a function of T only Fig 1: Phase diagram for a pure substance
Background image of page 2
3 The Phase Rule the phase rule for non-reacting systems is expressed as N F 2 (1) where F = number of independent intensive variables (or degrees of freedom) = number of phases in equilibrium N = number of components the total set of intensive variables for a system at equilibrium includes T , P and N -1 mole fractions for each phase the phase rule defines the number of variables which must be specified from this set in order to fix the values of the remaining intensive variables Example 1 For a pure component with L-V coexisting phases, F = 2 - 2 + 1 = 1. Therefore P is fixed once T is specified. This is in agreement with the fact that the vapour pressure of a pure liquid only depends on T . Since each value of T yields a single value of P , the L-V coexisting phase project as a line in the P - T plane. The triple point (S-L-V coexisting phases) projects as a point since F = 0 and neither T or P can be arbitrarily specified. Example 2 For a binary system with L-V coexisting phases, F = 2 - 2 + 2 = 2. If we use x to represent liquid composition and y for vapour composition, the total set of intensive variables is T , P , x 1 and y 1 . Thus for given values of T and P there is only one set of values for the vapour and liquid compositions. All equilibrium states of the system can therefore be represented in a three- dimensional P - T - xy phase diagram.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 Phase Diagrams for Binary Systems The Txy Diagram 00 . 20 . 40 . 60 . 81 70 80 90 100 Mole Fraction Hexane Temperature (deg C) T-x-y Diagram for the n-Hexane/n-Heptane System (total pressure 760 mmHg) Dew point curve Bubble point curve Two-phase region Tie line VAPOUR LIQUID Fig. 3 0 0.2 0.4 0.6 0.8 1 70 80 90 100 Mole Fraction Hexane T-x-y Diagram for the n-Hexane/n-Heptane System (total pressure 760 mmHg) I G H D F E C B A Isobaric heating process: path A to I Fig. 4 the Txy diagram is constructed from data at constant P consider the Txy
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/26/2012 for the course CHEM ENG CEIC at University of New South Wales.

Page1 / 13

unsw ceic3001 lecture w1 advance thermo - SCHOOL OF...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online