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ME 475/675 Introduction to Combustion

ME 475/675 Introduction to Combustion. Lecture 7. Announcements. HW 2 due Friday: Chapter 2 (30, 31,32) drop 57 New HW 3 due Monday Chapter 2 (57) (may add more later). Find equilibrium c omposition (reactants and products) for a given Temperature, Pressure & Mass. G. Q. T,P. a.

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ME 475/675 Introduction to Combustion

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  1. ME 475/675 Introduction to Combustion Lecture 7

  2. Announcements • HW 2 due Friday: Chapter 2 (30, 31,32) drop 57 • New HW 3 due Monday Chapter 2 (57) (may add more later)

  3. Find equilibrium composition (reactants and products) for a given Temperature, Pressure & Mass G Q T,P a • aA + bB + …  eE + fF + … • Use Q and boundary work to achieve P and T • Gibbs Function • is Gibbs function at P = Po = 1 atm • For a constant temperature, pressure, and mass, and only boundary work (PdV) • It can be shown that second Law requires for spontaneous changes (no outside influence) It can be shown…

  4. For General Reactions • aA + bB + …  eE + fF + … • dNA = -a(dk), dNB= -b(dk) • dNE= +e(dk), dNF= +f(dk)

  5. Solution Method • Equilibrium Constant • Standard State Gibbs Function Change • In terms of Gibbs functions of formation (tabulated in App. A and B) • Products are “favored” as increases, which happens when decreases

  6. Example 2.7 (p 43) Turn in next time for EC • Consider the dissociation of CO2 as a function of temperature and pressure: . • Find the composition of the mixture, i.e. the mole fractions of , and , that results from subjecting the originally pure to various temperatures, and pressures • T = 1500, 2000, 2500 and 3000K • P = 0.1, 1, 20 and 100 atm • Find final values of: , , • Initially ___? • MathCAD solution • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH.475.675.Combustion/index.htm

  7. Pressure and Temperature Dependence • For this reaction • > 0 ( > 0 exothermic) and Nproducts > Nreactants • (product) increases as T increases and P decreases

  8. Pressure and Temperature Dependence • ; • Products are “favored” as KP increases and decreases • Standard State Gibbs Function Change

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