Enthalpy of reaction or heat of reaction energy that

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Unformatted text preview: ing information is used for estimating energy to vaporize H2 and O2: (1) for H2, latent heat of vaporization 445.7 kJ/kg, boiling temperature ¼ À252.8 C, cp ~ 4.12 kJ/kg-K; (2) for O2, latent heat of vaporization 212.7 kJ/kg, boiling temperature ¼ À183 C, cp ~ 0.26 kJ/kg-K. 2.5 Chapter Summary The following shows the relations among different thermodynamics properties expressed in terms of mass fractions and mole fractions. 2.5 Chapter Summary Property Species densityri (kg/m3) 41 Mass fraction, yi r yi Mole fraction xi x r Pi Mi K xj Mj j¼ 1 Mole fraction, xi [À] yi =Mi K P – yj =Mj j¼1 Mass fraction, yi, xi Mi – K P xj M j j¼1 Mixture molecular mass, M (kg/kmol) K P K P 1 yj =Mj j¼1 Internal energy of mixture, u (kJ/kg) K P j¼1 Enthalpy of mixture, h (kJ/kg) K P j¼1 Entropy of mixture, s (kJ/kg-K) K P j¼1 Specific heat at constant pressure cp(kJ/kg-K) K P j¼1 Specific heat at constant volume cv (kJ/kg-K) K P j¼1 ^ Internal energy of mixture, u (kJ/kmol) M yj Á u j 1 M yj Á h j 1 M s j Á hj 1 M yj Á cpj 1 M yj Á cvj 1 M K P j¼1 ^ Enthalpy of mixture, h (kJ/kmol) M K P j¼1 Entropy of mixture, ^ (kJ/kmol-K) s M K P j¼1 ^ Specific heat at constant pressure cp (kJ/kmol-K) M K P j¼1 ^ Specific heat at constant volume cv (kJ/kmol-K) M j¼1 K P j¼1 yj Á uj yj Á hj yj Á sj yj Á cpj yj Á cvj xj Mj K P j¼1 K P j¼1 K P j¼1 K P j¼1 K P j¼1 K P j¼1 K P j¼1 K P j¼1 K P j¼1 K P j¼1 ^ xj Á uj ^ xj Á hj ^ xj Á sj ^ xj Á cpj ^ xj Á cvj ^ xj Á u j ^ xj Á h j ^ xj Á s j ^ xj Á cpj ^ xj Á cvj Definitions Enthalpy of combustion or heat of combustion: Ideal amount of energy that can be released by burning a unit amount of fuel. Enthalpy of reaction or heat of reaction: Energy that must be supplied in the form of heat to keep a system at constant temperature and pressure during a reaction. 42 2 Thermodynamics of Combustion Enthalpy of formation or heat of formation: Heat of reaction per unit of product needed to form a species by reaction from the elements at the most stable conditions. Combustion stoichiometry for a general hydrocarbon fuel, Ca Hb Og     bg b bg Ca Hb Og þ a þ À ðO2 þ 3:76N2 Þ ! aCO2 þ H2 O þ 3:76 a þ À N2 42 2 42 Variables to quantify combustible mixtures mf Fuel/air ratio by weight: f ¼ ma mf For stoichiometric mixture: fs ¼ mas f mas Equivalence ratio: f ¼ fs ¼ ma 1= AFR 1 1 Normalized air/fuel ratio l ¼ AFRs ¼ 1=ffs ¼ f =fs ¼ f Percent of excess air     ðma À mas...
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This document was uploaded on 01/20/2014.

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