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//(13.7) Calculate the enthalpy of combustion of gaseous methane, in kJ per kg of fuel, (a) at 25C, 1 atm with liquid water in the products, (b) at 25C, 1 atm with water vapor in the products. (c) Repeat part (b) at 1000 K, 1 atm.
//solution
//The combustion equation is
//CH4 + 2O2 + 7.52N2 ----> CO2 + 2H2O + 7.52N2
//part(a)
//With enthalpy of formation values from Table A-25
hfbarCO2 = -393520 //in kj/kmol
hfbarH2O = -285830 //in kj/kmol
hfbarCH4 = -74850 //in kj/kmol
hRPbar = hfbarCO2 + 2*hfbarH2O - hfbarCH4 //in kj/kmol
M = 16.04 //molar mass of CH4 in kg/kmol
hRP = hRPbar/M //in kj/kg
printf('part(a)the enthalpy of combustion of gaseous methane, in kJ per kg of fuel is: %f',hRP)
//part(b)
hfbarCO2 = -393520 //in kj/kmol
hfbarH2O = -241820 //in kj/kmol
hfbarCH4 = -74850 //in kj/kmol
hRPbar = hfbarCO2 + 2*hfbarH2O - hfbarCH4 //in kj/kmol
hRP = hRPbar/M //in kj/kg
printf('\n\npart(b)the enthalpy of combustion of gaseous methane, in kJ per kg of fuel is: %f',hRP)
//part(c)
//from table A-23
deltahbarO2 = 31389-8682 //in kj/kmol
deltahbarH2O = 35882-9904 //in kj/kmol
deltahbarCO2 = 42769-9364 //in kj/kmol
//using table A-21
function cpbar = f(T)
cpbar = (3.826 - (3.979e-3)*T + 24.558e-6*T^2 - 22.733e-9*T^3 + 6.963e-12*T^4)*8.314
endfunction
deltahbarCH4 = intg(298,1000,f)
var = deltahbarCH4
hRPbar = hRPbar + (deltahbarCO2 + 2*deltahbarH2O - var -2*deltahbarO2)
hRP = hRPbar/M //in kj/kg
printf('\n\npart(c)the enthalpy of combustion of gaseous methane, in kJ per kg of fuel is: %f',hRP)
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