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//(12.6) At steady state, 100 m3/min of dry air at 32C and 1 bar is mixed adiabatically with a stream of oxygen (O2) at 127C and 1 bar to form a mixed stream at 47C and 1 bar. Kinetic and potential energy effects can be ignored. Determine (a) the mass flow rates of the dry air and oxygen, in kg/min, (b) the mole fractions of the dry air and oxygen in the exiting mixture, and (c) the time rate of entropy production, in kJ/K . min
//solution
//variable initialization
T1 = 32 //temperature of dry air in degree celcius
p1 = 1 //pressure of dry air in bar
AV1 = 100 //volume rate of dry air in m^3/min
T2 = 127 //temperature of oxygen stream in degree celcius
p2 = 1 //pressure of oxygen stream in bar
T3 = 47 //temperature of mixed stream in degree celcius
p3 = 1 //pressure of mixed stream in bar
//part(a)
Rbar = 8314 //universal gas constant
Ma = 28.97 //molar mass of air
Mo = 32 //molar mass of oxygen
va1 = (Rbar/Ma)*(T1+273)/(p1*10^5) //specific volume of air in m^3/kg
ma1dot = AV1/va1 //mass flow rate of dry air in kg/min
//from table A-22 and A-23
haT3 = 320.29 //in kj/kg
haT1 = 305.22 //in kj/kg
hnotT2 = 11711 //in kj/kmol
hnotT1 = 9325 //in kj/kmol
modot = ma1dot*(haT3-haT1)/[(1/Mo)*(hnotT2-hnotT1)] //in kg/min
printf('the mass flow rate of dry air in kg/min is: %f',ma1dot)
printf('\nthe mass flow rate of oxygen in kg/min is: %f',modot)
//part(b)
nadot = ma1dot/Ma //molar flow rate of air in kmol/min
nodot = modot/Mo //molar flow rate of oxygen in kmol/min
ya = nadot/(nadot+nodot) //mole fraction of air
yo = nodot/(nadot+nodot) //mole fraction of oxygen
printf('\n\nthe mole fraction of dry air in the exiting mixture is: %f',ya)
printf('\nthe mole fraction of dry oxygen in the exiting mixture is: %f',yo)
//part(c)
//with the help of tables A-22 and A-23
sanotT3 = 1.7669 //in kj/kg.K
sanotT1 = 1.71865 //in kj/kg.K
sbarT3 = 207.112 //in kj/kmol.K
sbarT2 = 213.765 //in kj/kmol.K
sigmadot = ma1dot*[sanotT3-sanotT1-(8.314/Ma)*log(ya)] + (modot/Mo)*[sbarT3-sbarT2-8.314*log(yo)]
printf('\n\nthe time rate of entropy production, in kJ/K . min is: %f',sigmadot)
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