
Concept explainers
The entropy generated during the combustion of n-Octane.
The exergy destructed during the combustion of n-Octane.

Answer to Problem 87P
The entropy generated during the combustion of n-Octane is
The exergy destructed during the combustion of n-Octane is
Explanation of Solution
Write the complete balanced reaction for combustion of octane
Write the energy balance equation for the combustion of octane
Here, the amount of heat transfer for the combustion of octane gas is
Write the formula to calculate the entropy of an
Here, number of moles of i component is
Write the formula to calculate the entropy generation
Here, entropy of the products is
Write the expression to calculate the entropy generated per unit mass
Here, molar mass of the fuel is
Write the expression to calculate the exergy destructed per unit mass
Here, temperature of surroundings is
Conclusion:
Balance for the oxygen from combustion equation (I).
Rewrite the combustion reaction of propane with 95% theoretical amount of air.
Rewrite the Equation (II) for the heat transfer from combustion.
Here, number of moles of product is
From the Table A-18 through Table A-26, obtain the enthalpies of vaporization and the enthalpies of formation for different substance as follows,
Substance |
|
|
|
|
0 | 0 | 0 | ||
0 | ||||
0 | ||||
0 | ||||
0 |
Substitute
From the Table A-18 through Table A-26, obtain the entropy values for different substance and tabulate using the Equation (III).
Represent the entropy calculations for the reactants as in Table below.
Substance | |||||
1 | 466.73 | 14.79 | 451.94 | ||
21.25 | 0.21 | 226.35 | 1.81 | 4771.48 | |
79.9 | 0.79 | 212.07 | 12.83 | 15,919.28 | |
Entropy of the reactant, |
Represent the entropy calculations for the products as in Table below.
Substance | |||||
8 | 0.0757 | 292.11 | –6.673 | 2390.26 | |
9 | 0.0852 | 250.45 | –5.690 | 2305.26 | |
8.75 | 0.0828 | 257.97 | –5.928 | 2309.11 | |
79.9 | 0.7563 | 241.77 | –12.46 | 18,321.87 | |
Entropy of the product, |
Substitute
From the table A-2 of “Molar mass, gas constants, and critical-point properties”, select the molar masses of liquid octane as,
Substitute
Thus, the entropy generated during the combustion of n-Octane is
Substitute
Thus, the exergy destructed during the combustion of n-Octane is
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Chapter 15 Solutions
Thermodynamics: An Engineering Approach
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