Concept explainers
Reconsider Prob. 15–82. The combustion products are expanded in an isentropic turbine to 140 kPa. Calculate the work produced by this turbine in kJ/kg fuel.
The work produced by an isentropic turbine.
Answer to Problem 83P
The work produced by an isentropic turbine is
Explanation of Solution
Express the balanced equation.
Here, carbon is
Express the change in entropy of the mixture during the mixture when there is no entropy change during an isentropic process.
Here, final entropy is
Express the change in entropy of the mixture at temperature of
Express the change in entropy of the mixture at temperature of
Express the work produced during the isentropic expansion of combustion gases.
Here, initial and final enthalpy is
Express molar mass of the product gases.
Here, molar mass of carbon dioxide, water, sulfur dioxide, nitrogen and oxygen is
Express the work produced per kg of the fuel.
Conclusion:
Refer Equation (I), and write the number of moles.
Refer Table A-1, “molar mass, gas constant and critical point properties”, and write the molecular masses.
Refer Table A-1, “molar mass, gas constant and critical point properties”, and write the universal gas constant of air.
Substitute
Refer Table A-18, A-19, A-20, A-21, A-22, and A-23, and write the initial and final entropy at temperature of
Components |
|
|
307.992 | 269.215 | |
263.542 | 232.597 | |
251.424 | 228.057 | |
267.891 | 243.471 |
Substitute
Refer Table A-18, A-19, A-20, A-21, A-22, and A-23, and write the initial and final entropy at temperature of
Components |
|
|
307.992 | 297.307 | |
263.542 | 240.333 | |
251.242 | 234.115 | |
267.891 | 249.906 |
Substitute
Perform the interpolation method to obtain the final temperature.
Write the formula of interpolation method of two variables.
Here, the variables denote by x and y is entropy change and final temperature respectively.
Show the final temperature corresponding to entropy change as in Table (3).
Entropy change |
Final temperature |
1000 | |
1200 |
Substitute
Thus, the final temperature is,
Refer Table A-18, A-19, A-20, A-21, A-22, and A-23, and write the initial and final enthalpy during the isentropic expansion of combustion gases from
Components |
|
|
98,160 | 50,189 | |
80,352 | 42,037 | |
63,236 | 34,961 | |
66,223 | 36,527 |
Substitute
Substitute
Substitute
Hence, the work produced by an isentropic turbine is
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Chapter 15 Solutions
Thermodynamics: An Engineering Approach
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