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Questions and Answers
What is the primary reason for operating gas turbines at four times the air needed for complete combustion?
What is the primary reason for operating gas turbines at four times the air needed for complete combustion?
What happens to the working fluid temperature when intercooling and reheating are utilized?
What happens to the working fluid temperature when intercooling and reheating are utilized?
Why does the back work ratio of a gas-turbine cycle improve with intercooling and reheating?
Why does the back work ratio of a gas-turbine cycle improve with intercooling and reheating?
What is the effect of intercooling and reheating on the thermal efficiency of a gas-turbine cycle?
What is the effect of intercooling and reheating on the thermal efficiency of a gas-turbine cycle?
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What is the ideal limit of thermal efficiency that can be approached by a gas-turbine cycle with intercooling, reheating, and regeneration?
What is the ideal limit of thermal efficiency that can be approached by a gas-turbine cycle with intercooling, reheating, and regeneration?
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What is the primary goal of multistage compression with intercooling in a gas-turbine cycle?
What is the primary goal of multistage compression with intercooling in a gas-turbine cycle?
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What happens to the compression process as the number of stages is increased?
What happens to the compression process as the number of stages is increased?
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What is the effect of reheating on the expansion process in a gas-turbine cycle?
What is the effect of reheating on the expansion process in a gas-turbine cycle?
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What is the principle behind the effect of multistage compression with intercooling and multistage expansion with reheating on the net work output?
What is the principle behind the effect of multistage compression with intercooling and multistage expansion with reheating on the net work output?
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What is the ultimate goal of optimizing the compression and expansion processes in a gas-turbine cycle?
What is the ultimate goal of optimizing the compression and expansion processes in a gas-turbine cycle?
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Study Notes
Net Work of a Gas-Turbine Cycle
- Net work is the difference between turbine work output and compressor work input
- Net work can be increased by decreasing compressor work, increasing turbine work, or both
Multistage Compression with Intercooling
- Compression work can be decreased by carrying out compression in stages and cooling the gas in between
- As the number of stages increases, the compression process becomes nearly isothermal at the compressor inlet temperature
- Compression work decreases as the number of stages increases
Multistage Expansion with Reheating
- Turbine work output can be increased by expanding the gas in stages and reheating it in between
- Expansion process becomes nearly isothermal as the number of stages increases
- Maximum temperature in the cycle remains unchanged
Principle of Work
- Steady-flow compression or expansion work is proportional to the specific volume of the fluid
- Specific volume of the working fluid should be as low as possible during compression and as high as possible during expansion
- Intercooling and reheating accomplish this by reducing and increasing specific volume, respectively
Combustion in Gas Turbines
- Combustion typically occurs with four times the amount of air needed for complete combustion to avoid excessive temperatures
- Exhaust gases are rich in oxygen, allowing reheating by spraying additional fuel between expansion states
Effects of Intercooling and Reheating
- Working fluid leaves the compressor at a lower temperature and the turbine at a higher temperature
- Makes regeneration more attractive and increases potential for regeneration
- Back work ratio of a gas-turbine cycle improves
- Thermal efficiency decreases unless accompanied by regeneration
Ideal Gas-Turbine Cycle
- Ideal cycle with intercooling, reheating, and regeneration approaches the Ericsson cycle
- Thermal efficiency approaches the theoretical limit (Carnot efficiency) as the number of stages increases
- However, the contribution of each additional stage to thermal efficiency is less and less, and more than two or three stages are not economically justified
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Description
This quiz covers the principles of optimizing gas-turbine cycle network by decreasing compressor work or increasing turbine work, including multistage compression with intercooling. It's based on Chapter 7 and Fig. 9-42.
