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In a turbojet engine, subsequent to heat addition to compressed air, to get the power output, the working substance is expanded in
- a)Turbine blades, which is essentially an isentropic process.
- b)Turbine blades, which is a polytropic process.
- c)Exit nozzle, which is essentially an isentropic process.
- d)Exit nozzle, which is a constant volume process
Correct answer is option 'B'. Can you explain this answer?
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In a turbojet engine, subsequent to heat addition to compressed air, t...
Ans. (b)
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In a turbojet engine, subsequent to heat addition to compressed air, t...
Explanation:
In a turbojet engine, the working substance is the air that is compressed and mixed with fuel in the combustion chamber. The combustion process adds heat to the compressed air, increasing its temperature and pressure.
Expansion Process:
After heat addition, the working substance needs to be expanded in order to extract the power output from the engine. This expansion process occurs in the turbine blades. The turbine blades are mounted on a rotor and are driven by the high-velocity, high-temperature gases produced in the combustion chamber. The expansion process in the turbine blades is referred to as the power turbine stage.
Isentropic vs Polytropic Process:
The expansion process in the turbine blades is a polytropic process, not an isentropic process. An isentropic process is a special case of the polytropic process where there is no heat transfer and no irreversibilities. However, in the turbine blades, there is heat transfer to the blades due to the high-temperature gases flowing over them, and there are also some irreversibilities present. Therefore, the expansion process in the turbine blades cannot be considered isentropic.
Exit Nozzle Process:
The expansion process continues as the gases exit the turbine blades and pass through the exit nozzle of the engine. The exit nozzle is designed to accelerate the gases to a high velocity, which generates the thrust required for the aircraft to move forward. The expansion process in the exit nozzle is an isentropic process. This is because the nozzle is designed to maximize the conversion of the thermal energy in the gases into kinetic energy, with minimal losses due to irreversibilities.
Constant Volume Process:
The exit nozzle process cannot be considered a constant volume process. A constant volume process occurs when the volume of the system remains constant during the process, which is not the case in the exit nozzle. The gases are expanding and their volume is changing as they pass through the nozzle.
Therefore, the correct answer is option 'B' - the expansion process occurs in the turbine blades, which is a polytropic process.
In a turbojet engine, the working substance is the air that is compressed and mixed with fuel in the combustion chamber. The combustion process adds heat to the compressed air, increasing its temperature and pressure.
Expansion Process:
After heat addition, the working substance needs to be expanded in order to extract the power output from the engine. This expansion process occurs in the turbine blades. The turbine blades are mounted on a rotor and are driven by the high-velocity, high-temperature gases produced in the combustion chamber. The expansion process in the turbine blades is referred to as the power turbine stage.
Isentropic vs Polytropic Process:
The expansion process in the turbine blades is a polytropic process, not an isentropic process. An isentropic process is a special case of the polytropic process where there is no heat transfer and no irreversibilities. However, in the turbine blades, there is heat transfer to the blades due to the high-temperature gases flowing over them, and there are also some irreversibilities present. Therefore, the expansion process in the turbine blades cannot be considered isentropic.
Exit Nozzle Process:
The expansion process continues as the gases exit the turbine blades and pass through the exit nozzle of the engine. The exit nozzle is designed to accelerate the gases to a high velocity, which generates the thrust required for the aircraft to move forward. The expansion process in the exit nozzle is an isentropic process. This is because the nozzle is designed to maximize the conversion of the thermal energy in the gases into kinetic energy, with minimal losses due to irreversibilities.
Constant Volume Process:
The exit nozzle process cannot be considered a constant volume process. A constant volume process occurs when the volume of the system remains constant during the process, which is not the case in the exit nozzle. The gases are expanding and their volume is changing as they pass through the nozzle.
Therefore, the correct answer is option 'B' - the expansion process occurs in the turbine blades, which is a polytropic process.
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In a turbojet engine, subsequent to heat addition to compressed air, to get the power output, the working substance is expanded ina)Turbine blades, which is essentially an isentropic process.b)Turbine blades, which is a polytropic process.c)Exit nozzle, which is essentially an isentropic process.d)Exit nozzle, which is a constant volume processCorrect answer is option 'B'. Can you explain this answer?
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