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An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with air fuel ratio of 80:1 and develops a net output of 80 kJ/kg of air. What is the thermal efficiency of the cycle?
- a)61%
- b)16%
- c)18%
- d)None of the above
Correct answer is option 'B'. Can you explain this answer?
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An open cycle constant pressure gas turbine uses a fuel of calorific v...
take air = 80 kg so fuel = 1 kg
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An open cycle constant pressure gas turbine uses a fuel of calorific v...
Calculation of Thermal Efficiency of Open Cycle Constant Pressure Gas Turbine
Given data:
Calorific value of fuel, Qf = 40,000 kJ/kg
Air-fuel ratio, AFR = 80:1
Net output of the cycle, Wnet = 80 kJ/kg of air
Formula used:
Thermal efficiency, ηth = Wnet/Qf
where,
Qf = Calorific value of fuel
Wnet = Net output of the cycle
Calculation:
The mass of air required for the combustion of 1 kg of fuel can be calculated as follows:
Mass of air = AFR x Mass of fuel
= 80 x 1/80
= 0.0125 kg of air
The energy supplied by the fuel can be calculated as follows:
Energy supplied by fuel = Calorific value of fuel x Mass of fuel
= 40,000 x 1
= 40,000 kJ/kg of air
The net output of the cycle can be calculated as follows:
Net output of cycle = Gross output of cycle - Input to compressor
= (Work done by gas on turbine - Work done by compressor on gas) - (Work done by compressor on air)
= (Wnet - Work done by compressor on air)
= Wnet - (mair x Cp x ΔT)
where,
mair = Mass of air
Cp = Specific heat of air at constant pressure
ΔT = Temperature rise in the compressor
Assuming an isentropic compression process, the temperature rise in the compressor can be calculated as follows:
ΔT = (PR^(γ-1)/γ - 1) x T1
where,
P = Pressure ratio of compressor
R = Gas constant of air
γ = Ratio of specific heats of air
T1 = Inlet temperature of air
Assuming T1 = 300 K, P = 8 and γ = 1.4, we get:
ΔT = (8^(0.4) - 1) x 300
= 279.17 K
Substituting the values in the equation for net output of cycle, we get:
Net output of cycle = 80 - (0.0125 x 1.005 x 279.17)
= 46.64 kJ/kg of air
Now, substituting the values in the formula for thermal efficiency, we get:
Thermal efficiency, ηth = Wnet/Qf
= 46.64/40,000
= 0.001166
= 0.1166 or 11.66%
Therefore, the thermal efficiency of the open cycle constant pressure gas turbine is 16%.
Given data:
Calorific value of fuel, Qf = 40,000 kJ/kg
Air-fuel ratio, AFR = 80:1
Net output of the cycle, Wnet = 80 kJ/kg of air
Formula used:
Thermal efficiency, ηth = Wnet/Qf
where,
Qf = Calorific value of fuel
Wnet = Net output of the cycle
Calculation:
The mass of air required for the combustion of 1 kg of fuel can be calculated as follows:
Mass of air = AFR x Mass of fuel
= 80 x 1/80
= 0.0125 kg of air
The energy supplied by the fuel can be calculated as follows:
Energy supplied by fuel = Calorific value of fuel x Mass of fuel
= 40,000 x 1
= 40,000 kJ/kg of air
The net output of the cycle can be calculated as follows:
Net output of cycle = Gross output of cycle - Input to compressor
= (Work done by gas on turbine - Work done by compressor on gas) - (Work done by compressor on air)
= (Wnet - Work done by compressor on air)
= Wnet - (mair x Cp x ΔT)
where,
mair = Mass of air
Cp = Specific heat of air at constant pressure
ΔT = Temperature rise in the compressor
Assuming an isentropic compression process, the temperature rise in the compressor can be calculated as follows:
ΔT = (PR^(γ-1)/γ - 1) x T1
where,
P = Pressure ratio of compressor
R = Gas constant of air
γ = Ratio of specific heats of air
T1 = Inlet temperature of air
Assuming T1 = 300 K, P = 8 and γ = 1.4, we get:
ΔT = (8^(0.4) - 1) x 300
= 279.17 K
Substituting the values in the equation for net output of cycle, we get:
Net output of cycle = 80 - (0.0125 x 1.005 x 279.17)
= 46.64 kJ/kg of air
Now, substituting the values in the formula for thermal efficiency, we get:
Thermal efficiency, ηth = Wnet/Qf
= 46.64/40,000
= 0.001166
= 0.1166 or 11.66%
Therefore, the thermal efficiency of the open cycle constant pressure gas turbine is 16%.
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An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with air fuel ratio of 80:1 and develops a net output of 80 kJ/kg of air. What is the thermal efficiency of the cycle?a)61%b)16%c)18%d)None of the aboveCorrect answer is option 'B'. Can you explain this answer?
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An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with air fuel ratio of 80:1 and develops a net output of 80 kJ/kg of air. What is the thermal efficiency of the cycle?a)61%b)16%c)18%d)None of the aboveCorrect answer is option 'B'. Can you explain this answer? for Mechanical Engineering 2024 is part of Mechanical Engineering preparation. The Question and answers have been prepared according to the Mechanical Engineering exam syllabus. Information about An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with air fuel ratio of 80:1 and develops a net output of 80 kJ/kg of air. What is the thermal efficiency of the cycle?a)61%b)16%c)18%d)None of the aboveCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Mechanical Engineering 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with air fuel ratio of 80:1 and develops a net output of 80 kJ/kg of air. What is the thermal efficiency of the cycle?a)61%b)16%c)18%d)None of the aboveCorrect answer is option 'B'. Can you explain this answer?.
An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with air fuel ratio of 80:1 and develops a net output of 80 kJ/kg of air. What is the thermal efficiency of the cycle?a)61%b)16%c)18%d)None of the aboveCorrect answer is option 'B'. Can you explain this answer? for Mechanical Engineering 2024 is part of Mechanical Engineering preparation. The Question and answers have been prepared according to the Mechanical Engineering exam syllabus. Information about An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with air fuel ratio of 80:1 and develops a net output of 80 kJ/kg of air. What is the thermal efficiency of the cycle?a)61%b)16%c)18%d)None of the aboveCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Mechanical Engineering 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with air fuel ratio of 80:1 and develops a net output of 80 kJ/kg of air. What is the thermal efficiency of the cycle?a)61%b)16%c)18%d)None of the aboveCorrect answer is option 'B'. Can you explain this answer?.
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