SPPU Question Papers
BE Mechanical (2015 Course)
Subject: Energy Engineering
Unit 4B: Gas Turbine Power Plant
May 2016
Q. 5. a) Derive the equation
of thermal efficiency of Brayton cycle. [6
marks]
Q. 5. b) The pressure
ratio used in an open cycle gas turbine power plant is 6.5. The pressure and
temperature of air entering in the compressor are 1 bar, 300 K. Intercooling
arrangement is used to reduce the work of compression. The maximum temperature
of the cycle is limited to 850 K. If the power plant capacity is 10 MW, find
the thermal efficiency of the plant and air consumption per hour if calorific
value is 45000 kJ/kg. Assume compression in both the stages and expansion in
the turbine are isentropic. Take γ = 1.4 (air and gas), Cp = 1 kJ/kgK (air and
gas). Assume perfect intercooling. [10
marks]
OR
Q. 6. a) Write a short note on combine cycle plants. [6 marks]
Q. 6. b) An open cycle gas turbine plant works on Brayton cycle. The maximum pressure and temperature of the cycle are limited to 5 bar, 900 K. The pressure and temperature at the inlet to the compressor are 1 bar and 300 K. Reheating is used at the pressure of 2.5 bar where the temperature of the gases is increased to its original turbine inlet temperature. Mass flow rate of the air in the plant is 10 kg/s. Determine the thermal efficiency and capacity of the plant in MW. The exhaust pressure of the gases leaving the plant is 1 bar. Assume compression and expansion are isentropic. Take γ = 1.4 (air and gas), Cp = 1 kJ/kgK (air and gas), CV of the fuel 40000 kJ/kg. Neglect pressure losses in the system. Do not neglect the mass of the fuel. [10 marks]
December 2016
Q. 5. b) A gas turbine
unit has pressure ratio 6:1 & maximum cycle temperature of 610°C. The
isentropic efficiency of the compressor and turbine are 0.80 and 0.82
respectively. Calculate power output in kilowatts of an electrical generator
geared to the turbine when the air enters the compressor at 15°C at the rate of
16 kg/s. Also calculate thermal efficiency and work ratio of the plant. Assume (i)
Cp = 1.005 kJ/kgK and γ = 1.4 for compression processes, (ii) Cp = 1.11 kJ/kgK
and γ = 1.333 for expansion processes, (iii) Cp = 1.11 kJ/kgK for combustion
processes. [10 marks]
OR
Q. 6. b) In a Gas turbine the compressor takes in air at a temp. of 15°C and compresses it to four times the initial pressure with an isentropic efficiency of 82%. The air is then passed through heat exchanger heated by turbine exhaust before reaching combustion chamber. In the heat exchanger 78% of available heat is given to air. The maximum temp. after constant pressure combustion is 600°C and efficiency of turbine is 70%. Neglecting all losses except those mentioned and assuming working fluid throughout the cycle to have characteristics of air, find the thermal efficiency of cycle. Assume: R = 0.287 kJ/kgK and γ = 1.4 for air and constant specific heat throughout. [10 marks]
May 2017
Q. 5. b) In an open
cycle gas turbine power plant, compressor is driven by the high pressure turbine;
power is produced by low pressure turbine. The exhaust gases are passed through
the regenerator. Using the following data, determine the air flow rate for 2 MW
power produced & thermal efficiency of the plant.
i) Isentropic efficiency
of compressor and turbines: 88 %
ii) Compressor inlet
conditions: 27°C and 1 bar
iii) Pressure ratio: 7
iv) Regenerator
effectiveness: 0.8
v) Maximum temperature
in the cycle: 900°C
Assume air flow rate to
be equal to the gas flow rate, specific heat for air and gases as 1.005 kJ/kgK
and 1.128 kJ/kgK, γ for air and gases as 1.4 and 1.34 respectively. [10 marks]
OR
Q. 6. b) An open cycle gas turbine plant uses heavy oil as fuel. The maximum pressure and temperature in the cycle are 5 bar and 650°C. The pressure and temperature of the air entering into the compressor are 1 bar and 27°C. The exit pressure of the turbine is 1 bar. Assuming isentropic efficiencies of the compressor and turbine to be 80 % and 85 % respectively, find the thermal efficiency of the cycle. Overall air fuel ratio used is 60:1. Take Cp (for air and gas) = 1 kJ/kgK, γ for air and gas = 1.4. [10 marks]
December 2017
Q. 5. a) Explain with
neat sketch, combined cycle power plant. [8
marks]
OR
Q. 6. a) Discuss the working of semi closed cycle with neat sketch. [8 marks]
May 2018
Q.
5. a) Derive the equation of thermal efficiency of Brayton cycle. [8 marks]
Q. 5. b) An open cycle
gas turbine plant works on Brayton cycle. The maximum pressure and temperature
of the cycle are limited to 5 bar, 900 K. The pressure and temperature at the
inlet to the compressor are 1 bar and 300 K. Reheating is used at the pressure
of 2.5 bar where the temperature of the gases is increased to its original
turbine inlet temperature. Mass flow rate of the air in the plant is 10 kg/s.
Determine the thermal efficiency and capacity of the plant in MW. The exhaust
pressure of the gases leaving the plant is 1 bar. Assume compression and
expansion are isentropic. Take γ = 1.4 (air and gas), Cp = 1 kJ/kgK (air and
gas), CV of the fuel 40000 kJ/kg. Neglect pressure losses in the system. Do not
neglect the mass of the fuel. [10 marks]
OR
Q. 6. b) A gas turbine takes in air at 101 kN/m2 and 150°C. The air is compressed to a pressure of 606 kN/m2 and then passed through a regenerative heat exchanger of effectiveness 0.65. The air is then passed through the combustion chamber where its temperature is increased to 870°C by the combustion of fuel. The gases enter a turbine and are expanded to 101 kN/m2 pressure. Assuming a compressor efficiency of 85 % and a turbine efficiency of 80 %, determine the following for air flow rate of 4 kg/s:
i) The power output of
the plant
ii) Exhaust temperature
from heat exchanger
iii) Thermal efficiency
of the plant
iv) Thermal efficiency
without the heat exchanger. [10 marks]
December 2018
Q.
5. b) In a constant pressure open cycle gas turbine air
enters at 1 bar and 20°C and leaves the compressor at 5 bar. Using the
following data:
Temperature of gases
entering the turbine = 680°C, pressure loss in the combustion chamber = 0.1
bar, compressor efficiency = 85 %, turbine efficiency = 80 %, combustion
efficiency = 85 %, γ = 1.4 and Cp = 1.024 kJ/kgK for air and gas, find:
i) The quantity of air
circulation if the plant develops 1065 kW.
ii) Heat supplied per
kg of air circulation,
iii) The thermal
efficiency of the cycle.
Mass of fuel may be
neglected. [8 marks]
OR
Q. 6. a) Explain with details the Intercooling, reheating and regeneration of gas turbine power plant. [8 marks]
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