Gas turbine problems

1. 1. Air is drawn in a gas turbine at 150C and 1.01 bar and pressure ratio is 7:1. The compressor is driven by the M.P.
turbine and L.P. turbine drives a separate power shaft. The isentropic efficiencies of compressor and the M.P. and L.P. turbines
are 0.82, 0.85 and 0.85 respectively. If the max cycle temp is 6100C, calculate
(A)The pressure and temperature of the gases entering the power turbine
(B) The net power developed by the unit per kg/s mass flow
(C) The thermal efficiency of the unit
Neglect the mass of fuel and assume the following
For compression process Cpa = 1.005 kJ/kg K and r = 1.4.
For combustion and comparison process average g = 1.15 kJ/kg and r = 1.333. (Apri’ 05)
2. The simple gas turbine plant operates on Joule cycle and has the pressure ratio 6 and the maximum and minimum
temperatures of the cycle are 1000 K and 288 K respectively. Assume an ideal cycle, calculate the efficiency and specific work
output of the plant (April’ 07 OR)
3. A simple open type gas turbine plant consists of compressor, combustion chamber and turbine. The pressure and
temperature at the inlet of compressor are 1 bar and 150 C and the inlet of the turbine are 5 bar and 6500C. Compressor
isentropic efficiency is 82%. Turbine’s isentropic efficiency is 86% mechanical and combustion efficiencies are 90% and 98%.
Assuming Cpa = 1 kJ/kg-0K, Cpg = 1.2 kJ/kg0K and r= 1.4 for air and 1.334 for gases. Find
(1) The thermal efficiency and
(2) Work ratio of the cycle. If a regenerator of 65% effectiveness is introduced in the cycle, with a pressure
loss 0.2 bar to air side or well as gas side, find the percentage increase in the thermal efficiency of the cycle.
(

2. In a gas turbine plant, the compressor takes the air at 1 bar and 300 k and compressed to 4 bar. Heat is added in combustion
chamber to raise the temperature to 833 k. The calorific value of the fuel oil is 42000 kJ/kg. The air flow rate is 1.25 kg/sec. The
isentropic efficiencies of compressor and turbine are 85% and 83% respectively. Assume index for compression as 1.4 and Cp =
1.0 kJ/kg k and index for expansion as 1.32 and Cp = 1.05 kJ/kg k. Explain the thermal efficiency.
(Oct/Nov 2007 NR)
5. Air is drawn in a gas turbine at 150C and 1 bar and pressure ratio is 6:1. The compressor is driven by H.P. turbine and
L.P. turbine drives to produce power. The maximum cycle temperature is 6100C, calculate
(1) The pressure and temperature of the gases entering the power turbine.
(2) The net power developed by the unit power kg/s mass flow.
(3) The thermal efficiency of the unit. Assume the data if necessary.
(Oct/Nov 2007 OR)
6. In a gas turbine, hot combustion products with specific heats Cp = 0.98 kJ/kgK and Cv = 0.7538 kJ/kgK enter the turbine
at 20 bar, 1500 K and exit at 1 bar. Isentropic efficiency of turbine is 94%. What is the work developed by the turbine/kg of gas
flow?
(Mar/Apr 2008 NR)
7. In a constant pressure open cycle gas turbine, air enters at 1 bar and 200C and leaves the compressor at 5 bar. Using
the following data: temperature of gases entering the turbine = 6800C, pressure loss in the combustion chamber = 0.1 bar, η
compressor = 85%, ηturbine = 80%, η combustion = 85%, γ = 1.4 and Cp = 1.024 KJ/KgK for air and gas. Find
(1) The quantity of air circulation if the plant develops 1065 kW
(2) Heat supplied per kg of air circulation and
(3) The thermal efficiency of the cycle. Mass of the fuel may be neglected.

3. (a). A gas turbine draws in atmospheric air at 1.013 bar and 150C. There are two pressure stages with intercooler and the total
pressure ratio is 8:1. The maximum temperature of the cycle is 5930C and there is 1 turbine for expansion. A generator is used
and recovers 60% of the available heat. Determine the efficiency and the ratio of the useful work to turbine work. The machine
isentropic efficiency may be taken as 0.86 and 0.83 for the turbine and the compressor respectively.
(b). An open cycle gas turbine plant works between the pressure range of 1.01 bar and 6 bar and temperature range of
300 K and 1023 K. The calorific value of the fuel is 41,800 kJ/kg. Find (1) Air fuel ratio (2)Thermal efficiency of the plant (3)Power
developed if flow rate of air is 10 kg/s. Isentropic efficiency of compression and expansion is 80% and there is pressure loss of
0.15 bar in the combustion chamber. (Oct/Nov 2008 OR)
9. In gas turbine plant working on Braton cycle the air at the inlet is at 270C and 0.1 MPa. The pressure ratio is 6.25, and
the maximum temperature is 800oC, the turbine and compressor efficiencies are each 80%. Find
(i) the compressor work done per kg of air,
(ii) the turbine work done per kg of air,
(iii) heat supplied per kg of air,
(iv) the cycle efficiency, and
(v) the turbine exhaust temperature.

4. In a gas turbine plant, the air is compressed in a single stage compressor from 1 bar to 9 bar and from an initial temperature
of 300 K The same air is then heated to a temperature of 800 K and then expanded in the second turbine. Find the maximum
power that can be obtained from the installation, if the mass of air circulated per second is 2 kg. Take Cp = 1.006 kJ/kg C for
air. (Oct/Nov 2009 OR)
11. In a gas turbine, air at 15 C in compressed from 1.01 bar through a pressure ratio of 6:1, after which it is heated to a
temperature of 750 C. It is then expanded in a turbine to 1.01 bar. Assume the following :
Isentropic efficiency of compressor = 0.8
Isentropic efficiency of turbine= 0.85
Cp for air and combustion products = 1.005 kJ/Kg K
Ratio of specific heats = 1.4
Calculate the cycle efficiency and the work ratio. ` (Mar/Apr 2011 NR)
12. A gas turbine takes in air at 27°c and bar. The pressure ratio is 4 and the maximum temperature in the cycle is 560°
C. The compressor and the turbine efficiencies are 0.83 and 0.85 respectively. Determine the overall efficiency if the
regenerator effectiveness is 0.75.

5. The air enters the compressor of an open cycle constant pressure gas turbine at a pressure of 1 bar and temperature of
20°C. The pressure of the air after the compression is 4 bar. The isentropic efficiencies of compressor and turbine are 80%
and 85% respectively. The air fuel ratio used is 90:1. If flow rate of air is 3 kg/s, find
(i) Power developed
(ii) Thermal efficiency of the cycle.
Assume Cp = 1 kJ/kg K and r = 1.4 of air and gas. Calorific value of fuel = 41800 kJ/kg.
(Oct 2011 RR)
14. (a). In a gas turbine plant, air is compressed from 1 bar and 15°C through a pressure ratio of 4:1. It is then heated
to 650°C in a combustion chamber and expanded back to atmospheric pressure of 1 bar in a turbine. Calculate the cycle
efficiency and work ratio if a perfect heat exchanger is used. The isentropic efficiencies of the turbine and compressor are
85% and 80% respectively.
(b). A gas turbine takes in air at 27°C and 1 bar. The pressure ratio is 4 and the
maximum temperature in the cycle is 500°C then expanded to 1 bar. The compressor
and turbine efficiencies are 0.83 and 0.85 respectively. Determine the overall efficiency
of the cycle. (Mar/Apr 2012 RR)
15. The air enters the compressor of an open cycle constant pressure gas turbine at a pressure of 1 bar and
temperature of 20 C . The pressure of air after compressor is 4 bar. The isentropic efficiencies of compressor and turbine is
80 % and 85%. The A/F ratio is 90:1. The flow rate of air is 3 kg/s. Find (i) Power developed (ii) Thermal efficiency of the
cycle;
Assume Cp = 1 kJ/kg K , Υ = 1.4 for air and gases. Calorific value of fuel is 41800 kJ/kg.
Oct’ 12 RR