MANIPAL INTERNATIONAL UNIVERSITY
SCHOOL OF SCIENCE AND ENGINEERING
Diploma in Mechanical Engineering
EMD 2273 – THERMODYNAMICS II
Tutorial Chapter 2
1. List four processes of Ideal Brayton cycle.
2. If there is a fixed maximum and minimum temperatures, explain the effect of the pressure ratio
on
i.
the thermal efficiency
ii.
the net work output of a simple ideal Brayton cycle.
3. Somebody claims that at very high pressure ratios, the use of regeneration actually decreases
the thermal efficiency of a gas turbine engine. Is there any truth in this claim? Explain.
4. A simple ideal Brayton cycle with air as the working fluid has a pressure ratio of 10. The air
enters the compressor at 290 K and the turbine at 1100 K. Accounting for the variation of
specific heats with temperature, determine
i.
the air temperature at the compressor
ii.
the back work ratio and
iii.
thermal efficiency
Answer: (i) 555.6 K, (ii) 49.3% (iii) 46.5%
5. A gas turbine for an automobile is designed with a regenerator. Air enters the compressor of
this engine at 100 kPa and 20ºC. The compressor pressure ratio is 8; the maximum cycle
temperature is 800ºC; and the cold air stream leaves the regenerator 10ºC cooler than the hot
air stream at the inlet of the regenerator. Assuming both the compressor and the turbine to be
isentropic, determine the rates of heat addition and rejection for this cycle when it produces
150 kW. Use constant specific heats at room temperature.
Answer: 303 kW, 153 kW
6. A gas turbine power plant operates on the simple Brayton cycle between the pressure limits of
100 and 800 kPa. Air enters the compressor at 30°C and leaves at 330°C at a mass flow rate of
200 kg/s. The maximum cycle temperature is 1400 K. During the operation of the cycle, the
net power output is 60 MW. Assume constant properties of air at 300 K, with cv = 0.718
kJ/kg.K, cp = 1.005 kJ/kg.K, R = 0.287 kJ/kg. K, k = 1.4.
i.
Sketch the T-s diagram for the cycle.
ii.
Determine the isentropic efficiency of the turbine for these operating conditions.
iii.
Determine the cycle thermal efficiency.
Answer: (ii) 95.4% (iii) 37.5%
7. A Brayton cycle with the regeneration using air as the working fluid has a pressure ratio of 7.
The minimum and maximum temperature in the cycle are 310 and 1150 K. Assuming an
isentropic efficiency of 75 percent for the compressor and 82 percent for the turbine and an
effectiveness of 65 percent for the regenerator, determine
i.
the air temperature at the turbine exit,
ii.
the net work output,
iii.
thermal efficiency.
Answer: (i) 782.8 K (ii) 108.1 kJ/kg (iii) 22.5%