ME 300 Homework #13 - Spring 2016
Homework Due: Wednesday, April 27, 2016
Book Problem 9.3
Answer: c. 50.7%
Book Problem 9.26
Answer: d. 56.5%
SP 39 Otto, Diesel, and Dual Cycles
An air standard dual cycle has a compression ratio of 18 and a cutoff ratio of 1.1. The pressure
ratio during constant-volume heat addition process is 1.1. At the start of the compression,
P1=90 kPa, T1 = 18°C, and V1= 0.003 m3. How much power will this cycle generate when it is
executed 4000 times per minute? Use constant specific heats at room temperature.
Answer: 24.8 kW
Book Problem 9.42
Answer: c. 48.1%
Book Problem 9.49
Answer: a. 50.9%
Reference 9.48
SP 40 Gas Turbine Engines and Air Standard Brayton Cycle
In an air-standard Brayton cycle, the air enters the compressor at 0.1 MPa, 20°C. The pressure
leaving the compressor is 1 MPa, and the maximum temperature in the cycle is 1225°C. Assume
a compressor efficiency of 80%, a turbine efficiency of 85%, and a pressure drop between the
compressor and turbine of 25 kPa. The mass flow rate is 1 kg/s. Determine the a) compressor
work, b) the turbine work, and c) the thermal efficiency of the cycle.
Answer: a) -341.58 kW
Book Problem 9.56
Reference 9.55
Answer: a. 35.04%
SP 41 Brayton Cycle Irreversibilities and Regeneration
A gas turbine engine operates based upon the ideal Brayton cycle with regeneration, as shown in
the figure below. Now the regenerator is rearranged so that the air streams of states 2 and 5
enter at one end of the regenerator and streams 3 and 6 exit at the other end (i.e. parallel flow
arrangement of a heat exchanger). Consider such a system when air enters the compressor at 100
kPa and 20°C, the compressor pressure ratio is 7, the maximum cycle temperature is 727°C, and
the difference between the hot and cold air streams temperatures is 6°C at the end of the
regenerator where the cold stream leaves the regenerator. Is the cycle arrangement shown in the
figure more or less efficient than this new arrangement? Assume both the compressor and the
turbine are isentropic, and use constant specific heats at room temperature.
Answer: Rearranging the generator decreases thermal efficiency by 6.02%.