ENGR 2213 Thermodynamics

1
ENGR 2213 Thermodynamics

• F. C. Lai
• School of Aerospace and Mechanical
• Engineering
• University of Oklahoma

2
Brayton Cycles
George Brayton (1870)
Applications of Gas-Turbine Engines
Propulsion
Power Generation
- The first gas turbine for electric power
generation was installed in 1949 in Oklahoma.
- Before 1980s, gas power plants were mainly
used for peak-load power production.
- It is forecast that more than half of all power
plants to be installed in the future are gas
power plants.
3
Brayton Cycles
George Brayton (1870)
Open cycle Closed Cycle
4
Brayton Cycles
5
Brayton Cycles
3
Staedy-flow q w he hi
T
Qin
qin h3 h2
cp (T3 T2)
qout h4 h1
cp (T4 T1)
2
4
1
Qout
S
6
Brayton Cycles
The thermal efficiency increases with
the pressure ratio.
The highest temperature in the cycle is
limited by the maximum temperature that
the turbine blades can withstand.
7
Example 1

• A gas power plant operating on an ideal Brayton
  cycle
• has a pressure ratio of 8. The gas temperature
  is 300 K
• At the compression inlet and 1300 K at the
  turbine inlet.
• Utilizing the air-standard assumptions, determine
• the gas temperature at the exits of the
  compressor
• and the turbine,
• (b) the back work ratio,
• the thermal efficiency of this cycle.

8
Example 1 (continued)
(a)
State 1 air at the inlet of compressor, T1
300 K
Table A-17 h1 300.19 kJ/kg
pr1 1.386
Process 1-2 Isentropic compression
Table A-17 T2 540 K h2
544.35 kJ/kg
9
Example 1 (continued)
State 3 air at the inlet of turbine, T3 1300 K
Table A-17 h3 1395.97 kJ/kg
pr3 330.9
Process 3-4 Isentropic expanion
Table A-17 T4 770 K h4
789.11 kJ/kg
wcomp h2 h1
544.35 300.19 244.16 kJ/kg
10
Example 1 (continued)
wturb h3 h4
1395.97 789.11 606.86 kJ/kg
(b)
qin h3 h2
1395.97 544.35 851.62 kJ/kg
wnet wturb wcomp
606.86 244.16 362.7 kJ/kg
(c)
1 rp(1-k)/k 1 (8)-(0.4/1.4) 0.448
11
Brayton Cycles with Regeneration
12
Brayton Cycles with Intercooling, Reheating, and
Regeneration