ATDCHB2
Applied Thermodynamics 2B
BET
FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT (FEBE)
DEPARTMENT OF CHEMICAL ENGINEERING
ATDCHB2: Applied Thermodynamics 2B
INSTRUCTOR: Prof. C. Narasigadu
TUTORIAL 3 – LU3
QUESTION 1
A simple Brayton cycle using air as the working fluid has a pressure ratio of 8. The minimum and maximum
temperatures in the cycle are 310 K and 1160 K. Assuming an isentropic efficiency of 75 percent for the
compressor and 82 percent for the turbine, determine:
a) the air temperature at the turbine exit
b) the net work output
c) the thermal efficiency
QUESTION 2
Air enters the compressor of a gas-turbine engine at 300 K and 100 kPa, where it is compressed to 700 kPa and
580 K. Heat is transferred to air in the amount of 950 kJ/kg before it enters the turbine. For a turbine efficiency
of 86 percent, determine:
a) the fraction of the turbine work output used to drive the compressor
b) the thermal efficiency
QUESTION 3
A turbojet aircraft flies with a velocity of 260 m/s at an altitude where the air is at 35 kPa and –40 oC. The
compressor has pressure ratio of 10, and the temperature of the gases at the turbine inlet is 1100 oC. Air enters
the compressor at a rate of 45 kg/s. Using constant specific heats for air at room temperature, determine:
a) the temperature and pressure of the gases at the turbine exit
b) the velocity of the gases at the nozzle exit
ATDCHB2
Applied Thermodynamics 2B
BET
Figure 1: Basic components of a turbojet engine.
QUESTION 4
Air enters a gas turbine with two stages of compression and two stages of expansion at 100 kPa and 17 oC. This
system uses a regenerator as well as reheating as well as reheating and intercooling. The pressure ratio across
each compressor is 4; 300 kJ/kg of heat are added to the air in each combustion chamber; and the regenerator
operates perfectly while increasing the temperature of the cold air by 20 oC. Determine this system’s thermal
efficiency. Assume isentropic operations for all compressor and the turbine stages and use constant specific heats
at room temperature.