A simple air cooled system is used for an aeroplane totake a load of 10 tons.
Atmospheric temperature and pressure is 25°C and 0.9 atmrespectively. Due to
ramming the pressure of air is increased from 0.9 atm, to 1 atm.The pressure of air
leaving the main compressor is 3.5 atm and its 50% heat is removedin the air-cooled
heat exchanger and then it is passed through a evaporator forfuture cooling. The
temperature of air is reduced by 10°C in the evaporator. Lastly theair is passed
through cooling turbine and is supplied to the cooling cabin wherethe pressure is 1.03
atm. Assuming isentropic efficiency of the compressor and turbineare 75% and 70%,
find
a) Power required to take the load in the cooling cabin
b) COP of the system.
The temperature of air leaving the cabin should not exceed 25°C.(Solution)
7. True and False
1. COP of a Carnot system depends only on the refrigeration andheat rejection
temperatures only. (Answer)
2. As heat transfer from a gas can be done isothermally, Carnotcycle is easy to
implement practically. (Answer)
3. For a fixed heat rejection and refrigeration temperature, theCOP of a brayton
cycle is lower than COP of reverse Carnot cycle. (Answer)
4. Efficiency of dense air systems are low as operating pressuresare higher
(Answer)
5. DART is the temperature of the air at the exit of the coolingturbine. (Answer)
6. A Simple system is adequate to handle high Mach numbers.(Answer)