Question

A simple air cooled system is used for an aeroplane to take a load of 10 tons.
Atmospheric temperature and pressure is 25°C and 0.9 atm respectively. 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 removed in the air-cooled
heat exchanger and then it is passed through a evaporator for future cooling. The
temperature of air is reduced by 10°C in the evaporator. Lastly the air is passed
through cooling turbine and is supplied to the cooling cabin where the pressure is 1.03
atm. Assuming isentropic efficiency of the compressor and turbine are 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 and heat rejection
temperatures only. (Answer)
2. As heat transfer from a gas can be done isothermally, Carnot cycle is easy to
implement practically. (Answer)
3. For a fixed heat rejection and refrigeration temperature, the COP of a brayton
cycle is lower than COP of reverse Carnot cycle. (Answer)
4. Efficiency of dense air systems are low as operating pressures are higher
(Answer)
5. DART is the temperature of the air at the exit of the cooling turbine. (Answer)
6. A Simple system is adequate to handle high Mach numbers. (Answer)

Answer 1