In: Mechanical Engineering
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)