In the context of an aircraft refrigeration cycle, what is the temperature of the air at the exit of the cooling turbine in the absence of moisture condensation?

In the context of an aircraft refrigeration cycle, what is the temperature of the air at the exit of the cooling turbine in the absence of moisture condensation?

Right Answer is:

Dry air rated temperature (DART)

SOLUTION

Air-cycle Systems for Aircraft Refrigeration

  • When a supply of compressed air is available, it can be used to power a gas refrigeration system. The most common example of this application is the open-cycle air-conditioning system used in aircraft.
  • The gas refrigeration system is essentially a reverse Brayton cycle.
  • An airplane moving at high speed can bleed air from the engines at high pressure and divert this flow into a compressor.
  • The air leaving from the compressor is at a high temperature and pressure.
  • In context to air refrigeration DART or Dry Air, Rated Temperature is the temperature in terms which is used to compare the different types of refrigeration systems of an aircraft.
  • Heat is removed from the air in a high-temperature heat exchanger, and the cooler air then flows through a turbine.
  • The function of the turbine is to reduce the air temperature and help power the compressor. Cool air from the turbine is then directed into the airplane cabin.

Dry Air Rated Temperature (DART):

  • The concept of Dry Air Rated Temperature is used to compare different aircraft refrigeration cycles.
  • Dry Air Rated Temperature is defined as the temperature of the air at the exit of the cooling turbine in the absence of moisture condensation.
  • For condensation not to occur during expansion in the turbine, the dew point temperature and hence moisture content of the air should be very low, i.e., the air should be very dry.
  • The aircraft refrigeration systems are rated based on the mass flow rate of air at the design DART. The cooling capacity is then given by:

Q = mcp(Ti – TDART)

where

m = Mass flow rate

TDART =  Dry Air Rated Temperature

Ti = Cabin temperature

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