Question

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?

1. Saturated temperature
2. Dry air rated temperature (DART)
3. Super-saturated temperature
4. Dry air temperature (DAT)

Answer 1

Correct Answer - Option 2 : Dry air rated temperature (DART)

Explanation:

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, 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 = mc_p(T_i - T_DART)

where, m = Mass flow rate, T_DART =  Dry Air Rated Temperature, T_i = Cabin temperature.

• DART increases monotonically with Mach number for all the systems except the reduced ambient system.
• The simple system is adequate at low Mach numbers.
• At high Mach numbers either bootstrap system or regenerative system should be used.
• Reduced ambient temperature system is best suited for very high Mach number, supersonic aircrafts.