Reversed Brayton Cycle in Aircraft Refrigeration

The thermodynamic cycle used in aircraft refrigeration is the reversed Brayton cycle. Let's understand this cycle in detail:

What is the Brayton Cycle?

The Brayton cycle is a thermodynamic cycle that is used in gas turbine engines. It consists of four processes:

1. Isentropic compression: In this process, the air is compressed isentropically (i.e., without any heat transfer) by the compressor.

2. Constant pressure heat addition: In this process, heat is added to the compressed air at constant pressure in the combustion chamber, which causes the air to expand.

3. Isentropic expansion: In this process, the expanded air is expanded isentropically by the turbine, which extracts work from the air.

4. Constant pressure heat rejection: In this process, the air is cooled at constant pressure in the heat exchanger, which prepares the air for the next cycle.

What is the Reversed Brayton Cycle?

The reversed Brayton cycle is essentially the Brayton cycle run in reverse. It consists of four processes:

1. Isentropic expansion: In this process, the refrigerant is expanded isentropically by the turbine, which extracts work from the refrigerant.

2. Constant pressure heat rejection: In this process, the refrigerant is cooled at constant pressure in the heat exchanger, which removes heat from the refrigerant.

3. Isentropic compression: In this process, the refrigerant is compressed isentropically by the compressor.

4. Constant pressure heat addition: In this process, heat is added to the compressed refrigerant at constant pressure in the evaporator, which causes the refrigerant to evaporate.

What is the Role of Reversed Brayton Cycle in Aircraft Refrigeration?

The reversed Brayton cycle is used in aircraft refrigeration to cool the cabin air. The hot cabin air is passed through the evaporator, where it is cooled by the refrigerant, which evaporates due to the heat transfer. The refrigerant vapor is then compressed, which raises its temperature and pressure. The hot refrigerant vapor is then passed through a heat exchanger, where it is cooled by the outside air. The cooled refrigerant is then expanded through a turbine, which extracts work from the refrigerant and reduces its temperature and pressure. The cycle is then repeated.

Conclusion:

The reversed Brayton cycle is an important thermodynamic cycle used in aircraft refrigeration. It is essentially the Brayton cycle run in reverse, and it consists of four processes: isentropic expansion, constant pressure heat rejection, isentropic compression, and constant pressure heat addition. It is used in aircraft refrigeration to cool the cabin air.