The refrigerant used in reversed Brayton or Bell-Coleman cycle is

SOLUTION

Explanation:

Gas refrigeration cycle

• A gas refrigeration cycle works on the reverse Brayton cycle this cycle is also called Joule or Bell-Coleman cycle. 
• A gas cycle consists of two reversible isobaric and two reversible adiabatic processes.
• The gas does not undergo any phase change during the cycle, consequently, all the internal heat transfer processes are sensible heat transfer processes.
•  First air is compressed and then heat removed, this air is then expanded to a lower temperature than before it was compressed. Work must be taken out of the air during the expansion, otherwise, the entropy would increase.

• Reversed Brayton cycle used in the air refrigeration cycle which uses air as the refrigerant.

• It is used for air conditioning in aeroplanes.

Reverse Brayton cycle has following thermodynamic processes

Process 1-2 Isentropic (constant entropy) compression

Process 2-3 Isobaric (constant pressure) heat addition

Process 3-4 Isentropic expansion

Process 4-1 Isobaric heat rejection