In this article will discuss about the components, merits and demerits of air cycle refrigeration system.
Components of Air Cycle Refrigeration System:
The air cycle refrigeration system uses air as working fluid/refrigerant. This system is working on reversed Brayton cycle. Figure 6.18 shows a simple diagram of an air cycle refrigeration system known as Bell-Coleman cycle.
Following are the components of an air cycle refrigeration system:
(a) Compressor
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(b) Cooler (heat exchanger)
(c) Expander
(d) Refrigerator
In this system, cooling effect is produced in the refrigerator. The system has very low COP. In spite of the fact that this system has low COP, this is still popular in aircraft cooling system. In this system, work obtained by the expander is used for the operation of the compressor. This is why less work is required for the operation of the system. Figures 6.19(a) and 6.19(b) show p-V and T-S plot for the cycle.
Air drawn from the refrigerator at (1) is supplied to the compressor where it is compressed isentropically by Process (1-2). High-temperature and high-pressure compressed air is supplied to the cooler where it gets cooled at constant pressure up to (3). The air at (3) is expanded by isentropic process up to (4). The cooled air is supplied to the refrigerator to produce cold effect. The air gets heated at constant pressure process during (4-1). The process is repeated again and again.
Considering m kg of air, heat absorbed in refrigerator, Q2 = mcp(T1 – T4)
Heat rejected in cooler, Q1 = mcp(T2 – T3)
Work required for the operation = Q1 – Q2 = [mcp(T2 -T3) – mcp(T1 – T4)]
Merits and Demerits of Air Cycle Refrigeration:
Merits:
(a) Air is non-flammable, so there is no chance of fire hazards.
(b) Air is cheaply and easily available as compared to other refrigerants.
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(c) The weight of air refrigeration system per ton of refrigeration is much less as compared to other systems. Because of this reason, this system is employed in aircraft applications. Weight is an important consideration in aircrafts.
Demerits:
(a) The COP of the system is very low as compared to other systems.
(b) The amount of air required to be circulated for producing cold effect is more as compared to other refrigerants used in other systems. In this system, heat is carried by air in the form of sensible heats.