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Simple Vapor-Compression Refrigeration Cycle

Consider the simple

vapor-compression refrigeration cycle

shown below.

A substantial amount of work is lost at the expansion valve because the condenser operates at a much higer pressure than the evaporator.

Cascade refrigeration

will increase the

coefficient of performance

of the cycle, whether we use the same refrigerant in both cycles or not because Pcond >>Pevap.

Process flow diagram for a vapor-compression refrigeration cycle with the condenser and evaporator highlighted.

TS Diagram of a simple vapor-compression refrigeration cycle operating between a very high pressure condenser isobar and a very low pressure evaporator isobar.

Lesson
10C Blog

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Lesson 10C: page 3 of 9

When a simple V-C refrigeration cycle is used to make the refrigerated space very cood, the difference between the operating pressures in the evaporator and condenser become very large.
In this case, the expansion valve is highly irreversible and is therefore causing a great deal of lost work and a loss of efficiency.
We could install a turbine instead of an expansion valve, but the turbine would be expensive because it would need to handle a two-phase mixture.
Another solution is to use a cascade cycle. This will be helpful even if we use the same refrigerant in both the upper and the lower cycles.
Flip the page to see why.

Simple Vapor-Compression Refrigeration Cycle

vapor-compression refrigeration cycle

Cascade refrigeration

coefficient of performance

Ch 10, Lesson C, Page 3 - Simple Vapor-Compression Refrigeration Cycle