The Cascade Vapor-Compression Refrigeration Cycle

Ch 10, Lesson C, Page 2 - The Cascade Vapor-Compression Refrigeration Cycle

• The cascade vapor-compression refrigeration cycle is two simple V-C cycles is series.
• The lower cycle cools the refrigerated space and the upper cycle cools the lower cycle.
• This is accomplished with a heat exchanger.
• This heat exchanger acts like an evaporator for the upper cycle and like a condenser for the lower cycle.
• The energy released by the refrigerant in the lower cycle as it condenses in the heat exchanger is absorbed by the refrigerant in the upper cycle, causing it to evaporate.
• The flow rates through the two cycles must be carefully matched to obtain good efficiency and to avoid damaging the upper cycle compressor.
• The cascade cycle has one special advantage.  It can use different refrigerants in the two cycles.
• This makes it fairly easy to ensure that the pressure in the evaporator is above atmospheric by choosing the right refrigerant for the lower cycle.
• It also makes it fairly easy to get the operating pressure of the condenser in the optimal range.  Just pick a refrigerant with a low enough vapor pressure at the temperature of the condenser.
• OK, so now we see how the cascade cycle addresses the operating pressure problems in the cycle.
• But how does the cascade effect the coefficient of performance of the cycle ?
• Flip the page and let’s see.