Cascade refrigeration

(Bottom on mobile) The cascade cycle is often employed for devices such as ULT freezers.

The low temperature system removes heat from the space to be cooled using an evaporator, and transfers it to a heat exchanger that is cooled by the evaporation of the refrigerant of the high temperature system.

Peltier coolers may also be cascaded into a multi-stage system to achieve lower temperatures.

[6][7][8] Efficiency drops very rapidly as more stages are added but for very small heat loads down to near-cryogenic temperatures this can often be an effective solution due to being compact and low cost, such as in mid-range thermographic cameras.

[9] [10][11] For a Peltier cooler with seven stages, power consumption can be 65 W with a cooling capacity of 80 mW.

A two-cycle cascade refrigeration process schematic diagram
This is an auto-cascade process with two different refrigerants. The high-temperature refrigerant (red) condenses in the air condenser and is then separated and evaporated to cool the heat exchanger, which condenses the low-temperature refrigerant (blue). Purple signifies a mixture of both refrigerants.