R48 -- Ultralow-Temperature Refrigeration (SI)

Ultralow-temperature refrigeration is defined here as refrigeration in the temperature range of –58 to –148°F (–50 to –100°C). What is considered low temperature for an application depends on the temperature range for that specific application. Low temperatures for air conditioning are around 32°F (0°C); for industrial refrigeration, –31 to –58°F (–35 to –50°C); and for cryogenics, approaching 0°R (0 K) (absolute zero). Applications such as freeze-drying, as well as the pharmaceutical, chemical, and petroleum industries, use refrigeration in the ultralow-temperature range as designated in this chapter. The refrigeration cycles presented in this chapter may be used in both standard packaged and custom-designed systems. Cascade systems are emphasized, both autocascade (typical of packaged units) and two-refrigerant cascade (found in custom-engineered ultralow-temperature systems). Autocascade Systems Custom-Designed and Field-Erected Systems Single-Refrigerant Systems Cascade Systems Ultralow-Temperature Materials Insulation Heat Transfer Secondary Coolants