Final answer:
Oil separators are used in aircraft pneumatic systems to remove oil from engine bleed air and in large refrigeration systems to prevent oil accumulation in the evaporator and maintain system efficiency.
Step-by-step explanation:
Oil separators are typically required in aircraft pneumatic systems and some types of refrigeration systems. In aircraft, the pneumatic systems often use air that is taken from the engines, which contains oil and other contaminants. An oil separator is installed to remove this oil before it can reach and damage pneumatic devices or systems downstream. In the field of refrigeration, oil separators are used in large refrigeration systems, such as those in supermarkets or industrial settings, where compressors circulate a refrigerant and oil mixture throughout the system. The oil separator's role is to ensure that the oil does not accumulate in the evaporator or other parts of the system, which could decrease efficiency and increase wear. It does so by separating the oil from the refrigerant so that the oil can return to the compressor.