🔍 Key Concepts

• Difference between primary and secondary refrigerants in a refrigeration system • Properties needed for a secondary refrigerant (corrosion, toxicity, flammability, freezing point) • Typical examples used in shipboard brine systems and why they are chosen

💭 Think About

• Think about which listed fluid is normally circulated to carry cold from an evaporator to cargo spaces, rather than being directly compressed and expanded. • Consider which options are toxic, flammable, or reactive with metals, making them unsuitable for large circulating volumes near food or cargo. • Ask yourself which substance is well‑known in marine refrigeration for chilled cargo holds and provision rooms as the circulating cooling medium.

✅ Before You Answer

• Verify which choice is commonly described in textbooks as a chilled solution pumped around the system. • Check safety aspects: avoid fluids that are highly toxic, flammable, or chemically reactive for large circulation volumes. • Confirm that the substance you select is used primarily for heat transfer, not as the main working fluid in the compressor-evaporator cycle.