How is a closed cooling system characterized?

A closed cooling system is characterized by having a freshwater circuit that is completely self-contained. This means that the coolant within the system does not contact or mix with the environment, thereby preventing any loss of fluid and minimizing the potential for contamination. The closed design allows the system to maintain consistent temperatures and pressure levels while recirculating the coolant within an enclosed loop. This design is particularly advantageous for systems that require efficient heat exchange and reliable performance over time.

In contrast, the other options do not accurately describe a closed cooling system. For instance, a system that allows the coolant to mix with the environment indicates an open system, which would not offer the same benefits of efficiency and contamination control. Operating only at low temperatures does not define a closed system, as these systems can function across a variety of temperature ranges depending on design requirements. Lastly, a continuous water supply from an external source suggests an open system where external water serves as a coolant, contrasting with the self-contained nature of a closed cooling system.