What advantage does a closed feed-water heater provide over an open feed-water heater?

A closed feed-water heater provides the advantage of heating water to near the temperature of the steam, which is crucial for improving the efficiency of steam systems. In a closed system, the feed water is heated by indirect contact with the steam in a heat exchanger, allowing it to absorb a significant amount of thermal energy without directly mixing with the steam. This results in a higher water temperature as it approaches the steam's temperature, which minimizes thermal shock and can enhance the performance of the steam cycle.

This high-temperature water is beneficial because it reduces the amount of additional fuel needed to reach the steam generation temperature, leading to improved thermal efficiency. Additionally, maintaining a closed system helps prevent contamination of the feed water and can help in decreasing corrosion issues by controlling the water chemistry more effectively.

In contrast, other options highlight characteristics not primarily linked to the main functional advantage of closed feed-water heaters. For instance, lower temperatures, ease of flooding, and maintenance requirements do not capture the primary operational benefits that enhanced heating efficiency brings in a closed feed-water heating context.