What is a characteristic feature of cooling towers utilizing natural draft?

Cooling towers that utilize natural draft primarily function by making use of the buoyancy effect of hot air. This means that when warm air rises from the heated water in the cooling tower, it creates a vacuum that pulls in cooler air from the surrounding environment through the bottom of the tower. This process is enhanced by the design of the cooling tower, which is typically tall and narrow, promoting the upward movement of air and increasing the effectiveness of cooling without the need for mechanical fans.

The reliance on buoyancy is a defining characteristic of natural draft cooling towers; they do not require electrical compressors or fans to circulate air. Instead, they depend on the natural movement of air, making them more energy-efficient and suitable for specific applications where electrical power availability may be limited or where a lower carbon footprint is desired.

In contrast, the other aspects provided in the choices do not describe the fundamental operation of natural draft cooling towers. These towers are engineered to perform optimally at specific conditions but are not limited to operating at lower temperatures nor do they rely on gravity alone to facilitate the air movement.