Natural draft cooling towers are divided into which categories?

• A. Dry and wet types
• B. Updraft and down-draft types
• C. Wood fill and plastic fill types
• D. Atmospheric towers and chimney towers

Answer: (D)

Natural draft cooling towers rely on buoyancy to move air through the tower. There are two ways this draft is produced: atmospheric towers and chimney towers.

Atmospheric towers are the familiar large hyperboloid shapes. They rely on the buoyant rise of hot air inside the tower to draw in cooler air at the base and vent warm air upward, creating a natural draft without any external chimney. The distinctive wide base and narrow top help maximize this draft and stabilize flow.

Chimney towers achieve draft with a tall vertical stack. The tall chimney adds height to boost the stack effect and pull air through the cooling chamber, even if wind conditions aren’t ideal. This design places the draft responsibility in a separate, elongated vertical channel.

The other options describe different aspects of cooling towers (dry vs wet operation, fill material) but aren’t categories of natural-draft design.