Why Are Cooling Towers Hyperboloidal In Cross Section?

The purpose of a cooling tower is cooling and to accomplish this we want to create a draft - like a chimney. The narrow section is called a venturi and causes the warm moist air to accelerate, improving the "draft". This draws air in at the bottom, mixing it with the warm water that has been sprayed onto cooling fins or panels. The mixing helps to cool the water too.

Structurally it is a stable shape and and conducive to slip forming. The sides can be surprisingly thin, making it an efficient structure too.

How it is structurally stable ?

An hyperboloid of revolution can have straight lines drawn on its surface in two directions. So the thin shell has curvature in some directions which provides local stiffness against buckling but direct load paths to the ground to transmit the gravity loads to the foundations.

The waisted tube is a nice venturi as well.

Greg

Another major factor that helps the draft up a cooling tower is the simple concept of hot air. Cool air entering the bottom of the tower becomes heated while cooling the water and this forces the air to move up in the tower. This air moving up creates a suction effect (sort of like pulling from a straw) and this requires continuity increasing the flow of cool air from the bottom of the tower.

A cooling tower is divided into two sections: The bottom, where the cool air enters, and the top, where all the heat transfer takes place. I've been in a cooling tower on a still day and you wouldn't believe the how powerful the draft is when you open a door between the two sections. Simply amazing!!!

The hyperboloidal structure offers the best compromise between structural strength and a minimum use of structural materials.

Wiki it....

DELTA ( ALSO SOLD AS CARRIER) MAKES CYLINDRICAL TOWERS. THEY ARE AVAILABLE MADE WITH EPDM PLASTIC. EFFICIENCY AND STRUCTURAL STABILITY ARE NOT A PROBLEM.