Why cooling tower's are hyperbolic in section?

Question

In case of natural draft cooling towers, it is in hyperbolic in section; basically it can take load (wind, self weight)
How a hyperbolic section can take more load compared to conical or cylindrical sections.

Answer 1

This is actually a difficult engineering question. The superiority of a hyperboloidal shell over conical or cylindrical isn't clear cut, especially over a conical shell. But the chief difference is that at all surface points of both the cone and the cylinder have at least one principal curvature of zero, meaning that both can be "rolled out flat", or formed from a sheet of paper. The hyperboloid cannot be, so it resists local deformations everywhere on its surface, and hence it's "stiffer". Technically speaking, a hyperboloidal has a negative Gaussian curvature everywhere, while the other two have 0 Gaussian curvature everywhere.

A real hyperboloidal cooling tower is actually a compromise, because air accelerates as it rises inside the tower, and the cross section has to be reduced with height for efficient non-turbulent flow. Yet, a slight flaring at the top is found to be more efficient for dispersal of warm air. So, hyperboloidal cooling towers are generally wider at the bottom than at the top, and bottom part closely approximates a conical surface.

What the public isn't generally aware of is that hyperboloidal cooling towers are mostly empty space. All the cooling coils and surfaces are located at the bottom of the tower. The tower itself is designed to maximize air draft that would naturally occur with air rising after contact with heated surfaces.

Answer 2

Hyperbolic Cooling Tower

Answer 3

Frankly, I think a straight cylindrical section would be the strongest of all. It's also clearly more difficult and expensive to build a cooling tower with a hyperbolic section, so there must be some good reason they're done that way. I once visited the Rancho Seco nuclear power plant and took a guided tour. When we viewed the inside of a cooling tower, there was a three-blade turbine fitted inside the "waist" of the tower. Around the inside of the top edge there were nozzles that sprayed hot water onto the inside surface of the tower. The water appeared to cling to the inside surface as it ran down to a trench which collected the cooled water at the bottom. My hunch is that the hyperbolic section creates a larger interior surface area for a given turbine diameter and improves cooling efficiency. Perhaps there's a real nuclear power plant engineer out there who knows the correct answer to this mystery.

Answer 4

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RE:
Why cooling tower's are hyperbolic in section?
In case of natural draft cooling towers, it is in hyperbolic in section; basically it can take load (wind, self weight)
How a hyperbolic section can take more load compared to conical or cylindrical sections.

Answer 5

A conically reducing tower has its radius changing linearly with height. The cross-sectional area consequently decreases much faster as the square of the radius. This would result in an increase in velocity of flow in the same ratio. A hyperbolic section can be made to vary such that the area decreases linearly with height and make the velocity increase linearly with height, resulting in a more gradual variation and with lower pressure losses. Further the hyperbolic cross section will add stiffness and structural rigidity while withstanding wind loads and gusts.
Dr.Prasad M

Answer 6

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not all cooling towers are hyperbolic, whether they are used at nuclear power plants or not. It is simply an economic choice that depends on many factors.

Answer 7

Basically, cooling towers remove heat from process
water through evaporation and sensible heat transfer.
Towers are designed as either mechanical draft or natural
draft hyperbolic types. Mechanical draft towers use
fans to induce air through the tower shell. Natural draft
hyperbolic towers use the density difference between
warm moist air in the tower and cooler ambient air outside
the tower to create a draft in the tower shell. Both
tower types are designed in one of two air flow configurations-
crossflow or counterflow. In the crossflow configuration,
water dropping from the tower top interfaces with
air drawn horizontally through the tower by fans or chimney
effect. In the counterflow configuration. water dropping
from the tower top interfaces countercurrently with
air drawn upward by fans or chimney effect through louvers
located at the tower bottom.
The latest cooling tower option is a circular mechanical
draft tower. Crossflow in design and concrete in construction.
the circular tower offers several advantages not
realized by conventional mechanical or natural draft towers.
The circular concrete tower can cool the same
amount of water with the same temperature parameters
as two rectangular towers but would require less total
land area.

Hyperbolic natural draft cooling towers are generally, but not necessarily exclusively, constructed in conjunction with fossil fuel, nuclear energy, and the like, electrical generating power plants and similar facilities. It is known to construct up draft towers, cross draft towers, and other known flow systems within a structure in the form of a hyperbolic veil, with only the lower portion of the towers, that portion below and including the lintel beam, being effected to achieve the different flow systems.

The current, or conventional, method of constructing these hyperbolic veils is to use cast-in-place concrete, heavily reinforced with steel reinforcing bars. The veil sections are, from their hyperboloid form, thick at the bottom thereof and taper into thin sections at the throat of the tower, subsequently increasing in thickness from the throat to the top of the structure.
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Used in large power generation plants, hyperbolic natural draft cooling towers are known for their distinct shape. Although eye-catching in form, the distinct shape serves a functional purpose in that it cools the water received from the steam condensers at a much lower operating cost than mechanical draft cooling towers.