Components of a cooling tower
The basic components of a cooling tower
include the frame and casing, fill, cold-water basin,drift eliminators, air
inlet, louvers, nozzles and fans.
Frame and casing. Most
towers have structural frames that support the exterior enclosures (casings), motors, fans, and other
components. With some smaller designs, such as some glass fibre units, the
casing may essentially be the frame.
Fill. Most
towers employ fills (made of plastic or wood) to facilitate heat transfer by
maximizing water and air contact.
There are two types of
fill
Splash fill:
water falls over successive layers of horizontal splash bars, continuously
breaking into smaller droplets, while also wetting the fill surface. Plastic
splash fills promote better heat transfer than wood splash fills.
Film fill:
consists of thin, closely spaced plastic surfaces over which the water spreads,
forming a thin film in contact with the air. These surfaces may be flat,
corrugated, honeycombed, or other patterns. The film type of fill is the more
efficient and provides same heat transfer in a smaller volume than the splash
fill.
Cold-water basin. The
cold-water basin is located at or near the bottom of the tower, and it receives
the cooled water that flows down through the tower and fill. The basin usually
has a sump or low point for the cold-water discharge connection. In many tower
designs, the cold water basin is beneath the entire fill.
Drift eliminators. These
capture water droplets entrapped in the air stream that otherwise would be lost
to the atmosphere.
Air inlet. This
is the point of entry for the air entering a tower. The inlet may take up an
entire side of a tower (cross-flow design) or be located low on the side or the
bottom of the tower (counter-flow design).
Louvers.
Generally, cross-flow towers have inlet
louvers. The purpose of louvers is to equalize air flow into the fill and
retain the water within the tower. Many counter flow tower designs do not
require louvers
Nozzles. These spray water to wet the fill. Uniform water distribution at the top of the fill is essential to achieve proper wetting of the entire fill surface. Nozzles can either be fixed and spray in a round or square patterns, or they can be part of a rotating assembly as found in some circular cross-section towers.
Fans. Both axial (propeller type) and centrifugal fans are used in towers. Generally, propeller fans are used in induced draft towers and both propeller and centrifugal fans are found in forced draft towers. Depending upon their size, the type of propeller fans used is either fixed or variable pitch. A fan with non-automatic adjustable pitch blades can be used over a wide kW range because the fan can be adjusted to deliver the desired air flow at the lowest power consumption. Automatic variable pitch blades can vary air flow in response to changing load conditions.Tower
materials
Frame and casing.
Wooden towers are still available, but many
components are made of different materials, such as the casing around the
wooden framework of glass fibre, the inlet air louvers of glass fibre, the fill
of plastic and the cold-water basin of steel. Many towers (casings and basins)
are constructed of galvanized steel or, where a corrosive atmosphere is a
problem, the tower and/or the basis are made of stainless steel.
Fill. Plastics are widely used for fill, including PVC,
polypropylene, and other polymers. When water conditions require the use of
splash fill, treated wood splash fill is still used in wooden towers, but
plastic splash fill is also widely used. Because of greater heat transfer
efficiency
Nozzles.
Plastics are also widely used for
nozzles. Many nozzles are made of PVC, ABS, polypropylene, and glass-filled
nylon.
