Heat
Transfer Table of Content
Industrial Cooling Towers
The typical function of a cooling tower is to
cool the water of a steam power plant by air that is
brought into direct contact with the water. The water is
mixed with vapor that diffuses from the
condensate into the air. The formation of the vapor requires
a considerable removal of internal
energy from the water; the internal energy becomes
"latent heat" of the vapor. Heat and mass
exchange are coupled in this process, which is a steady-state
process like the heat exchange in
the ordinary heat exchanger.
Wooden cooling towers are sometimes employed
in nuclear facilities and in factories of various industries.
They generally consists of large chambers loosely filled with
trays or similar wooden elements
of construction. The water to be cooled is pumped to the top
of the tower where it is distributed
by spray or wooden troughs. It then falls through the tower,
splashing down from deck
to deck. A part of it evaporates into the air that passes
through the tower. The enthalpy needed
for the evaporation is taken from the water and transferred
to the air, which is heated while
the water cools. The air flow is either horizontal due to
wind currents (cross flow) or vertically
upward in counter-flow to the falling water. The counter-flow
is caused by the chimney effect of the warm humid air in the
tower or by fans at the bottom (forced draft) or at the
top (induced flow) of the tower. Mechanical draft towers are
more economical to construct and
smaller in size than natural-convection towers of the same
cooling capacity. |
