Common Industrial Cooling Industry Terms
Drift - Water
droplets that are carried out of the cooling
tower with the exhaust air. Drift droplets have the same concentration
of impurities as the water entering the tower. The drift rate is typically
reduced by employing baffle-like devices, called drift eliminators, through
which the air must travel after leaving the fill and spray zones of the
Blow-Out - Water
droplets blown out of the cooling tower by wind, generally at the air
inlet openings. Cooling water may also be lost, in the absence of wind,
through splashing or misting. Devices such as wind screens, louvers, splash
deflectors and water diverters are used to limit these losses.
Plume - The stream
of saturated exhaust air leaving the cooling tower. The plume is visible
when water vapor it contains condenses in contact with cooler ambient
air, like the saturated air in one's breath fogs on a cold day. Under
certain conditions, a cooling tower plume may present fogging or icing
hazards to its surroundings.
Note that the water evaporated in the cooling tower operation process is "pure" water, in contrast to the very small percentage of drift droplets or water blown out of the air inlets.
Blow-Down - The
portion of the circulating water flow that is removed in order to maintain
the amount of dissolved solids and other impurities at an acceptable level
- the higher the TDS concentration, the greater the risk of scale, biological
growth and corrosion.
Approach - is
the difference in temperature between the cooled-water temperature and
the entering-air wet bulb temperature. Since cooling towers use an evaporative
cooling design, cooling tower efficiency depends on the wet bulb temperature
of the air.
Range - is the
temperature difference between the water inlet and water exit.
Fill - Inside
the tower, fills are added to increase contact surface as well as contact
time between air and water. Thus they provide better heat transfer. The
efficiency of the tower also depends on them. The two most common types
of fill that currently in use are:
Film type fill - causes water to spread into a thin film)
Splash type fill - breaks up water and interrupts its vertical progress
The fill may consist of multiple, mainly vertical or sloped, wetted surfaces upon which a thin film of water spreads (film fill), or several levels of horizontal splash elements which create a cascade of many small droplets that have a large combined surface area (splash fill).
Recirculation - is a percentage of the hot, humid discharge air entering back into the inlet air stream thereby increasing the air inlet wet bulb temperature to a value higher than that of the ambient air condition.