The following terms are commonly used in cooling tower science, many of which are unique to the
cooling tower industry:

Packing — See "Fill".
Partition — An interior wall subdividing the tower into cells or into separate fan plenum chambers. Partitions may also be selectively installed to reduce windage water loss.
Performance — See "Capacity".
pH — A scale for expressing acidity or alkalinity of the circulating or make-up water. A pH below 7.0 indi-cates acidity and above 7.0 indicates alkalinity. A pH of 7.0 indicates neutral water.
Pitot Tube — An instrument that operates on the principle of differential pressures. Its primary use on a cooling tower is in the measurement of circulating water flow.
Plenum Chamber — The enclosed space between the drift eliminators and the fan in induced draft towers, or the enclosed space between the fan and the fill in forced draft towers.
Plume — The effluent mixture of heated air and water vapor (usually visible) discharged from a cooling tower.
Psychrometer — An instrument incorporating both a dry-bulb and a wet-bulb thermometer, by which si-multaneous dry-bulb and wet-bulb temperature read-ings can be taken.
Pump Head — See "Tower Pumping Head".
Range — Difference between the hot water temperature and the cold water temperature (HW - CW) Unit: °F.
Recirculation — Describes a condition in which a portion of the tower's discharge air re-enters the air inlets along with the fresh air. Its effect is an elevation of the average entering wet-bulb temperature compared to the ambient.
Riser — Piping which connects the circulating water supply line, from the level of the base of the tower or the supply header, to the tower's distribution system.
Shell — The chimney-like structure, usually hyperbolic in cross-section, utilized to induce air flow through a natural draft tower. Sometimes referred to as a "stack" or "veil".
Slowdown — Water discharged from the system to control concentrations of salts or other impurities in the circulating water. Units % of circulating water rate or gpm.
Speed Reducer — A mechanical device, incorporated between the driver and the fan of a mechanical draft tower, designed to reduce the speed of the driver to an optimum speed for the fan. The use of geared reduction units predominates in the cooling tower industry, although smaller towers will utilize differen-tail pulleys and V-belts for the transmission of relatively low power.
Splash Bar — One of a succession of equally-spaced horizontal bars comprising the splash surface of a fill deck in a splash-filled cooling tower. Splash bars may be flat, or may be formed into a shaped cross-section for improved structural rigidity and/or im-proved heat transfer capability. When flat, they are sometimes referred to as "slats" or "lath".
Splash-Filled — Descriptive of a cooling tower in which splash-type fill is used for the primary heat transfer surface.

Spray-Filled — Descriptive of a cooling tower which has no fill, with water-to-air contact depending entirely upon the water break-up and pattern afforded by pressure spray nozzles.
Stack — An extended fan cylinder whose primary pur-pose is to achieve elevation of the discharge plume. Also see "Fan Cylinder" and "Shell".
Stack Effect — Descriptive of the capability of a tower shell or extended fan cylinder to induce air (or aid in its induction) through a cooling tower.
Standard Air — Air having a density of 0.075 Ib per cu ft. Essentially equivalent to 70°F dry air at 29.92 in Hg barometric pressure.
Story — The vertical dimension between successive levels of horizontal framework ties, girts, joists, or beams. Story dimensions vary depending upon the size and strength characteristics of the framework material used. Unit: ft.
Sump — A depressed chamber either below or alongside (but contiguous to) the collection basin, into which the water flows to facilitate pump suction. Sumps may also be designed as collection points for silt and sludge to aid in cleaning.
Total Air Rate — Total mass flow of dry air per hour through the tower. Unit: Ib per hr. Symbol: G.
Total Water Rate — Total mass flow of water per hour through the tower. Unit: Ib per hr. Symbol: L
Tower Pumping Head — The static lift from the elevation of the basin curb to the centerline elevation of the distribution system inlet; plus the total pressure (converted to ft of water) necessary at that point to effect proper distribution of the water to its point of contact with the air. Unit: ft of water.
Transverse — Pertaining to occurrances in the direction of tower width.
Velocity Recovery Fan Cylinder — A fan cylinder on which the discharge portion is extended in height and outwardly flared. Its effect is to decrease the total head differential across the fan, resulting in either an increase in air rate at constant horsepower, or a decrease in horsepower at constant air rate.
Water Loading — Circulating water rate per horizontal square foot of fill plan area of the cooling tower. Unit: gpm per sq ft.
Water Rate — Mass flow of water per square foot of fill plan area of the cooling tower per hour. Unit: Ib per sq ft per hr. Symbol: L'.
Wet-Bulb Temperature — The temperature of the entering or ambient air adjacent to the cooling tower as measured with a wet-bulb thermometer. Unit: °F. Symbol: WB.
Wet-Bulb Thermometer — A thermometer whose bulb is encased within a wetted wick.
Windage — Water lost from the tower because of the effects of wind. Sometimes called "blowout".
Wind Load — The load imposed upon a structure by a wind blowing against its surface. Unit: lb per sq ft.