Page 212 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

210 Chapter 7 Industrial cooling systems

corrugated, honeycombed, or may have other patterns. Water spreads over it and forms a thin film in
contact with air. This provides maximum air-water interface.
Film fill is more efficient since it can result in significant power savings due to lower airflow re-
quirements. Nevertheless, its performance is affected in the case of mal-distribution of water. These
are chosen for applications where the circulating water is generally free of debris that could block the
fill passageways. Low-clog film fills with larger flute sizes are employed to handle water with high
turbidity. This is considered a preferred option over conventional splash type fills for seawater for
power savings and better performance.
Originally, cooling towers were constructed primarily with wood, including the frame, casing,
louvers, fill and cold-water basin. Sometimes the cold-water basin was made of
concrete. Today, manufacturers use a variety of materials to construct cooling
towers. Materials are chosen to enhance corrosion resistance, reduce mainte-
Tower material
nance and promote reliability and long service life. Galvanized steel, various
grades of stainless steel, glass fiber and concrete, are widely used in tower
construction and aluminum and plastics are adopted for some components. Frame and casing are
usually made of glass fiber, while PVC, polypropylene, and other polymers are widely used for fills.
When water conditions require the use of splash fill, treated wood splash fill is still used in wooden
towers, although plastic splash fill is mostly used. Nozzles are usually made of PVC, ABS, poly-
propylene and glass-filled nylon. Aluminum, glass fiber and hot-dipped galvanized steel are commonly
used fan materials. Centrifugal fans are often fabricated from galvanized steel. Propeller fans are made
from galvanized steel, aluminum, or molded glass fiber reinforced plastic.

7.2.3 Cooling tower parameters
The factors influencing the performance of the cooling tower are capacity, heat load, range, wet-bulb
temperature, approach temperature.
For a cooling tower intended to cool hot water received from the process plant at temperature T h

( C) to the cold water temperature T c ( C), at which it is returned to the plant, the parameters of interest
are described below. A diagrammatic representation showing the relationship between the various
parameters is depicted in Fig. 7.4.
Cooling range (R) is the difference between the inlet hot water (T h ) and outlet cold water tem-

perature (T c )in ð CÞ.

Rð CÞ¼ðT h T c Þ (7.1)
The range is decided not by the cooling tower but by the process it is serving.

FIGURE 7.4
Diagrammatic representation of the cooling tower
system and various parameters.