Acknowledgment This chapter is dedicated in memory of Dr. William Shuster, a former Chairman and Professor of Chemical and Environmental Engineering at the Rensselaer Polytechnic
Institute in Troy, New York, USA. Dr. Shuster mentored over 50 doctoral students from around the
world and was well-known in the field. The authors of this chapter salute Dr. Shuster for his lifelong
contributions to chemical engineering education.
Glossary
Approach The difference in temperatures of water temperature exiting the
tower vs. the dry bulb temperature of the air entering the tower. (ΔT, water
out vs. dry bulb air)
Basin The bottom of the tower, water is collected here after passing the tower.
Blow-down some of the water collected in the basin is exited from the tower rather
than recirculated within the tower. This prevents buildup of solids in the water.
(Note: the same term is used in wet scrubbing, as the objective is also the same.)
Cooling Range The temperature difference between hot water entering the tower
and cooled water exiting the tower.
Drift Also known as windage, small droplets of water, which are carried out of the
tower by the airflow, normally expressed as a % of total water flow rate.
Drift Eliminators Baffles, or other specialized collection products, placed in the air
exit path to capture water droplets. (Note, per the previous mention of scrubbing,
again, mist elimination in scrubbing is a similar application.)
Dry Bulb Temperature Air temperature, measured by standard means.
Heat Load Amount of heat exchanged within the tower between water and air,
expressed per unit of time. It can also be expressed as the product of the quantity
of water circulated within the tower per unit time and the cooling range.
Make-up Water Water that is added to the tower to replenish water losses due to
evaporation, drift, blow-down and other miscellaneous water losses.
Packing Also called fill, this is a product placed within the tower to promote
uniform water flow distribution and to enhance water-air contacts. (Note:
Again, note the similarity to wet scrubbing applications.)
Performance Normally expressed as the amount of cooling for a given quantity of
water at a given wet bulb temperature.
Relative Humidity The ratio of the partial pressure of water vapor in the air to the
vapor pressure of water at the temperature of the air, which contains the water
vapor.
Wet Bulb Temperature The temperature measured by an ordinary thermometer as
a thin film of water on the thermometer is evaporated into a surrounding air
stream. (Note: Recall the example earlier in this discussion of cooling in
Arizona vs. Florida – if the air surrounding the thermometer is already saturated
with water, no evaporation and hence no cooling of the water can take place. In
such an instance the wet and dry bulb temperatures are equal.)
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Institute in Troy, New York, USA. Dr. Shuster mentored over 50 doctoral students from around the
world and was well-known in the field. The authors of this chapter salute Dr. Shuster for his lifelong
contributions to chemical engineering education.
Glossary
Approach The difference in temperatures of water temperature exiting the
tower vs. the dry bulb temperature of the air entering the tower. (ΔT, water
out vs. dry bulb air)
Basin The bottom of the tower, water is collected here after passing the tower.
Blow-down some of the water collected in the basin is exited from the tower rather
than recirculated within the tower. This prevents buildup of solids in the water.
(Note: the same term is used in wet scrubbing, as the objective is also the same.)
Cooling Range The temperature difference between hot water entering the tower
and cooled water exiting the tower.
Drift Also known as windage, small droplets of water, which are carried out of the
tower by the airflow, normally expressed as a % of total water flow rate.
Drift Eliminators Baffles, or other specialized collection products, placed in the air
exit path to capture water droplets. (Note, per the previous mention of scrubbing,
again, mist elimination in scrubbing is a similar application.)
Dry Bulb Temperature Air temperature, measured by standard means.
Heat Load Amount of heat exchanged within the tower between water and air,
expressed per unit of time. It can also be expressed as the product of the quantity
of water circulated within the tower per unit time and the cooling range.
Make-up Water Water that is added to the tower to replenish water losses due to
evaporation, drift, blow-down and other miscellaneous water losses.
Packing Also called fill, this is a product placed within the tower to promote
uniform water flow distribution and to enhance water-air contacts. (Note:
Again, note the similarity to wet scrubbing applications.)
Performance Normally expressed as the amount of cooling for a given quantity of
water at a given wet bulb temperature.
Relative Humidity The ratio of the partial pressure of water vapor in the air to the
vapor pressure of water at the temperature of the air, which contains the water
vapor.
Wet Bulb Temperature The temperature measured by an ordinary thermometer as
a thin film of water on the thermometer is evaporated into a surrounding air
stream. (Note: Recall the example earlier in this discussion of cooling in
Arizona vs. Florida – if the air surrounding the thermometer is already saturated
with water, no evaporation and hence no cooling of the water can take place. In
such an instance the wet and dry bulb temperatures are equal.)
226
Y.-T. Hung et al.