Chapter hvac engineering Fundamentals: Part 1 Introduction

302
Chapter Nine
Air in
Water out
Tower fill
Water
sprays
Water
eliminator
Water in
Air out
Figure 9.14
Forced-draft cooling tower.
difference between the leaving cooling water temperature and the de-
sign ambient wet-bulb (wb) temperature. This is usually between 6
and 12
⬚
F, with 7 to 10
⬚
F being typical.
9.6.1
Open-circuit cooling towers
In Figs. 9.14, 9.15, and 9.16, there is only one water circuit, with a
portion of the cooling water being evaporated to cool the remainder.
Because the water is exposed to air, with all its contaminants, and
absorbs oxygen, which is corrosive to most piping, the water must be
carefully treated. To avoid increasing the concentration of solids as
water is evaporated, blowdown must be provided: A portion of the
water is wasted to the sewer, either continuously or intermittently. A
blowdown rate equal to the evaporation rate is common, but the blow-
down rate may be adjusted for the water quality. Ideally, treatment
additives and the blowdown rate should be controlled automatically
by a system which measures water quality and the solids concentra-
Equipment: Part 1
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