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INTERIOR DESIGN: The picture above shows the interior
of a typical Section. Integrally-cast longitudinal fins are
interrupted by swirl strips for higher heat transfer efficiency.
Advantages of this design are:
- More heat transfer surface is in contact with the process
fluid within the Sections where it is normally most needed.
- Relationship between the various factors influencing heat
transfer is improved by the use of fins and swirlers. The
equivalent diameter is reduced compared to the cross section
area because of the fins. Turbulent flow characteristics are
maintained under virtually all conditions because of the effect
of the swirlers which not only induce a turbulent action,
but also have a beneficial reducing effect on the L/d Ratio
resulting in a higher heat transfer rate. This turbulence
also has a definite effect on keeping the interior of the
Sections scrubbed clean.
- True radii of return bends produce gradual change in direction
of flow of fluid, minimizing the effects of erosion and decreasing
pressure drop.
- Several types of Sections with various thermal design characteristics
are available, making possible an installation effecting optimum
balance between heat transfer and pressure drop.
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EXTERNAL DESIGN: The exterior of the Sections is planned
for maximum efficiency and minimum maintenance, for sprayed
or submerged service. Various factors influencing the design
are:
- The smooth surface in contact with the cooling water presents
less opportunity for heavy scaling or growths. Maintenance
labor for keeping these surfaces clean is greatly reduced,
compared with other types of equipment using lugs or fins
on the exterior.
- To provide maximum water utilizations when operating in
sprayed service, small collector ribs are provided at the
top and bottom of the Sections. These enable the cooling water
to form a thin, cohesive film with its own surface tension.
This curtain of water is passed from one Section to another
with a minimum of splashing and consequent water wastage.
- The relatively close vertical spacing between the Sections
helps to maintain the water film uniformly over the Section.
A unit consisting of several closely spaced stacks of Sections
acts virtually as its own wind break. This provides maximum
water utilization. It also reduces corrosion, because the
metal is kept in a constantly wetted state. On other types
of cascade cooling equipment where alternate wetting and drying
is inherent, corrosion rates tend to become accelerated. In
addition, these other types require extensive supporting structures
and take up much more ground space for catch basin area.
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This
actual photograph of a cut-open portion of a AX Section
shows the internal ribs and swirler fins.