heating water

Figure 2-7
fluid 1
leakage path opening
outer wall
leakage path
inner wall
tank jacket
tank insulation
pressure vessel wall
fluid 1
fluid 2
helical coil double
wall heat exchanger
leakage path opening
Courtesy of HydroFlex Systems
Figure 2-8
heat
input
air
space
warmed
water
rising
cooled
water
descending
vent
heat
extraction
convection conditions between the
outer surface of each coil and the
tank water. In general, it’s desirable
to reduce or eliminate any thermal
penalty between the heat source and
the load. This is especially true for
heat sources that require relative low
operating temperatures to attain high
efficiency.
In some applications, multiple
submerged coil heat exchangers
are used to increase the total heat
transfer area. Figure 2-9 shows an
example of multiple copper coil heat
exchangers connected in parallel to
header piping.
Another approach is to “co-wind”
multiple copper tubes into a single
helical coil, as shown in Figure 2-10.
This provides additional surface area
while greatly reducing pressure drop
relative to a single coil of the same
total surface area. The individual coils
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