POWER February 2016 - 35

HEAT EXCHANGERS
Innovative Heat Exchanger Technology
Enhances Proven Designs
They say you can't teach an old dog a new trick, but sometimes you can upgrade
your dog. Innovations, such as twisted tubes, expanded metal baffles,
graphene-coated surfaces, and more are improving heat exchanger
and condenser performance, making some upgrades worth considering.
Aaron Larson
S
hell-and-tube heat exchangers have
been around longer than anyone reading
this article. The heat exchanger
offers many advantages. It can be used in
condensing, boiling, or single-phase applications;
it can be utilized over a wide range
of pressures and temperatures; it can be constructed
from a variety of materials to meet
corrosion and other design requirements;
maintenance is fairly simple and straightforward;
and it can accommodate various physical
orientations.
However, there are some limitations to the
design. The conventional shell-and-tube heat
exchanger contains baffles on the shell side
to provide support and direct flow through a
circuitous course across the tubes. The downside
is that low-flow areas, or dead zones,
result in the vicinity of the baffles where fouling
can occur, corrosion can go unchecked,
and heat transfer is reduced. The directional
changes caused by the baffles also consume
energy, and the shell-side pressure decrease
can be significant. The classic design is also
prone to flow-induced tube vibration, which
can ultimately result in failure.
Reinventing Heat Transfer
With these problems in mind, it's not surprising
that engineers have continued to
conduct research to enhance the shell-andtube
design, resulting in new technology
that improves heat exchanger performance,
counteracts fouling problems, saves space,
reduces cost, and increases efficiency. One
group that is leading the way in this effort is
Heat Transfer Research Inc. (HTRI).
Based in Navasota, Texas, HTRI is a research
and software development company
that tests various exchanger types and heat
transfer surfaces. Its staff conducts application-oriented
research on equipment and
uses these proprietary data to develop methods
and software for the thermal design and
analysis of heat exchangers and fired heatFebruary
2016 | POWER
www.powermag.com
35
ers. Its research includes physical testing,
computational fluid dynamics, and flow
visualization.
" HTRI has and continues to investigate
new commercialized exchanger types such as
plate and shell or helical baffle exchangers, "
said Joe Schroeder, senior vice president of
technical programs for HTRI.
In the helical baffle heat exchanger that
Schroeder mentioned, quadrant-shaped plate
baffles are placed at an angle to the tube axis
in a sequential arrangement to create a helical
flow pattern. The helical flow design improves
thermal effectiveness, enhances heat
transfer, reduces pressure loss, lessens fouling,
and significantly reduces vibration concerns.
One manufacturer of the helical style,
CB&I, says the design is well proven with
more than 1,800 of its HELIXCHANGER
heat exchangers in operation worldwide.
Expanded Metal Baffles
In addition to the helical baffle design,
Schroeder noted that expanded metal baffles
are also revolutionizing the industry.
The design-patented by EMbaffle B.V., a
group company of Italy-based Brembana &
Rolle-features an expanded metal baffle
grid made of plate material that has been
slit and expanded (Figure 1). The expanded
metal baffles create an open flow structure,
allowing longitudinal flow on the shell side,
which reduces pressure loss in the heat exchanger.
1.
Expanding on an idea. Expanded metal is used in many power plant applications, but
running tubes through the diamond-shaped voids in a heat exchanger is a fairly recent development.
Courtesy: EMbaffle B.V.

http://www.powermag.com

POWER February 2016

Table of Contents for the Digital Edition of POWER February 2016