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Heat Exchangers

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Heat Exchangers Heat exchangers are used to transfer heat from one stream to another. They are used to heat streams and to cool streams. The streams can be heated or ... – PowerPoint PPT presentation

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Title: Heat Exchangers


1
Heat Exchangers
  • Heat exchangers are used to transfer heat from
    one stream to another. They are used to heat
    streams and to cool streams. The streams can be
    heated or cooled by other process streams, or
    they can be heated by steam and cooled by cooling
    water.
  • Design Constraints
  • Cost wish to have an exchanger that costs the
    least.
  • Efficiency wish to have an exchanger that
    operates most efficiently, with minimum loss of
    energy in the transfer, and minimum drop in
    pressure of the fluids.
  • Space wish to have an exchanger that is small.
  • Materials want an exchanger built from
    materials that are compatible with the process
    streams and dont cost a lot.
  • Maintenance want an exchanger that can be
    easily cleaned.
  • Ease of construction.

2
Heat Exchangers
  • Typical questions that chemical engineers might
    have about heat exchangers
  • What size heat exchanger do I need in a new
    process?
  • What type of heat exchanger do I need in a new
    process?
  • What are the heat transfer coefficients on the
    tube side and on the shell side?
  • Is an existing heat exchanger operating properly?
  • How much fouling can the exchanger withstand
    before the performance is degraded? How do I
    know if this has occurred with an operating heat
    exchanger?

3
Heat Exchangers
The driving force for the operation of a heat
exchanger is the temperature difference between
the fluids. The higher the temperature
difference, the smaller the heat exchanger.
However, the temperature difference is limited by
boiling points of the liquids, scaling, materials
of construction, etc. The proper design of a
heat exchanger is a trade-off of price and
performance.
Heat Exchangers Chapter 15 in McCabe et al.,
6th edition.
4
Heat Exchangers - Types
  • Heat exchangers come in many different types
  • Co-current.
  • Counter-current
  • Double pipe
  • Spiral
  • Finned
  • Compact
  • Shell and tube (most common in chemical process
    industries)

5
Heat Exchangers - Types
Co- and Counter- current The exchanger is
constructed of concentric tubes. One fluid
occupies the outer pipe, the other the
inner. Co-current fluids flow in same
direction Counter-current fluids flow in
opposite direction
Co-current
Counter-current
6
Heat Exchangers - Types
Double-Pipe A heat exchanger built from
concentric tubes. These are simple to construct,
but may require a lot of physical space to
achieve the desired heat transfer area. Can be
used for gases and liquids.
7
Heat Exchangers - Types
Double-Pipe Heat Exchanger in our UO Lab
8
Heat Exchangers - Types
Double-Pipe Heat Exchanger in our UO Lab
9
Heat Exchangers - Types
Spiral Constructed from sheets of metal wound
in a circular fashion. The fluids flow in
adjacent chambers between the sheets of metal.
This design is based on the ease of fabrication.
10
Heat Exchangers - Types
Spiral Heat Exchanger in our UO Lab
11
Heat Exchangers - Types
Finned contain fins on one heat exchange
surface to increase the heat exchange surface.
Heat registers is a home hot water heating system
is an example of this type.
12
Heat Exchangers - Types
Compact heat exchangers constructed from round
or square channels. Car radiator is an example
of this type.
13
Heat Exchangers - Types
Shell and Tube Most common in chemical process
industries. This type provides a large heat
transfer surface in a small space, can operate at
high pressures, are easy to clean and can be made
of a wide variety of materials.
1-1 Counter Current Exchanger (1-shell, 1 tube
pass)
14
Heat Exchangers - Types
Shell and Tube Heat Exchanger in our UO Lab
15
Heat Exchangers - Types
1-2 Heat Exchanger 1 shell pass, 2 tube passes.
16
Heat Exchangers - Types
2-4 Heat Exchanger 2 shell passes, 4 tube
passes.
17
Heat Exchangers - Temperatures
18
Heat Exchangers - Types
1 shell pass 2 tube passes
Shell and Tube Heat Exchanger cutaway in computer
lab
19
Heat Exchangers - Types
End detail in heat exchanger
20
Heat Exchangers - Types
21
Heat Exchangers Problems with Calculations
Temperature of fluid changes (possibly on shell
and tube side). Baffles and leakage around
baffles. Easy part is tube side use existing
correlations to determine heat transfer
coefficient. Difficult side is shell side as
fluid flows across the tubes.
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