The Family of Shell and Tube Heat Exchangers

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The Family of Shell and Tube Heat Exchangers

• P M V Subbarao
• Professor
• Mechanical Engineering Department
• I I T Delhi

Family members with Simple Geometrical Features
for Complex Fluid Flow.
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Fixed tube sheet
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U-Tube STHE
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Floating Head STHE TEMA S
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Floating Head STHE TEMA T
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Cross Baffles

• Baffles serve two purposes
• Divert (direct) the flow across the bundle to Wet
  the the maximum tube surface area.
• Support the tubes for structural rigidity,
  preventing tube vibration and sagging.
• When the tube bundle employs baffles,
• The heat transfer coefficient is higher than the
  coefficient for undisturbed flow around tubes
  without baffles.
• For a baffled heat exchanger the higher heat
  transfer coefficients result from the increased
  turbulence.
• the velocity of fluid fluctuates because of the
  constricted area between adjacent tubes across
  the bundle.
• This also leads to developing flow for ever.

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Avoid Developed Flow
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Types of Baffle Plates Segmental Cut Baffles

• The single and double segmental baffles are most
  frequently used.
• They divert the flow most effectively across the
  tubes.
• The baffle spacing must be chosen with care.
• Optimal baffle spacing is somewhere between 40 -
  60 of the shell diameter.
• Baffle cut of 25-35 is usually recommended.

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Types of Baffle Plates
The triple segmental baffles are used for low
pressure applications.
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Types of Baffle Plates
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Types of Baffle Plates
Disc and ring baffles are composed of alternating
outer rings and inner discs, which direct the
flow radially across the tube field. The
potential bundle-to-shell bypass stream is
eliminated This baffle type is very effective
in pressure drop to heat transfer conversion
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Types of Baffle Plates
In an orifice baffle shell-side-fluid flows
through the clearance between tube outside
diameter and baffle-hole diameter.
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Thermal Analysis of Heat Exchanger

• Known as heat exchanger specification problems
  and their solutions.
• These are rating, design, and selection.

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Rating Analysis

• The rating problem is evaluating the
  thermo-hydraulic performance of a fully specified
  exchanger.
• The rating program determines
• the heat transfer rate and the fluid outlet
  temperatures for prescribed fluid flow rates,
  inlet temperatures, and
• the pressure drop for an existing heat exchanger
  
• therefore the heat transfer surface area and the
  flow passage dimensions are available.

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The Rating Analysis
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The Design (Sizing) Analysis

• Design is the process of determining all
  essential constructional dimensions of an
  exchanger that must perform a given heat duty and
  respect limitations on shell-side and tube-side
  pressure drop.
• In the Design (sizing) Analysis,
• An appropriate heat exchanger type is selected.
• The size to meet the specified hot and cold fluid
  inlet and outlet temperatures, flow rates, and
  pressure drop requirements, is determined.
• Constraints
• Minimum or maximum flow velocities,
• Size and/or weight limitations,
• Ease of cleaning and maintenance, erosion, tube
  vibration, and thermal expansion.
• Each design problem has a number of potential
  solutions, but only one will have the best
  combination of characteristics and cost.

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Basic Design Procedure
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Basic Design Procedure

• Heat exchanger must satisfy the Heat transfer
  requirements (design or process needs)
• Allowable pressure drop (pumping capacity and
  cost)
• Steps in designing a heat exchanger can be listed
  as
• Identify the problem
• Select an heat exchanger type
• Calculate/Select initial design
• parameters
• Rate the initial design
• Calculate thermal performance and pressure drops
  for shell and tube side.
• Evaluate the design.
• Is performance and cost acceptable?

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The Selection Analysis

• Selection means choosing a heat exchanger from
  among a number of units already existing.
• Typically, these are standard units listed in
  catalogs of various manufacturers.
• Sufficient manufacturers data usually exist to
  allow one to select comfortably oversized
  exchanger with respect to both area and pressure
  drop.