Heat%20Transfer%20OH%20Presentation

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Agenda

• Heat transfer review
• What is required to size a heat exchanger
• Compact heat transfer solutions
• Plate Heat Exchanger
• Spiral Heat Exchanger
• Welded Plate Heat Exchangers
• Specialty Plate Heat Exchangers
• Installation Photos
• Design of Heat Exchanger Solutions
• Order Flow Process

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Heat TransferBasics
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Three ways to transfer heat

• Radiation
• Electromagnetic waves
• When it reaches a body it has 3 options

Reflected
Absorbed
Transmitted

• Conduction
• Molecular or atomic vibrations
• No material transport

• Convection
• Energy is transferred by the motion and
  intermixing of small mass elements
• Natural convection caused by density difference
  
• Forced convection is man-made (ex., pump)

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Flow Principles

• Laminar
• Conduction low heat transfer rate
• Turbulent
• Convection high heat transfer rate
• Film layer at the wall - Conduction - Low
  heat transfer

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Data needed to design a heat exchanger

• Flows and temperatures for both sides
• Fluid properties including density, specific
  heat, thermal conductivity, and viscosity for at
  least two points.
• For condensers and evaporators data such as a
  condensing curve, boiling point elevation, and/or
  other parameters may be required.
• Process conditions and limitations such as
  system pressure, potential for fouling or
  plugging, pressure drop limitations etc.
• The supplier may be able to use their
  experience to assist in determining proper values
  from above.

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Heat Transfer
Q m Cp (T - T )
HI
HO

• Where
• Q heat transferred (Kbtu/hr)
• m mass flow rate (hot fluid) (lb/hr)
• C specific heat (hot fluid) (Btu/lb,F)
• T hot fluid entering temperature (F)
• T hot fluid leaving temperature (F)

p
HI
HO
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Thermodynamics at work!!
Q m Cp (T - T ) m Cp (T - T )
HI
HO
CO
CI
Temperature
Length of Channel
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Heat Transfer
Q U A (LMTD)

• Where
• Q heat transferred
• U overall heat transfer coefficient
• A heat transfer surface area
• LMTD log mean temperature difference

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Log Mean Temperature Difference
Temperature
Length of Channel
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Determining Heat Transfer Area
Q mCp(T T ) U A (LMTD)
HI
HO
Determining Proper U value is the key!!
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Items That Effect U value and Fouling Tendency

• Channel Geometry (turbulence)
• Fluid velocity and wall shear
• Fluid Properties (particularly viscosity)
• Viscosity also has a major impact on the
  pressure drop that will be seen in the
  heat exchanger

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Heat Flow
Hot Fluid
Fouling Layers
Cold Fluid
Metal
Temperature
Temperature
Temperature
Wall
Film Boundary Layers
1 U
1 h
1 h
t k
Rf



Q U A (LMTD)
and
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Heat Transfer Basics Three Wise Men
h
Nusselt Number
Prandtl Number
Reynolds Number
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Cocurrent Flow
Lower LMTD and no temperature cross means less
efficiency
Temperature
T
CO
Length of Channel