heat transfer review what is required to size a heat exchanger compact heat transfer solutions
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
9/2003
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• Heat transfer reviewHeat transfer review• What is required to size a heat exchangerWhat is required to size a heat exchanger• Compact heat transfer solutionsCompact heat transfer solutions
– Plate Heat ExchangerPlate Heat Exchanger– Spiral Heat ExchangerSpiral Heat Exchanger– Welded Plate Heat ExchangersWelded Plate Heat Exchangers– Specialty Plate Heat ExchangersSpecialty Plate Heat Exchangers
• Installation PhotosInstallation Photos• Design of Heat Exchanger SolutionsDesign of Heat Exchanger Solutions• Order Flow ProcessOrder Flow Process
Agenda
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Heat TransferHeat TransferBasicsBasics
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• RadiationRadiation– Electromagnetic wavesElectromagnetic waves
– When it reaches a body it has 3 options:When it reaches a body it has 3 options:
Reflected
Absorbed
Transmitted
• ConvectionConvection– Energy is transferred by the motion and Energy is transferred by the motion and
intermixing of small mass elementsintermixing of small mass elements
– Natural convection caused by density difference Natural convection caused by density difference
– Forced convection is man-made (ex., pump)Forced convection is man-made (ex., pump)
• ConductionConduction– Molecular or atomic vibrationsMolecular or atomic vibrations
– No material transportNo material transport
Three ways to transfer heatThree ways to transfer heat
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• LaminarLaminar– Conduction: low heat transfer rateConduction: low heat transfer rate
• TurbulentTurbulent– Convection: high heat transfer rateConvection: high heat transfer rate– Film layer at the wallFilm layer at the wall - - ConductionConduction
- - Low heat transferLow heat transfer
Flow PrinciplesFlow Principles
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• 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.
Data needed to design a heat exchanger
9/2003
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9/2003
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• WhereWhereQ = heat transferred (Kbtu/hr)Q = heat transferred (Kbtu/hr)
m = mass flow rate (hot fluid) (lb/hr)m = mass flow rate (hot fluid) (lb/hr)
C = specific heat (hot fluid) (Btu/lb,F)C = specific heat (hot fluid) (Btu/lb,F)
T = hot fluid entering temperature (F)T = hot fluid entering temperature (F)
T = hot fluid leaving temperature (F)T = hot fluid leaving temperature (F)HHII
HHOO
pp
HHII HHOOQ = m CQ = m Cpp (T - T ) (T - T )
Heat Transfer
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TTHHII
TT HHOO
TT CCOO
TTCCII
Tem
pera
ture
Tem
pera
ture
Length of ChannelLength of Channel
HHII HHOO CCOO CCIIQ = m CQ = m Cpp (T - T ) = m C (T - T ) = m Cpp (T - T ) (T - T )Thermodynamics at work!!
9/2003
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• WhereWhereQ = heat transferredQ = heat transferred
U = overall heat transfer coefficientU = overall heat transfer coefficient
A = heat transfer surface areaA = heat transfer surface area
LMTD = log mean temperature differenceLMTD = log mean temperature difference
Q = U A (LMTD)Q = U A (LMTD)
Heat TransferHeat Transfer
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(T -T ) - (T - T )(T -T ) - (T - T )HHII CCOO HHOO CCII
(T -T )(T -T )HHII CCOO
(T -T )(T -T )HHOO CCII
lnln
LMTD =LMTD =
TTHHII
TTHHOO
TTCCOO
TTCCII
Tem
pera
ture
Tem
pera
ture
Length of ChannelLength of Channel
Log Mean Temperature Difference
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Q = mCp(T – T ) = U A (LMTD) = U A (LMTD)HHII HHOO
Determining Heat Transfer Area
m C (T - T )m C (T - T )
U (LMTD)U (LMTD)HHII HHOOPP
A =A =
Therefore
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
TubeTube SpiralSpiral PlatePlate
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Hot Fluid Fouling Layers Cold Fluid
Metal
Wall
Film Boundary Layers
TemperatureTemperature
TemperatureTemperature
TemperatureTemperature
Q = U A (LMTD)Q = U A (LMTD)
Heat Flow
11UU
11hh
+ Rf+ Rf11hh
ttkk
++++==and
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Nu Pr B Rey n
NuDh
vDRe
Pr Cp
Nusselt NumberNusselt Number
Prandtl NumberPrandtl Number
Reynolds NumberReynolds Number
h
Heat Transfer Basics – Three Wise MenHeat Transfer Basics – Three Wise Men
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TTHHII
TTHHOO
TTCCOO
TTCCII
Tem
pera
ture
Tem
pera
ture
Length of ChannelLength of Channel
Lower LMTD and no temperature cross means
less efficiency
Cocurrent FlowCocurrent Flow