Download - HT Cengel Chapter 3 - Mazlan 2016
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HEAT
TRANS
SKMM 3443
CCHH
AA
SFER
LECTURER: ASSOC PROF. DR. MAZLAN ABDUL WAHIDhttp://www.fkm.utm.my/~mazlan
HEAT TRANSFERHEAT TRANSFER
AA
PP
TT
EE
RR
33DrDr Mazlan 2016Mazlan 2016
TEXT: Heat and Mass TransferFundamental and Applications, 5th Edition by Cengel & GhajarMc Graw Hill
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HEAT
TRANS Steady Heat Conduction
CCHH
AA
SFER
ASSOC. PROF. DR. MAZLAN ABDUL WAHIDC24-333
Steady Heat Conduction
AA
PP
TT
EE
RR
33DrDr Mazlan 2016Mazlan 2016
2
2
07-5534766
Towards an Entrepreneurial University
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Recap
• Generalized heat conduction equation may include:
– 3-D conduction– 3-D conduction
– Transient
– Heat generation
– Different coordinate system
• Conduction can be simpler:
– 1-D conduction– 1-D conduction
– Steady
– No heat generation
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One dimensional steady conduction
Thermal Contact Thermal
resistance
Contact
resistance
Conduction Fins (Extended
Conduction
with heat
generation
Fins (Extended
surface)
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Thermal resistance Contact resistance Heat generation Fins
One dimensional analysis
• Multi-dimensional conduction analysis is
complexcomplex
• Hard to determine temperature profile
• One-dimensional for the accurate engineering
analysis
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Thermal resistance Contact resistance Heat generation Fins
The plane wall
• 1-D (x-axis)
• Hot and cold fluid on • Hot and cold fluid on different sides
• No heat generation
• Convection from hot fluid to wall
• Conduction through • Conduction through wall
• Convection from wall to cold fluid
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Thermal resistance Contact resistance Heat generation Fins
Temperature distribution
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Thermal resistance Contact resistance Heat generation Fins
Temperature distribution
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Thermal resistance Contact resistance Heat generation Fins
Boundary conditions
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Thermal resistance Contact resistance Heat generation Fins
Thermal resistance
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Thermal resistance Contact resistance Heat generation Fins
Thermal resistance
Electrical analogy
Electrical Thermal circuit
Electrical
circuit
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Thermal resistance Contact resistance Heat generation Fins
Thermal resistance
Conductive
resistance
Convective
resistanceRadiative
resistanceresistance resistance resistance
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Thermal resistance Contact resistance Heat generation Fins
Thermal Resistance for plane wall
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Thermal resistance Contact resistance Heat generation Fins
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Thermal resistance Contact resistance Heat generation Fins
Composite wall
Express the following geometry in terms of an equivalent thermal circuit
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Thermal resistance Contact resistance Heat generation Fins
Composite wall
1
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Thermal resistance Contact resistance Heat generation Fins
Composite wall
What is the heat transfer rate
for this system?for this system?
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Thermal resistance Contact resistance Heat generation Fins
Composite wall
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Thermal resistance Contact resistance Heat generation Fins
Parallel thermal resistance
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Thermal resistance Contact resistance Heat generation Fins
Generalized thermal resistance
Draw thermal resistance
network for this circuitnetwork for this circuit
Work out the heat transfer
rate as a function of
temperatures and thermal
resistance
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Thermal resistance Contact resistance Heat generation Fins
Generalized thermal resistance
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Thermal resistance Contact resistance Heat generation Fins
Cylindrical coordinates
Hollow cylinder with different thermal conditions at the
inner and outer surfaces
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Thermal resistance Contact resistance Heat generation Fins
Cylindrical coordinates
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Thermal resistance Contact resistance Heat generation Fins
Spherical coordinates
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Thermal resistance Contact resistance Heat generation Fins
Problem 3-77
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Thermal resistance Contact resistance Heat generation Fins
Contact resistance
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Thermal resistance Contact resistance Heat generation Fins
Contact resistance
• Rough surface
produces air produces air
pockets
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Thermal resistance Contact resistance Heat generation Fins
Thermal contact conductance
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Thermal resistance Contact resistance Heat generation Fins
Thermal contact resistance
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Thermal resistance Contact resistance Heat generation Fins
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Thermal resistance Contact resistance Heat generation Fins
Problem 3-49
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Thermal resistance Contact resistance Heat generation Fins
Problem 3-49
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Thermal resistance Contact resistance Heat generation Fins
Problem 3-49
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Thermal resistance Contact resistance Heat generation Fins
Problem 3-49
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Thermal resistance Contact resistance Heat generation Fins
Conduction with heat generation
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Thermal resistance Contact resistance Heat generation Fins
Conduction with heat generation
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Thermal resistance Contact resistance Heat generation Fins
Plane wall
• One dimensional
• Steady state• Steady state
• Constant thermal
conductivity
• Uniform heat
generation
• Asymmetric surface • Asymmetric surface
condition
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Thermal resistance Contact resistance Heat generation Fins
Plane wall
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Thermal resistance Contact resistance Heat generation Fins
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Thermal resistance Contact resistance Heat generation Fins
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Thermal resistance Contact resistance Heat generation Fins
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Thermal resistance Contact resistance Heat generation Fins
Symmetrical Distribution
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Thermal resistance Contact resistance Heat generation Fins
Symmetrical Distribution
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Thermal resistance Contact resistance Heat generation Fins
Adiabatic surface
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Thermal resistance Contact resistance Heat generation Fins
Example
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Thermal resistance Contact resistance Heat generation Fins
Example
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Thermal resistance Contact resistance Heat generation Fins
Extended surface (fins)
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Thermal resistance Contact resistance Heat generation Fins
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Thermal resistance Contact resistance Heat generation Fins
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Thermal resistance Contact resistance Heat generation Fins
Extended surface (fins)
• Combined effect of
conduction + conduction +
convection (and
radiation)
• Heat transfer direction
transverse to that of
conductionconduction
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Thermal resistance Contact resistance Heat generation Fins
Types of fins
Uniform
cross section
Non-uniform
cross section
Annular
cross sectionPin fin
Uniform
cross section
Non-uniform
cross section
Annular
cross sectionPin fin
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Thermal resistance Contact resistance Heat generation Fins
Steady heat conduction
Increase
heat heat
transfer
rate
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Thermal resistance Contact resistance Heat generation Fins
Fin equation
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Thermal resistance Contact resistance Heat generation Fins
Fin equation
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Thermal resistance Contact resistance Heat generation Fins
Fin equation
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Thermal resistance Contact resistance Heat generation Fins
Tip boundary conditions
Infinitely Negligible Infinitely
long fin
Negligible
heat loss
Specified Specified
temperatureConvection
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Thermal resistance Contact resistance Heat generation Fins
Infinitely long fin
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Thermal resistance Contact resistance Heat generation Fins
Infinitely long fin
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Thermal resistance Contact resistance Heat generation Fins
Negligible heat loss
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Thermal resistance Contact resistance Heat generation Fins
Negligible heat loss
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Thermal resistance Contact resistance Heat generation Fins
Specified temperature
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Thermal resistance Contact resistance Heat generation Fins
Specified temperature
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Thermal resistance Contact resistance Heat generation Fins
Convective
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Thermal resistance Contact resistance Heat generation Fins
Corrected fin length
Rectangular fin
Cylindrical fin