ame 60634 int. heat trans. d. b. go 1 different coordinate systems cartesian cylindrical spherical
DESCRIPTION
AME Int. Heat Trans. D. B. Go 3 Work Examples p1p1 p0p0 CM W [3] Boundary Displacement ΔzΔz work done by the control mass so it is energy lost boundary work Gas Expansion Strain (Compression/Expansion) CM1 F ΔzΔz work done to the control mass so it is energy gained boundary work (constant area)TRANSCRIPT
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AME 60634 Int. Heat Trans.
D. B. Go 1
Different Coordinate Systemscartesian
cylindrical
spherical
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AME 60634 Int. Heat Trans.
D. B. Go 2
Work Examples
F
CM
Δx[1] Sliding Block
work done to the control mass so it is energy gained
[2] Shear Work on a FluidBelt
tCM
Liquid Bath
W vx
work done to the control mass so it is energy gained
shear stress × speed × area
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AME 60634 Int. Heat Trans.
D. B. Go 3
Work Examples
p1
p0
CM
W
[3] Boundary Displacement
Δz
work done by the control mass so it is energy lost
boundary work
Gas Expansion
Strain (Compression/Expansion)
CM1
F
Δz
work done to the control mass so it is energy gained
boundary work(constant area)
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AME 60634 Int. Heat Trans.
D. B. Go 4
Work Examples[4] Shaft/Propeller
[5] Electrical Work (Heat Generation)
W
CMtorque × angular speed
work done to the control mass so it is energy gained
CM
+ -
W
Joule (or resistive or Ohmic) heating
work done to the control mass so it is energy gained
V
R
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AME 60634 Int. Heat Trans.
D. B. Go 5
Work Examples[6] Surface Tension
surface tension × area change
work done to the control mass so it is energy gained
Soapbubble
air
CM
straw
CM
movablewire
Soap filminside awire
ΔA
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AME 60634 Int. Heat Trans.
D. B. Go 6
Work Examples[7] Spring Compression
F
Δx
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AME 60634 Int. Heat Trans.
D. B. Go 7
EnthalpyWe can literally define a new specific property enthalpy as the summation of the internal energy and the pressure × volume (flow work)
Porter, 1922
Thus for open systems, the first law is frequently written as
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AME 60634 Int. Heat Trans.
D. B. Go 8
Heat Transfer• Heat Transfer is the transport of thermal energy due to a
temperature difference across a medium(s)– mediums: gas, liquid, solid, liquid-gas, solid-gas, solid-liquid, solid-solid,
etc.– Thermal Energy is simply the kinetic energy (i.e. motion) of atoms and
molecules in the medium(s)
• Atoms/molecules in matter occupy different states– translation, rotation, vibration, electronic– the statistics of these individual molecular-level activities will give us
the thermal energy which is approximated by temperature
• Heat Transfer, Thermal Energy, and Temperature are DIFFERENT. DO NOT confuse them.
• Heat generation (electrical, chemical, nuclear, etc.) are not forms of heat transfer Q but forms of work W– Q is the transfer of heat across the boundary of the system due to a
temperature difference
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AME 60634 Int. Heat Trans.
D. B. Go 9
Definitions
Thermal Energy
Temperature
Heat Transfer
Energy associated with molecular behavior of matter
U [J] – extensive propertyu [J/kg] – intensive property
Means of indirectly assessing the amount of thermal energy stored in matter
Quantity Meaning Symbol/Units
T [K] or [°C]
Thermal energy transport due to a temperature gradient (difference)
various
Heat
Heat Rate/Heat Flow
Heat Flux
Thermal energy transferred over a time interval (Δt > 0)
Thermal energy transferred per unit time
Thermal energy transferred per unit time per unit surface area
Heat Transfer
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AME 60634 Int. Heat Trans.
D. B. Go 10
Modes of Heat Transfer
• Conduction & convection require a temperature difference across a medium (the interactions of atoms/molecules)
• Radiation transport can occur across a vacuum