Heat Transfer and Fluid Flow Over a Flat Plate

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Heat Transfer and Fluid Flow Over a Flat Plate
MANE 4020 Fall 2005
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Fluid Problem Friction and Boundary layer
U0
U?
U(y)
d(x)
xo
Shear stress
U(x,0)0
Boundary layer thickness dy , U(y)/ U? 0.99
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Measurement of the Velocity Profile
U
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Skin Friction Coefficient
Skin Friction Correlations
Laminar flow
Turbulent flow
Skin Friction Measurement
From
(difficult to get u near to wall)
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Boundary layer models
1/7th Power Law
More exact expression
y ? 5
y ? 30
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Boundary layer models
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Convection Heat Transfer

• It quantifies the energy transfer between a fluid
  at one temperature flowing over a solid object at
  a different temperature.

• - q is the heat flux (J/s m2 W/m2)
• - DT is the difference between fluid temperature
  (in the freestream) and the solid wall
  temperature
• A is the surface area of the solid.
• q is the total heat transfer from a surface
  (Watts).

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Two common questions of any convective heat
transfer problem

• Given the distribution of surface temperature as
  a function of position along a surface, what is
  the distribution of local heat flux?
• Given the distribution of local surface heat flux
  as a function of position along a surface, what
  is the distribution of surface temperature?

Tfluid
Tsolid
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Fluid flow and heat transfer over flat plate - A
complex problem
Rex U? x/n is the criterion for the
Turbulent/Laminar Rexgt105 for the flat plate
flow Red gt2300, for the pipe flow
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Dimensionless heat transfer coefficient (Stanton
)
Laminar flow can be derived
Turbulent flow - experimental
h is the property of flow Pr is the property of
fluid
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St decreases with the increase of Re. St
increases when the flow becomes turbulent flow.
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Measurement of heat transfer coefficient (I)
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Measurement of heat transfer coefficient (II)
T?
T?
Rrad
Rconv
Tplate
Rcond
Tblack
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The plate is constructed of four layers of
materials Four, 2 in. wide Ni-Chrome heating
strips which are embedded in fiberglass and epoxy
resin 3/8 in. balsa wood 5/8 in.
plywood 1/8 in. plywood.
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Measurement of heat transfer coefficient (III)
Qo VI
h
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Structure of Wind Tunnel
Wind supply Blower /Fan (quantity supply)
Settling chamber (quality supply)
Honeycomb, Mesh Screen
To reduce turbulence
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