Heat Transfer and Fluid Flow Over a Flat Plate MANE 4020 Fall 2005.

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Presentation transcript:

Heat Transfer and Fluid Flow Over a Flat Plate MANE 4020 Fall 2005

 (x) U0U0 U(y) UU xoxo U(x,0)=0 Boundary layer thickness:  y  U(y)/ U  =0.99 Fluid Problem: Friction and Boundary layer Shear stress

Measurement of the Velocity Profile U

Laminar flow Turbulent flow Skin Friction Coefficient Skin Friction Correlations Skin Friction Measurement From: (difficult to get u near to wall)

Boundary layer models y +  30 y +  5 1/7th Power Law More exact expression

Boundary layer models

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 m 2 = W/m 2 )  T 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).

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? T fluid T solid

Fluid flow and heat transfer over flat plate - A complex problem  (x) U 0, T 0 U(x,y) T w (x) T  (x) U  (x)   (x) T(x,y) xoxo qwqw qwqw qwqw qwqw U(x,0)=0 Tw>Tinf Re x = U  * x/  is the criterion for the Turbulent/Laminar Re x >10 5 for the flat plate flow Re d >2300, for the pipe flow

h is the property of flow Pr is the property of fluid Laminar flow – can be derived Turbulent flow - experimental Dimensionless heat transfer coefficient (Stanton #)

St decreases with the increase of Re. St increases when the flow becomes turbulent flow.

Measurement of heat transfer coefficient (I) Q0Q0 Q convection Q radiation Q conduction

T black TT TT T plate R conv R rad R cond Measurement of heat transfer coefficient (II)

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.

Q o = VI h Measurement of heat transfer coefficient (III)

Structure of Wind Tunnel Wind supply: Blower /Fan (quantity supply); Settling chamber (quality supply) Honeycomb, Mesh Screen To reduce turbulence