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Unformatted text preview: Extended Surfaces Extended Surfaces Chapter Three Chapter Three Section 3.6 Section 3.6 Nature and Rationale Nature and Rationale Nature and Rationale of Extended Surfaces • An extended surface (also know as a combined conductionconvection system or a fin ) is a solid within which heat transfer by conduction is assumed to be one dimensional , while heat is also transferred by convection ( and/or radiation ) from the surface in a direction transverse to that of conduction. – Why is heat transfer by conduction in the x direction not , in fact , one dimensional? – If heat is transferred from the surface to the fluid by convection , what surface condition is dictated by the conservation of energy requirement? Nature and Rationale (Cont.) Nature and Rationale (Cont.) – What is the actual functional dependence of the temperature distribution in the solid? – If the temperature distribution is assumed to be onedimensional, that is, T=T(x) , how should the value of T be interpreted for any x location? – How does vary with x ? , cond x q – When may the assumption of onedimensional conduction be viewed as an excellent approximation? The thinfin approximation . • Extended surfaces may exist in many situations but are commonly used as fins to enhance heat transfer by increasing the surface area available for convection (and/or radiation). They are particularly beneficial when is small, as for a gas and natural convection. h • Some typical fin configurations: Straight fins of (a) uniform and (b) nonuniform cross sections; (c) annular fin , and (d) pin fin of nonuniform cross section. Fin Equation Fin Equation The Fin Equation • Assuming onedimensional, steadystate conduction in an extended surface...
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This note was uploaded on 02/21/2009 for the course MAE 310 taught by Professor Kuznetsov during the Spring '08 term at N.C. State.
 Spring '08
 Kuznetsov
 Heat Transfer

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