class 6 - Extended Surfaces Chapter Three Section 3.6 How...

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Unformatted text preview: Extended Surfaces Chapter Three Section 3.6 How is heat transfer enhanced? Assume T s is fixed. Computer chip = lots of heat generated Increase h-Higher fluid velocity, lower fluid temperature Increase surface area-Add extended surface, usually easier and cheaper 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 useful when h is small. Straight fins of (a) uniform and (b) non-uniform cross sections; (c) annular fin , and (d) pin fin of non-uniform cross section. Extended Surfaces = Conduction within boundary + Convection between boundary and surroundings Assume: h and k are constant steady state negligible radiation no heat generation What is the energy balance for this system? a) b) c) d) e) g out in st E E E E +- = out in st E E E - = out in E E - = g in E E + = g out E E + = Assume: h and k are constant steady state negligible radiation no heat generation What is E in ?...
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class 6 - Extended Surfaces Chapter Three Section 3.6 How...

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