[PDF] Staedy Conduction Heat Transferpdf




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[PDF] Heat transfer to or from a fluid flowing through a tube

Heat transfer in Flow Through Conduits The flow in a commercial circular tube or pipe is usually laminar when the Reynolds number is below 2,300

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The pipes were heated at a uniform rate, giving a constant temperature gradient along its axis, and the flow experienced both centrifugal and buoyancy forces ( 

[PDF] Theoretical and Numerical Analysis of Heat Transfer in Pipeline

14 déc 2013 · The heat transfer process includes the convection inside the pipe, the conduction through the pipe, and the convection outside the pipe The 

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Keywords: Heat flux, Mean temperature, Micropipe, Nusselt number, Thermal conductivity, Viscosity Introduction Liquid flow through micro ducts is used to 

[PDF] Staedy Conduction Heat Transferpdf

Consider steady conduction through a large plane wall of thickness ?x = L and Steady state heat transfer through pipes is in the normal direction to the 

[PDF] HEAT TRANSFER IN PIPE FLOW McGraw-Hill Education

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[PDF] Staedy Conduction Heat Transferpdf 127912_3StaedyConductionHeatTransfer.pdf M.BahramiENSC388(F09)SteadyConductionHeatTransfer1

SteadyHeatConduction

Inthermodynamics,weconsideredtheamountofheattransferasasystemundergoesa processfromoneequilibriumstatetoanother.Thermodynamicsgivesnoindicationof howlongtheprocesstakes.Inheattransfer,wearemoreconcernedabouttherateof heattransfer.

Thebasicrequirementforheattransferis

thepresenceofatemperaturedifference.The temperaturedifferenceisthedrivingforceforheattransfer,justasvoltagedifferencefor electricalcurrent.ThetotalamountofheattransferQduringatimeintervalcanbe determined from:kJdtQQ t 0 Therateofheattransferperunitareaiscalledheatflux,andtheaverageheatfluxona surfaceisexpressedas 2 /mWAQq

SteadyHeatConductioninPlaneWallsConductionisthetransferofenergyfromthemoreenergeticparticlesofasubstanceto

theadjacentlessenergeticonesasresultofinteractionsbetweentheparticles.

Considersteadyconduction

throughalargeplanewallofthicknessȴx=Landsurfacearea

A.ThetemperaturedifferenceacrossthewallisȴT=T

2 -T 1 . Notethatheattransferistheonlyenergyinteraction;theenergybalanceforthewallcan beexpressed:dtdEQQ wall outin

ForsteadyͲstateoperation,

.constQQ outin Ithasbeenexperimentallyobservedthattherateofheatconductionthroughalayeris proportionaltothetemperaturedifferenceacrossthelayerandtheheattransferarea, butitisinverselyproportionaltothethicknessofthelayer.WxTkAQCond thickness)difference eraturearea)(temp (surfacefer heat trans of rate M.BahramiENSC388(F09)SteadyConductionHeatTransfer2 

Fig.1:Heatconductionthroughalargeplanewall.

Theconstantproportionalitykisthethermalconductivityofthematerial.Inthelimiting casewhereȴxї0,theequationabovereducestothedifferentialform:

WdxdTkAQCond

whichiscalledFourier'slawofheatconduction.ThetermdT/dxiscalledthetemperature gradient,whichistheslopeofthetemperaturecurve(therateofchangeoftemperature

Twithlengthx).

ThermalConductivity

Thermalconductivityk[W/mK]isameasureofamaterial'sabilitytoconductheat.The thermalconductivityisdefinedastherateofheattransferthroughaunitthicknessof materialperunitareaperunittemperaturedifference. Thermalconductivitychangeswithtemperatureandisdeterminedthroughexperiments.

Thethermal

conductivityofcertainmaterialsshowadramaticchangeattemperatures nearabsolutezero,whenthesesolidsbecomesuperconductors. Anisotropicmaterialisamaterialthathasuniformpropertiesinalldirections. Insulatorsarematerialsusedprimarilytoprovideresistancetoheatflow.Theyhavelow thermalconductivity. A A

ȴxQ

• T 1 T 2 M.BahramiENSC388(F09)SteadyConductionHeatTransfer3

TheThermalResistanceConcept

TheFourierequation,forsteadyconductionthroughaconstantareaplanewall,canbe written:

LTTkAdxdTkAQ

Cond21

ThiscanbereͲarrangedas:

)/()( 12

WCkALRW

RTTQ wallwall Cond  x R wall isthethermalresistanceofthewallagainstheatconductionorsimplytheconduction resistanceofthewall. Theheattransferacrossthefluid/solidinterfaceisbasedonNewton'slawofcooling: )/(1WChARWTThAQ Convs R conv isthethermalresistanceofthesurfaceagainstheatconvectionorsimplythe convectionresistanceofthesurface.

ThermalradiationbetweenasurfaceofareaAatT

s andthesurroundingsatT ь canbe expressedas:
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