HeatTransfer-I-Section-1

gz m h ve2 gz cv cv i i e e i e dt 2 2

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Unformatted text preview: . € € •  T must be in Kelvin [K] RadiaUon Heat Transfer •  A “black body” emits thermal radiaUon according to: E b = σTs4 or E = εE b = εσTs4 •  A body also receives or absorbs thermal radiaUon according to (α is the absorpUvity): 4 € Gabs = αG = ασTsur € •  For a simple engineering surface where (ε = α) or a “grey surface” as it is called, we have: € q' 'rad = εE b − αG or 4 q' 'rad = εσ(Ts4 − Tsur ) •  Radiant exchange is generally more complex as we shall see later. There are surfaces where α ≠ ε . € € 16 RadiaUon Heat Transfer •  Radia6on Heat Transfer is the most complex mode of heat transfer. •  Thermal radiaUon can be absorbed, reflected, and transmiSed by a body. •  Thermal radiaUon is an electromagneUc wave phenomena similar to light. •  Surface properUes depend on spectral (wave length) and direcUonality (specular or diffuse) characterisUcs. •  Radiant exchange between surfaces can be quite complicated. •  Thermal radiaUon is a “line of sight” transfer process an...
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