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Radiation Exchange EGR 4345 Heat Transfer

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Blackbody Radiation Exchange

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Rate at which radiation leaves surface i and is intercepted by surface j For a black surface, J i = E bi Net radiative exchange

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Blackbody Radiation Exchange Therefore Or Net radiation transfer from any surface in an enclosure of black surfaces

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Net Radiation Exchange at a Surface in an Enclosure

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Assumptions – Isothermal surfaces, T i is known – Uniform radiosity – Uniform irradiation – Opaque – Diffuse – Gray surface – Medium in enclosure is nonparticipating

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Net Radiation Exchange at a Surface in an Enclosure Determine the net rate at which radiation leaves surface i Where In terms of emissive power and absorbed radiation

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Net Radiation Exchange at a Surface in an Enclosure For an opaque, diffuse, gray surface Solve for G i and substitute into q i Or Driving Potential Surface Radiative Resistance

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Net Radiation Exchange Between Surfaces in an Enclosure

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Total rate at which radiation reaches surface i from all surfaces, including i Reciprocity Substituting in for G i

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Net Radiation Exchange Between Surfaces in an Enclosure Summation rule Therefore Or Use matrix operations to solve Space or Geometric Resistance

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Net Radiation Exchange in a Two-Surface Enclosure Two diffuse, gray surfaces that form an enclosure

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Net Radiation Exchange in a Two-Surface Enclosure General Equation Special equations

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Radiation Shields General Equation Low emissivity increase resistance

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Reradiating Surface Zero net radiation, q i = 0

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Reradiating Surface

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RADIATION IN ENCLOSURES WITH SOME SPECULARLY REFLECTING SURFACES Exchange Factor Net Radiation Method Curved Specularly Reflecting Surfaces.

RADIATION IN ENCLOSURES WITH SOME SPECULARLY REFLECTING SURFACES Exchange Factor Net Radiation Method Curved Specularly Reflecting Surfaces.

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