Radiation Exchange EGR 4345 Heat Transfer

Blackbody Radiation Exchange

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

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

Net Radiation Exchange at a Surface in an Enclosure

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

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

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

Net Radiation Exchange Between Surfaces in an Enclosure

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

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

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

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

Radiation Shields General Equation Low emissivity increase resistance

Reradiating Surface Zero net radiation, q i = 0

Reradiating Surface