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Heat Transfer
Convection & Radiation
GATE 2009
Hard

For the same two parallel plates (plate 1 at 727°C, plate 2 at 227°C, plate 2 emissivity 0.7), if plate 1 is also a diffuse and gray surface with an emissivity value of 0.8, the net radiation heat exchange (in kW/m²) between plate 1 and plate 2 is

  • A17.0
  • B19.5
  • C23.0
  • 31.7

Explanation

For two large parallel gray plates: q12=σ(T1⁴-T2⁴)/(1/ε1+1/ε2-1)=5.67e-8×(1000⁴-500⁴)/(1/0.8+1/0.7-1)=53156.25/1.67857≈31666 W/m²≈31.7 kW/m².

Source: GATE ME 2009 (2009)

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