Direction: Radiative heat transfer is intercepted between the inner surfaces of two very large isothermal parallel metal plates. While the upper plate (designated as plate 1) is a black surface and is the warmer one being maintained at 727°C, the lower plate (plate 2) is a diffuse and gray surface with an emissivity of 0.7 and is kept at 227°C. Assume that the surfaces are sufficiently large to form a two-surface enclosure and steady-state conditions to exist. Stefan-Boltzmann constant is given as 5.67 × 10-8W/m2K4.
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The irradiation (in kW/m2) for the plate (plate 1) is
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- 2.5
- 3.6
- 17.0
- 19.5
Correct Option: D
T1 = 1000 K
T2 = 500 K
ε = 0.7
Energy indicent upon plate 1 due to irradiation = Radiosity of plate 2
Energy leaving surface 2 = E2 + (1– α 2) Eb1
E2 = εσT24 = 0.7 × 5.67 × 10–8 × 5004
= 2480.62 w/m2
σ (1– α) Eb1 = Fraction of energy reflected from surface 2
= (1–0.7) × 5.67×10–8 × 10004
= 17010 w/m2
∴ Total energy incident upon plate 1 = 19.49 kW/m2
