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Two black surfaces, AB and BC, of length 5m and 6 m, respectively, are oriented as shown. Both surfaces extend infinitely into the third dimension. Given that view factor F12 = 0.5. T1 = 800 K, T2 = 600 K, Tsurrounding = 300 K and Stefan Boltzmann constant, a = 5.67 × 10-8 W/ (m2K4), the heat transfer rate from Surface 2 to the surrounding environment is _____kW.
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- 13.798
- 13.7
- 13.778
- 13.785
Correct Option: C
F12 = 0.5
T1 = 800 K, T2 = 600 K
Tsurrounding = 300 K
Let (3) denote the surrounding environment (Assume unit width perpendicular to plane of Fig.)
From summation rule:
F21 + F22 + F23 = 1
F21 + F23 = 1
∴ F22 = 0
or F23 = 1 – F21
A1 F12 = A2 F21 = 6 × 1 × 0.5
= (5 × 1) × F21
| F21 = | = 0.6 | 5 |
∴ F23 = 1 – F21 = 0.4
Since surrounding environment being large. No surface has a surface resistance
Heat transfer rate from (2) and (3)
| = | ||
| A2F23 |
| = | ||
| A2F23 |
| = | ||
| 5 × 1 × 0.4 |
= 13.778 kW/metre
Assume that heat exchange is per unit width perpendicular to plane of figure.
