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A stainless steel tube (ks = 19 W/mK) of 2 cm ID and 5 cm OD is insulated with 3 cm thick asbestos (ka = 0.2 W/mK). If the temperature difference between the inner most and outermost surfaces is 600°C, the heat transfer rate per unit length is
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- 0.94 W/m
- 9.44 W/m
- 944.72 W/m
- 9447.21 W/m
Correct Option: C
Given: d1 = 2 cm
r1 = 1 cm
d2 = 5 cm
r2 = 2.5 cm
d3 = 5 + 2 × 3 = 11
r3 = 5.5 cm
Equivalent thermal resistance
| Rt = | In | + | In | |||||
| 2πkst | r1 | 2πka | r2 |
| = | In | + | In | |||||
| 2π × 19 | 1 | 2π × 0.2 | 2.5 |
= 7.67 × 10–3 + 0.627 = 0.635
∴ Heat transfer rate per unit length
| = | = 944.88 W/m | |||
| Rt | 0.635 |
