Chemical Engineering - Heat Transfer - Discussion

Discussion Forum : Heat Transfer - Section 10 (Q.No. 39)
39.
The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C-1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m-2.°C-1. The rate of heat loss from the outer surface in W.m-2is
165.4
167.5
172.5
175
Answer: Option
Explanation:
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Discussion:
1 comments Page 1 of 1.

Shivaprasad said:   1 decade ago
(q/A) = h*(T-30) = (700-T)/(0.3/0.075).
Since K effective will be = 0.075.

Solve for T, => T = 38.271.
Therefore, q/A = 20*(38.271-30) = 165.4.
(1)

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