Determine the heat transfer through a plane of length 4 m, height 3 m and thickness 0.2 m. The temperatures of inner and outer surfaces are 150°C and 90°C respectively. Thermal conductivity of the wall is 0.5 W/mK.

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ESE Mechanical 2015 Paper 1: Official Paper
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  1. 1800 W
  2. 2000 W
  3. 2200 W
  4. 2400 W

Answer (Detailed Solution Below)

Option 1 : 1800 W
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ST 1: UPSC ESE (IES) Civil - Building Materials
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20 Questions 40 Marks 24 Mins

Detailed Solution

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Concept:

By Fourier’s law of heat conduction

\(Q = \; - kA\frac{{dT}}{{dx}}\)

k = thermal conductivity (W/m-k), A = area of cross section (m2), dT is temperature difference between the two ends of plate and dx is the thickness of the plate

Calculation:

Given, k = 0.5 W/mK, length = 4 m height = 3 m, dx = 0.2 m, T1 = 150°C and T2 = 90°C,

A = 3m × 4 m = 12 m2

dT = 90 -150 = -60°C 

\(Q = - kA\frac{{dT}}{{dx}} =- 0.5 × 12 × \frac{{\left( { - 60} \right)}}{{0.2}} = 1800\;W\)

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