The glass windows of a room have a total area of 10 m² and the glass is 4 mm thick. The quantity of heat that escapes from the room by conduction per second when the inside surface of the windows is 25°C and the outside surfaces are at 10°C is-

(The value of k is 0.84 W/mK)

Question

Question

This question was previously asked in

BDL MT Mechanical 16 April 2022 Official Paper

Answer 1

Concept: $Q = \frac{k A (T_{1} - T_{2})}{L}$

From Fourier's Law of Heat Transfer:

$Q = \frac{kA(T_1-T_2)}{L}$

where Q = Amount of Heat Transfer, k = Thermal Conductivity, L = Thickness of Wall, T1, T2 = Initial and Final Temperature respectively

Calculation:

Given:

k = 0.84 W/m-K, L = 4 mm = 0.004 m, T1 = 25°C , T2 = 10°C, A = 10 m2 $q = \frac{Q}{A} = \frac{0.75 \times (980 - 460)}{0.4}$

$Q = \frac{(0.84)(10)(25-10)}{0.004}$

Q = 31.5 kJ

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