Question

What is the rate of energy loss in watt per square metre through a glass window 5 mm thick if outside temperature in -20 °C and inside temperature is 25 °C?

(k_glass = 1 W/m K)

Answer 1

k_glass = 1W/m K, T₁ = 25 °C, T₂ = -20 °C

T₁ – T₂ = 25- (-20)°C = 45 °C

X = 5 mm = 5 × 10^-3 m

As one degree celsius equates to one kelvin, temperature difference of 450 C equals 45 K.

To find: Rate of energy loss per square metre \((\frac{P_{cond}}{A})\)

Formula: P_cond = \(\frac{Q}{t}=KA\,\frac{T_1-T_2}{x}\)

Calculation: From formula,

∴ The energy loss per square metre,

= 9 × 103 W/m²

Rate of energy loss per square metre is 9 × 10³ W/m².