Question

A glass window 0.35 cm thick measures 61 cm by 36 cm. How much heat flows through this window per minute if the inside and outside temperatures differ by 17° C? in kJ/min

Answer 1

By Fourier's law
∆Q/∆t = kA∆T/∆x eq (1)

Thermal conductivity of glass k = 1.1 W/mK
The area of the window A = 0.61x0.36 = 0.2196m²
temperature difference is given as ∆T = 17°C = 273 + 17K = 290 K
Also thickness of the window ∆x = 0.35cm = 0.0035m

putting all the above values in eq (1)
we get , ∆Q/∆t = 1.1 Wm⁻¹K⁻¹ ∙ 0.2196m² ∙ 290 K / 0.0035m
∆Q/∆t= 20014.971 W
∆Q = 20014.971 x 60 J/ min

=1200898026 J/min or 1.2 MJ/min