Question

Some properties of glass are listed here.
Density: 2300 kg/m³
Specific heat: 840 J/kg·C°
Coefficient of linear thermal expansion: 8.5 × 10^-6 (C°)^-1
Thermal conductivity: 0.80 W/(m·C°)
A glass window pane is 2.2 m high, 1.9 m wide, and 2.0 mm thick. The temperature at the inner surface of the glass is 14°C and at the outer surface 4.0°C. How much heat is lost each hour through the window under steady state conditions?

Some properties of glass are listed here.
Density: 2300 kg/m³
Specific heat: 840 J/kg·C°
Coefficient of linear thermal expansion: 8.5 × 10^-6 (C°)^-1
Thermal conductivity: 0.80 W/(m·C°)
A glass window pane is 2.2 m high, 1.9 m wide, and 2.0 mm thick. The temperature at the inner surface of the glass is 14°C and at the outer surface 4.0°C. How much heat is lost each hour through the window under steady state conditions?

1- 6×10⁴ J

2- 6×10⁷ J

3- 1.7×10⁴ J

4- 6×10⁵ J

5- 17 J

Answer 1

The rate of heat conduction (in W = J/s) is given by .. dH/dt = k A ∆θ/x .. (k= thermal conductivity, A = Area perp. to heat flow, ∆θ = temperature difference, x = material thickness) dH/dt = 0.80*(2.20m*1.90m)*(14 - 4)º / 0.002m = 16 720 J/h For 1hr .. heat loss = 16 720 J/s x 3600s .. .. ►H = 6.02*10^7 J (this calculation ignores the thin layer of air that normally adheres to glass surfaces (2) which considerably reduces the heat flow .. improving the insulation)