Question

You want to design a double-paned window. To reduce the amount of heat transfer by conduction through the window, you need to (more than one could be correct): You want to design a double-paned window. To reduce the amount of heat transfer by conduction through the window, you need to (more than one could be correct): Decrease the area of the window. Decrease the thickness of the window. Increase the thickness of the window. Increase the area of the window.

Answer 1

the correct answer to increase the thickness of the windows

Step-by-step explanation:

Thermal transfer by conduction is

P = k A
`( ( T_h - T_c)/(L) )`

where P is the heat transfer rate, A is the area and L is the thickness

In the given case we have that the window is made up of two materials, two layers of transparent glass and a layer of air between them, let us use the index 1 for the glass and the index 2 for the air, the equation remains

P =
`k_1 A_1 ( \Delta T )/(2 \ e_1) + k_2 A_2 ( \Delta T)/(e_2)`

where the number two (2) is due to the two layers of glass

the thermal conductivity of the glass is k₁ = 0.75 W/m K for a glass of

e₁ = 4 mm, this is more used for windows

the thermal conductivity of the air is k₂ = 0.024 W / m K for a temperature of T = 0ºC

In a window the area and the temperature difference are constant for each part for a given configuration

P =
`( (k_1)/(2 \ e_1) + (k_2 )/( e_2) )` A ΔT

To decrease the speed of thermal transfer we can decrease the area, but this also reduces the lighting in the room, which brings other costs.

We can also increase the thickness of the materials, as we see the thermal conductivity of the air is very less than that of glass

k₂ « k₁

increasing the thickness of the air layer would have the greatest effect is the decrease in heat transfer in window light

consequently the correct answer to increase the thickness of the windows