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Single-pane windows consist of a single layer of glass. They are light, but dou…

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Wize University Physics Textbook (Master) > Heat and Temperature

Heat Transfer: Conductors in Series and Parallel

3 Activities

Single-pane windows consist of a single layer of glass. They are light, but double-pane windows are much more energy-efficient; they have a layer of air between two thin layers of glass. In very cold places such as Yellowknife, you may also come across triple-pane windows.
Consider these windows when it is 20 degrees Celsius inside and -40 degrees Celsius outside. The area of the windows is 1 m2.
a) What is the energy loss if a single-pane window was used? (2.2 mm thick glass)
b) What is the energy loss with a double-pane window? (4mm glass layers, 20mm air)
c) What about for a triple-pane window? (The two inner panes are 6mm thick, outer pane 15mm thick, 16mm gaps.)
d) What if Krypton was used to fill the gaps instead of air?
Thermal conductivities: kglass=1WmK, kair=0.024WmK, kKr=0.0094 WmKk_{glass}=1\frac{W}{mK},\ k_{air}=0.024\frac{W}{mK},\ k_{Kr}=0.0094\ \frac{W}{mK}
Hint: you will save time in this problem by using R-values!
Enter all answers to two sig figs.

More Heat Transfer: Conductors in Series and Parallel Questions:
Consider a double-pane window (4mm glass layers, 20mm gap between them). When it is 20 degrees Celsius inside and -15 degrees Celsius outside, and if the area of the windows is 1 m2,
a) What is the energy loss if the gap is filled with air?
b) What if the gap is filled with Argon instead?
Using the following system, find the temperature at the copper/steel and steel/aluminum interfaces. What is the heat flow through each material? You may assume only conduction occurs, and that the fixed ends are held at constant temperature.
Givens:
ksteel=43[WmK], kCu=401[WmK], kal=205[WmK]k_{steel}=43\left[\frac{W}{mK}\right],\ k_{Cu}=401\left[\frac{W}{mK}\right],\ k_{al}=205\left[\frac{W}{mK}\right]
Why are double pane windows more effective at preventing heat loss than single pane windows of the same thickness? Draw a diagram to demonstrate this property.
How much more effective are double pane windows are if kglass=1.05[WmK]k_{glass}=1.05\left[\frac{W}{mK}\right], kair=0.025[WmK]k_{air}=0.025\left[\frac{W}{mK}\right]. The single pane is 7 mm7\ mmthick, and the double panes are 3 mm3\ mmthick (air accounts for the remaining 1 mm1\ mm).
If we could vacuum pump the double pane window, what could happen to the heat flow through the window?
A home has 4 walls, three of the walls have no window and are made of a layer 1m thick wood and a layer of 1m thick brick. Each wall is 2 meter by 2 meters and the window on one of the walls is 1 meter by 1 meter. The window is a double panned window which means its a 0.5 m layer of glass then 1 m layer of air then a 0.5 m layer of glass. Each wall is also 2 meters thick. If the inside temperature is 20°C20\degree C and the outside temperature is 0°C0\degree C. (Do not consider the roof or floor).
What is the power level that a generator need to provide such that the inside temperature stays at 20°C20\degree C, if the generator is only 70% efficient.
K wood: 0.12 wm⋅k\frac{w}{m\cdot k}
New Practice Question
A compound bar made up of 15cm of Cu with ACu=25cm2A_{Cu}=25cm^{2} and 20 cm of steel with ASt=10cm2A_{St}=10cm^2𝑎𝑡 𝑇 = 293𝐾 is fixed at both ends as shown in the diagram below. How much is the stress in each metal if the system is heated uniformly by a 700 watt heater for 5 minutes?
CCu=390JKg⋅KCSt=470JKg⋅KYCu=11×1010Nm2YSt=20×1010Nm2aCu=1.7×10−51KaSt=1.2×10−51KρCu=9gcm3ρSt=7.85gcm3\begin{array}{cc}C_{Cu}=390 \frac{J}{Kg\cdot K}&C_{St}=470\frac{J}{Kg\cdot K}\\Y_{Cu}=11\times 10^{10} \frac{N}{m^2}&Y_{St}=20\times 10^{10} \frac{N}{m^2}\\a_{Cu}=1.7\times 10^{-5}\frac{1}{K}&a_{St}=1.2\times 10^{-5}\frac{1}{K}\\\rho_{Cu}=9\frac{g}{cm^3}&\rho_{St}=7.85\frac{g}{cm^3}\end{array}