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Heat Transfer: Conduction

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Wize University Physics Textbook (Master) > Heat and Temperature

Heat Transfer: Conduction

2 Activities

If object A touches object B in a thermally insulated room and heat flows from object B to object A. What can we say?
More Heat Transfer: Conduction Questions:
The glass of a car window is rectangular in shape and has dimensions of 40 cm by 60 cm and is 3cm thick. How much heat will be transferred by conduction in 10.0 s through the gas if there is a temperature difference of 3.5º between the inner and outer surfaces? (kglass=0.84 J/m s ºC)
What is the average temperature of a burning log if it releases an average of 10 kW of heat in a room at 5°C. Assume maximum emissivity for a blackened log that has a diameter of 20 cm and a length of 50 cm. (Hint: the surface area of a log has two circles as well as a rectangular part connecting these two circles. The "width" of this rectangle is the circumference of the log.)
How much heat is transferred in 20 minutes across the following system? Assume all metallic parts are cubes and each side has a length of 20 cm20\ cm.
kAl=205wm⋅kkcu=385wm⋅kkBr=109wm⋅kkSt=50.2wm⋅k\begin{aligned} k_{Al}=205 \frac{w}{m\cdot k}&&k_{cu}=385 \frac{w}{m\cdot k}\\ k_{Br}=109 \frac{w}{m\cdot k} && k_{St}=50.2 \frac{w}{m\cdot k} \end{aligned}
A cubic room with a length of 4 m4\ m is isolated from the outside by a 2 cm2\ cm layer of wood and a 15 cm15\ cm layer of insulating brick.
If the temperature outside is −20°C-20\degree C, what should be the power of a heater to keep the inside temperature at 25°C25\degree C? Assume that the heat is only transferred through side walls.
We put a 2 m×1.5 m2\ m \times 1.5\ m window in one of the walls when the thickness of the glass is 2 cm2\ cm. What is the temperature inside using the same heater? (kBrick=0.15wm⋅k,kwood=0.12wm⋅k,kglass=0.8wm⋅k)(k_{Brick}=0.15 \frac{w}{m\cdot k},\quad k_{wood}=0.12 \frac{w}{m\cdot k},\quad k_{glass}=0.8\frac{w}{m\cdot k})
A solar array powering a satellite is shown below. The array is connected to satellite by a thin aluminium rod. The array is facing the sun, and has a temperature of 1100 [K]1100\ \left[K\right], the satellite body has a temperature of15 K15\ K. Find the net heat transfer from the array to the satellite body.
The rod has a cross sectional area of 0.5 [m2]0.5\ \left[m^2\right].The square array and the satellite are facing one another and have 3 ×3 [m]3\ \times3\ \left[m\right]faces, they are 10 m10\ m apart.
kal=205 [WmK]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 square cooler contains drinks for a party at the beach. It contains the drinks and 1kg of ice and 2 kg of water. The cooler has side lengths of 50 cm50\ cm and is 5 cm5\ cm thick. The temperature during the day is 30°C30\degree C. The cooler is made of a layer of plastic that is 2.5 cm2.5\ cm thick and a 2.5 cm2.5\ cm thick layer of polyester. If the cooler got to the beach at 8 am how long would it take for all the ice to melt.
K values
Polystyrene: 0.033 wm⋅k\frac{w}{m\cdot k}
New Practice Question
Liquid helium is stored at its boiling point, 4.2 K, in a spherical capsule that is separated by a vacuum space from a surrounding container that is maintained at the temperature of liquid nitrogen, 77K. The capsule has a radius of 0.1 m and it is blackened on the outside. Calculate the amount of helium that boils away in one day. Now imagine the vacuum is replaced by a 20cm glass layer around the spherical capsule. How much helium boils away per day in this new condition?
LHe=20.9×103 JKgL_{He}=20.9\times10^3\ \frac{J}{Kg}
(kglass=1.05 wm⋅K)\left(k_{glass}=1.05\ \frac{w}{m\cdot K}\right)
A glass window pane has an area of 5.00 m2 and a thickness of 0.800 cm. If the temperature difference between its faces is 25.0°C, what is the rate of energy transfer by conduction through the window. (thermal conductivity of glass: kglass=0.8W/(m C))
Compound bar
A compound bar is made as shown below. It is insulated perfectly on its sides. If the cross-section of the bar is 5 cm25\ cm^2, what is the temperature at the junction of two metals and what is the total rate of heat flow? (kSt=50.2wm⋅K, kBr=109wm⋅K)(k_{St}=50.2 \frac{w}{m\cdot K},\ k_{Br}=109 \frac{w}{m\cdot K})