In another experiment, you place a layer of this cryoprotectant between one 10 cm × 10 cm cold plate maintained at −40°C and a second cold plate of the same size maintained at liquid nitrogen’s boiling temperature (77 K). Then you measure the rate of heat transfer . Another lab wants to repeat the experiment but uses cold plates that are 20 cm × 20 cm, with one at −40°C and the other at 77 K. How thick does the layer of cryoprotectant have to be so that the rate of heat transfer by conduction is the same as that when you use the smaller plates? (a) One-quarter the thickness; (b) half the thickness; (c) twice the thickness; (d) four times the thickness.
In another experiment, you place a layer of this cryoprotectant between one 10 cm × 10 cm cold plate maintained at −40°C and a second cold plate of the same size maintained at liquid nitrogen’s boiling temperature (77 K). Then you measure the rate of heat transfer . Another lab wants to repeat the experiment but uses cold plates that are 20 cm × 20 cm, with one at −40°C and the other at 77 K. How thick does the layer of cryoprotectant have to be so that the rate of heat transfer by conduction is the same as that when you use the smaller plates? (a) One-quarter the thickness; (b) half the thickness; (c) twice the thickness; (d) four times the thickness.
In another experiment, you place a layer of this cryoprotectant between one 10 cm × 10 cm cold plate maintained at −40°C and a second cold plate of the same size maintained at liquid nitrogen’s boiling temperature (77 K). Then you measure the rate of heat transfer. Another lab wants to repeat the experiment but uses cold plates that are 20 cm × 20 cm, with one at −40°C and the other at 77 K. How thick does the layer of cryoprotectant have to be so that the rate of heat transfer by conduction is the same as that when you use the smaller plates? (a) One-quarter the thickness; (b) half the thickness; (c) twice the thickness; (d) four times the thickness.
The average thermal conductivity of the walls (including windows) and roof of a house in the figure shown below is 4.8 x 104 kW/m - °C, and their average thickness is 20.8 cm. The house is heated with natural gas, with a heat of combustion (energy given off per cubic
meter of gas burned) of 9,300 kcal/m3. How many cubic meters of gas must be burned each day to maintain an inside temperature of 27.3°C if the outside temperature is 0.0°C? Disregard surface air layers, radiation, and energy loss by heat through the ground.
m3
37.0
5.00 m
8.00 m
10.0 m
The average thermal conductivity of the walls (including windows) and roof of a house in the figure shown below is 4.8 x 104 kW/m - °C, and their
average thickness is 21.4 cm. The house is heated with natural gas, with a heat of combustion (energy given off per cubic meter of gas burned) of
9,300 kcal/m3. How many cubic meters of gas must be burned each day to maintain an inside temperature of 24.0°C if the outside temperature is
0.0°C? Disregard surface air layers, radiation, and energy loss by heat through the ground.
34.68
Your response is within 10% of the correct value. This may be due to roundoff error, or you could have a mistake in your calculation. Carry out all
intermediate results to at least four-digit accuracy to minimize roundoff error. m3
137.00
5.00 m
00
8.00 m
10.0 m
A Styrofoam box used to keep drinks cold has a total wall area (including the lid) of 0.80 m?
and wall thickness 3.0 cm. It is filled with mixture of ice, water, and cans of soda at 0°C. (a)
What is the rate of heat flow into the box if the temperature of the outside wall is 30°C? (b)
How much ice melts in one day?
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