Construct Your Own Problem Consider a person outdoors on a cold night. Construct a problem in which you calculate the rate of heat transfer from the person by all three heat transfer methods. Make the initial circumstances such that at rest the person will have a net heat transfer and then decide how much physical activity of a chosen type is necessary to balance the rate of heat transfer. Among the things to consider are the size of the person, type of clothing, initial metabolic rate, sky conditions, amount of water evaporated, and volume of air breathed. Of course, there are many other factors to consider and your instructor may wish to guide you in the assumptions made as well as the detail of analysis and method of presenting your results.
Construct Your Own Problem Consider a person outdoors on a cold night. Construct a problem in which you calculate the rate of heat transfer from the person by all three heat transfer methods. Make the initial circumstances such that at rest the person will have a net heat transfer and then decide how much physical activity of a chosen type is necessary to balance the rate of heat transfer. Among the things to consider are the size of the person, type of clothing, initial metabolic rate, sky conditions, amount of water evaporated, and volume of air breathed. Of course, there are many other factors to consider and your instructor may wish to guide you in the assumptions made as well as the detail of analysis and method of presenting your results.
Consider a person outdoors on a cold night. Construct a problem in which you calculate the rate of heat transfer from the person by all three heat transfer methods. Make the initial circumstances such that at rest the person will have a net heat transfer and then decide how much physical activity of a chosen type is necessary to balance the rate of heat transfer. Among the things to consider are the size of the person, type of clothing, initial metabolic rate, sky conditions, amount of water evaporated, and volume of air breathed. Of course, there are many other factors to consider and your instructor may wish to guide you in the assumptions made as well as the detail of analysis and method of presenting your results.
During a chemistry lab, you take a 0.4 kg sample of ice and put it in a beaker with a thermometer. You then place the beaker with the ice on
0 the temperature of the ice is -18
=
a hot plate, and turn on the hot plate. This hot plate adds heat to the ice at a rate of 330 W. At time t
°C.
Because of the large heat capacity of water and ice, you may assume in this problem that all the heat goes into the sample of ice, and that
we can ignore the amount of heat going into the beaker and thermometer. Also assume no heat escapes from the system.
Some useful values:
●
Specific heat of water: C =
Specific heat of ice: Ci
= 2100 J/kg K
• Latent heat of fusion: L = 334 000 J/kg
●
4200 J/kg K
=
1a) At what time does the ice reach a temperature of -3.5°C?
answer=
units?
1b) At what time has all the ice melted?
answer=
units?
Check your answer
Check your answer
1c) After the ice has completely melted, we're left with 0.4 kg of water.
Check your answer
answer=
units?
not yet solved
not yet solved…
4) A ground source heat pump heats a building by extracting heat from the ground and pumping
it into the building.
Define: Qc = heat extracted from the ground, Qn= heat pumped into the building,
W = electric energy used by the heat pump, Tc= temperature of the ground, T = temperature
of building (Qc, Qn, and W are positive by definition). Assume Tr > Tc.
a)
Draw a diagram showing energy flow in and out of the heat pump.
b)
Write a general expression for the change AS in the entropy of the "universe", that
is the heat pump plus the cold and hot reservoirs, in terms of the quantities defined above.
Now assume ideal (reversible) operation, and take Te= 10 °C and Tp= 20 °C.
What is the coefficient of performance (ČOP) of the heat pump? By what factor would
this change if we had Tc = 0 °C instead?
A bag containing ice is much more effective in absorbing energy than one containing the same amount of water. (a) How much heat transfer is necessary to raise the temperature of 0.800 kg of water from to ? (b) How much heat transfer is required to first melt 0.800 kg of ice and then raise its temperature?
a. How much heat transfer is necessary to raise the temperature of .739kg of water from 0C to 34 C.
b. How much heat is transfer is required to first mel .739kg of 0C ice to then raise its temperature?
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