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Math Help - Heat flow questions

  1. #1
    Member MathBlaster47's Avatar
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    Heat flow questions

    This is a four part question that deals with heat flow in an apartment with the fridge open.
    I'd like to check whether or not my answers satisfy the questions.

    A)
    Where does the heat go which is given off by the condensation coils of the refrigerator.

    B)
    On a hot day it is 90(degrees) in your friend Eustace's kitchen. Eustace decides to close all the doors and windows so no further heat transfer occurs between the outdoors and his apartment, and then he opens his refrigerator. If Eustace leaves his refrigerator open all day, will it cool down the kitchen?
    Why or why not? Describe the flow of heat in the room after the refrigerator door is opened.

    C)
    After 5 minutes, if the refigerator door is still open, would the air in the refrigerator be changing less quickly, more quickly, or at the same rate as it did when the refrigerator's door was first opened? Why?

    D)
    If the refrigerator is unplugged, what will eventually happen to the flow of heat in the room?

    My answers:
    A) It dissipates into the air.

    B) His efforts would net no effect, since any cooling action that might have resulted from the cool air flowing out would be negated by the heat introduced by the condensation coils.
    Heat would flow into the fridge, an area of lower heat, and radiate out to the back because of the function of the condensation coils.

    C) It would change less quickly because of the relatively small volume of cool air compared to the large volume of warm air in the apartment.

    D) The temperature will eventually equalize and the flow of air will stagnate.

    If my answers are incomplete, or could be better presented, please tell me.
    Thank you!
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by MathBlaster47 View Post
    This is a four part question that deals with heat flow in an apartment with the fridge open.
    I'd like to check whether or not my answers satisfy the questions.

    A)
    Where does the heat go which is given off by the condensation coils of the refrigerator.

    B)
    On a hot day it is 90(degrees) in your friend Eustace's kitchen. Eustace decides to close all the doors and windows so no further heat transfer occurs between the outdoors and his apartment, and then he opens his refrigerator. If Eustace leaves his refrigerator open all day, will it cool down the kitchen?
    Why or why not? Describe the flow of heat in the room after the refrigerator door is opened.

    C)
    After 5 minutes, if the refigerator door is still open, would the air in the refrigerator be changing less quickly, more quickly, or at the same rate as it did when the refrigerator's door was first opened? Why?

    D)
    If the refrigerator is unplugged, what will eventually happen to the flow of heat in the room?

    My answers:
    A) It dissipates into the air.

    B) His efforts would net no effect, since any cooling action that might have resulted from the cool air flowing out would be negated by the heat introduced by the condensation coils.
    Heat would flow into the fridge, an area of lower heat, and radiate out to the back because of the function of the condensation coils.

    C) It would change less quickly because of the relatively small volume of cool air compared to the large volume of warm air in the apartment.

    D) The temperature will eventually equalize and the flow of air will stagnate.

    If my answers are incomplete, or could be better presented, please tell me.
    Thank you!
    OK except (C) it is changing more slowly but you need to be more specific about why (assuming we are talking about its temprature).
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  3. #3
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    i would say B is not quite correct, because the fridge needs electrical energy input to work, which is also converted in heat

    it doesnt cool the apartment, but it doesnt 'net no effect'. it actually heats the apartment
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  4. #4
    Member MathBlaster47's Avatar
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    Ok! Thank you for your help! Would (B) be better put like this:
    Eustace's efforts would net exactly the opposite effect that he intended, since the refrigerator uses condenser coils to cool the air inside the compartment. The fridge radiates the heat it extracts from the coils and negates the effect of the cool air flowing into the room. Also, since the unit requires electricity in order to function, the small amount of heat waste from the flow of energy would heat the room very slowly.

    Is this a better version of (C)?:
    The air would change the temperature more slowly after 5 minutes because of the far greater volume warm air compared to the cool air generated by the unit. After the initial rush of cool air the condenser coils would have to work harder to cool the large mass of air and put out greater heat.

    Are those more complete explanations?
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