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Thread: Which specific heat to use?

  1. #1 Which specific heat to use? 
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    I'm doing a lab report for one of my class. The experiment is about heating a brass with some dimension lengthxwidthxthickness and mass to about 110degC and then cooling it down to about 60deg with air at certain velocity(about 15m/sec). Time and temperature were recorded. The task is to find h(heat coefficient).
    I'm using newton's cooling law equation:
    -m*Cp*dT/dt=Qconvection+Qconduction+Qradiation
    Qconduction is 0 in this case due to the experimental setup.
    What I am wondering is which Cp should I use here? Is it of the fluid(air) or the brass? I remember my TA said it's for the fluid, but I haven't figured out exactly which one and why? Could you guys help me?


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  3. #2  
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    What you are trying to do is measure the amount of heat that is transferred from the piece of brass to its surroundings within a certain period of time.

    Theoretically you could either measure the heat lost by the brass or the heat gained by whatever is being heated. The air is being heated by convection but there is also radiation, which is heating.. what? Also, to find the heat transferred to the air you would need not only velocity but volume, and you'd have to measure its temperature before and after it was heated.


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  4. #3  
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    The surface temperature of the brass is measured and recorded. I assume you suggest using the specific heat of the air, Harold14370?
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    Quote Originally Posted by app43
    The surface temperature of the brass is measured and recorded. I assume you suggest using the specific heat of the air, Harold14370?
    No.
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  6. #5  
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    So its the specific heat of the brass then?
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  7. #6  
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    Ive probably already given you more than I should, within the forum's homework help guidelines.

    You really need to try to understand what you are calculating, not just plug numbers into a formula.
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  8. #7  
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    Harold14370, i understand the method that you said about measuring inlet and outlet temperatures. It'd be easy to deal with problem like this with those information. But we weren't asked to measure these values. I assume there are some assumptions here. Thanks for trying though. I'll let you know when I figure it out.
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