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Need help with heat(steel vs aluminum)

  1. Nov 9, 2011 #1
    what experiment can be used to calculate which handle of a spoon can be better aluminum or steel so it wont get hot quickly while stirring.
     
  2. jcsd
  3. Nov 9, 2011 #2
    attach a digital thermometer to the back of a spoon
    put a pan with soup on the stove, turn it on to a given setting, put a thermometer in it and wait until it stabilizes at some temperature.
    put the spoon into the soup and measure how long it takes for the thermometer to report an increase of 1 degree, 2 degrees, 3 degrees...plot

    do the same with a steel spoon

    my 2 cents
     
  4. Nov 9, 2011 #3

    NascentOxygen

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    I suppose you mean when the entire spoon is made from a solid piece of the metal? As you are unlikely to readily find an actual aluminium spoon to make real-world tests, maybe it would suffice to use a rod of each metal? -- rods of identical dimensions. See how long you can stir a saucepan of boiling water before having to let go. I expect that the results will be stark, needing no more precision in determining the best for short-term stirring. If you intend continuous stirring, and holding the spoon with a bare hand, then results might be more equivocal.
     
  5. Nov 9, 2011 #4
    If you want to do an experiment, get some aluminium piece and heat it up for lets say 30Seconds and measure with a thermometer, then do the same with the steel piece.

    If you just want to know which one has better heat transfer. check the following link
    No need to do anything, its already proven.

    http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
     
  6. Nov 10, 2011 #5
    This is actually one of my favorite illustrations of the differential thermal transparency of Al and Fe: It just so happens that I love to cook, and, as I use both a cast-iron skillet and aluminum pans (some commercially manufactured, and some makeshift pans that I fold myself from aluminum foil), it's obvious to me that iron is relatively opaque to heat, but a massively capacious reservoir of the same, which means that it takes a long time and a lot of BTU's to heat up an iron pan, but, once it's hot, it stays hot for a long time. Aluminum, on the other hand, is relatively transparent to heat energy, such that it heats up much more quickly than does iron, but, take it off the heat, and you can safely touch it with your bare fingers in just a few seconds.

    ***

    Alternatively, you can just use the good ole' CRC Handbook of Chemistry and Physics, and see the "Thermal Conductivity of the Elements" section on page 4-150 and 4-151 (of my edition, which is the 71st Edition (1990-1991)), which states that the thermal conductivity of Al is 2.36 at 273.2K, 2.37 at 298.2K, and 2.40 at 373.2K, whereas the thermal conductivity of Fe is 0.865 at 273.2K, 0.804 at 298.2K, and 0.720 at 373.2K. So, not only is Al much more transparent to thermal energy than is Fe, but the transparency of Al to heat INCREASES as a function of temperature, while the transparency of Fe to heat actually DECREASES as a function of temperature.

    ***

    If you want to see a great example of the relative thermal opacity of Fe, just visit the kitchen of a Chinese restaurant, and see the cooks throw an iron wok onto the stove, and then use a foot pedal to pump gas into the burner to throw BTU's into the wok at an amazing rate. I really wouldn't suggest anyone even try to do that with an aluminum vessel.
     
    Last edited: Nov 10, 2011
  7. Nov 10, 2011 #6
    thx for the help but can anyone tell me a experiment to use like finding the heat capacity of the items or something and explain or link me to where i can know the steps
     
  8. Nov 10, 2011 #7

    NascentOxygen

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    This question is quite different from your original one, though that is okay.

    It would help if we knew your year at school, to gauge the sophistication appropriate. But how about this: set up a pot of boiling water on the stove, and drop into it a lump of aluminium and one of iron. These can be equal sizes, or of equal weight; you choose which is best. Leave them to soak up heat for 5 mins. Turn off the gas, and wait a minute while heating evens out.

    In two identical china or pyrex jars, have equal depths of room temperature water, say, 1.5cm, providing that will cover the metal when you drop it in. Take out the hot metal pieces, and drop one into each bowl of water. Stir evenly with a plastic spoon, and measure temperature of the water after about 1 min.
     
    Last edited: Nov 10, 2011
  9. Nov 10, 2011 #8
    Your experiment requires a lot of indirect measurement. I would just use an infrared thermometer (available online: http://www.google.com/products/cata...IsQLWqJylCA&sqi=2&ved=0CJQBEPMCMAA#ps-sellers ) and a lump of Fe and a lump of Al of equal mass (which means, if you can get lumps of pure metal, sp gr. Al = 2.6989, sp. gr. Fe = 7.874, you need a block of Al 2.9 times the volume of your block of Fe). Heat them in boiling water for an equal amount of time, then remove them and record the temperatures with your IR thermometer as they cool. Continue measurements until each has reached room temperature, and compare the amount of time it takes for them to cool, as well as the starting temperature, which will show you the extent of heating which occurred upon subjection to the same amount of heat input from the boiling water ambiance.
     
  10. Nov 10, 2011 #9

    sophiecentaur

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    aamof, a given mass of Aluminium requires MORE heat to produce the same change in temperature than the same mass of iron. Most alloys / mixtures have higher specific heat values than pure substances. Because of the issue of strength as well as the thermal characteristic of metals used for implements, the comparison is not always obvious because their masses may be different.

    The word "transparency" should really be replaced with the word "conductivity", which has a well defined meaning and is better for making meaningful comparisons. The thermal conductivity of aluminium is higher than that of iron so the temperature distribution in the metal of an aluminium pan will be more 'even' allowing the heat to get to the surface and be lost to the air quicker.

    Several things at work here and a different set-up can yield apparently different comparative results. The original 'spoon' question concerns conductivity rather than heat capacity (unless you are using a massive spoon and a small amount of hot liquid).
     
  11. Nov 10, 2011 #10
    Kindly offer a demonstration of this assertion.

    In any case, the experiment I've suggested should offer proof one way or the other. Equal masses of each metal subjected to the same thermal input over the same amount of time will provide a clear demonstration of the relative receptivity of the two elements to heat by virtue of their initial temperature measurement upon removal from the boiling water.
     
    Last edited: Nov 10, 2011
  12. Nov 11, 2011 #11

    sophiecentaur

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    Look up 'specific heat measurement'. You should do as much as you can on your own of your assignments, I think.
     
  13. Nov 11, 2011 #12
    Thanks.

    By the way, I'm not a teacher, so I can only give suggestions, not assignments. :wink:
     
    Last edited: Nov 11, 2011
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