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  • mass vs heat storage ability

    While we're at it- here's a question that came into mind a few days ago- how does the heat storage ability of a material relate to its mass?

    Going with simple materials that don't alter with heating or cooling except for expansion and contraction, and keeping within the solid state- will a 1 lb block of steel have the same heat absorbing capability as 1 lb of say aluminum, or plastic?

    I seem to recall someone saying that it isn't true. I understand that if a phase change occurs then this would change things. This is probably most evident in 'phase change' materials that have been designed or optimized for heat absorption like certain salts, etc. My question is limited to temperature ranges where this does not occur- though it would be interesting to discuss phase change materials as well.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Are we talking about absorption or retention ? I believe the retention is obvious .. but .. how do
    you figure/measure the absorption ?
    John Titor, when are you.

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    • #3
      https://en.wikipedia.org/wiki/Heat_capacity

      You need twice as many energy to increase the same amount of temperature 1 unit of mass of aluminium over 1 unit of mass of steel.

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      • #4
        It's Q from memory, change being delta Q, look up specific heat cap for the material, or fluid.
        Steam gets fun though
        Mark

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        • #5
          Different materials have different heat capacities, meaning the energy necessary to raise the temperature one degree.

          So the materials you mention should have different heat capacity. I do not recall what the difference is offhand for those.
          CNC machines only go through the motions

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          • #6
            Water wins if you want more from less.

            Water is not so good if you want less from more. ;-)

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            • #7
              At 20 Celsius:
              Mass specific heats C:
              Steel C = 464 Watt.second per kilogram.Kelvin
              Aluminum C = 934 Watt.second per kilogram.Kelvin

              For steel, for example, it takes 464 Watt applied for 1 second to raise 1 kilogram by 1 Celsius.

              In furnace heating, we often use volume flow, so we use the volume specific heats:

              Steel Cy = 3.65e6 Watt.second / metre-cubed.Kelvin
              Aluminum Cy = 2.52e6 Watt.second / metre-cubed.Kelvin

              The mass and volume specific heats are related by the densities:
              Steel ( 0.3%C) d = 7860 kilogram/metre-cubed
              Aluminum d = 2697 kilogram/metre-cubed

              The specific heat of steels in solid state, varies with temperature
              For example steel at forging temperature of 1230 celsius has a volume specific heat of:
              Cy = 5.10e6 Watt.second / metre-cubed.Kelvin

              Ref for Cy:
              Davies E. J. "Conduction and induction heating" 1990 Peregrinus Pages 346~347
              Last edited by wombat2go; 06-11-2017, 10:49 PM. Reason: Add ref

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              • #8
                So there is a difference- you can't just calculate based on weight, though off-hand it would seem that you could. From what I've just been reading, heat is absorbed into a material according to how the atomic and/or molecular structure accepts it. I'm beginning to understand it now.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                • #9
                  http://www.engineersedge.com/materia...tals_13259.htm

                  Water
                  http://www.engineeringtoolbox.com/wa...es-d_1508.html

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                  • #10
                    Hi Darryl.
                    I would agree with your comment except I don't understand it enough after many years.
                    As I understand, science has caught up with the mechanics of the specific heat for pure elements and crystals,
                    but maybe not with accuracy sufficient for industry.
                    With metal "mixtures", and "alloys" including the carbon steels,
                    we seem to be still in the days of having to measure it by empirical research.

                    The reference I added to post #7 is accurate to +/- 2% in my experience, for steels up to about 0.4%C
                    In USA, you can search on NASA and NIST.
                    You might find enthalpy functions and graphs there.
                    A step change in enthalpy ( for example by the heat of phase change of carbon steel at 727 Celsius )
                    is differentiated to be an impulse in specific heat.
                    Is it so? ... I am not saying.

                    Hope you can study and let us know what you find!

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                    • #11
                      According to the one link that CalM posted, aluminum has twice the capacity to absorb heat as does steel, with silicon about in the middle between them. Lithium has almost four times the capacity of aluminum to absorb heat. I find that interesting. Lithium is an interesting material in more ways than one. Perhaps its ability to make a high capacity cell is related to its specific heat. Just trying to understand things-
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                      • #12
                        Yes,
                        in your context
                        By weight Al has 2 times the heat capacity of steel.

                        By volume, steel has 1.5 times the heat capacity of Al

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                        • #13
                          There is a difference between heat and temperature. Temperature is a measure of the effect of heat (energy increase or decrease) on a substance. Different substances are affected by heat to differing degrees which is listed in table of specific heats, among other things.

                          Water has a high specific heat - the highest, I think, of common substances

                          The specific heats of steel Vs aluminum are considerably different as mentioned above.

                          You think about one aspect of a material's response to heat - change in temperature - and you have to consider rates of expansion, melting point, latent heat of fusion, eutectic triple point, emissivity, thermal conductivity, etc. Materials science is fun when it's not maddening.
                          Last edited by Forrest Addy; 06-12-2017, 03:17 AM.

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                          • #14
                            Let me know if I'm just being an idiot here- but I'm trying to grasp the concept of what actually happens when matter increases in temperature. There is an expansion in almost every material, but what is actually going on in the atoms or molecules- do the electrons speed up as they travel longer distances in their orbits, or do the atoms vibrate to a greater extent (brownian motion?). Seems to me that if the electrons travel around the nucleus of an atom at a fixed rate (speed of light?) then they can't traverse a larger orbit without speeding up. If they are circulating at less than the speed of light, then it would seem that at a certain temperature limit they would achieve the speed of light- after which a further increase in temperature would have the effect of changing the entire dynamic.

                            It seems to me that Brownian motion would have the electrons changing their orbital speed constantly, and at a pretty high frequency also as the atoms jiggle around.

                            If we just look at expansion and contraction, do the atoms of a material space themselves farther apart of come closer together, or does the size of the atom change with temperature changes?

                            Personally, I don't like the idea of limits- so when it comes to something heating up to beyond millions of degrees, or cooling to absolute zero- first of all why is there an absolute zero? Can matter cool below that temperature by some mechanism? And is there any limit to how how matter can get- is there a point at which a fundamental change in known physics occurs?
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                            • #15
                              Hi Darryl

                              Start with article about "ideal gas". It is a simplified model of heat and temperature of gas. This model assumes that atoms are infinitely small and hard particles. Calculations based on this model are useful only on limited range of temperatures and pressures - but it's value lies in fact that it's simple and gives some "intuitive feel". If you're interested in effects of temperature on electrons - im afraid the only way is to study quantum mechanics - but as far i know these effects become interesting if you are operting at very high temperatures (plasma) or with semiconductors that react very strong to such changes (it's funny that our computer technology is based on such minute changes )


                              Wysłane z mojego GT-N7100 przy użyciu Tapatalka

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