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Difference between revisions of "v0.34:Specific heat"

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#REDIRECT [[DF2012:temperature#Specific heat]]
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The various SPEC_HEAT tokens control a material's '''specific heat''' capacity.
 
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Specific heat is not a temperature.  It is, more or less, the amount of energy it takes to raise the temperature of the material from one temperature to another.  Gold, for instance, has a very low specific heat, so it takes very little energy to raise its temperature by one degree.  Water, with a very high specific heat, takes 32 times as much energy to raise its temperature by one degree. For more information, see [[wikipedia:Specific heat capacity|Wikipedia]] [http://hypertextbook.com/physics/thermal/heat-sensible/ hypertextbook], and [http://scienceworld.wolfram.com/physics/SpecificHeat.html scienceworld].
 
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<!-- this needs verification, so I'm yanking it:
 
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As '''Dwarf Fortress''' does not have a concept of insulation,'''SPEC_HEAT''' can be used to "cheat" by causing a material which ''should'' be quite insulative to actually take more energy to heat up, or lose more energy to cool down, than more normal materials. The result is a material which, if used in clothing, will keep a dwarf form freezing longer than normal cloth or leather would. -->
 
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'''SPEC_HEAT''' appears to be in units of '''J kg<sup>-1 </sup>K<sup>-1</sup>''' at '''STP'''; i.e. '''1000''' times the normally reported '''c<sub>p</sub>''' in joules per gram per kelvin, or exactly the more rarely reported '''c<sub>p</sub>''' in joules per kilogram per kelvin.
 
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It is not understood why the game uses the '''&deg;C''' or '''K''' scale here, while using the '''&deg;U''' = '''&deg;F + 9968''' scale elsewhere.
 
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=== Sample specific heats as used by Dwarf Fortress ===
 
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The following values are from Dwarf Fortress version 0.28.181.40d, though most also apply to other versions as well.
 
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{| class="wikitable"
 
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! width="50%" | Material
 
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! width="25%" | c<sub>p</sub> in J kg<sup>-1 </sup>K<sup>-1</sup>
 
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! width="25%" | DF uses
 
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|-
 
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| Adamantine
 
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| n/a
 
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| 7500
 
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|-
 
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| Aluminum
 
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| 897
 
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| 900
 
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|-
 
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| Copper
 
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| 385
 
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| 385
 
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|-
 
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| Carbon (Graphite)
 
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| 710
 
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| 409
 
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|-
 
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| Carbon (Diamond)
 
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| 519
 
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| 409
 
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|-
 
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| Gold
 
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| 129.1
 
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| 129
 
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|-
 
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| Iron, cast <!-- http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html -->
 
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| &asymp;500
 
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| 450
 
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|-
 
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| Iron, pig
 
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| >500
 
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| 500
 
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|-
 
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| Iron, pure
 
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| 443
 
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| 450
 
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|-
 
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| Iron, wrought <!-- http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html http://www.gutenberg.org/files/22657/22657-h/chapters/measurement.html -->
 
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| 480-500
 
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| 450
 
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|-
 
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| Nickel
 
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| 444
 
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| 444
 
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|-
 
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| Zinc
 
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| 388
 
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| 390
 
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|-
 
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|
 
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|
 
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|
 
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| Alcohol, ethyl, anhydrous
 
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| 2440
 
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| 2440 (default for plant alcohol)
 
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|-
 
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| Alcohol, ethyl, 100 proof
 
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| 3856
 
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| not in raws
 
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|-
 
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| Meat (beef, carcass, not frozen) <!-- http://www.engineeringtoolbox.com/specific-heat-capacity-food-d_295.html -->
 
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| 2850
 
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| 4181
 
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|-
 
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| Charcoal
 
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| &asymp; 1000
 
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| 409 (hardcoded)
 
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|-
 
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| Cheese (Cheddar, aged 60 weeks) <!-- http://jds.fass.org/cgi/reprint/73/7/1671.pdf  You really can find anything on the Internet! -->
 
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| 3012
 
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| 4181 (0.31), 2000 (40d)
 
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|-
 
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| Coke
 
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| 850
 
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| 409 (hardcoded)
 
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|-
 
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| Glass, crystal <!-- http://en.wikipedia.org/wiki/Specific_heat_capacity -->
 
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| &asymp; 500
 
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| 700 (hardcoded)
 
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|-
 
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| Glass, silica <!-- http://www.engineeringtoolbox.com/specific-heat-solids-d_154.html http://www.gutenberg.org/files/22657/22657-h/chapters/measurement.html -->
 
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| &asymp; 840
 
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| 700 (hardcoded)
 
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|-
 
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| Granite <!-- http://en.wikipedia.org/wiki/Specific_heat_capacity -->
 
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| 790
 
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| 800 (default for all stone)
 
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|-
 
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| Sand
 
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| 835
 
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| 835 (hardcoded)
 
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| Silk (silkworm?) <!-- http://www.engineeringtoolbox.com/specific-heat-solids-d_154.html -->
 
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| &asymp; 1380
 
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| not in raws
 
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| Silk (hornet) <!--  http://joam.infim.ro/JOAM/pdf4_1/Ishay.pdf --> <!-- but a paper named Hornet silk: thermophysical properties: J. S. Ishay et al. abstract claims "a specific heat of over 2 J/g K" -->
 
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| &asymp; 1500
 
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| not in raws
 
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| Silk (spider, viscid) <!-- http://www.doitpoms.ac.uk/tlplib/bioelasticity/printall.php -->
 
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| &asymp; 1400
 
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| 420 (0.31), 1000 (40d)
 
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|-
 
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| Water, liquid, at STP
 
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| 4218
 
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| 4181 (hardcoded)
 
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|-
 
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| Water, solid, at STP
 
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| 2114
 
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| 4181 (hardcoded)
 
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| Wood [[Creature_Tokens/SPEC_HEAT#footnote2|&#91;&dagger;&#93;]]
 
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| 1700 to 2900
 
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| 420 (hardcoded prior to 0.31)
 
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|-
 
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|}
 
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<!-- if anyone knows a better way to do footnotes, go for it. -->
 
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<small id="footnote2"><tt>&#91;&dagger;&#93;</tt><small>&nbsp;&nbsp;The specific heat of wood varies somewhat between different species.  However, the variance is dominated by the moisture content of the wood.  Moreover, wet wood behaves very differently below freezing.  See [http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr09.pdf]</small></small><br/>
 
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<!-- <small id="footnote3"><tt>&#91;&Dagger;&#93;</tt><small>&nbsp;&nbsp;footnote 3 text</small></small><br/> -->
 
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----
 
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The default value for '''SPEC_HEAT''' depends on the material and on the version of Dwarf Fortress in question.
 
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----
 
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[[wikipedia:Specific heat capacity#Table of specific heat capacities|Wikipedia]] and [http://www.engineeringtoolbox.com/specific-heat-solids-d_154.html engineeringtoolbox] have tables with other materials' specific heats.
 
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References may report specific heat in joules per gram per degree Celsius. Because the Celsius and Kelvin systems use the same scale, differing only in their zero points, this is exactly the same as reporting in joules per gram per kelvin. '''J/g&deg;C''' is equal to '''J/gK'''.
 
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Sometimes references will give specific heat in calories per gram kelvin, or calories per kilogram kelvin. To convert calories per gram kelvin to '''&deg;U''', multiply by '''4184'''.  To convert calories per kilogram kelvin to '''&deg;U''' units, multiply by '''4.184'''.
 
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Older references may give specific heat in B.T.U. per pound per degree Fahrenheit.  1 B.T.U. per pound per degree Fahrenheit is by definition equal to 1 calorie per gram per kelvin.  '''Btu/lb&deg;F''' is equal to '''cal/gK'''. So just multiply by '''4184''' to convert to '''&deg;U'''.
 
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Sometimes references will report specific heat of liquids or gases in joules (or calories) per [[wikipedia:Mole (unit)|mole]] per kelvin.  The symbol for this is '''C<sup>p</sup>''' (with a capital C).  This is less useful for our purposes, as you will need to know the molecular weight (in grams per mole) of the compound to convert it. 
 
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:An example: the molar heat capacity of ethyl alcohol is 113 Joules per mole per degree Centigrade.  The molecular weight of ethyl alcohol is 46.07 grams per mole.  Divide 113 J/mol&deg;C by 46.07 g/mol, resulting in 2.45 J/g&deg;C.  Multiply by 1000 g/kg, resulting in 2450 J/kg&deg;C.  That is our desired result in '''DF''' units.
 
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Note that specific ''latent'' heat is a different concept; do not use those values for '''SPEC_HEAT'''.
 
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[[Category:Modding]]
 
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[[Category:Tokens]]
 

Latest revision as of 02:23, 23 October 2012

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