Specifik varmeledningsevne

I fysik er specifik varmeledningsevne eller specifik termisk konduktivitet, k, en stofegenskab, som indikerer stoffets evne til at lede varmeenergi.

Varmeledningsevne er defineret som mængden af varme, Q, overført per tidsenhed t over afstanden L, i retningen vinkelret på tværsnitsarealet A, under en temperaturforskel ΔT, under ligevægtsbetingelser.

varmeledningsevne = varmestrømshastighed × afstand / (tværsnitsareal × temperaturforskel)

k={\frac {Q}{t}}\times {\frac {L}{A\times \Delta T}}

SI-enheden for varmeledning er "Watt per meter Kelvin", W/(m·K) = watt per meter per grads temperaturforskel mellem de to temperaturer, dette er også kendt som λ-værdi (lambda værdi).

Varmeledningsevnetabel

Varmeledningsevnetabel for nogle kendte stoffer, sorteret efter Varmeledningsevne (typisk værdi eller middelværdi):

Stof	Varmeledningsevne (W·m⁻¹·K⁻¹) (λ-værdi)	Temperatur (K)	Temperatur (°C)	Bemærkninger
Helium-II	~100.000	<2,2
Heat-pipe, heat-spreader	>=5000			Virker kun i det temperaturinterval, som heat-pipen er dimensioneret til.
Kulstof: Ren syntetisk diamant	2000-2500
Kulstof: grafit(∥)	1950			I krystalgitterretning
Borarsenid	1300			Pt bedste opdagede legeringshalvleder.
Kulstof: Diamant, uren (C+0,1%N)	1000	273	0	Type I (98,1% af Diamantædelsten)
Sølv, rent	406 - 429 (418)	300	27
Kobber, ren	385 - 401 (386 - 390)	273-373(293)	0-100 (20)
Guld, ren	314 - 318	273 - 373	0-100
Aluminium, ren	205 - 237 (220)	293	20
Beryllium	218		25
Wolfram	174
Magnesium, magnium	156		25
Iridium	147		25
Molybdæn	138		25
Zink	116
Messing (Cu+(35-15)%Zn)	109 - 159 (151)	296	23
Cadmium	92		25
Nikkel	90,7
Natrium	84		25
Jern, ren	71,8 - 80,4 (79,5 - 80,2)	273-373(300)	0-100
Platin	71,6
Tin	66,6
Støbejern (Fe+(2-3,5)%C+(1-3)%Si)	55
Bronze (Cu+11%Sn)	42 - 50 ((25%Sn)26)	296	23
Stål (Fe+(1,5-0,5)%C)	36 - 54 (50,2)
Bly, ren	34,7 - 35,3 (35)	273 - 373	0-100
Uran	27,6
Monel	26		25
Konstantan	22		25
Titanium	21,9
Rustfrit stål(Fe+18%Cr+8%Ni)	14 - 16,3	273 - 296	0-23
Kviksølv	8,34
Plutonium	6,74
Kulstof: grafit(⊥)	5,7			Vinkelret på krystalgitterretning
Granit (Si+14%Al+4%K+3%Na)	1,73 - 3,98			70,18%SiO₂
Kvarts	3		25
Marmor	2,07 - 2,94			hovedsagelig CaCO₃
Sandsten	1,83 - 2,90			~95%-71%SiO₂
Is	1,6 - 2,2 (2,1)	273 (293)	0-(20?)
Mørtel, cement	1,73		25
Kulstof (amorf, kul)	1,7		25
Sand	0,27 (0,35(tørt)-2,7(vandmættet))
Kalksten	1,26 - 1,33			hovedsageligt CaCO₃
Beton	0,8 - 1,28	293	20	~61%-67%CaO
Porcelæn	1,05		25
en:Fire brick (Molersten?)	1,04		500
Pyrex-glas	1,005		25
Mursten	0,18 (0,69-1,31)		(25)
Glas	0,8−0,93((96%SiO₂)1,2-1,4)	293	20
Vand	0,6	293	20	(<3%Na+Mg+Ca)
Asfalt	0,15-0,52
Fiberforstærket plast	0,23 - 0,7 (1,06)	296 (293)	23	10-40%GF eller CF
Jord	1-2			Ved vandindhold på 0,2 m³/m³. Varierer med vandindhold og vægtfylde: 0,2-2,8.
Epoxy	0,35		25
HD Polymerer	0,33 - 0,52	296	23
Neopren	0,15-0,45
Glycerol	0,29	293	20
Glimmer	0,26
Teflon	0,25
Paraffin-voks	0,25		25
Akryl	0,2		25
Olivenolie	0,17		25
Brint	0,168		25
Alkoholer eller Olier	0,1 - 0,21	293	20
Træ (+12% vand)	0,09091 - 0,21 (0,16 - 0,4)	(298 - 293)	20-25	Varierer med træarten
Gummi (92%)	0,16	303	30
Helium	0,152	>4,2
Læder	0,14		25
Træ (ovntør)	0,07692 - 0,17 (0,16 - 0,4)	(298 - 293)	20-25	Ceder - Hickory
LD Polymerer	0,04 - 0,33 (0,16 - 0,25)	296 (293)	23 (20)
EPS/XPS skum (PS+Luft+CO₂+C_nH_2n+x)	0,033 (0,1 - 0,13)	98-298 (296)	(-175)-25 (23)
Krydsfiner	0,11
Sne, tør	0,11
Silikoneolie	0,1		25
Asbest	0,05-0,15
Papir	0,04-0,09
Tæppe	0,03-0,08
Strå-isolation	0,05 (0,09)		(25)
savsmuld	0,06		25
Zirkon	0,056
Filt	0,06 (0,04)		(25)
Kork	0,04 - 0,07	293	20
Balsatræ	0,048		25
Stenuld	0,045 (Eksempel: Rockwool Flexibatts: 0,037 )		25
Glasuld	0,04		25
bomuld	0,04
Uld	0,03-0,04
Fjer	0,034
Kapok-isolation	0,034		25
Helium-I	0,0307	2,2<t<4,2
metan	0,03		25
PUR skum	0,02-0,03
PIR Thermo set skumisolering (Polyisocyanate)	0,022-0,03		10
Phenol Thermo set skumisolering	0,018-0,026		10
Luft (78%N+21%O+1%Ar) (1 atm)	0,024 – 0,0262 (0,025)	273-300(293)	0-27 (20)
Oxygen (O₂) (1 atm)	0,0238	293	20
Nitrogen (N₂) (1 atm)	0,0234 – 0,026	293 – 300	20-27
Ammoniak	0,022		25
Vanddamp	0,016-0,025	273-373	0-100
Argon	0,016		25
Siliciumbaseret aerogel	0,003	98 – 298	(-175)-25
Mylar	0,15 checkes
Vakuum	0

Kilder/referencer

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^æ ^ø ^å ^aa ^ab ^ac ^ad The Physics Hypertextbook: Conduction
^ EDN, October 17, 2006, Ultrathin heat spreader uses fluid core to cool processors, displays (Webside ikke længere tilgængelig) Citat: "...new heat spreader...1.44-mm-thick vaporization zone and boast a thermal conductivity of more than 5000W/mK, compared with 386W/mK for copper or 205W/mK for aluminum...", celsia, nanospreader technology Arkiveret 8. maj 2011 hos Wayback Machine
^ Kang, Joon Sang; Li, Man; Wu, Huan; Nguyen, Huuduy; Hu, Yongjie (2018). "Experimental observation of high thermal conductivity in boron arsenide". Science. 361 (6402): 575-578. Bibcode:2018Sci...361..575K. doi:10.1126/science.aat5522. PMID 29976798.
^ Citat: "...high mobility to both electrons and holes, it has excellent thermal conductivity. It is the best semiconductor material ever found, and maybe the best possible one, according to the researchers...The earlier experiments demonstrated that the thermal conductivity of cubic boron arsenide is almost 10 times greater than that of silicon...Not only is the material’s thermal conductivity the best of any semiconductor, but the scientists also say it has the third-best thermal conductivity of any material — next to diamond and isotopically enriched cubic boron nitride..."
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z "CRC handbook of chemistry and physics". Arkiveret fra originalen 24. juli 2017. Hentet 29. december 2006.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w Georgia State University - Hyperphysics
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^æ ^ø ^å ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah GoodFellow
^ ^a ^b ^c ^d ^e "Physical Properties and Moisture Relations of Wood" (PDF). Arkiveret fra originalen (PDF) 13. februar 2007. Hentet 29. december 2006.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Engineers Edge
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^æ ^ø ^å Hukseflux Thermal Sensors
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^æ ^ø ^å ^aa ^ab ^ac ^ad he Engineering Tool Box: Thermal Conductivity of some common Materials
^ ^a ^b ^c ^d ^e ^f ^g ^h Marble Institute
^ Soil Temperature Changes with Time and Depth: Theory, D.L. Nofziger
^ "Rockwool Flexibatts information". Arkiveret fra originalen 6. maj 2011. Hentet 2011-03-02.
^ http://usa.dupontteijinfilms.com/wp-content/uploads/2017/01/Mylar_Physical_Properties.pdf

Se også

[hypertextbook-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^æ ^ø ^å ^aa ^ab ^ac ^ad The Physics Hypertextbook: Conduction

[2] EDN, October 17, 2006, Ultrathin heat spreader uses fluid core to cool processors, displays (Webside ikke længere tilgængelig) Citat: "...new heat spreader...1.44-mm-thick vaporization zone and boast a thermal conductivity of more than 5000W/mK, compared with 386W/mK for copper or 205W/mK for aluminum...", celsia, nanospreader technology Arkiveret 8. maj 2011 hos Wayback Machine

[3] Kang, Joon Sang; Li, Man; Wu, Huan; Nguyen, Huuduy; Hu, Yongjie (2018). "Experimental observation of high thermal conductivity in boron arsenide". Science. 361 (6402): 575-578. Bibcode:2018Sci...361..575K. doi:10.1126/science.aat5522. PMID 29976798.

[4] Citat: "...high mobility to both electrons and holes, it has excellent thermal conductivity. It is the best semiconductor material ever found, and maybe the best possible one, according to the researchers...The earlier experiments demonstrated that the thermal conductivity of cubic boron arsenide is almost 10 times greater than that of silicon...Not only is the material’s thermal conductivity the best of any semiconductor, but the scientists also say it has the third-best thermal conductivity of any material — next to diamond and isotopically enriched cubic boron nitride..."

[CRChandbook-5] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z "CRC handbook of chemistry and physics". Arkiveret fra originalen 24. juli 2017. Hentet 29. december 2006.

[hyperphysics-6] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w Georgia State University - Hyperphysics

[goodfellow-7] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^æ ^ø ^å ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah GoodFellow

[fpl-8] "Physical Properties and Moisture Relations of Wood" (PDF). Arkiveret fra originalen (PDF) 13. februar 2007. Hentet 29. december 2006.

[engineersedge-9] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Engineers Edge

[hukseflux-10] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^æ ^ø ^å Hukseflux Thermal Sensors

[engineeringtoolbox-11] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^æ ^ø ^å ^aa ^ab ^ac ^ad he Engineering Tool Box: Thermal Conductivity of some common Materials

[marble-institute-12] ^ ^a ^b ^c ^d ^e ^f ^g ^h Marble Institute

[notziger-13] Soil Temperature Changes with Time and Depth: Theory, D.L. Nofziger

[14] "Rockwool Flexibatts information". Arkiveret fra originalen 6. maj 2011. Hentet 2011-03-02.

[15] ttp://usa.dupontteijinfilms.com/wp-content/uploads/2017/01/Mylar_Physical_Properties.pdf

Specifik varmeledningsevne

Varmeledningsevnetabel

Kilder/referencer

Se også

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