Qhov tshwm sim ntawm thermal conductivity yog kev hloov pauv ntawm lub zog nyob rau hauv daim ntawv ntawm tshav kub nyob rau hauv kev sib cuag ncaj qha ntawm ob lub cev yam tsis muaj kev sib pauv ntawm cov teeb meem los yog nrog nws sib pauv. Hauv qhov no, lub zog dhau los ntawm ib lub cev lossis thaj chaw ntawm lub cev nrog qhov kub siab dua mus rau lub cev lossis thaj chaw uas muaj qhov kub thiab txias. Cov yam ntxwv ntawm lub cev uas txiav txim siab qhov tsis hloov pauv ntawm cov cua sov yog thermal conductivity. Dab tsi yog thermal conductivity, thiab nws piav qhia hauv physics li cas? Kab lus no yuav teb cov lus nug no.
Lub tswv yim dav dav ntawm thermal conductivity thiab nws qhov xwm
Yog tias koj teb cov lus yooj yooj yim cov lus nug ntawm dab tsi thermal conductivity yog nyob rau hauv physics, ces nws yuav tsum tau hais tias cov cua sov hloov ntawm ob lub cev los yog ntau qhov chaw ntawm tib lub cev yog ib tug txheej txheem ntawm internal zog pauv ntawm cov hais. tsim lub cev (molecules, atoms, electrons thiab ions). Lub zog sab hauv nws tus kheej muaj ob qhov tseem ceeb: lub zog kinetic thiab lub zog muaj peev xwm.
Dab tsi yog thermal conductivity hauv physics los ntawm qhov pom ntawm qhov xwm txheej ntawm qhov notus nqi? Ntawm qib microscopic, lub peev xwm ntawm cov ntaub ntawv los ua cua sov nyob ntawm lawv cov microstructure. Piv txwv li, rau cov kua thiab gases, cov txheej txheem ntawm lub cev no tshwm sim vim muaj kev sib tsoo ntawm cov molecules; nyob rau hauv cov khib nyiab, qhov sib faib tseem ceeb ntawm cov hluav taws xob xa mus poob rau ntawm kev sib pauv ntawm lub zog ntawm cov hluav taws xob dawb (hauv cov tshuab hlau) lossis phonons (cov khoom tsis yog xim hlau.), uas yog txhua yam kev vibrations ntawm cov siv lead ua lattice.
lej sawv cev ntawm thermal conductivity
Cia peb teb cov lus nug ntawm qhov thermal conductivity yog dab tsi, los ntawm kev ua lej ntawm qhov pom. Yog hais tias peb coj ib tug homogeneous lub cev, ces tus nqi ntawm tshav kub kis los ntawm nws nyob rau hauv ib tug muab kev taw qhia yuav proportional rau lub nto cheeb tsam perpendicular mus rau cov kev taw qhia ntawm tshav kub hloov lwm lub tsev, thermal conductivity ntawm cov khoom nws tus kheej thiab qhov kub ntawm qhov sib txawv ntawm qhov kawg. lub cev, thiab tseem yuav hloov pauv mus rau qhov tuab ntawm lub cev.
Qhov tshwm sim yog tus qauv: Q/t=kA(T2-T1)/x, ntawm no Q/t - tshav kub (zog) kis los ntawm lub cev nyob rau hauv lub sij hawm t, k - coefficient ntawm thermal conductivity ntawm cov khoom los ntawm lub cev txiav txim siab yog tsim, A - cross-sectional cheeb tsam ntawm lub cev, T 2 -T 1 - kub sib txawv ntawm qhov kawg ntawm lub cev, nrog T2>T1, x - tuab ntawm lub cev los ntawm qhov cua sov Q hloov mus.
Txoj kev hloov pauv thermal zog
Xav txog cov lus nug ntawm dab tsi yog qhov thermal conductivity ntawm cov ntaub ntawv, peb yuav tsum hais txog cov txheej txheem ntawm kev hloov cua sov. Lub zog cua sov tuaj yeem hloov pauv ntawm lub cev sib txawv sivCov txheej txheem hauv qab no:
- conductivity - cov txheej txheem no mus yam tsis muaj teeb meem hloov pauv;
- convection - hloov hluav taws xob ncaj qha rau kev txav ntawm qhov teeb meem nws tus kheej;
- hluav taws xob - hloov hluav taws xob yog ua los ntawm hluav taws xob hluav taws xob, uas yog, nrog kev pab ntawm photons.
txhawm rau kom cov cua sov hloov mus siv cov txheej txheem ntawm kev sib txuas lossis kev sib txuas, kev sib cuag ncaj qha ntawm lub cev sib txawv yog qhov tsim nyog, nrog rau qhov sib txawv ntawm cov txheej txheem ntawm conduction tsis muaj macroscopic txav ntawm cov teeb meem, tab sis nyob rau hauv tus txheej txheem ntawm kev sib txawv. convection no txav yog tam sim no. Nco ntsoov tias kev txav mus los ntawm microscopic tshwm sim hauv txhua qhov kev hloov pauv cua sov.
Rau qhov kub ib txwm ntawm ntau kaum degrees Celsius, nws tuaj yeem hais tias convection thiab conduction account rau feem ntau ntawm cov cua sov xa mus, thiab tus nqi ntawm lub zog xa mus rau hauv cov txheej txheem hluav taws xob yog negligible. Txawm li cas los xij, hluav taws xob pib ua lub luag haujlwm tseem ceeb hauv cov txheej txheem hloov hluav taws xob ntawm qhov kub thiab txias ntawm ntau pua thiab txhiab Kelvin, txij li lub zog Q hloov mus rau hauv txoj kev no nce ntxiv rau 4 lub zog ntawm qhov kub thiab txias, uas yog, ∼ T. 4. Piv txwv li, peb lub hnub poob feem ntau ntawm nws lub zog los ntawm hluav taws xob.
Thermal conductivity ntawm solids
Vim nyob rau hauv cov khib nyiab txhua molecule los yog atom nyob rau hauv ib txoj hauj lwm thiab tsis tuaj yeem tawm ntawm nws, kev hloov ntawm tshav kub los ntawm convection yog tsis yooj yim sua, thiab tsuas yog cov txheej txheem ua tau.conductivity. Nrog rau qhov nce hauv lub cev kub, lub zog kinetic ntawm nws cov khoom sib xyaw ua ke nce, thiab txhua lub molecule lossis atom pib oscillate ntau dua. Cov txheej txheem no ua rau lawv sib tsoo nrog cov molecules nyob sib ze lossis atoms, vim tias qhov kev sib tsoo zoo li no tau hloov pauv los ntawm cov khoom mus rau cov khoom kom txog rau thaum tag nrho cov khoom ntawm lub cev raug them los ntawm cov txheej txheem no.
Raws li qhov tshwm sim ntawm qhov tau piav qhia lub tshuab ua kom pom tseeb, thaum ib qho kawg ntawm tus pas hlau hlau tau rhuab, qhov kub thiab txias txawm tawm tag nrho cov pas nrig tom qab ib ntus.
Kub tsis hloov sib npaug hauv cov khoom sib txawv. Yog li, muaj cov ntaub ntawv uas muaj thermal conductivity zoo. Lawv yooj yim thiab sai ua cua sov los ntawm lawv tus kheej. Tab sis kuj tseem muaj cov khoom siv hluav taws xob tsis zoo lossis cov insulators los ntawm qhov tsawg lossis tsis muaj cua sov tuaj yeem dhau mus.
Coefficient ntawm thermal conductivity rau cov khoom
Cov thermal conductivity coefficient rau cov khib nyiab k muaj lub ntsiab lus hauv qab no: nws qhia txog cov cua sov uas dhau los ntawm ib chav tsev ib lub sij hawm los ntawm ib cheeb tsam ntawm chav nyob hauv ib lub cev ntawm chav tsev thickness thiab ntev ntev thiab dav nrog qhov kub thiab txias sib txawv ntawm nws xaus sib npaug rau ib degree. Nyob rau hauv lub thoob ntiaj teb system ntawm units SI, tus coefficient k yog ntsuas nyob rau hauv J / (smK).
Qhov coefficient hauv cov khib nyiab no nyob ntawm qhov kub thiab txias, yog li nws yog ib txwm ua los txiav txim siab nws ntawm qhov kub ntawm 300 K txhawm rau sib piv lub peev xwm ua kom sov.ntau yam ntaub ntawv.
Thermal conductivity coefficient rau cov hlau thiab cov khoom tsis yog xim hlau
Txhua cov hlau, yam tsis muaj kev zam, yog cov khoom siv hluav taws xob zoo, rau kev hloov pauv uas lawv yog lub luag haujlwm rau cov roj hluav taws xob. Nyob rau hauv lem, ionic thiab covalent cov ntaub ntawv, raws li zoo raws li cov ntaub ntawv nrog ib tug fibrous qauv, yog zoo tshav kub insulators, uas yog, lawv ua cua sov tsis zoo. Txhawm rau ua kom tiav qhov kev nthuav tawm ntawm cov lus nug ntawm qhov thermal conductivity yog dab tsi, nws yuav tsum tau muab sau tseg tias cov txheej txheem no yuav tsum muaj lub luag haujlwm tseem ceeb ntawm cov teeb meem yog tias nws tau ua tiav vim yog convection lossis conduction, yog li ntawd, hauv lub tshuab nqus tsev, cov cua sov tuaj yeem hloov mus rau hauv lub tshuab nqus tsev. electromagnetic tawg.
Cov npe hauv qab no qhia txog qhov tseem ceeb ntawm thermal conductivity coefficients rau qee cov hlau thiab cov hlau tsis muaj hlau hauv J / (smK):
- steel - 47-58 nyob ntawm qib steel;
- aluminium - 209, 3;
- bronze - 116-186;
- zinc - 106-140 nyob ntawm purity;
- copper - 372, 1-385, 2;
- brass - 81-116;
- kub - 308, 2;
- silver - 406, 1-418, 7;
- rubber - 0, 04-0, 30;
- fiberglass - 0.03-0.07;
- bib - 0, 80;
- ntoo - 0, 13;
- iav - 0, 6-1, 0.
Yog li, cov thermal conductivity ntawm cov hlau yog 2-3 qhov kev txiav txim siab ntau dua li cov thermal conductivity qhov tseem ceeb rau cov insulators, uas yog ib qho piv txwv tseem ceeb ntawm cov lus teb rau cov lus nug ntawm qhov tsawg thermal conductivity yog dab tsi.
Tus nqi ntawm thermal conductivity plays lub luag haujlwm tseem ceeb hauv ntau yamcov txheej txheem kev lag luam. Hauv qee cov txheej txheem, lawv nrhiav kom nws los ntawm kev siv cov khoom siv hluav taws xob zoo thiab ua rau thaj chaw sib cuag, thaum lwm tus lawv sim txo cov thermal conductivity los ntawm kev txo qhov chaw sib cuag thiab siv cov khoom siv hluav taws xob.
Convection hauv kua thiab roj
Kev hloov pauv ntawm cov cua sov hauv cov kua dej yog ua los ntawm cov txheej txheem ntawm convection. Cov txheej txheem no suav nrog kev txav ntawm cov molecules ntawm cov khoom nruab nrab ntawm thaj chaw uas muaj qhov sib txawv ntawm qhov kub thiab txias, uas yog, thaum lub sij hawm convection, cov kua los yog roj sib xyaw. Thaum cov kua dej tso tawm cua sov, nws cov molecules poob ib co ntawm lawv lub zog kinetic thiab qhov teeb meem yuav denser. Ntawm qhov tsis sib xws, thaum cov kua dej yog rhuab, nws cov molecules nce lawv lub zog kinetic, lawv lub zog yuav hnyav dua, raws li, qhov ntim ntawm cov teeb meem nce, thiab qhov ntom ntom. Tias yog vim li cas cov khaubncaws sab nraud povtseg ntawm cov teeb meem txias yuav poob rau hauv lub zog ntawm lub ntiajteb txawj nqus, thiab cov khaubncaws sab nraud povtseg kub sim nce. Cov txheej txheem no ua rau kev sib xyaw ntawm cov teeb meem, ua kom yooj yim hloov cov cua sov ntawm nws cov khaubncaws sab nraud povtseg.
Thermal conductivity ntawm qee cov kua
Yog tias koj teb cov lus nug ntawm dab tsi yog qhov thermal conductivity ntawm dej, nws yuav tsum to taub tias nws yog vim cov txheej txheem convection. Lub thermal conductivity coefficient yog 0.58 J / (smK).
Rau lwm cov kua, tus nqi no tau teev tseg hauv qab no:
- ethyl cawv - 0.17;
- acetone - 0, 16;
- glycerol - 0, 28.
Qhov ntawd yog, qhov tseem ceebThermal conductivities rau cov kua yog piv rau cov khoom siv hluav taws xob insulators.
Convection hauv huab cua
Atmospheric convection tseem ceeb vim nws ua rau muaj tshwm sim xws li cua, cua daj cua dub, huab tsim, nag thiab lwm yam. Tag nrho cov txheej txheem no ua raws li cov cai ntawm lub cev ntawm thermodynamics.
Ntawm cov txheej txheem ntawm convection nyob rau hauv cov huab cua, qhov tseem ceeb tshaj plaws yog lub voj voog dej. Ntawm no peb yuav tsum xav txog cov lus nug ntawm dab tsi yog qhov thermal conductivity thiab kub muaj peev xwm ntawm dej. Lub peev xwm ntawm cov dej yog to taub raws li lub cev kom muaj nuj nqis uas qhia tias muaj cua sov ntau npaum li cas yuav tsum tau xa mus rau 1 kg dej kom nws qhov kub thiab txias nce los ntawm ib qho degree. Nws yuav muab 4220 J.
Lub voj voog dej yog ua raws li hauv qab no: lub hnub sov cov dej ntawm dej hiav txwv, thiab ib feem ntawm cov dej evaporates rau hauv qhov chaw. Vim cov txheej txheem ntawm convection, dej vapor nce mus rau qhov siab zoo, txias, huab cua thiab huab cua, uas ua rau nag lossis daus los nag.
