myte?
- Trådstarter montesi
- Startdato
G
Gjestemedlem
Gjest
En isoporplate er jo fylt med luft/gass lommer og virker isolerende på temperatur. Kan ikke se hvorfor det skal være en ulempe å bruke dette i kaldt vær.
Glimrende liggeunderlag.
Den reflekterer nok. Isopor blir jo støpt ned nedenfor varmekablene i et gulv. Det er så at varmen skal gå opp i gulvet og ikke ned i bakken.
Jeg har dog ikke prøvd å legge meg ute en vinternatt på et stykke isopor.
Jeg har dog ikke prøvd å legge meg ute en vinternatt på et stykke isopor.
Dette lar seg jo lett teste ut montesi.
Mens en fremdeles kan oppleve minusgrader om natta regner jeg med at du stiller som
prøvekanin nå i natt.
Hører vi ifra deg i morgen tidlig er myten død. Ev. kaninen ble kylling.
Hører vi ikke ifra deg i morgen tidlig er myten sann. Ev. kaninen ble større kylling.
Å, hvor jeg gleder meg til morgengry.
Mens en fremdeles kan oppleve minusgrader om natta regner jeg med at du stiller som
prøvekanin nå i natt.
Hører vi ifra deg i morgen tidlig er myten død. Ev. kaninen ble kylling.
Hører vi ikke ifra deg i morgen tidlig er myten sann. Ev. kaninen ble større kylling.
Å, hvor jeg gleder meg til morgengry.
Det må være en myte og i tillegg en myte ingen noengang har hørt om før ;D
Isopor har dårlig varmeledingsevne og liten varmekapasistet. Ypperlig som isolasjon mao. Hva er da problemet? Hadde den absorbert mye varme, noe det selvfølgelig ikke gjør, hadde den vært dårlig til isolasjon men god til varmemagasinering.
Isopor har dårlig varmeledingsevne og liten varmekapasistet. Ypperlig som isolasjon mao. Hva er da problemet? Hadde den absorbert mye varme, noe det selvfølgelig ikke gjør, hadde den vært dårlig til isolasjon men god til varmemagasinering.
Forslag til morosamt experiment:
Legg en frossen kylling på et isoporstykke, og en frozen kanin i ei stålpanne. Kaninen mykner først, og hva kan så grunnen være?
En mulighet er at isoporen er en dårlig varmeleder...
En annen er at kyllingen har tatt seg en flyvetur og på den måten undradd seg fysikkens lover.
Sånn kan det gå.
Delle
Legg en frossen kylling på et isoporstykke, og en frozen kanin i ei stålpanne. Kaninen mykner først, og hva kan så grunnen være?
En mulighet er at isoporen er en dårlig varmeleder...
En annen er at kyllingen har tatt seg en flyvetur og på den måten undradd seg fysikkens lover.
Sånn kan det gå.
Delle
Isolasjon har den evnen at den ikke overfører varme. Det er ikke slik at den reflekterer varme.
Hvis noen har krabbet litt på isopor, så opplever man rask at man kan få brennmerker - dette skyldes at friksjonsvarmen som oppstår, ikke blir overført til underlaget, derfor oppstår det høy temperatur.
Hvis man skal beskytte seg mot kulde, ønsker man å ha et isolerende lag mellom seg og de kalde omgivelsene for at din kroppsvarme ikke skal transportres bort. Jeg kan ikke skjønne annet enn at å sove på en isoporplate skal være helt greit. Men jeg er ikke sikker på at den har bedre isoleringsevne enn et dedikert liggeunderlag med luft.
Men legg deg nå ikke ut i tanga og to isoporplater og skyld på meg hvis du fryser ihjel!
Mvh
OMF
J
jjev
Gjest
Hva da om man legger seg på en plate av kleberstein. Det er jo et materiale med god varmemagasinering....
Hmmm.....??!!??
K
knutinh
Gjest
En god test er vel å stikke tunga bortpå materialet i 25 minusgrader. Hvis den slipper taket er det greit, hvis den sitter fast bør du unngå å bruke det som liggeunderlag ;-)
-k
-k
O
OldBoy
Gjest
Man kan sikkert fryse i hjel dersom man forøvrig ikke beskytter seg på annen måte mot nedkjøling.
Men et isoporunderlag vil uansett forsinke nedkjølingen, og dermed øke sannsynligheten for å overleve en kald vinternatt ute.
Grunnen til at man fryser i hjel er at kroppens varmetap i en lengre periode er større enn kroppens varmeproduksjon. Varmetap er en funksjon av temperaturforskjell (mellom kropp og omgivelser) og varmeledningsevne til det vi kler kroppen med.
Tykt, tørt og luftfylt = liten varmeledningsevne = lurt å ha på seg og/eller ligge på når det er kaldt.
Tynt, vått og kompakt = høy varmeledningsevne = dumt å ha på seg og/eller ligge på når det er kaldt.
Isopor er en utmerket isolator, og vil derfor hindre varmetap. Til bakken, hvis man bruker det som liggeunderlag, og hele veien rundt, hvis man pakker seg inn i det.
Kler man i tillegg isoporen med et varmereflekterende lag, blir varmetapet enda mindre enn uten dette reflekterende laget. Et knep man benytter seg av når man skal redde mennesker som er blitt utsatt for ekstrem nedkjøling. Da pakker man dem inn i noe som både isolerer og reflekterer, slik at varmetapet blir minimalt. Til vanlig turbruk holder det lenge med vanlig isopor.
G
Gjestemedlem
Gjest
Hvis platen var oppvarmet på forhånd og isolert mot hurtig varmetap ville det sikkert være en god ide. Men har den ligget ute vil du nok oppdage at den samme magasineffekten gjør den svært tung å varme opp. Du skal ihvertfall ikke bruke din egen kropp til dette.
- Ble medlem
- 19.10.2006
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Alle som har ligget på OP i militæret en vinternatt, vet at liggeunderlaget er gull verdt
O
OldBoy
Gjest
Du er inne på noe veldig viktig her. Fordamping er en stor varmetyv, og er farlig for den som er forfrossen.
Ettersom luft i bevegelse setter fart på fordampingen, vil det å pakke inn forfrosne mennesker i reflekterende folie, helt sikkert bidra til å redusere fordampingen, men en slik effekt kunne man jo få til med en vanlig vindtett folie også, for eksempel en plastduk. Det reflekterende belegget bidrar, i tillegg til å redusere fordampingen, til å redusere varmeutstrålingen, så med vindtett + reflekterende får man i pose og sekk.
K
knutinh
Gjest
http://en.wikipedia.org/wiki/Heat
"In physics, heat, symbolized by Q, is defined as energy in transit.[1] Generally, heat is a form of energy transfer, sometimes called thermal energy, associated with the different motions of atoms, molecules and other particles that comprise matter when it is hot and when it is cold. High temperature bodies, which often result in high heat transfer, can be created by chemical reactions (such as burning), nuclear reactions (such as fusion taking place inside the Sun), electromagnetic dissipation (as in electric stoves), or mechanical dissipation (such as friction). Heat can be transferred between objects by radiation, conduction and convection. Temperature is used as a measure of the internal energy or enthalpy, that is the level of elementary motion giving rise to heat transfer. Heat can only be transferred between objects, or areas within an object, with different temperatures (as given by the zeroth law of thermodynamics), and then, in the absence of work, only in the direction of the colder body (as per the second law of thermodynamics). The temperature and state of a substance subject to heat transfer are determined by latent heat and heat capacity.
Heat transfer mechanisms
As mentioned previously, heat tends to move from a high temperature region to a low temperature region. This heat transfer may occur by the mechanisms conduction and radiation. In engineering, the term convective heat transfer is used to describe the combined effects of conduction and fluid flow and is regarded as a third mechanism of heat transfer
Conduction
Conduction is the most significant means of heat transfer in a solid. On a microscopic scale, conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring atoms. In insulators the heat flux is carried almost entirely by phonon vibrations.
The "electron fluid" of a conductive metallic solid conducts nearly all of the heat flux through the solid. Phonon flux is still present, but carries less than 1% of the energy. Electrons also conduct electric current through conductive solids, and the thermal and electrical conductivities of most metals have about the same ratio. A good electrical conductor, such as copper, usually also conducts heat well. The Peltier-Seebeck effect exhibits the propensity of electrons to conduct heat through an electrically conductive solid. Thermoelectricity is caused by the relationship between electrons, heat fluxes and electrical currents.
Convection
Convection is usually the dominant form of heat transfer in liquids and gases. This is a term used to characterize the combined effects of conduction and fluid flow. In convection, enthalpy transfer occurs by the movement of hot or cold portions of the fluid together with heat transfer by conduction. For example, when water is heated on a stove, hot water from the bottom of the pan rises, heating the water at the top of the pan. Two types of convection are commonly distinguished, free convection, in which gravity and buoyancy forces drive the fluid movement, and forced convection, where a fan, stirrer, or other means is used to move the fluid. Buoyant convection is because of the effects of gravity, and hence does not occur in microgravity environments.
Radiation
Radiation is the only form of heat transfer that can occur in the absence of any form of medium and as such is the only means of heat transfer through a vacuum. Thermal radiation is a direct result of the movements of atoms and molecules in a material. Since these atoms and molecules are composed of charged particles (protons and electrons), their movements result in the emission of electromagnetic radiation, which carries energy away from the surface. At the same time, the surface is constantly bombarded by radiation from the surroundings, resulting in the transfer of energy to the surface. Since the amount of emitted radiation increases with increasing temperature, a net transfer of energy from higher temperatures to lower temperatures results.
The frequencies of the emitted photons are described by the Planck distribution. A black body at higher temperature will emit photons having a distributional peak at a higher frequency than will a colder object, and their respective spectral peaks will be separated according to Wien's displacement law. The photosphere of the Sun, at a temperature of approximately 6000 K, emits radiation principally in the visible portion of the spectrum. The solar radiation incident upon the earth's atmosphere is largely passed through to the surface. The atmosphere is largely transparent in the visible spectrum. However, in the infrared spectrum that is characteristic of a blackbody at 300K, the temperature of the earth, the atmosphere is largely opaque. The blackbody radiation from earth's surface is absorbed or scattered by the atmosphere. Though some radiation escapes into space, it is the radiation absorbed and subsequently emitted by atmospheric gases. It is this spectral selectivity of the atmosphere that is responsible for the planetary greenhouse effect.
The behavior of a common household lightbulb has a spectrum overlapping the blackbody spectra of the sun and the earth. A portion of the photons emitted by a tungsten light bulb filament at 3000K lie in the visible spectrum. However, the majority of the photonic energy is associated with longer wavelengths and will transfer heat to the environment, as can be deduced empirically by observing a household incandescent lightbulb. Whenever EM radiation is emitted and then absorbed, heat is transferred. This principle is used in microwave ovens, laser cutting, and RF hair removal.
"
"In physics, heat, symbolized by Q, is defined as energy in transit.[1] Generally, heat is a form of energy transfer, sometimes called thermal energy, associated with the different motions of atoms, molecules and other particles that comprise matter when it is hot and when it is cold. High temperature bodies, which often result in high heat transfer, can be created by chemical reactions (such as burning), nuclear reactions (such as fusion taking place inside the Sun), electromagnetic dissipation (as in electric stoves), or mechanical dissipation (such as friction). Heat can be transferred between objects by radiation, conduction and convection. Temperature is used as a measure of the internal energy or enthalpy, that is the level of elementary motion giving rise to heat transfer. Heat can only be transferred between objects, or areas within an object, with different temperatures (as given by the zeroth law of thermodynamics), and then, in the absence of work, only in the direction of the colder body (as per the second law of thermodynamics). The temperature and state of a substance subject to heat transfer are determined by latent heat and heat capacity.
Heat transfer mechanisms
As mentioned previously, heat tends to move from a high temperature region to a low temperature region. This heat transfer may occur by the mechanisms conduction and radiation. In engineering, the term convective heat transfer is used to describe the combined effects of conduction and fluid flow and is regarded as a third mechanism of heat transfer
Conduction
Conduction is the most significant means of heat transfer in a solid. On a microscopic scale, conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring atoms. In insulators the heat flux is carried almost entirely by phonon vibrations.
The "electron fluid" of a conductive metallic solid conducts nearly all of the heat flux through the solid. Phonon flux is still present, but carries less than 1% of the energy. Electrons also conduct electric current through conductive solids, and the thermal and electrical conductivities of most metals have about the same ratio. A good electrical conductor, such as copper, usually also conducts heat well. The Peltier-Seebeck effect exhibits the propensity of electrons to conduct heat through an electrically conductive solid. Thermoelectricity is caused by the relationship between electrons, heat fluxes and electrical currents.
Convection
Convection is usually the dominant form of heat transfer in liquids and gases. This is a term used to characterize the combined effects of conduction and fluid flow. In convection, enthalpy transfer occurs by the movement of hot or cold portions of the fluid together with heat transfer by conduction. For example, when water is heated on a stove, hot water from the bottom of the pan rises, heating the water at the top of the pan. Two types of convection are commonly distinguished, free convection, in which gravity and buoyancy forces drive the fluid movement, and forced convection, where a fan, stirrer, or other means is used to move the fluid. Buoyant convection is because of the effects of gravity, and hence does not occur in microgravity environments.
Radiation
Radiation is the only form of heat transfer that can occur in the absence of any form of medium and as such is the only means of heat transfer through a vacuum. Thermal radiation is a direct result of the movements of atoms and molecules in a material. Since these atoms and molecules are composed of charged particles (protons and electrons), their movements result in the emission of electromagnetic radiation, which carries energy away from the surface. At the same time, the surface is constantly bombarded by radiation from the surroundings, resulting in the transfer of energy to the surface. Since the amount of emitted radiation increases with increasing temperature, a net transfer of energy from higher temperatures to lower temperatures results.
The frequencies of the emitted photons are described by the Planck distribution. A black body at higher temperature will emit photons having a distributional peak at a higher frequency than will a colder object, and their respective spectral peaks will be separated according to Wien's displacement law. The photosphere of the Sun, at a temperature of approximately 6000 K, emits radiation principally in the visible portion of the spectrum. The solar radiation incident upon the earth's atmosphere is largely passed through to the surface. The atmosphere is largely transparent in the visible spectrum. However, in the infrared spectrum that is characteristic of a blackbody at 300K, the temperature of the earth, the atmosphere is largely opaque. The blackbody radiation from earth's surface is absorbed or scattered by the atmosphere. Though some radiation escapes into space, it is the radiation absorbed and subsequently emitted by atmospheric gases. It is this spectral selectivity of the atmosphere that is responsible for the planetary greenhouse effect.
The behavior of a common household lightbulb has a spectrum overlapping the blackbody spectra of the sun and the earth. A portion of the photons emitted by a tungsten light bulb filament at 3000K lie in the visible spectrum. However, the majority of the photonic energy is associated with longer wavelengths and will transfer heat to the environment, as can be deduced empirically by observing a household incandescent lightbulb. Whenever EM radiation is emitted and then absorbed, heat is transferred. This principle is used in microwave ovens, laser cutting, and RF hair removal.
"