What is thermal conductivity? (article) | Khan Academy
Thermal conductivity varies with temperature of the body rather than the error as the thermal conductivity and temperature generally follow a linear relation. IN GENERAL, the thermal conductivity of gases increases with temperature. Thermal conductivity of liquids decreases with increasing temperature as the liquid . I am looking for a relationship between thermal conductivity of water as a. thermal resistivity (Θ=T/κ) to interpret these completely different κ~T relations. metallic film whose temperature dependent thermal conductivity has been.
The general results of the careful analysis of the table Thermal conductivity of the liquids is more than the gasses and the metals have the highest. Thermal conductivity of the gases and liquids increases with the increase in temperature. Thermal conductivity of the metal decreases with the increase in temperature.
Thermal conductivity is affected by the phase change. These differences can be explained partially by the fact that while in gaseous state, the molecules of a substance are spaced relatively far away and their motion is random.Intuition behind formula for thermal conductivity - Physics - Khan Academy
Electrical conductivity[ edit ] In metals, thermal conductivity approximately tracks electrical conductivity according to the Wiedemann—Franz lawas freely moving valence electrons transfer not only electric current but also heat energy. However, the general correlation between electrical and thermal conductance does not hold for other materials, due to the increased importance of phonon carriers for heat in non-metals.
Highly electrically conductive silver is less thermally conductive than diamondwhich is an electrical insulatorbut due to its orderly array of atoms it is conductive of heat via phonons.
Magnetic field[ edit ] The influence of magnetic fields on thermal conductivity is known as the thermal Hall effect or Righi—Leduc effect. Gaseous phases[ edit ] Exhaust system components with ceramic coatings having a low thermal conductivity reduce heating of nearby sensitive components Air and other gases are generally good insulators, in the absence of convection.
Therefore, many insulating materials function simply by having a large number of gas-filled pockets which obstruct heat conduction pathways. Examples of these include expanded and extruded polystyrene popularly referred to as "styrofoam" and silica aerogelas well as warm clothes. Natural, biological insulators such as fur and feathers achieve similar effects by trapping air in pores, pockets or voids, thus dramatically inhibiting convection of air or water near an animal's skin.
Thus, in multicomponent gas mixtures energy transfer is also accomplished, in addition to convection and heat conduction, by diffusion flow of molecules relative to the bulk velocity and by the Dufour effect. It characterizes the velocity of propagation of isothermal surfaces in a body. The degree of accuracy depends on the initial and boundary conditions. Numerous theoretical and experimental investigations have led to the discovery of some specific features and regularities.
Amongst the metals silver shows the highest thermal conductivity and bismuth the lowest. For metals it depends to a great extent on their treatment. The values of the coefficient of thermal conductivity for various substances at atmospheric pressure and moderate temperatures Thermal conductivity of nonmetallic liquids under normal conditions is much lower than that of metals and ranges from 0.
Thermal conductivity - Wikipedia
In the interval between the melting point and the boiling point, thermal conductivity of liquids may change by a factor of 1. Finally, the lowest thermal conductivity is observed in gases under normal conditions it is from 0.
Hydrogen and helium are distinguished among gases for the highest thermal conductivity. The coefficients of thermal conductivity presented in the table evidence that this parameter varies widely. It is determined using various techniques based on the molecular kinetic theory, the phenomenological approaches of the generalized conductivity theory, and generalization of experimental data.
Below the investigation results are presented for the different classes of substances. The Theory of Gas Thermal Conductivity Thermal conductivity in gases is brought about by energy transfer by gas molecules in the same way as viscosity is related with momentum transfer and diffusion, with mass transfer.
Therefore, all these phenomena appreciably depend onthat is the mean free path of molecules. Contemporary kinetic theory takes into account the existence of the attraction and repulsion forces between molecules. Expression for these forces can in principle be derived from quantum mechanics although this is a laborious task if all atoms and molecules are considered, except in the simplest ones. Therefore, the molecular interaction is described, as a rate, by simple empirical functions, that is interaction potentials containing variable parameters.
Selection of interaction potentials allows us to construct theoretical models, which quite adequately approximate experimental data for nonatomic gases over the entire temperature range, except for the very lowest temperatures, where light gases exhibit quantum effects.
Euken's relation can be explained theoretically if we assume that energy exchange between translational and the remaining degrees of freedom takes little time, i. Euken's hypothesis better agrees with reality at high temperatures when the number of collisions per second is great.
Many efforts have been made to attain a better consistency with experimental data for polyatomic gases by a further complication of the model of energy exchange between degrees of freedom. Thus, Mason and Monchick discussed another limit case when the time of relaxation is long. Taking into account this fact leads to a smaller contribution of translational and a larger contribution of rotational degrees of freedom to thermal conductivity.