Thermal conductivity is to transfer heat from the hotter parts of the compound in a less heated, resulting in the alignment of temperature of the material.Molecules of substances with greater energy, transfer it to molecules with lower energy.It relates conductivity Fourier law which is due to the temperature gradient between the environment and the heat flow density.Gradient - a vector indicating the direction of change of the scalar field.Deviations from this law may be in very strong shock waves (high values of the gradient), at very low temperatures, and in rarefied gases when molecules of a substance often faced with the vessel walls than among themselves.In the case of rarefied gas heat transfer it is not seen as heat, and as the heat trans
fer between bodies in the gaseous environment.
Convection - is the transfer of heat in liquids, gases or solids, according to the kinetic theory of acting.The essence of the kinetic theory is that all of the body (material) composed of atoms and molecules that are in continuous movement.Based on this theory, a convection heat transfer between the materials at the molecular level, with the proviso that the body under the action of gravity and unevenly heated.The heated material, by gravity, moves relatively less heated material in the direction opposite to gravity.Hotter material to rise and cooler - are omitted.The attenuation action of convection is observed in cases of high thermal conductivity and a viscous medium, as well as in the ionized gas convection greatly affects the degree of ionization and the magnetic field.
Thermal radiation.The substance of the internal energy of an electromagnetic radiation with a continuous spectrum, which can be transmitted between substances.On how the substance is heated, it depends on the position of the maximum of the spectrum.The higher the temperature, the more energy is released substance and, therefore, the more heat can be transferred.
Heat transfer can occur through the thin partition wall, or between bodies from a warmer substance to a less warm.Hotter material transfers the heat to the wall, after which the process of heat transfer from the wall and the wall is less than heat transfer to the heated substance.The intensity of the transmitted heat amount depends on the heat transfer coefficient, which is defined as the amount of heat transmitted through a unit area per unit time partitions temperature difference between the substances in one Kelvin.
- Physical encyclopedia