Thermal conductivity of Gases

Thermal conductivity (λ) is an intrinsic property of a material which relates its ability to conduct heat. Heat transfer by conduction involves transfer of energy within the material without the motion of the material as a whole. Thermal conductivity can be defined as the quantity of heat (Q) in a direction normal to a surface of unit area (A) transmitted through a unit thickness (L) because of a unit temperature gradient (ΔT) under steady state conditions and when the heat transfer is dependent on the temperature gradient only. Thermal conductance is the quantity of heat which passes in unit time through a plate of specific area and thickness when its opposite faces differ in temperature by one Kelvin. Conduction takes place when the temperature gradient is present in a solid medium. Conductive heat flow occurs in direction of decreasing temperature because higher temperature equates to the higher molecular energy or more molecular movement. Energy is transferred from more energetic to the less energetic molecules when the nearby molecules collide.  Thermal conductivity is quantity of heat transmitted through the unit thickness in a direction normal to a surface of unit area, because of a unit temperature gradient under steady state conditions. The thermal conductivity of a substance is a measure of the capacity of it to conduct heat. Heat tends to flow in the homogeneous body in the direction of temperature gradient, from regions of higher temperature towards region of lower temperature. The rate of heat flow or the amount of heat which flows though a given cross section per unit time is proportional to the area of the cross section and to the magnitude of temperature gradient normal to this cross section.  Heat transfer by conduction involves transfer of energy within the material without any motion of the material as a whole. The rate of heat transfer depends upon temperature gradient and thermal conductivity of material. Gases transfer heat by direct collisions between molecules, and as would be expected, their thermal conductivity is low compared to most solids as they are dilute media. Conceptually, thermal conductivity may be thought of as the container for medium-dependent properties which relate rate of heat loss per unit area to the rate of change of temperature.