ISO 9288:2022 断熱 — 放射による熱伝達 — 用語、語彙 | ページ 10

7.1

spectral directional extinction coefficient

Note 1 to entry: Expressed in .

7.2

spectral directional absorption coefficient

Note 1 to entry: Expressed in .

7.3

spectral directional scattering coefficient

Note 2 to entry: Expressed in .

7.4

mass spectral directional extinction coefficient

Note 1 to entry: Expressed in .

7.5

mass spectral directional absorption coefficient

Note 1 to entry: Expressed in .

7.6

mass spectral directional scattering coefficient

Note 2 to entry: Expressed in .

7.7

spectral directional optical thickness

Note 1 to entry: A layer of thickness , is a measure of the ability of a given path length of semi-transparent material to attenuate thermal radiation of wavelength λ and for homogeneous isotropic and isothermal layers = constant, and .

7.8

phase function

Note 1 to entry: It represents the probability for an incident radiation inside the solid angle around the direction to be scattered in the unit solid angle around direction .

Note 2 to entry: It characterizes an anisotropic scattering material if the scattered radiation is isotropic .

7.9

spectral directional albedo

Note 1 to entry: For isotropic media, is independent of the direction and the spectral term ω_λ may replace it. For absorbing, non-scattering media , and for non-absorbing scattering media .

7.10

semi-transparent plane layer

semi-transparent layer of thickness , limited by two infinite, plane and parallel boundaries of given thermal and optical characteristics

7.11

equation of radiative transfer

mathematical relation describing the variation along a path of the spectral radiance (4.6) in an absorbing, emitting and scattering medium

Note 1 to entry: The solution of this equation depends on the radiative properties of the medium, e.g. spectral extinction coefficient, spectral albedo and spectral phase function (7.8), and on the thermal and optical boundary conditions.

7.12

Rosseland diffusion approximation

approximation of the equation of radiative transfer (7.11) considering the medium optically thick and without taking into consideration the boundary conditions

7.13

Schuster-Schwartzschild two-flux approximation

approximation of the equation of radiative transfer (7.11) for one dimensional planar geometry based on the assumption that the spectral radiances (4.6) with positive components of direction can be integrated in a single term, , while spectral radiances with negative components can be integrated in a single term,

Note 1 to entry: One dimensional planar geometry is a semi-transparent plane layer (7.10) .

7.14

radiative thermal conductivity

Note 1 to entry: These relations are the consequence of Rosseland approximation (7.12) and their advantage is that they provide simple relations to express the total radiative density of heat flow rate, similar to Fourier's law for pure conductive heat transfer.

Note 2 to entry: Expressed in .

7.15

transfer factor

Note 1 to entry: It can be derived from the measurement of , and in a guarded hot plate; it is a material property only when (see Figure 4), where is thickness and is the thickness when become constant.

7.16

radiativity

Note 1 to entry: It can be derived from the measurement of , and under vacuum when the conduction heat transfer in the solid matrix is negligible.

Note 2 to entry: Expressed in .

Note 3 to entry: In case of insulating materials, there can be situations where the thickness is high enough to allow for the characterization of the layer through the sum of two independent terms, one corresponding to conduction through the solid matrix and enclosed gas, and another to radiation. The last term is then called"radiativity", , as opposed to"conductivity". While considering only radiation heat transfer within an insulating material, radiativity is formally defined as radiative thermal conductivity, but to adhere to test procedures, it is best understood, thinking of material layers of increasing thickness, as an increment in layer thickness divided by the corresponding increment in layer resistance when the conditions outlined in 7.15 to 7.18 apply (see also Figure 4). In this case, 7.14 is identical to 7.16.

7.17

combined gaseous and solid conductivity

Note 1 to entry: Generally, is computed from a theoretical model.

Note 2 to entry: Expressed in .

7.18

thermal transmissivity

Note 1 to entry: According to the preceding definitions, the thermal transmissivity can also be written as .

Note 2 to entry: Thermal transmissivity can be seen as the limit reached by the transfer factor (7.15) in thick layers where combined conduction and radiation heat transferred are considered.