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Hagen-Poiseuille law Hagen-Rubens relation, between electrical and optical constants, Hall Taylor, N S, Halogenated hydrocarbons: Handley and Heggs equation for fixed bed pressure drop, Hankinson and Thomson method, for liquid density: Hardening (precipative) of stainless steels, Hardwick, R, Harris, D, Hausen equation for developing laminar flow, Hays, G F Headers in shell-and-tube heat exchangers, Heads, in heat exchangers: Heat and mass transfer: Heat exchanger design, introduction, Heat exchangers: Heat of vaporisation (see Enthalpy of vaporisation), of pure substances Heat pipes: Heat pumping, relation to heat exchanger network design, Heat storage (see Regenerators and thermal energy storage) entropy generation in, Heat transfer: Heat transfer coefficient: Heat transfer media, Heat transfer salt, Heat transfer regimes: Heat of vaporization, Heated cavity reflectometer, Heating media, for reboilers, Heavy water, physical properties of, Heggs, P J, Helical coils of circular cross section: Helical coils of rectangular cross section, Helical inserts, for enhancement of heat transfer in boiling, Helium: Helmholtz reciprocity principle, in radiative heat transfer, Henry, J A R, Henry-Fauske model, for critical two-phase flow, Henry's law, for partial pressure, Heptadecane: Heptadecene: Heptane: 1-Heptanol: 1-Heptene: Herman, K W, Hermes, C L L, Heterogeneous conveyance in horizontal pipes, Heterogeneous nucleation in boiling, Hewitt, G F Hexachloroethane (Refrigerant 116): Hexacyclopentane, superheated vapor properties, Hexadecane: Hexadecene: 1,5-Hexadiene: Hexagonal cells, in free convection, Hexamethylbenzene: Hexane: Hexanoic acid: 1-Hexanol: 1-Hexene: Hexylbenzene: Hexylcyclohexane: Hexylcyclopentane, Hicks equation, for fixed-bed pressure drop, High pressure closures, ASME VIII code guidance for, High-chrome steels, thermal and mechanical properties, High-finned tubes, correlations for single-phase heat transfer in flow over, Hills, P D Hohlraum cavity, Holdup, in liquid-liquid flow, Holland, guide to national practice for mechanical design of heat exchangers, Homogeneous condensation (fog formation), Homogeneous model: Homogeneous nucleation: Honeycombs: Hopkins, D, Horizontal condensers: Horizontal cylinders: Horizontal layers, of fluid, free convection heat transfer in, Horizontal pipes: Horizontal shell-side evaporator, Horizontal surfaces: Horizontal thermosiphon reboilers: Horizontal tube-side evaporator, Horizontal tubes: Hottel's rule, in absorption of radiation by gases, Hsu criterion, for onset of nucleate boiling, Hybrid cooling towers, Hydraulic conveyance: Hydraulic expansion, of tubes into tube sheets in shell-and-tube heat exchangers, Hydraulic turbine, lost work in, Hydraulic resistance, in flow of supercritical fluids, Hydraulically smooth surface, Hydrazine: Hydrocarbons: Hydrodynamic entrance length, in single-phase flow in ducts, Hydrogen: Hydrogen bromide: Hydrogen chloride: Hydrogen cyanide: Hydrogen fluoride: Hydrogen iodide: Hydrogen peroxide: Hydrogen sulfide: Hydrostatic testing of shell-and-tube heat exchangers, Hysteresis:
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Gas Radiation Properties

DOI 10.1615/hedhme.a.000208

2.9 HEAT TRANSFER BY RADIATION
2.9.5 Gas radiation properties

A. The equation of transfer

Up to this point, a diathermanous medium has been assumed. In such a medium the radiant intensity I of a stream of photons is unaffected by passage through the medium. More generally, the photons and matter interact. Three processes may be distinguished: (1) net absorption (total absorption minus induced emission), (2) spontaneous emission, and (3) scattering. The latter can be broken down into scattering out of the beam and scattering into the beam. The result is that in slant path increment ds there is an incremental change in intensity dI as pictured in Figure 1. The equation giving dI/ds is named the equation of transfer.

Figure 1 Change of intensity I along incremental path length ds

The absorption, emission, and scattering properties of matter are sometimes characterized by cross sections. For example, visualize a spherical oil droplet such as is sprayed into a combustion chamber. The droplet of radius R has a total surface area of 4πR2, but its projected area is πR2. The latter is said to be the geometric cross section. If one examines the shadow behind a droplet that is large compared to the wavelength, one finds, due to diffraction, a shadow area of 2πR2 but a bright halo contains half of the radiant power missing due to the shadow, half of I dΩ 2πR2. Whether the droplet is large or small, the radiant power missing from the incident beam divided by that incident on an area of πR2 is termed the extinction efficiency Qe. Thus if one considers the halo radiation as scattered, that is, caused to deviate in direction, the extinction efficiency of a large particle is 2; but, if one considers the halo as undeviated, a more reasonable view for engineering power transfer calculations, then Qe is 1 for a large particle.

The power missing from the shadow may have been absorbed, or it may have been scattered into other directions. The fraction scattered into other directions is called the albedo for single scatter ωs. The fraction 1 – ωs is sometimes called the particle emissivity. Actually it would be better called the particle absorptivity, but Kirchhoff’s law is invoked. The quantity ωsQe is called the scattering efficiency Qs, and (1 – ωs)Qe is called the absorption efficiency Qa.

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