Radiation luminosity

In ProgrRept No 10 (Ref 6) luminosity time tests employing a wide band Tektronix 517 oscillograph and frequency compensated photomultiplier anode circuitry are briefly described. Fig 2 of the rept (reproduced here as Fig 5) shows radiation luminosity waveform from a stepped rod of Tetryl. 

Luminous Flames Luminosity conventionally refers to soot radiation it is important when combustion occurs under such conditions that the hydrocarbons in the flame are subject to heat in the absence of sufficient air well mixed on a molecular scale. Because soot parti-... 

Luminosity is the amount of chemical energy in the fuel that is released as thermal radiation. 

The carbon/hydrogen ratio of gas is considerably lower than oil or coal, which results in a flame of very low luminosity. Radiation from the flame is therefore low and furnace design must allow for heat transfer to be primarily by convection and conduction, together with re-radiation from hot surfaces. 

The luminosity of a star, L, is the total rate at which energy is radiated by the black body over all wavelengths. Assuming that the star is a sphere, the total surface area is given by A = 4ttR2, where R is the radius of the star, then the luminosity of the star is given by ... 

Note the potential confusion between luminosity of the Sun L and the flux at the Earth. The latter is quite naturally written as the amount of radiation arriving on every square metre of the Earth s surface and analogously the flux per square metre from the black body is also F. This calculation requires the total amount of radiation emitted by the Sun to be known, which is the luminosity of the Sun and not its flux. 

Consider the amount of radiation arriving on the surface of the Earth at a distance of 1 AU or 1.5 x 1011 m. The total flux of the Sun is distributed evenly over a sphere of radius at the distance of the planet, d. From the luminosity calculation of the Sun, F, the solar flux at the surface of Earth, FEarth, is F/47t(1.5 x 1011)2 = 1370 Wm-2 from the least-square law of radiation discussed in Example 2.4 (Equation 2.4). Substituting this into Equation 7.6 with the estimate of the albedo listed in Table 7.2 gives a surface temperature for Earth of 256 K. 

The current models of the Sun suggest that its luminosity would have been some 20-30 per cent lower than its present value during the early part of the formation of the Earth. After the enormous temperatures of the Hadean period, the early precambrian may have been cooler, requiring prebiotic chemistry to occur below a layer of ice, perhaps heated by volcanic activity such as that found in geothermal vents. A layer of ice several hundreds of kilometres thick may have formed over the entire surface of the early Earth, providing protection from UV radiation and some global warming - conditions such as these may exist on the Jovian moon Europa. 

Show that the Eddington limiting luminosity, at which the gradient of radiation pressure balances gravity near the surface, is given by... 

No attempt will be made here to enter into a more detailed discussion of the physics of the SFR, but a few comments will be made on the basis of some very simple parameterizations. Considering for example the exponential time-dependence of Eq. (7.12), the restriction on b(T) in Eq. (7.5) implies that v-1 > 0.9 T 10 Gyr. A related argument can be made about the past evolution of the luminosity of the disk - closely related to both the SFR and the IMF - from considerations of nuclear fuel consumption. All energy radiated corresponds to the synthesis of helium and/or heavy elements from hydrogen at a rate... 

The last point is worth considering in more detail. Most hydrocarbon diffusion flames are luminous, and this luminosity is due to carbon particulates that radiate strongly at the high combustion gas temperatures. As discussed in Chapter 6, most flames appear yellow when there is particulate formation. The solid-phase particulate cloud has a very high emissivity compared to a pure gaseous system thus, soot-laden flames appreciably increase the radiant heat transfer. In fact, some systems can approach black-body conditions. Thus, when the rate of heat transfer from the combustion gases to some surface, such as a melt, is important—as is the case in certain industrial furnaces—it is beneficial to operate the system in a particular diffusion flame mode to ensure formation of carbon particles. Such particles can later be burned off with additional air to meet emission standards. But some flames are not as luminous as others. Under certain conditions the very small particles that form are oxidized in the flame front and do not create a particulate cloud. 

For most astronomers, the solution to these cosmological problems resides in a combination of various methods. The luminosity-redshift test must be combined with independent techniques, such as anisotropies in the cosmic background radiation and statistical study of gravitational lenses. 

The use of certain surrounds (such as propane) eliminates or substantially reduces these luminosities which are undesirable if one is attempting to observe the radiation emitted by the deton products in the deton wave... 

Dunkle (Ref 17) reviews the literature on luminosity and radiation from 1958 to I960 incl. Some of these papers describe detn of temperature developed on detonation, others deal with plasma phenomena [See also under Detonation (and Explosion), Temperature Developed on and also under Detonation and Plasma Phenomenon]... 

Sultanoff s work on luminosity) 202 (Discussion on "dark waves and observable radiation in the interior of the crystal) ... 

Poulter on luminosity) 305-06(Detn of temp by radiation and spectra methods) 384 (Discussion on work done at PicArsn on radiation of pyrotechnic compns) 386 (Effect of radiation from a shock wave in an atmosphere at ordinary pressure is negligible in comparison to an endothermic reaction capable of absorbing thousands of kcal per kg of air at 10000°K) 396 (Discussion on energy loss by radiation from the body of the gas mainly in the form "Bremsstrahlung produced when electrons are deflected by ions) 398, 400, 401 403 (More discussion on radiation) 14) Cook (1958), 97, 150-53, 155 158 15) M.A. Cook et al,... 

Detonation (and Explosion), Radiation Emitted on. See Detonation (and Explosion), Luminosity (Luminescence) Produced on... 

---