Absorption volumetric radiation

Absorptivity for radiation Activity Activity coefficient, molal basis Coefficient of expansion a a T Diffusivity Molecular, volumetric Thermal Emissivity ratio for radiation Dv,8 a ft /(h) (ft) ft2/h a = k/cp, ft2 /h... 

Gases and liquids are partly transparent to thermal radiation. Therefore emission and absorption of radiation takes place inside the gas or liquid space. In gases and liquids emission and absorption are volumetric effects. In contrast, on the surface of a solid object, radiation is completely absorbed within a very thin layer (a few micrometres). Radiation from the interior of a solid body does not penetrate the surface, emission is limited to a thin surface layer. It can therefore be said that emission and absorption of radiation by a solid body are surface effects. This means that it is allowed to speak of radiating and absorbing surfaces rather than correctly of radiating solid bodies. 

The main difference between photochemical and thermal reaction is the presence of a radiation-activated step. The rate of reaction of this step is proportional to the local volumetric rate of energy absorption (LVREA). For any emission model, the LVREA is a function of the spatial variables, of the physical properties and geometrical characteristics of the lamp-reactor system, and some physicochemical properties of the reacting mixture. The most important design parameter that is pertinent in photochemical and photocatalytic reactions is the effective attenuation coefficient. 

It is rather atypical that a photochemical reaction will proceed in a single molecular pathway. Thus, several elementary steps are involved. Normally, the majority of them are dark (thermal) reactions while, ordinarily, one activation step is produced by radiation absorption by a reactant molecule or a catalyst. From the kinetics point of view, dark reactions do not require a different methodological approach than conventional thermal or thermal-catalytic reactions. Conversely, the activation step constitutes the main distinctive aspect between thermal and radiation activated reactions. The rate of the radiation activated step is proportional to the absorbed, useful energy through a property that has been defined as the local volumetric rate of photon absorption, LVRPA (Cassano et ak, 1995 Irazoqui et al., 1976) or the local superficial rate of photon absorption, LSRPA (Imoberdorf et al., 2005). The LVRPA represents the amount of photons that are absorbed per unit time and unit reaction volume and the LSRPA the amount of photons that are absorbed per unit time and unit reaction surface. The LVRPA is a property that must be used when radiation absorption strictly occurs in a well-defined three-dimensional (volumetrical) space. On the other hand, to... 

Alfano, O.M., Romero, R.L., and Cassano, A.E. A cylindrical photoreactor irradiated from the bottom. 111. Measurement of absolute values of the local volumetric rate of energy absorption. Experiments with polychromatic radiation . Chem. Eng. Sci. 41,1163 (1986). 

In general, the determination of these components is complex and can be strongly influenced by volumetric effects within the medium. However, in many engineering applications the medium is opague to the incident radiation so that G i, trans 0 nd the absorption and reflection processes are treated as surface phenomena. 

Properties of Composite Fiber/Matrix Systems. The volume fraction of fibers in most filament-wound structures and in laid-up composite layers can exceed 60 percent. For carbon fibers at this volume fraction, the composite has such a high absorption coefficient that it can be treated as opaque [251] however, for glass-epoxy composites, the absorption coefficient is small enough, particularly in some spectral windows, that radiation must be treated as a volumetric effect. The situation is complicated by the high fiber volume fraction, which causes the fiber absorption and scattering to be in the dependent regime however, some data are presented in Ref. 251. 

The gold content in catalysts was analyzed by Atomic absorption method and made by the Analytical Center of the CNRS, Lyon, France. The XRD patterns were obtained with a Philips PW 170 diffiactometer, using Cu Ka (1.54178 A) radiation. High resolution transmission electron microscopy (HRTEM) analysis was performed on a Jeol JEM-3010 microscope at 300 kV. Nitrogen adsorption-desorption isotherms and specific surface areas were measured at -196 °C over a wide relative pressure range from 0.01 to 0.995 with a volumetric adsorption analyzer TRISTAR 3000 manufactured by Micromeritics. The pore diameter and the pore size distribution were determined by the Barret-Joyner-Halenda (BJH) method using the adsorption branch of isotherms [15]. 

Three different but connected problems must be studied (i) the reaction kinetics model (ii) the development of the rate of electron-hole generation in a material particle of the solid suspension and (iii) the model for characterizing the radiation field to evaluate the local volumetric rate of photon absorption (LVRPA). Point (iii) has been already described in section 6.6.1 for quantum yield determinations. In the first part of this section, we will concentrate on problems (i) and (ii). 

The purpose of a photobioreactor is to absorb incident light in order to convert it into biomass via coupling with photosynthesis. On the one hand, efficient light absorption usually corresponds to heterogeneous radiation fields (x) within the reaction volume (see Section 3). On the other hand, the coupling law (Eq. (4)) is usually a non-linear function of (x) (the law obtained in Section 5 is non-linear, but this is also the case for most of other models reported in the literature). Therefore, the coupling between radiative transfer and photosynthesis must be formulated locally, which implies that determination of the volumetric rate < > requires... 

In general, work and heat can be a added through boundaries or through volumetric influences body forces, radiation absorption, and so on. In addition, work can be dissipated internally as heat through deformation for some materials. The entropy T L of the system is the portion of the internal energy that cannot be recovered as work and that exists as heat... 

The penetration depth is defined as the distance from the sample surface where the absorbed power is 1/e of the absorbed power at the surface. Beyond this depth, volumetric heating due to absorption of microwave energy is negligible. The penetration depth (Dp) is proportional to the wavelength of the radiation and depends on the dielectric properties of the material. For lossy dielectrics e"/e 1), the penetration depth (Dp) can be calculated from the equation"... 

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