Thermal radiation fundamentals

In order to compute the thermal radiation effects produced by a burning vapor cloud, it is necessary to know the flame s temperature, size, and dynamics during its propagation through the cloud. Thermal radiation intercepted by an object in the vicinity is determined by the emissive power of the flame (determined by the flame temperature), the flame s emissivity, the view factor, and an atmospheric-attenuation factor. The fundamentals of heat-radiation modeling are described in Section 3.5. 

The fundamentals of thermal radiation modeling are treated in Chapter 3. The value for emissive power can be computed from flame temperature and emissivity. Emissivity is primarily determined by the presence of nonluminous soot within the flame. The only value for flash-fire emissive power ever published in the open literature is that observed in the Maplin Sands experiments reported by Blackmore... 

This chapter describes the fundamental principles of heat and mass transfer in gas-solid flows. For most gas-solid flow situations, the temperature inside the solid particle can be approximated to be uniform. The theoretical basis and relevant restrictions of this approximation are briefly presented. The conductive heat transfer due to an elastic collision is introduced. A simple convective heat transfer model, based on the pseudocontinuum assumption for the gas-solid mixture, as well as the limitations of the model applications are discussed. The chapter also describes heat transfer due to radiation of the particulate phase. Specifically, thermal radiation from a single particle, radiation from a particle cloud with multiple scattering effects, and the basic governing equation for general multiparticle radiations are discussed. The discussion of gas phase radiation is, however, excluded because of its complexity, as it is affected by the type of gas components, concentrations, and gas temperatures. Interested readers may refer to Ozisik (1973) for the absorption (or emission) of radiation by gases. The last part of this chapter presents the fundamental principles of mass transfer in gas-solid flows. 

Thermal radiation differs from heat conduction and convective heat transfer in its fundamental laws. Heat transfer by radiation does not require the presence of matter electromagnetic waves also transfer energy in empty space. Temperature gradients or differences are not decisive for the transferred flow of heat, rather the difference in the fourth power of the thermodynamic (absolute) temperatures of the bodies between which heat is to be transferred by radiation is definitive. In addition, the energy radiated by a body is distributed differently over the single regions of the spectrum. This wavelength dependence of the radiation must be taken as much into account as the distribution over the different directions in space. 

In this section a brief introduction to the fundamental concepts of thermal radiation modeling is given. The main purpose of this survey is to elucidate the basic assumptions involved deriving the conventional engineering model of thermal radiation fluxes. To this end the thermal radiation flux is determined in terms of a heat transfer coefficient. 

Sources Incropera, F. R, and D. P. DeWitt, Fundamentals of Heat and Mass Transfer, 4th ed., Wiley, New York, 1996 Siegel, R., and J. R. Howell, Thermal Radiation Heat Transfer, 3rd ed.. Hemisphere, Washington, 1992 and Hottel, H. C., and A. F. Sarofim, Radiative Transfer, McGraw-Hill, New York, 1967. 

The book begins with a discussion of the fundamental definitions and concepts of classical spectroscopy, such as thermal radiation, induced and spontaneous emission, radiation power and intensity, transition probabilities, and the interaction of weak and strong electromagnetic (EM) fields with atoms. Since the coherence properties of lasers are important for several spectroscopic techniques, the basic definitions of coherent radiation fields are outlined and the description of coherently excited atomic levels is briefly discussed. 

Radiative processes include generation of free carriers due to thermal radiation and the inverse mechanism, the recombination of a free electron and a free hole with a simultaneous emission of a light quantum. They are interband processes, directly determined by the semiconductor band stracture, and thus represent an intrinsic or fundamental mechanism. A theory of radiative g-r processes was first given by van Roosbroeck and Shockley [17]. Figure 1.2 shows a schematic presentation of radiative recombination and generation. 

Photocatalysis is a fundamental feature of life processes on our planet [1] (it provides photosynthesis in plants and bacteria) and of the chemistry of its atmosphere [2]. Work is under way to develop photocatalytic technologies for abatement of environmental problems [3,4]. Photocatalysis is anticipated to become in the coming years important also for selective organic synthesis [4]. In a more distant future thermal catalytic processes induced by heating with solcir radiation, together with photocatalytic processes may become important for environmentally friendly technologies of solar energy utilization [5-9]. 

Emission spectroscopy is exclusively related to atoms whereas a number of other spectroscopic techniques deal with molecules. The fundamental fact of emission spectroscopy is very simple, wherein the atoms present in a sample undergo excitation due to the absorption of either electrical or thermal energy. Subsequently, the radiation emitted by atoms in an excited sample is studied in an elaborated manner both qualitatively and quantitatively. Therefore, emission spectroscopy is considered to be an useful analytical tool for the analysis of ... 

In recent years, two different approaches, deterministic [9,19] and stochastic [10,20], have been used with a good level of success to model the radiation chemistry of water. Each approach leads to reasonable agreement between calculated results and experimental data obtained for a wide range of LET from room temperature up toca. 300°C [9,10]. There are, however, fundamental differences between the two models. The deterministic model is based on the concept of an average spur [8,9,19,23] at the end of the physicochemical stage (ca. 10 sec), which contains the products of processes (I), (II), (III), (IV), and (V) in certain yields and spatial distributions, and in thermal equilibrium with the liquid. For low LET... 

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