Particle clouds, thermal radiation with

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. 

Problem Most of the Earth s thermal energy is received from the short wave radiation of the sun. Although it receives radiation from other bodies in space, it is negligible compared to with the solar energy. Incoming solar energy is at approximately at the same intensity as when it left the surface of the sun, before it enters the earth s atmosphere. However once it enters the atmosphere approximately 6% is reflected by particles in the atmosphere, 16% is absorbed by the atmosphere, 20-30% is reflected by the clouds, and 3% is absorbed by the clouds. On any given day all of these factors can limit the amount of net solar radiation received by a solar panel. 

The linear burning rate of a propellant is the velocity with which a chemical reaction progresses as a result of thermal conduction and radiation (at right angles to the current surface of the propellant). It depends on the chemical composition, the pressure, temperature and physical state of the propellant (porosity particle size distribution of the components compression). The gas (fume) cloud that is formed flows in a direction opposite to the direction of burning. 

A problem of overriding importance for planetary atmospheres as a whole is that of the albedo, the ratio of the energy radiated to space by the planet to that incident upon it [1.39]. Particles and cloud droplets are responsible for reflection back to space of a part of the incident energy, while they play roles in the capture and thermalization of the thermal emissions of the "solid" earth. In this latter regard, particles may be particularly important in the question of stratospheric heating [1.40,41]. Besides particle interaction with light, microphysics and kinetic theory may also be important in understanding aspects of the thermal transfer problem. 

Molecular observations are almost always concerned with specific discrete transitions. These are generally observed at millimeter or centimeter wavelengths. The intensity of a source is determined by the rate of collisional versus radiative transitions between levels. Because of the extremely low densities usually associated with molecular environments, whether in a circumstellar envelope or a molecular cloud, pressure broadening is unimportant. Instead, the molecule radiates at its local velocity into the line of sight. This dispersion of velocity may be due strictly to the thermal motions of the particles, or it may be due to the presence of turbulence or large-scale chaotic motions within the medium. Either way, the local profile, < (v) is a Gaussian with a finite width in frequency. 

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