Radiation exchange factor

Outside diameter of inner of concentric tubes Inside diameter of outer of concentric tubes Fin efficiency Radiation exchange factor Bypass correction factor, heat transfer Bypass correction factor, pressure drop Leakage correction factor, heat transfer Leakage correction factor, pressure drop Tube row correction factor... 

The radiative heat flux depends on the radiation exchange factor cl2, which is a function of the Stefan-Boltzmann constant sigma , the emissivities epsilonl and epsilon2 of the ooncernde bodies, and of the view factor phil2 , and it depends on the radiation area A1 of body 1, and it depends on the difference of the 4th power of the absolute temperatures T1 and T2 of the involved bodies. 

Angle factor The geometrical shape factor used in calculating radiation exchange between surfaces / and /. 

Radiation shape factor The angle factor representing the fraction of the angular field of view from which energy exchange is trading places. 

Heat transfer in the furnace is mainly by radiation, from the incandescent particles in the flame and from hot radiating gases such as carbon dioxide and water vapor. The detailed theoretical prediction of overall radiation exchange is complicated by a number of factors such as carbon particle and dust distributions, and temperature variations in three-dimensional mixing. This is overcome by the use of simplified mathematical models or empirical relationships in various fields of application. 

Consider two black surfaces Ai and A2, as shown in Fig. 8-8. We wish to obtain a general expression for the energy exchange between these surfaces when they are maintained at different temperatures. The problem becomes essentially one of determining the amount of energy which leaves one surface and reaches the other. To solve this problem the radiation shape factors are defined as... 

All the preceding discussions have considered radiation exchange between diffuse surfaces. In fact, the radiation shape factors defined by Eq. (8-21) hold only for diffuse radiation because the radiation was assumed to have no preferred direction in the derivation of this relation. In this section we extend the analysis to take into account some simple geometries containing surfaces that may have a specular type of reflection. No real surface is completely diffuse or completely specular. We shall assume, however, that all the surfaces to be considered emit radiation diffusely but that they may reflect radiation partly in a specular manner and partly in a diffuse manner. We therefore take the reflectivity to be the sum of a specular component and a diffuse component ... 

To account for the effects of orientation on radiation heat transfer between two surfaces, we define a new parameter called the vieu factor, which is a purely geometric quantity and is independent of the surface properties and temperature. It is also called the shape factor, configuration factor, and angle factor. The view factor based on the assumption that the surfaces are diffuse emitters and diffuse reflectors is called the diffitse view factor, and the view factor based on the assumption that the surfaces are diffuse emitters but specular reflectors is called the specular view factor. In lliis book, we consider radiation exchange between diffuse surfaces only, and ihu.s the term view factor simply means diffuse view factor. 

So fill, we have considered the nature of radiatiou, the radiation properties of materials, and the view factors, and we arc now in a position to consider the rate of heal transfer between surfaces by radiation. The analysis of radiation exchange between surfaces, in general, is complicated because of reflection a radiation beam leaving a surface may be reflected several times, with partial refleclion occurring at each surface, before it is completely absorbed. The analysis is simplified greatly when the surfaces involved can be approximated... 

The concept of view factors is quite convenient in the analysis of diffuse and gray radiation exchanges. Under these assumptions, the view factor, Fu2, is purely a geometric quantity. Physically, it means the fraction of radiative energy leaving surface 1 that reaches surface 2. In other words, it describes how much surface 1 sees surface 2, thus the name view factor. Due to the restricted nature of this chapter, the expression for the view factors will not be derived here. Instead, the expression will be given here and the reader will be referred to a more-detailed discussion in References 2, 18, and 19. Mathematically, the view factor is defined as... 

Here Taw> commonly called the adiabatic wall temperature or the recovery temperature, is the equilibrium temperature the surface would attain in the absence of any heat transfer to or from the surface and in the absence of radiation exchange between the surroundings and the surface. In general the adiabatic wall temperature is dependent on the fluid properties and the properties of the bounding wall. Generally, the adiabatic wall temperature is reported in terms of a dimensionless recovery factor r defined as... 

M. E. Larsen and J. R. Howell, The Exchange Factor Method An Alternative Zonal Formulation of Radiating Enclosure Analysis, ASME Journal of Heat Transfer, 107, pp. 936-942,1985. 

Obviously the most effective thermal treatment is realized with a high E, which implies an increase of the residence time t of particle in the plasma, of the convective exchange factor hy, of the wall temperature (to decrease radiation losses) and also a decrease of the particle diameter]... 

Form view factor A factor which describes the effects of the relative area of two surfaces, the geometry of the surfaces in relation to each other, and the two emissivities on radiation heat exchange between the surfaces. 

Corrosion of solders used in the electronics industry is usually a function of the presence of residues from various manufacturing and assembly operations. Corrosion in heat exchangers, particularly in automobiles is a more significant problem and a test methodology has been described as well as various factors controlling the corrosion of tin-lead alloys in radiators... 

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