Gases radiation

Infrared spectroscopy is routinely used for the analysis of samples in the gas, liquid, and solid states. Sample cells are made from materials, such as NaCl and KBr, that are transparent to infrared radiation. Gases are analyzed using a cell with a pathlength of approximately 10 cm. Longer pathlengths are obtained by using mirrors to pass the beam of radiation through the sample several times. 

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. 

Figure 9.44. Emissivity of water vapour in a mixture of non-radiating gases at iOl.3kN/m2(54)...

To find the heat flux resulting from radiating gases with an arbitrary optical thickness, consider the heat flux given by Eqs. (1034) and (10.42) (Fig. 10.11). It can be shown for an arbitrary optical thickness that the heat flux, based on the assumption of isotropic radiation stress (pressure), is... 

Finally, we may summarize what we have learned so far on the heat flux associated with radiating gases. Figure 10.12 shows separately the effect of emission (a measure of the hotness) and that of absorption (a measure of the optical thickness). 

Radiative boundary condition, denoted by . This boundary condition involves radiative heat transfer from the duct to the environment. The wall heat flux is proportional to the fourth power of the absolute wall temperature, and the environment temperature is uniform in the axial direction. This boundary condition can be found in high-temperature systems such as space radiators, liquid-metal exchangers, and heat exchangers involving heat-radiating gases. 

Wideband Models. The narrowband models introduce significant simplification over the line-by-line calculations however, the accurate predictions depend not only on the rigor of the model but also on the accuracy of input data, such as the local temperature, the temperature profile, the partial pressures of the radiating gases, and so on. In most practical systems, these data are not available with good accuracy. This suggests that even simpler approximations may be more appropriate for calculation of gas properties in practical systems. 

J. D. Felske and C. L. Tien, A Theoretical Closed Form Expression for the Total Band Absorptance of Infrared-Radiating Gases, ASME Journal of Heat Transfer, vol. %, pp. 155-158,1974. 

Issues that are covered in the OSHA construction regulations for occupational health are first aid sanitation noise exposure radiation gases, vapors, fumes, dusts, and mists (including silica) spray booths illumination ventilation and hazard communication. Since most of these issues are (or will be) represented in this collection of toolbox talks, let s look (briefly) at a few other occupational health issues not found in the regulation but being currently looked at by OSHA for some type of action. 

Treatment of Refractory Walls Partially Enclosing a Radiating Gas Another modification of the results in Table 5-10 becomes important when one of the surface zones is radiatively adiabatic the need to find its temperature can be eliminated. If surface A9, now called A, is radiatively adiabatic, its net radiative exchange with Aj must equal its net exchange with the gas. 

Parenteral drug products are required to be sterile. There are principally five different ways to sterilize a product. These are steam, dry heat, radiation, gas. 

There is no net radiative exchange between the enclosing walls (fire-box), and the radiating gas and tubes. Heat is lost from the enclosing wall to the surroundings only. 

A physical interpretation of Equation (35) is possible if one notes that it is mathematically analogous to Fourier law of heat conduction. The constant factor in the right-hand side plays the role of thermal conductivity, and the local incident radiation GA(r) plays the role of temperature. In that sense, differences in the latter variable among neighboring regions in the medium drive the diffusion of radiation toward the less radiated zone. Note that the more positive the asymmetry parameter, the higher the conductivity that is, forward scattering accelerates radiation diffusion while backscatter-ing retards it. 

If the recommended factor of 0.7 on the refractory area is used, the effective area of the tubes is [22.0-1- (0.7)(3.18)]/22.0= 1.10 mVm of actual area. The exact evaluation of the outside tube temperature from the known oil temperature would involve a knowledge of the oil-film coefficient, tube-wall resistance, and rate of heat flow into the tube, the evaluation usually involving trial and error. However, for the present purpose the temperature drop through the tube wall and oil film will be assumed to be 41.7°C ( 5°F), making the tube surface temperatures 357°C (675°F) and 468°C (875°F) the average is 412°C (775°F). The radiating gas temperature is... 

Tritium has proved a useful tracer, as the tritium content of a compound can be deduced from its /S-activity. For the measurement of such low-energy radiation gas-counting is used (p. 31). 

With this mean beam length, the mean irradiance EG of the total surface A of the radiating gas space of volume V is found to be... 

The radiative exchange in a gas filled enclosure is more difficult to calculate than the exchange dealt with in 5.5.3, without an absorbing and therefore self radiating gas. In the following we will consider two simple cases, in which an isothermal gas is involved in radiative interchange with its boundary walls that are likewise at a uniform temperature. At the end of this section we will point to more complex methods with which more difficult radiative exchange problems may be solved. 

Parenteral drug products are required to be sterile. There are principally five different ways to sterilize a product. These are steam, dry heat, radiation, gas and filtration. Selection of which method to use is based on the product that requires sterilization. For example, protein-based drugs are heat-sensitive, so the normal means for sterilizing these products is filtration. The rationale for sterilization validation is to show the reduction in microbial load or destruction of biological indicators. 

Consider air at 300 K and 1 atm and the radiation gas at the same temperature. We wish to compare (a) internal energies, and (b) pressures of both gases. 

Now, consider an enclosure filled with monochromatic radiation Ga, and place a monochromatically opaque (r =0) body into this enclosure (Fig. 8.12). Let the monochromatic reflectivity and emissive power of the body be pi and Fa, respectively. Under equilibrium, the first law of thermodynamics for the system enclosing the body gives... 

Consider a hemisphere of radiating gas of radius L, with a black element of receiving surface dA located on the base of the hemisphere at its center. The rate of energy transfer dq 2 from the gas to the element of area is then... 

Thickness of material, radius of hemisphere or mean beam length in radiating gas, m or ft Absorption length, m or ft... 

Pressure, atm pg, partial pressure of radiating gas Heat flow rate, W or Btu/h q-f, total by conduction-convection q, by radiation q,2, net exchange between surfaces 1 and 2 radia-... 

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