Distributed Gas Radiation

In this section we restrict ourselves to gray gases, as we did in the foregoing brief discussion on the lumped gas radiation. Spectral considerations, although important for the quantitative effects of radiation, are beyond the scope of this text Consequently, our objective is to gain some knowledge only on the qualitative foundations of gas radiation. 

Our starting point is the balance of radiation energy (transfer equation), obtained from the average of Eq. (10.5) over the wavelength spectrum, 

In terms of Fig. 10.9, the integration of this equation with respect to s yields 

Clearly, Eq. (10.23) expresses the fact that the intensity at point s and in direction m (Fig. 10.9) results from the emission of all the interior points such as s and from the emission of the boundary s 0, respectively reduced by factors ancj M) t0 

To simplify our discussion, we neglect for the time being the effect of the boundaries by eliminating I (O)e-T, 0l from Eq. (10.23). Then we have 

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Having reduced the problems of lumped gas radiation to enclosure problems with transparent partitions, we proceed next to problems of distributed gas radiation. 

Their results gave a value of log (70, sec-1) = 1.316 — 4.18/0 (for Ar as carrier gas) radiation at wavelengths greater than 8750 A, which was as far as they measured the intensity distribution, was ignored. Assuming a linear increase in intensity up to 11,000 A, they estimated the preexponential factor of 70 to be 120 sec-1. The preexponential factor of ki3, was argued to be approximately the same as that of ki3-. The results were... 

Fig. 4.2. Waste heat boiler for a copper smelting flash furnace (Peippo et al, 1999). Note, left to right (i) flash furnace gas offtake (ii) boiler radiation section with water tubes in walls (iii) suspended water tube baffles in radiation section to evenly distribute gas flow (iv) convection section with hanging water tubes. Steam from the boiler is used to generate electricity, to power the acid plant s main blower and for general heating and drying.

The gas molecules and the suspended partic e.s in the atmosphere emit radiation as well as absorbing it. The atmospheric emission is primarily due to the COj and H2O molecules and is concentrated in the regions front 5 to 8 p.m and above 13 p.m. Although this emission is far from resembling the distribution of radiation from a blackbody, it is found convenient in radiation calculations to treat the atmosphere as a blackbody at some lower fictitious temperature that emits an equivalent amount of radiation energy. This fictitious temperature is called the effective sky teniperatur Then the radiation emission from the atmosphere to the earth s surface is expressed as... 

The system under study includes one cogeneration unit (a Stirhng Engine) and a backup boiler, both fueled by natural gas. The system supphes heat to two heat storage tanks one for the heating system, the other for the domestic hot water (dhw). The temperature in the heat distribution system (radiator system) is controlled by a 3-way valve and the temperature set point is determined as a function of the ambient and room temperatures using a heat loss model and heat distribution model. 

Stratospheric ozone is produced at maximum rates in equatorial regions, where solar radiation is most intense. Ozone does not really occur as a layer, but instead as a broadly distributed gas whose peak concentration occurs in midstratosphere. The total amount of ozone present in the atmosphere is small, typically between 200 and 400 Dobson units. A Dobson unit is the amount of ozone that, if gathered together in a thin layer covering Earth s surface at a pressure of 1 atm, would occupy a thickness of 1/100 of a millimeter (10 gm). The entire ozone shield, which protects life on Earth from damage by the UV-B radiation of the Sun (ultraviolet radiation in the 280-320 nm range), is equivalent to a layer of ozone only 2 to 4 mm thick at sea level pressure. 

K. C. Tang and M. Q. Brewster, -Distribution Analysis of Gas Radiation with Non-gray, Emitting, Absorbing, and Anisotropic Scattering Particles, in S. T. Thynell et al. (eds.), Developments in Radiative Heat Transfer, ASME-HTD-vol. 203, pp. 311-320,1992. 

To study the stresses in the system, it is first necessary to calculate the temperature distributions of the SOFC stack. Owing to the coupled nature of the SOFC multi-physics, the temperatures in the stack wiU affect both the electrochemical performance and the mechanical stresses of the stack [49]. The electrochemical performance of the SOFC is coupled to the temperature through the Nernst equation [Eq. (26.11)]. Stack-level models are often used to consider the temperature distributions and how the operating conditions and design of the stack affect the temperatures [1, 48, 49]. In these models, the energy conservation equation [Eq. (26.7)] is solved in the gas and sohd phases, and includes the effects of convection in the fuel and air charmels, radiation between the soHd tri-layer and the gas, radiation between the stack and its surroundings, conduction through the tri-layer, and heat sources due to chemical and electrochemical reactions [1, 50]. The balance... 

The method implies injection of a mixture of 3 radioactive tracers each being distributed into one of the 3 phases. The tracers must show such differences in the emitting y-radiation energy spectra that they can be simultaneously detected by on line y-spectrometry. Candidate tracers are Br-82 as bromobenzene for oil, Na-24 or La-140 for water, and Kr-85 for gas. The tracers are injected simultaneously at a constant rate into the flow in the pressurised pipe, and the concentration is detected as series of instantaneous measurements taken downstream as illustrated in figure 2. 

The thermal radiation intensity of a flash fire can be calculated after parameters such as cloud shape and gas or vapor concentration distribution have been determined through dispersion calculations. Subsequently, the thermal radiation intensity is calculated through the following steps ... 

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