Heat by radiation

We have estimated the likely heat that may be generated by a particular size of conductor and enclosure for a certain current rating and then have counterchecked whether the conductor and the enclosure so chosen can dissipate this heat by radiation and natural convection, and reach a state of thermal stability within permissible limits or we may have to increase the size of the conductor... 

Operative The theoretical uniform temperature of an enclosure in which an occupant would exchange the same amount of heat by radiation and convection as in the actual nonuniform space. 

Microporous insulation materials consist mainly of highly dispersed silica with a particle size of only 5-30 nm. The highly dispersed silica powder is pressed to plates, which receive heat treatment up to 800 °C, after which the plates are self-supporting and possess a micropore structure with pore diameter of 0.1pm. The addition of opacifiers to the highly dispersed silica starting material reduces the loss of heat by radiation. The dates for such insulation boards are shown in Table 18. 

The variable gap method is a steady-state method, with the merit that transport of heat by radiation can be separated from the total heat flow ... 

The transfer of heat by radiation in general can be said to occur simultaneously with heat transfer by convection and conduction. Transfer by radiation tends to become more important than that by the other two mechanisms as the temperature increases. It is useful to gain an appreciation of the basic definitions of the energy flux terms, the surface property terms and their relationships while discussing radiative heat transfer. With this objective, reference may be made to Table 3.4 in which these are presented. 

The lower tubes in the shield bank in the convection section will receive heat by radiation from the radiant section. This can be allowed for by including the area of the lower row of tubes with the tubes in the radiant section. 

Binary liquid metal systems were used in liquid-metal magnetohydrodynamic generators and liquid-metal fuel cell systems for which boiling heat transfer characteristics were required. Mori et al. (1970) studied a binary liquid metal of mercury and the eutectic alloy of bismuth and lead flowing through a vertical, alloy steel tube of 2.54-cm (1-in) O.D., which was heated by radiation in an electric furnace. In their experiments, both axial and radial temperature distributions were measured, and the liquid temperature continued to increase when boiling occurred. A radial temperature gradient also existed even away from the thin layer next to the... 

Figure 9 shows an arrangement for measuring secondary electron emission. An electron gun with an incandescent tungsten cathode and the electrodes Bi and Bi is situated in the lower part of the cell. The secondary emitting target P carries the catalyst. A layer of the latter can also be evaporated from Ey or Ei, and deposited on P, which can be heated by radiation or electron bombardment from D. The leads FF of a... 

To determine how far the thickness of bodies affected their heating by radiation, he used a metal plate coated -with layers of varnish —... 

The furnace in Figure 21-8a performs better than a simple graphite tube. Sample is injected onto a platform that is heated by radiation from the furnace wall, so its temperature lags behind that of the wall. Analyte does not vaporize until the wall reaches constant temperature (Figure 21-8b). At constant furnace temperature, the area under the absorbance peak in Figure 21-8b is a reliable measure of the analyte. A heating rate of 2 000 K/s rapidly dissociates molecules and increases the concentration of free atoms in the furnace. 

Figure 21-8 (a) Transversely heated graphite furnace maintains nearly constant temperature over its whole length, thereby reducing memory effect from previous runs. The i vov platform is uniformly heated by radiation from the outer wall, not by conduction. The platform is attached to the wall by one small connection that is hidden from view. [Courtesy Perkin-Bmer Corp., Norwalk, Cl] (to) Heating profiles comparing analyte evaporation from wall and from platform. [From W. Slavin, Atomic Absorption Spectroscopy, Anal. Chem. 1982,54,685A.]... 

At the end of the fifties, Ya.B. gave a qualitative picture of the structure of shock waves with radiation transfer taken into account [20], In front of a compression shock there is a layer heated by radiation from the compressed gas. Behind the discontinuity there is a temperature peak. The simultaneously developed quantitative theory of these effects allowed detailed explanation of the experimentally observed patterns of luminescence of the front in strong shock waves and of the radiation in the early stage of a fire ball in... 

The Lagoon Nebula in the constellation Sagittarius. These interstellar gas clouds consist largely of atomic hydrogen, the most abundant element in the universe. The gas is heated by radiation from nearby stars. Can you explain its characteristic red glow (Recall Section 5.3.)... 

Applying a correction to the temperature rise observed makes an allowance for losses of heat by radiation from the calorimeter. This correction is expressed by a formula that appears to be complicated, but if the various temperature figures are set out on the laboratory sheet methodically, it is not only easy to apply, but the liability of introducing arithmetic errors is reduced. 

Radiative heat transport through olivine has been discussed extensively (e.g., Fukao et al., 1968 Shankland, 1970 Schatz and Simmons, 1972 Scharmeli, 1979 Shankland et al., 1979). The radiative thermal conductivity, Kt of forsteritic olivine increases with rising temperature and would contribute to heat flow in the Upper Mantle (Shankland et al., 1979). However, values of Kt for olivine are considered to be rather low to satisfactorily explain the dissipation of the Earth s internal heat by radiation and lattice conduction alone. Note, however, that Fe2 CF transitions in almandine, pyroxenes (M2 site) and, perhaps, silicate perovskites absorb strongly in the wavelength range 1,250 to... 

Two extremely big parallel plates at 900°C and 300°C exchange heat by radiation. Calculate the heat transfer per unit area. Assume that e = 1 for the plates. 

A solar collector surface receives solar radiation at 1 kW/m2, and its other side is insulated. The absorptivity of the surface to solar radiation is a = 0.8 while its emissivity is e = 0.6. Assuming the surface loses heat by radiation into a clear sky at an effective temperature of 10°C, calculate the temperature of the surface. 

The calculation of the flame temperature for a combustible gas like hydrogen, carbon monoxide, or methane at first sight appears to be a simple problem since the apparently necessary data are only the heat of combustion and the specific heats of the products. Such calculations always yield very high results much above those recorded by direct experimental measurements. The discrepancy is probably due to a combination of several causes. On account of the temperature of the flame the products are partially dissociated,1 so that combustion is not complete m the flame. The specific heat of gases increases with rise m temperature, so that the value obtained at the ordinary temperature for the specific heat is too low. In addition to these two causes, another contributory factor is the loss of heat by radiation, which may be very considerable even m nou-lummous flames, whilst the general presence of an excess of the supporter of combustion and the non-instantaneous character of the combustion also detract from the accuracy of the calculation.2... 

A blackened ceramic sphere of 10 cm diameter is initially uniform in temperature at 1000°K and is suddenly placed in outer space where it loses heat by radiation (no convection) according to... 

Repeat Prob. 4-50 with the top surface also losing heat by radiation according to... 

Combustion process is usually a more complex chemical reaction. Often these reactions lead to the temporary formation of solid particles, which incandesce and dissipate heat by radiation. 

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