Heating radiation

The aluminium absorbs the radiation, heats up and transfers the heat to xenon gas contained in the cell. As the temperature of the gas varies the curvature of a flexible mirror of antimony-coated collodion, forming a part of the cell, changes. Reflection of a light beam from this mirror, which is on the outside of the Golay cell, indicates its curvature and therefore the intensity of radiation absorbed by the cell. 

Al—Si, eutectic (I) BAlSi preforms, wine, rods. aluminum and car radiators, heat... 

Resiilts for a large number of other cases are given by Hottel and Sarofim (op. cit., chap. 2) and Hamilton and Morgan (NACA-TN2836, December 1952). A comprehensive bibliography is provided by Siegel 3.nd [owe Thermal Radiation Heat Transfer, McGraw-HiU, 1992). 

In rotary devices, reradiation from the exposed shelf surface to the solids bed is a major design consideration. A treatise on furnaces, including radiative heat-transfer effects, is given by Ellwood and Danatos [Chem. Eng., 73(8), 174 (1966)]. For discussion of radiation heat-transfer computational methods, heat fliixes obtainable, and emissivity values, see Schornshort and Viskanta (ASME Paper 68-H 7-32), Sherman (ASME Paper 56-A-III), and the fohowing subsection. 

Fig. 17-4. Radiation heat balance. The 100 units of incoming shortwave radiahon are distributed reflected from earth s surface to space, 5 reflected from cloud surfaces to space, 20 direct reaching earth, 24 absorbed in clouds, 4 diffuse reaching earth through clouds, 17 absorbed in atmosphere, 15 scattered to space, 9 scattered to earth, 6. The longwave radiation comes from (1) the earth radiating 119 units 101 to the atmosphere and 18 directly to space, and (2) the atmosphere radiating 105 units back to earth and 48 to space. Additional transfers from the earth s surface to the atmosphere consist of latent heat, 23 and sensible heat, 10. Source After Lowry (4).

Fig. 18-3. Dense fog maintaining stability in a valley. It reflects shortwave radiation during the dav and radiates heat from the top of the fog at night. Source Adapted from Schrenk et...

Monthly evaporation estimates can be made using the Kohler-Nordenson-Fox equation with a pan coefficient of 0.7. The Kohler-Nordenson-Fox equation describes evaporation as the combination of water loss due to radiation heat energy and the aerodynamic removal of water vapor from a saturated surface. The general form for the combination equation is ... 

Above we considered the question of which temperature the damp cloth settles to when it is thermally insulated against all surroundings but the airflow, and when it can be assumed that there is no radiation heat transfer between the cloth and the airflow. In this consideration the state of the air has been constant. 

The net heat transfer between two surfaces according to Eq. (4.159) is proportional to the first or second power of the temperature difference hence the radiation heat transfer dominates at a high temperature or for large temperature differences. When the temperature difference is small, a heat transfer factor is used similar to that used for convective heat transfer ... 

Radiation heat transfer in a hollow can be represented by electrical analogy as... 

Radiation heat transfer. The radiation heat transfer between two parallel planes is reduced by placing a parallel aluminum sheet in the middle of the gap. The surface temperatures are (9j = 40 °C and 62 = 5 °C, respectively the emissivities are ej = e, = 0.8.5. The emissivity of both sides of the aluminum... 

In wall heat balance Eqs. (8.14) and (8.15), the radiation heat flows T and V from the heat sources and V 0 y2i from upper zone wall surfaces to lower zone wall surfaces are assumed to increase the temperature of the walls. In practical cases it is quite complicated to determine how much of the radiation flow rate will be distributed to outer walls and to other surfaces. 

The radiation heat transfer (cf> ) from the heat loads such as machines, lamps, persons, and sun has to be determined separately for the lower zone ( ./ ) and upper zone (4>nn The radiation between zone wall surfaces ( 4 u uJ has to be determined as well. 

Siegel R., and Howell J. R. Thermal radiation heat transfer. Washington, DC, Philadelphia, PA, London Hemisphere Publishing, 1992. 

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. 

Radiation heat flux is strongly time dependent, because both the flame surface area and the distance between the flame and intercepting surfaces vary during the eourse of a flash fire. The path of this curve ean be approximated by calculating the radiation heat flux at a sufficient number of discrete points in time. 

Thus, the final steps for calculating the radiation heat flux are as follows ... 

Figure 8.3. Graphical presentation for sample problem of the radiation heat flux as a function of time.

Radiation heat flux is graphically represented as a function of time in Figure 8.3. The total amount of radiation heat from a surface can be found by integration of the radiation heat flux over the time of flame propagation, that is, the area under the curve. This result is probably an overstatement of realistic values, because the flame will probably not bum as a closed front. Instead, it will consist of several plumes which might reach heights in excess of those assumed in the model but will nevertheless probably produce less flame radiation. Moreover, the flame will not bum as a plane surface but more in the shape of a horseshoe. Finally, wind will have a considerable influence on flame shape and cloud position. None of these eflects has been taken into account. 

In tliis category, ignition results from converted or radiated heat from adjoining or nearby facilities. 

A boding liquid-expanding vapor explosion occurs when a pressure vessel containing a liquid is heated to a temperature liigh enough to cause tlie metal to lose strength and rupture. The source of tlie heat is nonnally another fire near tlie vessel. The effects of a BLEVE depend on whether tlie liquid in tlie vessel is flammable. If the liquid is flammable, it may eitlier cause a fire, which radiates heat, or fonii a vapor cloud, which could result in a second explosion. 

The air-mass thunderstorm is the least severe of all thunderstorms. In its simplest form, an air-mass thunderstorm grows as a single cell when solar radiation heats the surface air in an unstable atmosphere. Its life cycle lasts around 30 minutes. Towering cumulus clouds are formed as in-cloud updrafts push moisture upward. The tower may reach a height about five times the diameter of the cloud base in the growth phase. 

---