Radiation heat source

An infinite plate of thickness 2L is suddenly exposed to a constant-temperature radiation heat source or sink of temperature T,. The plate has a uniform initial temperature of T,. The radiation heat loss from each side of the plate is given by q - surface area. Assuming that the plate behaves as a lumped capacity, that is, k — =0, derive an expression for the temperature of the plate as a function of time. 

This capsule with the radioactive material is called a radiation heat source (RHS). Heat may be produced in dynamic or static cycles using the temperature difference between RHS and environment. Similar to the reactor sources, static conversion systems, particularly thermoelectric ones, were widely used both in the USSR and in the USA. Systems on their basis have been named as radioisotope thermoelectric generators (RTG). 

The RTG basic units include the radiation heat source (RHS), thermoelectric unit (TEU), radiation shielding (RS), and radiator. (Space systems need radiators also to cool them.) RTGs merits are determined by the following unique properties spontaneous release of thermal power, its direct conversion into electricity, a simple design, high-energy output, a long lifetime, the opportunity of employment practically in all scopes of activities under water, at the surface of the Earth and planets, and in space. 

A radiant panel apparatus consists of a radiating heat source maintained at 1238°F. A vertically mounted, porous refractory panel acts as a radiating heat source. A... 

FIGURE 10.12 Typical pressure thermoforming process, (a) The clamped sheet is heated to the processing temperature by means of infrared heaters, (b) The heated sheet is removed from the radiation heating source and placed into position for forming, (c) Vacuum is applied to the underside of the sheet or air pressure is applied to the top side of the sheet, forcing the heated sheet into the mold. 

Because almost all alpha radiation is stopped within the solid source and its container, giving up its energy, polonium has attracted attention for uses as a lightweight heat source for thermoelectric power in space satellites. 

Equation (12-47) assumes that all heat sources are at the same temperature and that the convection coefficients to the evaporating surface and to the unwetted portions of the tray are equal. When radiation occurs from a source at a different temperature, the radiation coefficient can be corrected to the same basis by multiplying by the ratio (t — f()/(U i ), where t, t, and t are the diying-gas, evaporating-surface, and radiator temperatures respectively. 

Because indirect-heat calciners frequently require close-fitting gas seals, it is customaiy to support aU parts on a selFcontained frame, for sizes up to approximately 2 m in diameter. The furnace can employ elec tric heating elements or oil and/or gas burners as the heat source for the process. The hardware would be zoned down the length of the furnace to match the heat requirements of the process. Process control is normaUy by shell temperature, measured by thermocouples or radiation pyrometers. When a special gas atmosphere must be maintained inside the cyhnder, positive rotaiy gas se s, with one or more pressurized and purged annular chambers, are employed. The diaphragm-type seal ABB Raymond (Bartlett-Snow TM) is suitable for pressures up to 5 cm of water, with no detectable leakage. 

Heat sensitive materials need to be stored away from heat sources such heaters and windows where they are subject to solar radiation. 

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...

Technology Description Infrared radiators can be used as the heat source in the destruction of hazardous waste. This system (Figure 35) is made up of a primary chamber consisting of a rectangular carbon steel box lined with layers of a light weight. 

Lines or equipment which can be left full of liquid under non-flow conditions and which can be heated while completely blocked-in must have some means of relieving pressure built up by thermal expansion of the contained liquid. Solar radiation, as well as other heat sources, must be considered. Lines or equipment which are hotter than ambient when blocked in and which cannot otherwise be heated above the blocked-in temperature do not need protection against liquid thermal expansion. The following are common examples of some thermal expansion mechanisms. 

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 distribution of solar radiation, including surface radiation exchange, can account for solar heat source variations in time and local space. 

In the simulation, the time dependency of the energy release of such sources is defined in so-called schedules. The heat sources transfer energy to the room air by convection and to the surfaces by long-wave radiation. In principle, heat sources can be modeled by two kinds of parameterization ... 

Radiation from internal heat sources is not directly considered in thermal comfort calculations. 

For a person at a certain location in a room, direct radiation from internal heat sources may significantly affect the thermal comfort level. However, in the codes, room (or operative) temperatures are calculated on the basis of the room air and the wall surface temperatures only (both calculated considering the internal heat source, however). 

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. 

In normal atmospheric conditions, fire usually is initialed by a combustible material coming in contact with a heat source. The spread of fire occurs due to direct flame impingement or the transfer of heat to the surrounding combustible materials. Heat transfer occurs by three principal mechanisms - conduction, convection, and radiation. Conduction is the movement of heat through a stationary medium, such as solids, liquids or gases. Steel is a good conductor of heat as is aluminum, therefore they can pass the heat of a fire if left unprotected. 

Figure 58A-C shows that the heat source promoting the drying process changes during the course of the batch combustion. At times to and ti there is an artificial heat source located in the over-bed section. At time t2 the flaming combustion has started. The flames feed back heat to the bed by means of radiation. At time t3 the basic heat flow comes from the char combustion and the ignition front, by means of conduction and radiation. [12,24]...

Pyrolysis commences at bed surface temperatures in the range of 150-300°C [22,23]. Almost simultaneously, flaming combustion takes place in the combustion system above the fuel bed (see Figure 58C). At t2 the pyrolysis is sustained by heat from over-bed flames. The heat is transported by radiation. At times ts to t4 the dominant heat source has changed to the char combustion zone (ignition front) instead. The heat from the ignition front is also transported by means of conduction and radiation. 

Some other fission products were considered as suitable for radiation sources (heat sources, radiography, etc.). Thus, processes were designed to isolate these from the rest of the fission products. Today, there is little interest in such applications. 

---