Radiant heating elements

Similar technology is also being used in induction hotplates and radiant heating elements and in the silicon nitride hotplates currently under development and which are characterized by an excellent heat transfer between heat source, sensor and saucepan. Gas hotplates could also be provided with the latest in domestic temperature sensing technology by fitting them with electric temperature control circuitry. 

Clamp-on band heaters, for use up to 700°C, are specified when high-watt densities are required or the external vessel area is limited. Heating elements can be woven into a quartz fabric to permit flexibility and ease of removal. These heaters are typically specified for lower-temperature demands because of their lower watt density. More rigid heater designs employ fully exposed, radiant heating elements or heating elements embedded within a ceramic fiber matrix. The latter are the heater of choice for high-temperature applications. 

Heat can be transferred to the sheet in several ways. The most common for thermo-forming is radiation from heater elements. The sheet is moved into or through an oven with radiant heating elements. In some thermoform/fiH/seal equipment, heating is by conduction. In this case, the sheet is pulled up against a heated plate,... 

The bottom- and side-loading thermobalances shown in Figs. 3.2a and 3.2b utilize conventional resistive heating elements, while the bottom-loading example selected in Fig. 3.2c utilizes radiant heating elements necessitating a transparent tube to constrain the atmospheric flow. 

Fig. 3.8. Influence of pot base bow and maximum surface temperature on the heating-up time. Glass ceramic low and medium IR-transmittance, adjustment Tmax = 1000-1080 °F (540-580 °C), heating element radiant heating element, diameter = 180 mm, P = 1700 W (coils, highly insulated)...

The latest innovation is the further development of the material to produce the new Ceran Suprema glass-ceramic cooktop panel. Optimization of the composition of the material plus a new manufacturing process resulted in a further improvement of the heat transmission and temperature resistance of the glass ceramic. In consequence, built-in radiant heating elements can now be adjusted to higher cooking zone temperatures. And boil-up time, depending on the cookware used, can be as much as 20% less (see also Sect. 3.2.3). 

The recent introduction of alternative lower-mass radiant heating elements highlights the industry s growing recognition of the opportunity for improvement. 

Another design, shown ia Figure 5, functions similarly but all components are iaside the furnace. An internal fan moves air (or a protective atmosphere) down past the heating elements located between the sidewalls and baffle, under the hearth, up past the work and back iato the fan suction. Depending on the specific application, the flow direction may be reversed if a propeUer-type fan is used. This design eliminates floorspace requirements and eliminates added heat losses of the external system but requires careful design to prevent radiant heat transfer to the work. 

Perhaps the closest approach to pure oxidation in everyday conditions arises in domestic electric heating appliances where the elements are exposed to the air. At some points the elements are necessarily in contact with supporting refractories, and if these are not of adequate purity, accelerated corrosion leading to early failure can occur. In a similar way the sheathed radiant-type elements of electric cookers usually fail owing to the corrosive effects of contaminants such as animal fats or salts from spilled liquids. 

Radiant heat transfer can result in burns to personnel and can heat up unprotected process equipment and structural elements. If the heat is not dissipated by the application of cooling or conduction, the process equipment or structure may fail. 

Zone Method Let a zone of a furnace enclosure be an area small enough to make all elements of itself have substantially equivalent views of the rest of the enclosure. (In a furnace containing a symmetry plane, parts of a single zone would lie on either side of the plane.) Zones are of two classes source-sink surfaces, designated by numerical subscripts and having areas Ai, Aa,. . ., and emissivities El, and surfaces at which the net radiant-heat flux is zero (ful-... 

Another key element in the PLD apparatus is the substrate heater. Thin film synthesis of oxide materials may be carried out at temperatures as high as 800 °C in oxygen. These highly oxidizing conditions place severe demands on heating elements, although two general types of heaters, radiant and resistive, have been used successfully. Radiant heaters utilize lamps as a heat source. A simpler solution to this problem is to utilize simple resistance heaters. Resistance heaters are easily... 

We have already encountered the application of electrical analogy to conduction. Now we proceed to the use of electrical analogy for radiation. This method is based on two circuit elements. For the first element, reconsider the opaque gray surface of Fig. 9.3. The radiant heat flux from this surface is... 

Radiant tubes are used in industry for heat treatment applications in which products are treated under a protective gas atmosphere within heat treatment furnaces. Therefore the heating of such furnaces are performed with indirect fuel-fired systems or electrical heating elements. For indirect fired applications, the flue gas of the combustion process can not enter into the furnace. The combustion takes place within radiant tubes and the heat is transferred—via radiation—from the outer surface of the tube to the process. There are different types of radiant tubes available. For all types the maximum transferred heat is one of the important features of such systems. That means that the maximum radiant tube temperature and the temperature uniformity are important characteristics of radiant tubes. Another issue is the efficiency of the radiant tubes. In... 

A bolometer is a type of resistance thermometer constructed of strips of metals, such as platinum or nickel, or of a semiconductor. Semiconductor bolometers are often called thermistors. These materials exhibit a relatively large change in resistance as a function of temperature, The responsive element is kept small and blackened to absorb radiant heat. Bolometers are not so extensively used as other infrared transducers for the mid-infrared region, Flowever, a germanium bolometer. operated at 1..3 K, is nearly an ideal transducer for radiation in the. 5 to 400 cm (2000 to 2.3 pm) range. 

Whilst the calculation of the radiant heat flux from a gas to an adjoining surface embraces inherent spectral and directional effects, a simplified approach has been developed by Hottel and Manglesdorf " which involves the determination of radiation emission from a hemispherical mass of gas of radius L, at temperature Tg to a surface element, dL4i, near the centre of the base of the hemisphere. Emission from the gas per unit area of the surface is then ... 

Radiant Ceiling Panels - Ceiling panels that contain electric resistance heating elements embedded within them to provide radiant heat to a room. 

Radiant Heating System - A heating system where heat is supplied (radiated) into a room by means of heated surfaces, such as electric resistance elements, hot water (hydronic) radiators, etc. 

---