September 2007
In This Issue...
Resources
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Infrared Application of the Month #1:
Carbon IR Heating for Confectionary Application
Four carbon medium wave infrared heating systems from Heraeus Noblelight, are helping a major confectioner achieve better control over the quality of their filled chocolate products, as well as saving energy and space when compared with the previous chocolate heating system.
In this application, the application of heat is an important process step. Previously this had been carried out by using hot air blowers but the temperature profile proved difficult to control. The chocolate was sometimes not at the right consistency. This caused quality control problems and could also cause problems at the subsequent chilling and wrapping stages, and with quality control in general.
The confectioner installed four 8.4kW, pyrometer-controlled, Carbon medium wave infra-red systems on their production lines. Apart from the quality improvements and the more consistent presentation of the finished product, the new infrared heating system has also provided significant savings in space and energy over the previous system. In addition, the virtually instantaneous response of the carbon heaters means that they can be switched off instantly in the event of unexpected production line stoppage, ensuring that product spoilage is kept to a minimum.
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Infrared Application of the Month #2:
Removing Creases From Car Seat Covers
An auto manufacturer requred process heat to soften and remove creases from leather and/or textile car seat covers. Their existing system made use of a low-efficiency metal heater. Installation of a Carbon infrared single-tube heater from Heraeus Noblelight increased efficiency and quality, and gave operators increased power control over the process.
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Tech Center Spotlight:
Shortwave Heaters
Fast and Intensive
Shortwave IR heaters from Heraeus are suitable for all applications in which the attainment of high temperatures in the shortest possible time is what counts. Their emission maximum is between 0.9 and 1.6 micron.
Performance advantages include high radiation density in the most compact space; near-instant heating-up and cooling down times; optimized reflection; much more.
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Special Designs:
Short Wave Plug-in Heater
Heraeus offers the short wave infrared heater with a plug in connection. This design makes initial assembling as well as maintenance during production very simple. The plug in heater type helps to reduce maintenance costs.
Technical Data
- Short Wave
- Twin tube, 23 x 22 mm
- Gold reflector
- Single end connection
- Up to 10 Amp current
- 55-480 Volts possible
Advantages
- Simple installation
- Quick disconnect
- Fast replacement
- Tool-free replacement
- Reduce downtime
Click HERE to download a brochure on this product.
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Engineering Aspects of Radiation Theory
continued from last month's issue
Laws of Radiaiton and Their Practical Significance
Turning now to the oscillatory nature, the radiation passes through successive identical states at precise time intervals measured in seconds. The rate at which the states recur, or frequency, is measured in cycles per second so that frequency is equal to the reciprocal of time. The velocity of propagation (in a vacuum ) for all radiation is 3 x 10 8 meters per second: the speed of light. From this we can deduce that the distance between successive identical states -- the wavelength -- is the product of velocity and time. See figure below.
Expressing these statements mathematically ,
t = time interval in seconds which separates the passage of radiation through two successive identical states
f = frequency in cycles per second
λ = wavelength in meters per second
V = speed of light in meters per second
Infrared and visible wavelengths are normally expressed in microns (or micro -meters), this unit being one millionth of a meter. Radiaiton visible to the human eye occurs over a very narrow band, from 0.4 to 0.76 microns. The broad region occupied by infrared extends from 0.76 microns (that is just beyond the red end of the visible end of the spectrum) to 400 microns. However, the radiation used for process heating occurs between wavelengths of 1 and 5 microns in order to obtain adequate source temperatures. This represents a temperature range of 2200 °C to 300°C.
Continuing well beyond the infrared or thermal region to much longer wavelengths of the order of centimeters and meters, the spectrum is occupied by microwave, radar, television and radio communications equipment.
The radiation emitted by a body can be determined if the temperature and nature of its surface (emissivity) are known.
These are the key parameters required to calculate the radiation emitted by a surface at a particular wavelength or over a band of wavelengths.
the starting point in the discussion on the laws of thermal radiation is the concept of the "black body" or Planckian radiator. This is an ideal body which totally absorbs all incident radiation at all wavelengths. The reflectivity is therefore zero (Note that the term "black body" does not have any color connotation in the visual sense). In addition to being a perfect absorber, it is also a perfect radiator: it will radiate the maximum amount of energy at any given temperature. This concept is very convenient in the mathematical and graphical treatment of infrared theory and the development of relationships.
A near approximation to the black body is provided by an isothermal enclosure (see graphic at right), which represents a hollow metal sphere with a small radial hole through its wall. Any radiation entering this hole undergoes multiple internal reflections and absorptions until total absorption is achieved. Conversely, if the sphere is heated, the hole will radiate as if it were a black body. This applies even if the sphere is heated to an incandescent temperature.
From this theoretical phenomenon, it is possible, for example, to visualize the interior of an enclosed furnace with all the walls at a constant temperature behaving almost as a black body. However, in practice all bodies are less than perfect radiators or absorbers, and are therefore referred to as "grey bodies," or more strictly "nonblack bodies." The maximum radiation intensity W produced by a black body unit interval of wavelength is obtained from Planck's Law...
This article will be continued in our next issue.
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That's it for this month's issue of Application Notes for IR Heating. Feel free to encourage your colleagues to subscribe. Just click HERE to send them an invitation to subscribe. It's quick, easy, FREE, and no-obligation.
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