INFRA-RED HEATING – AN INTRODUCTION
Infra-red is a very radiant form of heating. A good infra-red heat source has the ability to heat objects and people directly, without having to heat the air in between!
Infra-red radiation occupies the portion of the electromagnetic spectrum between visible light and radio waves. It derives its name from Latin. The prefix ‘infra’ means ‘below’ and refers to the wavelengths that are just below the red end of the visible spectrum, hence ‘infra-red’.
Infra-red heating is generally split into three categories: – Short-wave Infra-red, Medium-wave Infra-red and Long-wave Infra-red. Short-wave infra-red is sometimes referred to as ‘Near’ infra-red and Long-wave infra-red is sometimes described as ‘Far’ infra-red. These descriptions refer to the relative distance they are away from the visible portion of the spectrum
Infra-red technology can be used for heating everything from people to products. The selection of the correct wavelength for a particular application is critical.
Short-wave infra-red and certain medium infra-red products are generally used to heat people. Leisure Heating products are designed to match the absorbency characteristics of the human body and in doing so are extremely efficient at transfering heat directly without having to heat the air in between. This makes Leisure Heating products the ideal choice for a wide range of applications including church heating, warehouse heating and many outdoor areas such as smoking shelters and patios.
Industrial Process Heating
Heat Infra-red is the industrial division of Leisure Heating Ltd. It offers a free feasibility trial to test the use of infra-red on an industrial proces such as paint drying or forced curing. If there is a mismatch between the emitted wavelength and the absorbency characteristics of the substrate, the efficient heat transfer will simply not take place. The services offered by Heat Infra-red Ltd can be most useful in ensuring the correct form of infra-red radiation is used.
INFRA-RED WAVELENGTHS EXPLAINED
A short-wave infra-red emitter operates at white-hot. It is sealed in a quartz enclosure which may be tubular or shaped like a spot lamp bulb (known as a ‘blown bulb’). Tubular emitters are available in a range of lengths and require an appropriate reflector system (focused or diffusing) to concentrate the heat on the target. The spot lamp types have integral reflectors. Short-wave emitters are very responsive. They may be switched on and off within seconds but generally require electronic control.
Industrial Use. – Industrial installations may be designed with very high power densities and these give correspondingly high rates of product heating. Short-wave heating is used extensively for industrial process pre-heating including metal castings, powder coating applications and adhesive bonding.
Domestic and Commercial Use. – Short-wave infra-red heating elements are now quite extensively used in electric patio heating as well as indoor infra-red heaters used in churches, village halls etc.
The emitter operates at bright red heat. It is generally located in a quartz tube but is not sealed. Some designs use metal emitters on an insulating panel. Tubular or ‘cassette’ emitter configurations are available depending upon the application it is required for. Recent designs of cassettes provide much better performance than earlier linear types. Response times vary considerably between different designs.
Industrial Use. – Medium-wave is used extensively for drying and curing.
Domestic and Commercial Use. – Medium-wave elements are used in many applications including; bathroom heaters, gazebo heaters, pendant heaters, some wall-mounted heaters and in the commercial food processing industry.
The emitter operates at dull red or ‘black’ heat. Several designs are available including tubular metal-clad types or ceramic plaques. Metal clad emitters are very robust but energy intensity is limited and response times are relatively slow when compared to that of medium-wave and short-wave infra-red emitters.
Industrial Use. – Long-wave infra-red is ideal for soak-out of components after other forms of infra-red heating have been used to do the main radiant heating. The use of long-wave elements creates a higher degree of hot-air than other wavelengths so is also used where a combination of infra-red and hot-air is required in a process.
Domestic and Commercial Use. – Long-wave infra-red is widely used in the catering industry and, indeed, in many household appliances! Grill elements and toaster elements are good examples of long-wave infra-red heat sources.