Infrared heater
Encyclopedia
An infrared heater is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation. Depending on the temperature of the emitting body, the wavelength of the infrared
radiation ranges from 780 nm to 1 mm. The relationship between temperature and wavelength is expressed by the Wien's displacement law
. No contact or medium between the two bodies is needed for the energy transfer.
A rough classification of infrared heaters is connected to wavelength bands of major emission of the energy: short wave or near infrared for the range from 780 nm to 1400 nm, these emitters are also named bright because still some visible light with glare is emitted; medium infrared for the range between 1400 nm and 3000 nm; far infrared or dark emitters for everything above 3000 nm.
s. These emitters use the same materials and principle as an incandescent light bulb.
The most common filament material used for electrical infrared heaters is tungsten
wire, which is coiled to provide more surface area. Low temperature alternatives for tungsten are carbon
, or alloys of iron, chromium and aluminum (brand name ‘kanthal
’).
While carbon filaments are more fickle to produce, they heat up much more quickly than a comparable medium-wave heater based on a FeCrAl filament.
Industrial infrared heaters sometimes use a gold coating on the quartz tube that reflects the infrared radiation and directs it towards the product to be heated. Consequently the infrared radiation impinging on the product is virtually doubled. Gold is used because of its oxidation resistance and very high IR reflectivity of approximately 95%.
Infrared heaters are usually classified by the wavelength
they emit. Near infrared (NIR) or short-wave infrared heaters operate at high filament temperatures above 1800 °C and when arranged in a field reach high power densities of some hundreds of kW/m². Their peak wavelength is well below the absorption spectrum for water, making them unsuitable for many drying applications. They are well suited for heating of silica where a deep penetration is needed.
Medium-wave and carbon (CIR) infrared heaters operate at filament temperatures of around 1000 °C. They reach maximum power densities of up to 60 kW/m² (medium-wave) and 150 kW/m² (CIR).
Far infrared emitters (FIR) are typically used in the so-called low-temperature far infrared sauna
s. These constitute only the higher and more expensive range of the market of infrared sauna. Instead of using carbon, quarz or high watt ceramic emitters, which emit near and medium infrared radiation, heat and light, far infrared emitters use low watt ceramic plates that remain cold, while still emitting far infrared radiation.
that is used for the principal purpose of creating heat. The spectrum of black body radiation emitted by the lamp is shifted to produce more infrared light. Many heat lamps include a red filter to minimize the amount of visible light emitted. Heat lamps often include an internal reflector.
Heat lamps are commonly used in shower and bathrooms to warm bathers and in food-preparation areas of restaurants to keep food warm before serving. They are also commonly used for animal husbandry
. Lights used for poultry are often called brooding lamps. Aside from young bird
s, other types of animal
s which can benefit from heat lamps include reptile
s, amphibian
s, insect
s, arachnid
s, and the young of some mammal
s.
The sockets used for heat lamps are usually ceramic
because plastic
sockets can melt or burn when exposed to the large amount of waste heat produced by the lamps, especially when operated in the "base up" position. The shroud or hood of the lamp is generally metal. There may be a wire guard over the front of the shroud, to prevent touching the hot surface of the bulb.
Ordinary household white incandescent bulbs can also be used as heat lamps, but red and blue bulbs are sold for use in brood lamps and reptile lamps. 250 watt
heat lamps are commonly packaged in the "R40" (5" reflector lamp) form factor with an intermediate screw base.
Heat lamps can be used as a medical treatment to provide dry heat when other treatments are ineffective or impractical.
The ceramic infrared heaters (emitters) are manufactured with three basic emitter faces:
Trough (concave), flat and bulb or Edison screw element for normal installation via an E27 ceramic lamp holder.
, these lamps produce about 100 watts/inch (4 w/mm) and can be combined to radiate 500 watts per square foot (54000 watts/square m). To achieve even higher power densities, halogen lamp
s were used. Quartz infrared lamps are used in highly-polished reflectors to direct radiation in a uniform and concentrated pattern.
Quartz heat lamps are used in food processing, chemical processing, paint drying, and thawing of frozen materials. They can also be used for comfort heating in cold areas, in incubators, and in other applications for heating, drying, and baking. During development of space re-entry vehicles, banks of quartz infrared lamps were used to test heat shield materials at power densities as high as 28 kW/ square foot (300 kW/square meter).
Most common designs consist of either a satin milky-white quartz glass
tube or clear quartz
with an electrically resistant element, usually a tungsten wire, or a thin coil of iron-chromium-aluminum alloy.
The atmospheric air is removed and filled with inert gases such as nitrogen
and argon
then sealed. In quartz halogen lamps a small amount of halogen
gas is added to prolong the heater's operational life.
Much of the infrared
and visible energy released is caused by the direct heating of the quartz
material, 97% of the near infrared is absorbed by the silica quartz glass tube causing the temperature of the tube wall to increases, this causes the silicon-oxygen bond to radiate far infrared rays.
Quartz glass heating elements were originally designed for lighting applications, but when a lamp is at full power less than 5% of the emitted energy is in the visible spectrum.
Radiant tube gas-fired heaters used for industrial and commercial building space heating use combustion of a fuel gas such as natural gas
or propane
to heat a steel emitter tube. Gas is released from a valve
, and is either pushed or pulled through a cup burner, or in the case of more technologically advanced units, through a venturi
. Once the proper air-fuel ratio
is achieved, the gas is then ignited, which heats the emitter tube. As the tube heats, radiant energy from the tube strikes floors and other objects in the area, warming them. The advantage of this form of heating is maintained warmth even when a large volume of cold air is suddenly introduced, such as in maintenance garages
for vehicles. The efficiency of an Infrared heater is a rating of the total energy consumed by the heater compared to the amount of Infrared energy generated. While there will always be some amount of convective heat generated through the process, any introduction of air motion across the heater will reduce its Infrared conversion efficiency
in Europe. Unfortunately, this technology does not appear to be always suitable to patients with electromagnetic and radiation sensitivities, many of whom react strongly to the far-infrared radiation of the panels. Because far infrared technology does not heat the air of the room directly, and infrared rays are directional, only the person who is receiving directly the far infrared rays will feel warm in the room. Therefore, in the case of far infrared space heaters, it is extremely important to make a study of the room and place the far infrared panels directed to the places where people stay most of the time (sofa, dining table, bed, etc.). As the air of the room is not heated directly, and only the limited areas where people stay in the room are heated, far-infrared heaters save energy compared to heaters that heat totally or partially (like near and medium infrared heaters) the air of the room.
For practical applications, the efficiency of the infrared heater depends on matching the emitted wavelength and the absorption spectrum of the material to be heated.
For example, the absorption spectrum for water
has its peak at around 3000 nm. This means that emission from medium-wave or carbon infrared heaters are much better absorbed by water and water-based coatings than NIR or short-wave infrared radiation.
The same is true for many plastics like PVC or polyethylene. Their peak absorption is around 3500 nm. On the other hand, some metals absorb only in the short-wave range and show a strong reflectivity in the medium and far infrared. This makes a careful selection of the right infrared heater type important for energy efficiency in the heating process.
Ceramic elements operate in the temperature of 300°C to 700°C (572°F - 1292°F) producing infrared wavelengths in the 2 - 10 micron range. Most plastics and many other materials absorb infrared best in this range, which makes the ceramic heater most suited for this task.
IR heaters are used in industrial manufacturing processes including curing of coatings, shrink tunnel
s, heating of plastic prior to forming, plastic welding, processing glass,and cooking and browning food. They are used when high temperatures are required, fast responses or temperature gradients are needed or products need to be heated in certain areas in a targeted way. Their application is difficult for objects with undercuts.
They are also used to provide warmth to suckling animals whose mother cannot or will not provide them with natural warmth as well as to captive animals in zoos or veterinary clinics, especially for lizards and other reptiles, and tropical animals such as birds.
Another recent use is in house heating, various companies sell infrared heaters for house use, claiming some medical benefits due to better circulation and total lack of fumes emissions. Infrared saunas claim same benefits too.
and opacity of the aqueous humor, so exposure should be moderated.
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
radiation ranges from 780 nm to 1 mm. The relationship between temperature and wavelength is expressed by the Wien's displacement law
Wien's displacement law
Wien's displacement law states that the wavelength distribution of thermal radiation from a black body at any temperature has essentially the same shape as the distribution at any other temperature, except that each wavelength is displaced on the graph...
. No contact or medium between the two bodies is needed for the energy transfer.
A rough classification of infrared heaters is connected to wavelength bands of major emission of the energy: short wave or near infrared for the range from 780 nm to 1400 nm, these emitters are also named bright because still some visible light with glare is emitted; medium infrared for the range between 1400 nm and 3000 nm; far infrared or dark emitters for everything above 3000 nm.
Elements
Infrared heaters use either a fuel to heat an emitter, or an electrically heated filament as the emitting body. An infrared lamp will protect the filament with a heat-resistant quartz glass tube. Some heat lamps used halogen lampHalogen lamp
A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. The chemical halogen cycle redeposits evaporated tungsten back on to the filament, extending the life of...
s. These emitters use the same materials and principle as an incandescent light bulb.
The most common filament material used for electrical infrared heaters is tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
wire, which is coiled to provide more surface area. Low temperature alternatives for tungsten are carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, or alloys of iron, chromium and aluminum (brand name ‘kanthal
Kanthal
Kanthal is the trademark for a family of iron-chromium-aluminium alloys used in a wide range of resistance and high-temperature applications. Kanthal FeCrAl alloys consist of mainly iron, chromium and aluminium . The first Kanthal FeCrAl alloy was developed by Hans von Kantzow in Hallstahammar,...
’).
While carbon filaments are more fickle to produce, they heat up much more quickly than a comparable medium-wave heater based on a FeCrAl filament.
Industrial infrared heaters sometimes use a gold coating on the quartz tube that reflects the infrared radiation and directs it towards the product to be heated. Consequently the infrared radiation impinging on the product is virtually doubled. Gold is used because of its oxidation resistance and very high IR reflectivity of approximately 95%.
Types
Infrared heaters are commonly used in infrared modules (or emitter banks) combining several heaters to achieve larger heated areas.Infrared heaters are usually classified by the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
they emit. Near infrared (NIR) or short-wave infrared heaters operate at high filament temperatures above 1800 °C and when arranged in a field reach high power densities of some hundreds of kW/m². Their peak wavelength is well below the absorption spectrum for water, making them unsuitable for many drying applications. They are well suited for heating of silica where a deep penetration is needed.
Medium-wave and carbon (CIR) infrared heaters operate at filament temperatures of around 1000 °C. They reach maximum power densities of up to 60 kW/m² (medium-wave) and 150 kW/m² (CIR).
Far infrared emitters (FIR) are typically used in the so-called low-temperature far infrared sauna
Infrared sauna
An infrared sauna uses infrared heaters to emit infrared radiant heat which is absorbed directly into the human body, unlike traditional saunas which heat the body indirectly via air or steam.- Health benefit claims :...
s. These constitute only the higher and more expensive range of the market of infrared sauna. Instead of using carbon, quarz or high watt ceramic emitters, which emit near and medium infrared radiation, heat and light, far infrared emitters use low watt ceramic plates that remain cold, while still emitting far infrared radiation.
Heat lamps
A heat lamp is an incandescent light bulbIncandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...
that is used for the principal purpose of creating heat. The spectrum of black body radiation emitted by the lamp is shifted to produce more infrared light. Many heat lamps include a red filter to minimize the amount of visible light emitted. Heat lamps often include an internal reflector.
Heat lamps are commonly used in shower and bathrooms to warm bathers and in food-preparation areas of restaurants to keep food warm before serving. They are also commonly used for animal husbandry
Animal husbandry
Animal husbandry is the agricultural practice of breeding and raising livestock.- History :Animal husbandry has been practiced for thousands of years, since the first domestication of animals....
. Lights used for poultry are often called brooding lamps. Aside from young bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, other types of animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s which can benefit from heat lamps include reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s, insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...
s, and the young of some mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s.
The sockets used for heat lamps are usually ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
because plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
sockets can melt or burn when exposed to the large amount of waste heat produced by the lamps, especially when operated in the "base up" position. The shroud or hood of the lamp is generally metal. There may be a wire guard over the front of the shroud, to prevent touching the hot surface of the bulb.
Ordinary household white incandescent bulbs can also be used as heat lamps, but red and blue bulbs are sold for use in brood lamps and reptile lamps. 250 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
heat lamps are commonly packaged in the "R40" (5" reflector lamp) form factor with an intermediate screw base.
Heat lamps can be used as a medical treatment to provide dry heat when other treatments are ineffective or impractical.
Ceramic infrared heat systems
Ceramic infrared heating elements are used in a diverse range of industrial processes where long wave infrared radiation, is required. Their useful wavelength range is 2-10 microns. They are often used in the area of animal / pet healthcare too.The ceramic infrared heaters (emitters) are manufactured with three basic emitter faces:
Trough (concave), flat and bulb or Edison screw element for normal installation via an E27 ceramic lamp holder.
Quartz heat lamps
Quartz infrared heating elements emit medium wave infrared energy and are particularly effective in systems where rapid heater response is required. Tubular infrared lamps in quartz bulbs produce useful infrared radiation in wavelengths of 1.5-8 microns. The enclosed filament operates at around 2500 K, producing more shorter-wavelength radiation than open wire-coil sources. Developed in the 1950s at General ElectricGeneral Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
, these lamps produce about 100 watts/inch (4 w/mm) and can be combined to radiate 500 watts per square foot (54000 watts/square m). To achieve even higher power densities, halogen lamp
Halogen lamp
A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. The chemical halogen cycle redeposits evaporated tungsten back on to the filament, extending the life of...
s were used. Quartz infrared lamps are used in highly-polished reflectors to direct radiation in a uniform and concentrated pattern.
Quartz heat lamps are used in food processing, chemical processing, paint drying, and thawing of frozen materials. They can also be used for comfort heating in cold areas, in incubators, and in other applications for heating, drying, and baking. During development of space re-entry vehicles, banks of quartz infrared lamps were used to test heat shield materials at power densities as high as 28 kW/ square foot (300 kW/square meter).
Most common designs consist of either a satin milky-white quartz glass
Fused quartz
Fused quartz and fused silica are types of glass containing primarily silica in amorphous form. They are manufactured using several different processes...
tube or clear quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
with an electrically resistant element, usually a tungsten wire, or a thin coil of iron-chromium-aluminum alloy.
The atmospheric air is removed and filled with inert gases such as nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
then sealed. In quartz halogen lamps a small amount of halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
gas is added to prolong the heater's operational life.
Much of the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
and visible energy released is caused by the direct heating of the quartz
Fused quartz
Fused quartz and fused silica are types of glass containing primarily silica in amorphous form. They are manufactured using several different processes...
material, 97% of the near infrared is absorbed by the silica quartz glass tube causing the temperature of the tube wall to increases, this causes the silicon-oxygen bond to radiate far infrared rays.
Quartz glass heating elements were originally designed for lighting applications, but when a lamp is at full power less than 5% of the emitted energy is in the visible spectrum.
Quartz tungsten
Quartz tungsten infrared heaters emit medium wave energy reaching operating temperatures of up to 1500°C (medium wave) and 2600°C (short wave). It reaches top temperatures within seconds. Peak wavelength emissions of approximately 1.6 microns (medium wave infrared) and 1 micron (short wave infrared).Carbon
Carbon heaters are relatively recent and produce high quality, long wave far infrared heat, but the problem is they do not produce a big amount of it. For this reason it is not a popular solution for space heating, but it is widely use in many infrared saunas.Gas-fired
There are two basic types of infrared radiant heaters.- Luminous of High Intensity
- Radiant Tube Heaters
Radiant tube gas-fired heaters used for industrial and commercial building space heating use combustion of a fuel gas such as natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
or propane
Propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...
to heat a steel emitter tube. Gas is released from a valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
, and is either pushed or pulled through a cup burner, or in the case of more technologically advanced units, through a venturi
Venturi
-People:*Giovanni Battista Venturi , physicist*Ken Venturi , professional golfer*Remo Venturi , Italian motorcycle racer*Rick Venturi , American football coach*Robert Venturi , architect...
. Once the proper air-fuel ratio
Air-fuel ratio
Air–fuel ratio is the mass ratio of air to fuel present in an internal combustion engine. If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture, often abbreviated to stoich...
is achieved, the gas is then ignited, which heats the emitter tube. As the tube heats, radiant energy from the tube strikes floors and other objects in the area, warming them. The advantage of this form of heating is maintained warmth even when a large volume of cold air is suddenly introduced, such as in maintenance garages
Automobile repair shop
An automobile repair shop is a place where automobiles are repaired by auto mechanics and electricians.- Types :The automotive garage can be divided in so many category....
for vehicles. The efficiency of an Infrared heater is a rating of the total energy consumed by the heater compared to the amount of Infrared energy generated. While there will always be some amount of convective heat generated through the process, any introduction of air motion across the heater will reduce its Infrared conversion efficiency
Far-infrared
This expensive heating technology has been in use for years in the most expensive infrared saunas. In recent years it is also starting to be applied to space heaters. They use low watt ceramic emitters (usually fairly big panels) which emit long wave infrared radiation. Because the heating elements always remain cold, far-infrared heaters enjoy a total absence of emissions and smell from dust, dirt, formaldehyde, toxic fumes from paint-coating, etc. This has made this new type of space heating very popular among people with severe allergies and multiple chemical sensitivityMultiple chemical sensitivity
Multiple chemical sensitivity is a chronic medical condition characterized by symptoms the affected person attributes to exposure to low levels of chemicals. Commonly suspected substances include smoke, pesticides, plastics, synthetic fabrics, scented products, petroleum products and paints...
in Europe. Unfortunately, this technology does not appear to be always suitable to patients with electromagnetic and radiation sensitivities, many of whom react strongly to the far-infrared radiation of the panels. Because far infrared technology does not heat the air of the room directly, and infrared rays are directional, only the person who is receiving directly the far infrared rays will feel warm in the room. Therefore, in the case of far infrared space heaters, it is extremely important to make a study of the room and place the far infrared panels directed to the places where people stay most of the time (sofa, dining table, bed, etc.). As the air of the room is not heated directly, and only the limited areas where people stay in the room are heated, far-infrared heaters save energy compared to heaters that heat totally or partially (like near and medium infrared heaters) the air of the room.
Efficiency
Electrically-heated infrared heaters radiate up to 86% of their input as radiant energy. Nearly all the electrical energy input is converted into infrared radiant heat in the filament and directed onto the product by reflectors. Some energy is lost due to conduction or convection.For practical applications, the efficiency of the infrared heater depends on matching the emitted wavelength and the absorption spectrum of the material to be heated.
For example, the absorption spectrum for water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
has its peak at around 3000 nm. This means that emission from medium-wave or carbon infrared heaters are much better absorbed by water and water-based coatings than NIR or short-wave infrared radiation.
The same is true for many plastics like PVC or polyethylene. Their peak absorption is around 3500 nm. On the other hand, some metals absorb only in the short-wave range and show a strong reflectivity in the medium and far infrared. This makes a careful selection of the right infrared heater type important for energy efficiency in the heating process.
Ceramic elements operate in the temperature of 300°C to 700°C (572°F - 1292°F) producing infrared wavelengths in the 2 - 10 micron range. Most plastics and many other materials absorb infrared best in this range, which makes the ceramic heater most suited for this task.
Applications
Shrink tunnel
A Shrink tunnel or Heat tunnel is a heated tunnel mounted over or around a conveyor system. Items such as packaging, have shrink film loosely applied; with heat, the film shrinks to fit snugly around the wrapped object.-Uses:* Shrink labels...
s, heating of plastic prior to forming, plastic welding, processing glass,and cooking and browning food. They are used when high temperatures are required, fast responses or temperature gradients are needed or products need to be heated in certain areas in a targeted way. Their application is difficult for objects with undercuts.
They are also used to provide warmth to suckling animals whose mother cannot or will not provide them with natural warmth as well as to captive animals in zoos or veterinary clinics, especially for lizards and other reptiles, and tropical animals such as birds.
Another recent use is in house heating, various companies sell infrared heaters for house use, claiming some medical benefits due to better circulation and total lack of fumes emissions. Infrared saunas claim same benefits too.
Health effects
In addition to the dangers of touching the hot bulb or element, infrared heaters may cause indirect thermal burns when the skin is exposed for too long or the heater is positioned too close to the subject. Individuals exposed to large amounts of infrared radiation over an extended period of time may develop depigmentation of the irisIris (anatomy)
The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...
and opacity of the aqueous humor, so exposure should be moderated.
Further reading
- Deshmukh, Yeshvant V.: Industrial Heating, Principles, Techniques, Materials, Applications, and Design. Taylor and Francis, Boca Raton, Fl: 2005.
- Siegel, Robert and Howell, John R.: Thermal Radiation Heat Transfer. 3rd Ed. Taylor and Francis, Philadelphia, PA.