วันจันทร์ที่ 14 มิถุนายน พ.ศ. 2553
Elements of infrared heaters
For practical purposes, most infrared heaters are constructed by either using the emission of a flame (usually soot or a heated matrix) or an electrically heated filament as the emitting body. If an electrically operated infrared heater (infrared lamp) is used, the filament is usually protected by a heat-resistant quartz glass tube. Depending on the filament temperature, a filling of the quartz tube with inert gas (e.g., halogen) may be required to prevent filament degradation. These emitters use the same materials and principle as a 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 quicker 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 %
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 quicker 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 %
วันอังคารที่ 1 มิถุนายน พ.ศ. 2553
Types of infrared heaters
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 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 100s 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 heaters are typically used in low-temperature infrared saunas.
Heat lamps
A heat lamp is an incandescent light bulb 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 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 birds, other types of animals which can benefit from heat lamps include reptiles, amphibians, insects, arachnids, and the young of some mammals.
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.
Tubular infrared lamps in quartz bulbs produce useful infrared radiation in wavelengths shorter than 5 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 Electric, 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 lamps were used. Quartz infrared lamps are used in highly-polished reflectors to direct radiation in a uniform and concentrated pattern. Lamps are used in food processing, chemical processing, paint drying, and thawing of frozen materials. Quartz heat lamps 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)
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 100s 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 heaters are typically used in low-temperature infrared saunas.
Heat lamps
A heat lamp is an incandescent light bulb 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 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 birds, other types of animals which can benefit from heat lamps include reptiles, amphibians, insects, arachnids, and the young of some mammals.
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.
Tubular infrared lamps in quartz bulbs produce useful infrared radiation in wavelengths shorter than 5 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 Electric, 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 lamps were used. Quartz infrared lamps are used in highly-polished reflectors to direct radiation in a uniform and concentrated pattern. Lamps are used in food processing, chemical processing, paint drying, and thawing of frozen materials. Quartz heat lamps 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)
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