ELECTRICAL HEATING – HIGH FREQUENCY HEATING METHODS- INFRARED OR RADIANT HEATING
Infrared radiation was discovered in 1800 by German-born British astronomer.
Frederick William Herschel and born on 15th November 1738.
Herschel constructed his first large telescope in 1774, after which he spent nine years carrying out sky surveys to
investigation of double stars.
In the course of an observation on 13 March 1781 he realized that one celestial body he had observed was not a star, but a planet, Uranus.
Herschel became famous overnight. As a result of this discovery, George III appointed him 'Court Astronomer'.
On 11th February 1800, Herschel was testing filters for the sun and he observed sun spots. When using a red filter he found there was a lot of heat produced.
Herschel discovered infrared radiation in sunlight by passing it through a prism and holding a thermometer just beyond the red end of the visible spectrum. He was shocked when it showed a higher temperature than the visible spectrum. Further experimentation led to Herschel's conclusion that there must be an invisible form of light beyond the visible spectrum.
During his career, he constructed more than four hundred telescopes.
The largest and most famous of these was a reflecting telescope with a 49 1⁄2-inch-diameter (1.26 m) primary mirror and a 40-foot (12 m) focal length.
Herschel also coined the word "asteroid” in the year 1802.
He died on 25th August 1822. He lived for 83 years in this planet.
His house at 19 New King Street in Bath, Somerset where he made many telescopes and first observed Uranus, is now home to the Herschel Museum of Astronomy.
Infrared (IR) is an invisible radiant energy, electromagnetic radiation with longer wavelengths than those of visible light. Infrared radiation extends from the nominal red edge of the visible spectrum at 700 nanometers (nm) to 1 mm. This range of wavelengths corresponds to a frequency range of approximately 430 THz down to 300 GHz. Its photon energy is 1.24mev – 1.7ev. Most of the thermal radiation emitted by objects near room temperature is infrared.
Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 400×10−9 m to 700×10−9 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).This wavelength means a frequency range of roughly 430–750 terahertz (THz). Often, infrared and ultraviolet are also called light. Its photon energy is 1.7eV – 3.3eV.
INFRARED HEATING – In the ordinary resistance furnaces the heat is transferred from heating elements to the charge partly by radiation and convection.
ADVANTAGES - Rapid heating, flexibility, compactness of units and safety.
APPLICATIONS - Drying of wood furniture, pre-heating of plastics and drying of paper pottery textiles etc., where moisture content is not large.
Frederick William Herschel and born on 15th November 1738.
Herschel constructed his first large telescope in 1774, after which he spent nine years carrying out sky surveys to
investigation of double stars.
In the course of an observation on 13 March 1781 he realized that one celestial body he had observed was not a star, but a planet, Uranus.
Herschel became famous overnight. As a result of this discovery, George III appointed him 'Court Astronomer'.
On 11th February 1800, Herschel was testing filters for the sun and he observed sun spots. When using a red filter he found there was a lot of heat produced.
Herschel discovered infrared radiation in sunlight by passing it through a prism and holding a thermometer just beyond the red end of the visible spectrum. He was shocked when it showed a higher temperature than the visible spectrum. Further experimentation led to Herschel's conclusion that there must be an invisible form of light beyond the visible spectrum.
During his career, he constructed more than four hundred telescopes.
The largest and most famous of these was a reflecting telescope with a 49 1⁄2-inch-diameter (1.26 m) primary mirror and a 40-foot (12 m) focal length.
Herschel also coined the word "asteroid” in the year 1802.
He died on 25th August 1822. He lived for 83 years in this planet.
His house at 19 New King Street in Bath, Somerset where he made many telescopes and first observed Uranus, is now home to the Herschel Museum of Astronomy.
Infrared (IR) is an invisible radiant energy, electromagnetic radiation with longer wavelengths than those of visible light. Infrared radiation extends from the nominal red edge of the visible spectrum at 700 nanometers (nm) to 1 mm. This range of wavelengths corresponds to a frequency range of approximately 430 THz down to 300 GHz. Its photon energy is 1.24mev – 1.7ev. Most of the thermal radiation emitted by objects near room temperature is infrared.
Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 400×10−9 m to 700×10−9 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).This wavelength means a frequency range of roughly 430–750 terahertz (THz). Often, infrared and ultraviolet are also called light. Its photon energy is 1.7eV – 3.3eV.
INFRARED HEATING – In the ordinary resistance furnaces the heat is transferred from heating elements to the charge partly by radiation and convection.
- In this method heating elements consists of tungsten filament lamps together with reflectors to direct the whole of the heat emitted on to the charge.
- The lamps are operated at about 2300 degree centigrade instead of 3000 degree centigrade giving greater proportion infra-red radiations and a longer life.
- The reflectors are plated with rhodium [Rhodium means - A white hard metallic element that is one of the platinum group and is found in platinum ores; used in alloys with platinum]
- With the help of reflectors these infrared radiations are focused on the surface to be heated.
- The lamps employed are usually of rating between 250 and 1100 watts operating at 115 V.
- Lower voltage results in a robust filaments.
- With this arrangement the charge temperature between 200 and 300 degree centigrade can be obtained.
- The heat emission intensity obtained is about 7000W per square metre.
- The heating absorption remains practically constant.
- For getting best results, the infrared lamps should be located at a distance of 25-30cms from objects to be heated.
ADVANTAGES - Rapid heating, flexibility, compactness of units and safety.
APPLICATIONS - Drying of wood furniture, pre-heating of plastics and drying of paper pottery textiles etc., where moisture content is not large.