Changes

==Composition==

==Composition==

Heating elements are made from a conductive (though resistive) material--although other materials may be usable, metal is generally preferred.  They are usually made from alloys containing primarily either iron or nickel. One of the most common compositions uses  nichrome, an alloy of about 80 percent nickel and 20 percent chromium. Nichrome is a resistant conductor, does not oxidize regardless of temperature, has a very high melting temperature (about 2550°F), and expands very little when heated.  For these reasons it is a very good material for heating elements.  All other alloys used also must satisfy these basic requirements as well.  However, there are many other specific requirements, and resistance must be carefully calibrated.<ref name="explainthatstuff.com">http://www.explainthatstuff.com/heating-elements.html</ref>

Heating elements are made from a conductive (though resistive) material—although other materials may be usable, metal is generally preferred.  They are usually made from alloys containing primarily either iron or nickel. One of the most common compositions uses  nichrome, an alloy of about 80 percent nickel and 20 percent chromium. Nichrome is a resistant conductor, does not oxidize regardless of temperature, has a very high melting temperature (about 2550&nbsp;°F), and expands very little when heated.  For these reasons it is a very good material for heating elements.  All other alloys used also must satisfy these basic requirements as well.  However, there are many other specific requirements, and resistance must be carefully calibrated.<ref name="explainthatstuff.com"/>

==Types==

==Types==

Most heating elements are used for convection heating.  In this case, air or fluid is heated directly, at which point it becomes lighter than the surrounding substance and rises, drawing colder atoms/molecules in to take its place by the element.  Electric stoves, toasters, coffee makers, heaters, and many other appliances usually use convection. Some devices use a fan or pump to more the heat more quickly.  This process is called forced air convection.<ref name="ehow.com">http://www.ehow.com/how-does_4966716_heating-elements-work.html</ref><br />

Most heating elements are used for convection heating.  In this case, air or fluid is heated directly, at which point it becomes lighter than the surrounding substance and rises, drawing colder atoms/molecules in to take its place by the element.  Electric stoves, toasters, coffee makers, heaters, and many other appliances usually use convection. Some devices use a fan or pump to more the heat more quickly.  This process is called forced air convection.<ref name="ehow.com">http://www.ehow.com/how-does_4966716_heating-elements-work.html</ref><br />

A less common but often more efficient method uses infrared to heat objects directly, but not air.  A specialized heating element is encased in quartz, which seals in the heat it produces.  However, it allows infrared radiation to escape.  This radiation passes through air with no effect.  However, this radiation is converted to heat when it reaches most kinds of solid material.  People, furniture, food, and many other objects exposed to it are heated with relatively minimal waste.<ref name="ehow.com">http://www.ehow.com/how-does_4966716_heating-elements-work.html</ref>

A less common but often more efficient method uses infrared to heat objects directly, but not air.  A specialized heating element is encased in quartz, which seals in the heat it produces.  However, it allows infrared radiation to escape.  This radiation passes through air with no effect.  However, this radiation is converted to heat when it reaches most kinds of solid material.  People, furniture, food, and many other objects exposed to it are heated with relatively minimal waste.<ref name="ehow.com"/>

==References==

==References==