Editing Heating element (section)

== Types ==
Heating elements are generally classified in one of three frameworks: ''suspended, embedded,'' or ''supported''.<ref name=":1" />{{Rp|pages=164–166}}
* In a suspended design, a resistance heater is attached at two or more points to normally either a ceramic or mica insulator. Suspended resistance heaters can transfer heat via convection and radiation, but not conduction as they are surrounded by air.
* In an embedded heating element, the resistance heater is encased in the insulator. In this framework the heater can only transfer heat via conduction to the insulator.
* Supported heating elements are a combination of the suspended and embedded frameworks. In these assemblies, the resistance heater can transfer heat via conduction, convection, or radiation.

=== Tubes (Calrods®) ===
[[File:Tubular Electric Heater diagram.svg|thumb|Tubular electric heater. {{ordered list|Resistance heating element|Electrical insulator|Metal casing}}]]
[[File:Calrod-1A.jpg|alt=Tubular Heating Element|thumb|Tubular oven heating element]]Tubular or sheathed elements (also referred to by their brand name, Calrods®<ref>{{Cite web |title=Electric Stoves, Calrods and Cooking with Electricity |url=https://edisontechcenter.org/Cooking.html |access-date=2024-11-15 |website=Edison Tech Center |language=en}}</ref>) normally comprise a fine coil of resistance wire surrounded by an electrical insulator and a metallic tube-shaped sheath or casing. Insulation is typically a [[magnesium oxide]] powder and the sheath is normally constructed of a copper or steel alloy. To keep moisture out of the [[hygroscopic]] insulator, the ends are equipped with beads of insulating material such as ceramic or silicone rubber, or a combination of both. The tube is [[Wire drawing|drawn through a die]] to compress the powder and maximize heat transmission. These can be a straight rod (as in [[toaster oven]]s) or bent to a shape to span an area to be heated (such as in [[electric stove]]s, [[oven]]s, and [[coffee maker]]s).

=== Screen-printed elements ===
[[Screen printing|Screen-printed]] metal–ceramic tracks deposited on [[ceramic]]-insulated metal (generally steel) plates have found widespread application as elements in kettles and other domestic appliances since the mid-1990s.

=== Radiative elements ===
Radiative heating elements (heat lamps) are high-powered [[incandescent lamp]]s that run at less than maximum power to radiate mostly [[infrared]] instead of visible light. These are usually found in [[radiant heating|radiant space heaters]] and food warmers, taking either a long, tubular form or an ''R40'' reflector-lamp form. The reflector lamp style is often tinted red to minimize the visible light produced; the tubular form comes in different formats:

* Gold-coated{{dash}} HeLeN quartz infrared heat lamps as originally patented and manufactured by Philips. A gold [[dichroic]] film is deposited on the inside that reduces the visible light and allows most of the short and medium wave infrared through. These tubular quartz lamps are designed for services other than illumination.{{#tag:ref|Philips Lamp Specification & Application Guide 2004, pp. 116|name="philips"}}
* Ruby-coated{{dash}}Same function as the gold-coated lamps, but at a fraction of the cost. The visible glare is much higher than the gold variant.
* Clear{{dash}}No coating and mainly used in production processes.

=== Removable ceramic core elements ===
Removable ceramic core elements use a coiled resistance heating alloy wire threaded through one or more cylindrical ceramic segments to make a required length (related to output), with or without a center rod. Inserted into a metal sheath or tube sealed at one end, this type of element allows replacement or repair without breaking into the process involved, usually fluid heating under pressure.

=== Etched foil elements ===
Etched foil elements are generally made from the same alloys as resistance wire elements, but are produced with a subtractive photo-etching process that starts with a continuous sheet of metal foil and ends with a complex resistance pattern. These elements are commonly found in precision heating applications like medical diagnostics and aerospace.

=== Polymer PTC heating elements ===
[[File:Standard zpi medium.jpg|thumb|A flexible PTC heater made of conductive rubber]]
Resistive heaters can be made of conducting [[PTC rubber]] materials where the [[resistivity]] increases exponentially with increasing temperature.<ref>{{Cite patent|country=US|number=6,734,250|status=patent}}</ref> Such a heater will produce high power when it is cold, and rapidly heat itself to a constant temperature. Due to the exponentially increasing resistivity, the heater can never heat itself to warmer than this temperature. Above this temperature, the rubber acts as an electrical insulator. The temperature can be chosen during the production of the rubber. Typical temperatures are between {{convert|0|and|80|C|F}}.

It is a point-wise [[self-regulating heater|self-regulating]] and [[self-limiting heater]]. ''Self-regulating'' means that every point of the heater independently keeps a constant temperature without the need of regulating electronics. ''Self-limiting'' means that the heater can never exceed a certain temperature in any point and requires no overheat protection.

=== Thick-film heaters ===
[[File:Thick film heater Mica.jpg|thumb|A thick-film heater printed on a mica sheet]]{{More citations needed|section|date=June 2023}}
[[File:Datec-Metal_Thick-film_Heater.jpg|thumb|Thick-film heaters printed on a metal substrate]]

Thick-film heaters are a type of resistive heater that can be printed on a thin substrate. Thick-film heaters exhibit various advantages over the conventional metal-sheathed resistance elements. In general, thick-film elements are characterized by their low-profile form factor, improved temperature uniformity, quick thermal response due to low thermal mass, high energy density, and wide range of voltage compatibility. Typically, thick-film heaters are printed on flat substrates, as well as on tubes in different heater patterns. These heaters can attain power densities of as high as 100&nbsp;W/cm<sup>2</sup> depending on the heat transfer conditions.<ref name=":0">{{Cite book |last1=Prudenziati |first1=Maria |title=Printed films: materials science and applications in sensors, electronics and photonics |last2=Hormadaly |first2=Jacob |date=2012 |publisher=Woodhead Publishing |isbn=978-0857096210 |location=Cambridge, UK |oclc=823040859}} {{Google books|zX9wAgAAQBAJ|title=Preview}}</ref> The thick-film heater patterns are highly customizable based on the [[sheet resistance]] of the printed resistor paste.

These heaters can be printed on a variety of substrates including metal, ceramic, glass, and polymer using metal- or alloy-loaded thick-film pastes.<ref name=":0" /> The most common substrates used to print thick-film heaters are aluminum 6061-T6, stainless steel, and [[muscovite]] or [[phlogopite]] mica sheets. The applications and operational characteristics of these heaters vary widely based on the chosen substrate materials. This is primarily attributed to the thermal characteristics of the substrates.

There are several conventional applications of thick-film heaters. They can be used in griddles, waffle irons, stove-top electric heating, humidifiers, tea kettles, heat sealing devices, water heaters, clothes irons and steamers, hair straighteners, boilers, heated beds of [[3D printing|3D printers]], thermal print heads, glue guns, laboratory heating equipment, clothes dryers, baseboard heaters, warming trays, heat exchangers, deicing and defogging devices for car windshields, side mirrors, refrigerator defrosting, etc.<ref name="printed_films">{{cite book |last1=Radosavljević |first1=Goran |title=Printed Films: Materials Science and Applications in Sensors, Electronics and Photonics |last2=Smetana |first2=Walter |date=2012 |publisher=Woodhead Publishing |isbn=978-1-84569-988-8 |editor-last1=Prudenziati |editor-first1=Maria |location=Oxford |pages=429–468 |chapter=Printed heater elements |doi=10.1533/9780857096210.2.429 |editor-last2=Hormadaly |editor-first2=Jacob}}</ref>

For most applications, the thermal performance and temperature distribution are the two key design parameters. In order to maintain a uniform temperature distribution across a substrate, the circuit design can be optimized by changing the localized power density of the resistor circuit. An optimized heater design helps to control the heating power and modulate the local temperatures across the heater substrate. In cases where there is a requirement of two or more heating zones with different power densities over a relatively small area, a thick-film heater can be designed to achieve a zonal heating pattern on a single substrate.

Thick-film heaters can largely be characterized under two subcategories{{dash}}negative-temperature-coefficient (NTC) and positive-temperature-coefficient (PTC) materials{{dash}}based on the effect of temperature changes on the element's resistance. NTC-type heaters are characterized by a decrease in resistance as the heater temperature increases and thus have a higher power at higher temperatures for a given input voltage. PTC heaters behave in an opposite manner with an increase of resistance and decreasing heater power at elevated temperatures. This characteristic of PTC heaters makes them self-regulating, as their power stabilizes at fixed temperatures. On the other hand, NTC-type heaters generally require a thermostat or a [[thermocouple]] in order to control the heater runaway. These heaters are used in applications which require a quick ramp-up of heater temperature to a predetermined set-point as they are usually faster-acting than PTC-type heaters.

=== Liquid ===
An [[electrode boiler]] uses electricity flowing through streams of water to create steam. Operating voltages
are typically between 240 and 600 volts, single or three-phase [[Alternating current|AC]].<ref>{{cite web |date=July 2019 |title=Electrode and Electric Resistance Steam Generators and Hot Water Heaters for low carbon process heating |url=https://genless.govt.nz/assets/Business-Resources/Electrode-electric-resistance-steam-generators-hot-water-heaters-for-low-carbon-process-heating.pdf |access-date=2 October 2023 |publisher=EECA Energy Efficiency and Conservation Authority |location=New Zealand}}</ref>

=== Laser heaters ===
[[Laser]] heaters are heating elements used for achieving very high temperatures.<ref>{{cite journal |last1=Rashidian Vaziri |first1=M R |display-authors=etal |year=2012 |title=New raster-scanned CO2 laser heater for pulsed laser deposition applications: design and modeling for homogenous substrate heating |url=http://opticalengineering.spiedigitallibrary.org/article.aspx?articleid=1183406 |url-status=live |journal=Optical Engineering |volume=51 |issue=4 |pages=044301–044301–9 |bibcode=2012OptEn..51d4301R |doi=10.1117/1.OE.51.4.044301 |archive-url=https://web.archive.org/web/20161010215507/http://opticalengineering.spiedigitallibrary.org/article.aspx?articleid=1183406 |archive-date=2016-10-10|url-access=subscription }}</ref>