Editing Heating element (section)

=== 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.