As specialists in the design, manufacture and supply of large industrial electric fan heaters we thought it might be interesting to have a little look at one of the key components in them; the heating element.
In addition to being a key part in industrial electric space heaters, resistive heating elements are one of the most significant and influential inventions in human history. It’s safe to say that without it modern life would be very different as this relatively simple piece of equipment gave us large electric fan heaters, toasters, showers, hair dryers and more everyday items that we now take for granted.
What is a heating element?
A heating element is something that simply converts electrical energy into heat through resistance, a process that is also known as Joule heating. Simply put it passes an electric current through a resistive material, called a conductor, that causes it to get hot.
Normally the material used as a conductor in an element is a coil, ribbon or strip of wire just like the filament in a light bulb (another by product of resistance is light). An electric current is then passed through the ribbon or wire which converts the electrical energy into heat as the current causes the conductor to become very, very hot. This heat then radiates outward in every direction.
How does a heating element work?
In order to understand how a resistive heating elements help convert electricity into heat then we need to stretch our memories all the way back to high school and remind ourselves of some of the basics of electricity.
Conductors are good carriers of electricity and on the other side to that you have insulators which are very poor carriers of electricity. Both conductors and insulators provide resistance to any electric current that is applied to them, although in different amounts. All materials, both conductors and insulators have different levels of resistance but generally conductors offer a low resistance whereas insulators offer a very high level of resistance.
Electronic circuits will use different levels of resistance to regulate the flow of electrical energy using components called resistors, which utilise the specific resistances of certain conductors to control the current flow across a PCB.
“Resistors work by converting electrical energy to heat energy; in other words, they get hot when electricity flows through them. But it’s not just resistors that do this. Even a thin piece of wire will get hot if you force enough electricity through it. That’s the basic idea behind incandescent lamps (old-fashioned, bulb-shaped lights). Inside the glass bulb, there’s a very thin coil of wire called a filament. When enough electricity flows through it, it glows white hot, very brightly—so it’s really making light by making heat.”
As a result, heating elements provide a sturdy electrical component that produces heat when a large electric current flows through it. We then use this process to produce heat for comfort or a process, such as cooking or drying our hair.
Types of Heating Elements
There are many, many different types of appliances that contain heating elements, which means mean that heating elements come in all sorts of different shapes, sizes, thickness and materials depending what they’re being used for.
Metal Heating Elements
Usually made from an alloy called nichrome, which is composed of 80% nickel and 20% chromium. Thanks to the fact that it has a very high level of resistance for a conductor, Nichrome 80/20 makes an excellent heating element and so is very commonly used.
Another common type of metal heating element is resistance wire, which you’ll tend to find in everyday household items such toasters, hair dryers domestic fan heaters and electric floor heating. Finally we have etched foil, which is also made from similar substances to resistance wire and commonly used in precision heating applications.
PTC Heating Elements
PTC heating elements, which are made by using a substance called PTC rubber increase resistivity exponentially with increasing temperatures. These elements will produce large amounts of heat in the cold but that will reduce quickly as the temperature rises, until it reaches a point where the PTC rubber actually changes from a conductor to an insulator. The temperature at which this happens is selected during the manufacturing process and is usually somewhere 0⁰C-80⁰. As a result, these heat up quickly and maintain a constant temperature.
Composite Heating Elements
The most commonly used type of element in industrial heaters and especially large industrial fan heaters, composite heating elements are usually a fine coil of nichrome resistant heating alloy wire, surrounded by an insulating substance such as magnesium oxide and all housed in a tough metal tube made from stainless steel, copper or incolloy. As well as industrial electric fan heaters composite heating elements can be found in appliances such as a ovens, electric hobs and kettles. Composite elements are normally manufactured as long, straight rods then formed into the most suitable shape for the application.
Another version of composite elements are screen-printed metal–ceramic tracks, which are deposited on ceramic insulated metal (generally steel) plates. These have found widespread application kettle elements, together with other domestic appliances since sometime in the mid-1990s.
Radiative heating elements (also known as heat lamps) are a high-powered incandescent lamp normally run below maximum power to radiate mostly infrared instead of visible light. These are commonly found in radiant space heaters and food warmers (like where the contestants on masterchef will put the food they’ve just made during the restaurant challenges). These generally take 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 whereas the tubular form comes in different formats:
- Gold coated –As made famous by the patented Phillips Helen lamp. A gold dichroic film is deposited on the inside to reduce the visible light but allow most of the short and medium wave infrared through. These are primarily used for heating people.
- Ruby coated –In essence the ruby coating produces the same effect the dichroic gold-coating mentioned above, but at a fraction of the cost. The visible glare is also much higher than the gold variant. You can find this type of element in our infrared heater range.
- Clear – No coating and mainly used in production processes.
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 centre 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.
Combination heating element systems
Heating elements for high-temperature furnaces are often made of exotic materials, including platinum, Tungsten disilicide/Molybdenum disilicide, molybdenum (vacuum furnaces) and silicon carbide. Silicon carbide igniters are common in gas ovens.
Thick Film heaters
These are a type of resistive heater that can be printed on a thin substance or layer. Thick film heaters have some advantages over conventional metal-sheathed resistance elements. In general, thick film elements are usually characterized by a very low profile form factor, improved temperature uniformity, fast thermal response due to low thermal mass, low energy consumption, high watt density and wide range of voltage compatibility. Typically, thick film heaters are printed or flat substrates, as well as on tubes in different heater patterns. Depending on the heat transfer conditions thick film heaters can attain watt densities of as much as 100W/cm2. The thick film heater patterns are highly customizable based on the sheet resistance of the printed resistor paste.
Thick film heaters can be printed on a wide range of substrates including metal, ceramic, glass or polymer using metal/alloy-loaded thick film pastes. The most common substrates used to accommodate thick film heaters are Aluminium 6061-T6, Stainless steel and Muscovite or Phlogopite mica sheets. The suitable applications and operational characteristics of these heaters will vary widely depending on what substrate materials have been used. This is, in the main, down to the thermal characteristics of the material used for the substrate.
The main applications for thick film heaters are griddles, waffle irons, stove-top electric heating, humidifiers, tea kettles, heat sealing devices, water heaters, iron and cloth steamers, hair straighteners, boilers, 3D printer heated beds, thermal print heads, glue guns, laboratory heating equipment, clothes dryers, baseboard heaters, de-icing, or defogging devices, warming trays, car side mirrors, fridge defrosting, heat exchangers, etc.
In most applications it’s the thermal performance and temperature distribution which are used as the primary design parameters. In order to avoid any hotspots and 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 heater output and modulate the local temperatures across the heater substrate. In cases where there is a requirement of 2 or more heating zones with different output power 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 normally be characterized under two subcategories- (Negative Temperature Coefficient) NTC or (Positive Temperature Coefficient) PTC based on the effect of temperature increase on the element’s resistance. The NTC type heaters are characterized by a decrease in resistance as the heater temperature increases and thus have a higher output power at higher temperatures for a given input voltage. The PTC heaters behave in an opposite manner with an increase of resistance and decreasing heater power at elevated temperatures. This characteristic of the PTC heaters make them self regulating too, as their output power saturates at a fixed temperature. 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 the PTC type heaters.
At Broughton EAP, we have been in the industrial heating business for over 30 years. We have provided solutions for a host of prestigious big names including end users such as the Bugatti Owners Club and the Ministry of Defence and climate control specialists Andrews Sykes, ICS Cool Energy and Carrier Rental. We’ve designed, manufactured and supplied industrial space heaters to provide warmth everywhere from small industrial units all the way up t huge aircraft hangars, offices to mines and everywhere in-between. Our equipment is built to last, fully serviceable with full spare parts availability and comes backed up with a two year warranty.
Details on our full range of portable HVAC equipment including large industrial space heaters, portable industrial air conditioning, man cooler fans, ventilation fans, dehumidifiers and evaporative coolers can be found on our site. Should you wish to discuss your requirements or need help in selecting the best possible and most cost-effective system for your specific application then please do not hesitate to contact us on either +44(0)1527 830610 or by sending a message to sales@broughtoneap.co.uk.