How Heating Elements Work: Types, Construction, and Their Uses

Introduction

A heating element is a component used for converting electrical energy into heat through resistive heating or the principle of Joule heating. The heat is then transferred to the surroundings through processes such as radiation, convection, and conduction. 

How Heating Elements Work

Heating elements convert electrical energy into heat. They use a physical effect called Joule heating or resistive heating. The process generally relies on the electrical resistance of the material the element is made from. 

Joule Heating Mechanism

When an electric current is applied to a heating element, electrons flow through the resistive material. As the electrons move, they constantly collide with the fixed atoms of the resistive material. 

These collisions transfer the kinetic energy from the moving electrons to the atoms. This causes the atoms to vibrate with more intensity. The increased vibration leads to thermal energy, or heat. 

Joule’s Law determines the amount of heat produced: P=I²R (Power = Current squared × Resistance). The formula shows that a higher current or higher resistance results in more heat being generated. 

Material Properties 

Heating elements are made from specific materials, such as Nichrome, Kanthal, and others, which have properties that make them effective heating elements. Such properties include:

• High resistivity: They have sufficient electrical resistance to generate significant heat. 
• High melting point: They can withstand high operating temperatures without melting.
• Oxidation resistance: The material should not oxidize or corrode at high temperatures. This extends the lifespan of the heating element. 

Heat Transfer 

Once generated internally, heat is transferred to the surrounding environment, such as air, water, or a cooking surface. It can be done through one or a combination of these methods:

• Conduction: In this case, heat is transferred directly through contact with a cooler object. 
• Convection: The heating element warms the adjacent liquid or air, which circulates due to density differences. This means the heat is carried throughout the space. 
• Radiation: Heat is emitted as infrared electromagnetic waves, which directly warm objects and people without heating the air in between. 

Materials Used in Making Heating Elements

Heating elements utilize different types of materials that are selected for specific properties, such as high electrical resistivity and oxidation resistance. Here are the common materials used in making heating elements. 

Nichrome 

This has become the industry standard for heating elements due to its many benefits. It is composed of 80% nickel and 20% chromium. 

Nichrome has a high electrical resistivity, which means it generates significant heat when current passes through it. This property allows for a practical wire thickness to be used rather than keeping it very thin. 

The material is also oxidation-resistant. Whenever heated in air to red-hot temperatures, the alloy forms a stable protective outer layer. This layer resists further oxidation, which prevents the element from burning out or becoming brittle. 

You will also like Nichrome for having good workability. It is ductile and easy to form into various shapes, such as the coiled wires are used in hair dryers and toasters. This makes the material highly versatile for manufacturing. 

Kanthal Alloys 

In this case, the alloys are made by combining iron, chromium, and aluminum. The alloys are primarily used in industrial furnaces and high-temperature applications because their performance is better than that of Nichrome. 

Kanthal A-1 can operate up to 1,400⁰C, while that of Nichrome is up to 1,200⁰C. Also, the aluminum in Kanthal alloys forms a tough self-healing aluminum oxide layer when heated. This is an excellent electrical insulator and a more effective barrier against corrosion. 

Having superior oxidation resistance, Kanthal elements have a lifespan two to four times that of Nichrome at the same operating temperature. 

Since Kanthal alloys have a higher electrical resistivity, they allow for using materials with a larger cross-section. This improves their mechanical strength even at high temperatures. 

Types of Heating Elements

Heating elements are primarily categorized based on the resistive materials used and their design configuration for specific applications. 

1. Resistive wire heating elements 

These are the most common types. They use a resistance wire held by an insulating support. Examples of such elements include Nichrome, Kantal, Cupronickel, and more. 

Nichrome is a top choice for most applications up to 1,200⁰C. You will find them in hair dryers, toasters, and electric ovens. They are valued for their excellent balance of high resistivity, good oxidation resistance, and workability. 

Kanthal alloy is used in high-temperature industrial applications such as kilns and industrial furnaces. Expect it to have a longer lifespan and superior oxidation resistance compared to Nichrome at more extreme temperatures. 

2. Ceramic Heating Elements 

Ceramic materials are used mostly as structural insulation or as a primary resistive medium. Ceramic insulated resistive heaters use ceramic as an insulating material and are covered by a metal sheath. The ceramic material provides electrical insulation while allowing efficient heat transfer. 

Ceramic infrared emitters are elements with ceramic plates or bulbs that heat up and emit long-wave infrared radiation. This is suitable for thermoforming, paint curing, food warming, and saunas. 

3. Infrared Heating Elements 

The infrared heaters use a hot element to emit electromagnetic radiation, which heats objects and people directly rather than the surrounding air. 

Quartz IR heaters are a good example. In this case, they contain a tungsten or nichrome filament inside a sealed quartz glass tube. The glass tube can be filled with a noble gas. They provide a high intensity, rapid heat-up, which makes them suitable for industrial applications such as flash drying, medical sterilization, and powder coating. 

4. Industrial Heating Elements 

These are robust, custom-engineered elements designed for specific high-demand industrial processes. 

Examples of such elements include tubular heating elements, oven heating elements, cartridge heaters, immersion heaters, band heaters, and strip heaters. 

5. Flexible and Modern Heating Elements 

These are the newer technologies that offer unique form factors and performance features. The common examples include silicone rubber heaters, polyamide heaters, printed flexible heaters, and graphene and nanomaterial heaters. 

In the case of silicon rubber heaters, an etched foil or wire element is laminated between layers of silicone rubber. They are flexible, moisture-resistant, and sustainable for applications that need flexible, form-fitting heat. Such applications are medical devices and outdoor electronics. 

Applications of Heating Elements

Heating elements are essential components in many devices across residential, commercial, medical, and industrial sectors. 

1. Household appliances 

Heating elements are fundamental to modern domestic comfort and convenience, facilitating daily tasks. Examples of appliances with heating elements include electric ovens, water heaters, kettles, toasters and irons, hair dryers, and heaters. 

2. Industrial and commercial use 

In industrial settings, heating elements provide a reliable and high-temperature heat source necessary for manufacturing and processing. 

Examples of such applications include furnaces, kilns, mold heaters, extruder heaters, food processing equipment, and HVAC systems. It is expected that such elements can handle very high temperatures to maintain the performance. 

3. Automotive and transport 

Heating elements also provide safety, comfort, and performance in vehicles. This is quite common in electric vehicles now. Other common applications of heating elements include car seat heaters, battery warming elements, defoggers, and de-icers. 

4. Medical and scientific equipment 

Precision and sterility are critical in these fields. This means using specialized heating elements that ensure accurate results and safe conditions. Examples include sterilizers and autoclaves. These are immersion elements used to generate high-temperature, pressurized steam for sterilizing surgical instruments. 

5. Electronics and technology 

Heating elements are crucial in ensuring the reliability of electronic devices. For example, you can get wearable tech heating components. These are flexible, low graphene heaters used in heated clothing, smart textiles, and gloves. They provide a comfortable, localized warmth as small battery packs power them. 

How to Choose the Right Heating Element

Choosing the right heating element requires a proper evaluation of your application, performance specifications, and operating environment. Here is how to choose correctly. 

1. Define the application requirements

The first step is to understand what your application needs. This includes the desired outcome and medium being heated. 

Is the medium solid, liquid, or gas? This dictates the optimal heat transfer and watt density. 

Also, the operating temperature determines which element to use that meets the application’s requirements. 

Look at how quickly the heating elements can reach the target temperature. This can influence the required power density and the material choice. 

2. Select the appropriate type and material 

Based on your requirements above, you can now choose the right heating element type that is compatible with the temperature range and environment. 

The element’s sheath or exposed material must also withstand the surrounding environment, including corrosive chemicals, moisture, and specific atmospheric conditions. 

In case the elements are operating at high temperatures, the materials should have excellent oxidation resistance. Examples include Kanthal and Nichrome to ensure longevity. 

3. Determine power requirements 

Accurate power calculation ensures the heater operates more efficiently without premature failure. 

Calculate the total power needed to raise the mass of your material to the target temperature within the required timeframe. Make sure to account for system heat losses. Adding a 10-30% safety margin is recommended. 

4. Consider safety and controls 

Safety features are important for preventing accidents and ensuring reliable operation. Look at the rated voltage and match it to the application requirements. 

Overheat protection is also important. Some heating elements come with thermostats and independent high-limit cut-off sensors to prevent runaway heating events. 

Check that the heating elements comply with the relevant safety standards, such as UL, CE, and ATEX for hazardous areas. 

5. Evaluate cost and maintenance 

Consider the total cost of ownership and not just the initial purchase price. A more durable element will save you money in the long run by reducing downtime and replacement costs. 

Also, consider the ease of installation and replacement. Some models have sealed elements, which means less maintenance than the open-coil types, which need regular cleaning. 

Common Problems, Failures & Troubleshooting of Heating Elements

Common problems with heating elements are largely due to operating conditions that exceed the material’s limits. This then leads to predictable failures, which can be diagnosed with simple tests. 

Burnout and Wire Breakage 

Burnout occurs when the resistive wire or ribbon within the element fails completely. This leads to an open circuit. 

Common causes for such are overheating, high watt density, cycling fatigue, and physical damage. 

Overheating can occur when you keep operating the element above the maximum design temperature. As for high watt density, you keep using a watt density that exceeds the material’s ability to dissipate heat effectively. 

So, how do you know there is burnout? The heating element simply stops heating entirely. 

Hot Spots and Uneven Heating 

Hot spots are when localized areas run significantly hotter compared to the rest of the heating element. This leads to premature failure in that specific location. Uneven heating also affects the process quality. 

Common causes for this include inconsistent watt density, uneven contact, material buildup, and sagging coils. 

Inconsistent watt density results from design flaws or manufacturing variations that concentrate power in one area. Also, uneven contact between a sheath heater and the surface it is supposed to heat results in poor heat transfer. This leads to inadequate heat dissipation in the contact-poor area. 

Oxidation and Corrosion Issues 

Oxidation and corrosion can degrade the heating elements over time. A lack of a protective layer due to extreme temperatures or an acidic environment is a major factor in such cases. 

Also, a chemical attack on the sheath material can lead to such issues. This is because you are using the wrong sheath material depending on the environment. 

Maintenance Tips to Improve Lifespan

Proactive maintenance and proper use of heating elements extend lifespan. Here is how you can extend the lifespan of the heating element. 

• For water heaters, drain and flush the tank periodically to remove the scale buildup. For ovens or air heaters, clean the elements of dust and grease, ensuring proper heat dissipation. 
• You should never operate the air heaters without a proper fan function. Ensure immersion heaters are always fully submerged before they are activated. 
• Make sure that you choose a heating element whose sheath material is designed to work in the chemical environment it will operate in. 
• Use reliable temperature controllers, such as PID controllers, for safety, and add high-limit cut-offs to prevent over-temperature conditions. 
• Always inspect connections to ensure they are tight. Loose connections can cause high resistance, leading to localized heating, terminal failure, and eventual element malfunction. 

Conclusion 

Heating elements are quite versatile in terms of how they are used today. You can find them in household appliances, high-demand industrial systems, and much more. Their operating principle is simple, but yet powerful. Make sure that you choose a heating element that can operate in the expected environment. Always look at the manufacturer’s data sheet to understand where to use it.