This article presents all the information you need to know about infrared heating.
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Infrared heating is a method for heating materials that uses electromagnetic waves to transfer energy from the infrared source to the product without heating the air in between. The emitted infrared energy is between 0.7 microns (µ) and 6 µ. At peak efficiency, wavelengths are selected for the product to be heated to minimize energy usage.
Thermal energy is transferred directly to a material at a lower temperature. The surrounding air is not heated and is uninvolved in the transfer of heat, making infrared heaters energy efficient, convenient, and healthy. Power is supplied by electricity, natural gas, or propane to create heat efficiently and economically.
The electromagnetic waves in the infrared spectrum have a wide range of wavelengths, from 780 nm up to 10 microns for industrial processes. The shorter wavelengths in the infrared spectrum have higher frequencies and associated energies. Heat produced by infrared waves ranges from hundreds of degrees Celsius up to 6,512 °F (3,600 °C).
In recent years, developments have been made to harness energy based on these scientific principles. Today, infrared heaters are available with different features and designs to flexibly accommodate industrial, commercial and residential needs. They heat surfaces in living spaces, offices, workplaces, garages, and warehouses. Industries benefit from infrared heaters as they can perform several processes such as drying, curing, printing, and thermoforming. In medicine, infrared heaters are used in physiotherapy to improve rehabilitation.
The infrared region was discovered by Sir William Herschel, a British-German astronomer, during the first Industrial Revolution (1760-1840). Infrared heating was not widely used, however, until World War II, where it was recognized by the military and used for drying the paints and lacquers applied to military equipment. This exceptionally-efficient heating process replaced fuel-consuming convection ovens that were far more expensive and depleted precious fuel reserves.
Infrared heaters during the war were frequently seen in workshops and factories. Their popularity radically declined after World War II as more people started to venture into central heating systems.
With the drive for greener technologies, the development of infrared heaters resumed between the late 20th century and early 21st century. The range of infrared heating has expanded to more uses during this period. Design flexibility and new configurations have been studied such that infrared heaters could be installed in multiple locations including homes and offices, or be used in industrial facilities for manufacturing. Rapid technological advancements and improvements in control systems have led to the continued growth and development of infrared heating use.
Infrared heat is the most basic form of heating and is the direct transfer of heat from a heater to an object or material without heating the air. The type of heat produced by an infrared heater is the same as environmental heat from the sun.
In an infrared heater, panels are heated until they get hot enough to emit infrared radiation that continually travels until it meets a solid object or workpiece. It is a direct heat transfer process that is similar to the transfer of heat between metals, coils, and materials using radiant waves.
With traditional heating, the air in an environment is heated before any objects will feel the increase in temperature. Infrared heaters are designed to project heat to warm objects directly and not change the temperature in a space. Aside from their ability to rapidly raise the temperature of objects or materials, infrared heaters complete the heating process using a minimal amount of energy at lower cost.
Electromagnetic waves are composed of waves that oscillate perpendicular to each other. One of the waves is an electric field, while the other is a magnetic field.
Electromagnetic waves are described by wavelength and frequency, with wavelengths being the distance between adjacent crests in the cycle of a wave. In the electromagnetic spectrum, wavelengths are usually expressed in nanometers or angstroms. Frequency is the number of wave cycles per second, which is expressed in Hertz (Hz), which is used to classify electromagnetic waves.
Wavelength and frequency are inversely related to each other. The energy of a wave is directly proportional to the frequency but inversely proportional to the wavelength. Waves with higher frequencies and shorter wavelengths carry higher energy and are more transmissive. Waves with lower frequencies and longer wavelengths carry less energy.
Unlike mechanical waves, electromagnetic waves do not require a medium to generate. Sound waves or mechanical waves move through the air and do not need surrounding molecules to move through the air, objects, or even a vacuum. It is the reason it is possible to feel the warmth of the sun, though it is thousands of miles away from the earth, as well as the surrounding cold air, when we stay under the sun. This principle is also applied in the operation of infrared heaters, which are comparable to the sun.
The infrared region is between the visible and the microwave regions of the electromagnetic spectrum. Infrared waves have a wavelength ranging from 700 nm (430 THz) – 1 mm (300 GHz).
The infrared region is broad, as is its associated energy and temperature range, with its waves classified into:
Radiative heating is one of the many applications of infrared waves. They are also useful in spectroscopy, imaging, and communications.
Radiation is the mechanism of heat transfer caused by the emission, absorption, and reflection of electromagnetic waves of bodies. All bodies above the absolute temperature (-459.4 °F or -273 °C) emit thermal radiation. The release of thermal radiation is caused by random movements, vibrations, and collisions of atoms and molecules and their constituting protons and electrons.
Various types of materials, items, and objects radiate heat based on their temperature. As they get hotter, these objects radiate thermal energy that is transferred by radiation but does not affect the surrounding molecules. Thermal energy easily travels through the air, objects, and even a vacuum and is independent of the amount of radiation emitted by a receiving material. Other factors affecting radiation are the nature of the surface and the angle of incident radiation.
Conduction and convection are other mechanisms of heat transfer that can happen simultaneously with radiation. In conduction, heat is transmitted through collisions and vibrations between neighboring atoms or molecules that readily occur in solids. The direction of heat transfer in conduction is from a region of higher kinetic energy to a region of lower kinetic energy.
In convection, thermal energy is transferred through the displacement of molecules in a bulk fluid. When a portion of the fluid is heated, the molecules closest to the primary heat source expand and travel away from it. Thermal energy is carried along with the molecules’ movement and is transferred to a cooler portion of the fluid mass.
Infrared heaters are composed of a heating system and a reflector. The heating system converts electrical energy or chemical energy from fuel sources into thermal energy. The reflector then directs the thermal energy produced by the heating system as radiant heat to the objects in its surroundings.
Reflectors greatly determine the efficiency of an infrared heater. They must have high reflectivity and must absorb minimal radiation from the heating system in order to store less heat. Their shapes and contours are designed to bend the infrared waves to space and prevent them from bouncing back. Other desirable properties of reflectors are high resistance to corrosion and moisture, ability to withstand high temperatures during their service life, and ability to be easily cleaned.
Reflective materials that are commonly used are aluminum, stainless steel, ceramics, and quartz. Some reflectors are plated with gold or ruby to increase their reflectivity and focus more heat on the surrounding objects.
Several industrial applications require the use of flameless heating as part of drying processes, preparing a surface for different applications, and enhancing workflow. In each of the applications, precision and controlled heating are required to ensure the quality of products. Modern technological manufacturing depends on heat and heating methods that are efficient, economical, and accurate while still supplying the necessary levels of heat.
Infrared heating systems can be engineered and designed to heat a surface rapidly, evenly, and homogeneously. When activated, heat is immediately available and ready to be applied for preparing a workpiece for stamping, pressing, or welding – all of which are performed at a lower cost due to the energy savings provided by infrared heaters.
There are any number of industrial processes that involve the application of coatings (which can be powders or liquids that are sprayed or brushed on), paints, varnishes, or other forms of surface protection. Regardless of the type of application, a central part of the successful adherence of a coating is the method used to dry it.
In the case of liquid coatings, infrared heaters are used to dry a coating quickly to produce a smooth, even surface finish. Powder coatings are not dried but need gelling or curing. Infrared heaters are used to speed up the gelling and curing processes to reduce production times.
Infrared welding is mainly used on plastics to seal and connect fan components. It is also used on plastic containers and pipes that need to withstand pressure. In the sealing of pressure vessels, infrared welding connects parts without leaving particles or debris in plastic containers and tubes.
In some plastic manufacturing processes, infrared heating is combined with vibration welding, a process that uses both vibration and pressure to connect components. Infrared radiation prepares the surface of a plastic for vibration welding and minimizes particle formation.
When the surface of a plastic is going to be embossed or laminated, it has to be heated evenly to avoid the loss of the applied materials, especially along the borders. The ability of infrared heaters to be engineered and configured to precisely heat and prepare surfaces makes them ideal for embossing and laminating processes.
In the auto industry, infrared laminating ovens create fusion between layers of material which results in superior protection and enhanced durability. Car doors, consoles, and dashboards have plastic parts that are covered in foil. Infrared heaters heat the foil quickly to secure it to the surfaces of these parts. The quick and efficient work of infrared heaters reduces cycle times and saves on energy.
The three types of industrial infrared heaters are quartz, ceramic, and metal-sheathed. They are electromagnetic infrared radiation heaters that, depending on the material employed, rapidly reach temperatures between 1300 °F and 1600 °F (704 °C to 871 °C) for enhanced efficiency and productivity. Quartz infrared heaters can reach the highest temperatures, while ceramic infrared heaters are the most economical.
Infrared heaters can also be classified based on the wavelength of the infrared waves they emit:
NIR heaters instantaneously warm the environment and are typically used in outdoor heating applications.
Some infrared heaters can be distinguished by the material used in their construction. A few of such infrared heaters are listed here:
The following are a few types of infrared heaters categorized by their application:
Infrared heaters are versatile, easy to install and maintain, and are available in different designs to suit various needs. The benefits of infrared heating are as follows:
Despite all this, infrared heaters can be a safety hazard. The hot core material of an infrared heater must be maintained to radiate heat to its surroundings. This may cause serious burns when touched or when one is exposed for a long period at too close a distance. Looking directly at the glow of high-intensity infrared heaters may cause impairment to the vision. Injuries and harm can be prevented by placing engineering controls and practicing vigilance when around an infrared heater. These few negative considerations, however, will never outweigh the benefits that an infrared heater can bring.
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