Radiant heaters are systems that generate heat internally and then radiate it to the nearby objects and people. The sun is a basic example of a radiant heater. When we feel warm on our bodies on a sunny day...
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This article presents all the information you need to know about Infrared Heating.
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Infrared heating is a heating method used to warm surrounding bodies by infrared radiation. Thermal energy is transferred directly to a material with a lower temperature through electromagnetic waves in the infrared region. The surrounding air is not heated and is uninvolved in the transfer of heat, which makes infrared heaters energy-efficient, convenient, and healthy. Using electricity, natural gas, or propane, infrared heaters create heat efficiently and economically.
The electromagnetic waves in the infrared spectrum have a wide range of wavelengths from 780 nm up to 10 micron (µ) 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 centigrade up to 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. Infrared heating was not used until World War II, where it was recognized by the military and used for drying the paints and lacquers applied to military equipment. The exceptionally efficient heating process replaced fuel consuming convection ovens that were far more expensive and depleted precision 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 heating has expanded to more regions in the infrared spectrum. Design flexibility and new configurations have been studied such that infrared heaters could be installed in multiple locations including homes and offices or used in industrial facilities for manufacturing. The rapid advance of technology and improvements in control systems has 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 travels continuously 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 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 waves composed of two waves oscillating perpendicularly to one another. One of the waves is an oscillating electric field while the other is an oscillating magnetic field.
Electromagnetic waves can be described by their wavelength and frequency. Wavelength is the distance between two adjacent crests in a cycle of a wave. Wavelengths in the electromagnetic spectrum are usually expressed in nanometers or angstroms. Frequency is the number of wave cycles per second and is usually expressed in Hertz (Hz). Electromagnetic waves are classified based on these properties.
Wavelength and frequency are inversely related to each other. Furthermore, 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 energies and are more transmissive. Waves with lower frequencies and longer wavelengths carry lower energies.
Unlike mechanical waves, electromagnetic waves do not require a medium to propagate. They do not need surrounding molecules to travel unlike sound waves (mechanical waves) that traverse through the air. They can travel through air, objects, and even a vacuum. This is why we 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, in which infrared heaters are analogous to the sun.
The infrared region lies between the visible and microwave region of the electromagnetic spectrum. Infrared waves have a wavelength ranging from 700 nm (430 THz) – 1 mm (300 GHz). As stated earlier, their existence was discovered in 1800 by Sir William Herschel, a British-German astronomer, while measuring the temperature of the invisible region in the spectrum lower than the red light, which exhibited the highest temperature.
The infrared region is broad, as is its associated energy and temperature range. Infrared waves are classified into:
|Region||Abbreviation||Wavelength(µm)||Frequency (THz)||Photo Energy (meV)||Temperature Range (°C)|
|Near-infrared||NIR||0.75 - 1.4||214 - 400||886 - 1653||3,591 - 1,797|
|Short wavelength infrared||SWIR||1.4 - 3||100 - 214||413 - 886||1,797 - 693|
|Mid-wavelength infrared||MWIR||3 - 8||37 - 100||155 - 413||693 - 89|
|Long-wavelength infrared||LWIR||8 - 15||20 -37||83 - 155||89 - -80 (negative temperature)|
|Far infrared||FIR||15 - 1000||0.3 – 20||1.2 - 83||-80.15 – -270.15|
Radiative heating is one of the many applications of infrared waves. Infrared waves 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 (-273°C) emit thermal radiation. When thermal radiation is released, it 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, they radiate thermal energy that is transferred by radiation and does not affect the surrounding molecules but is dependent on the materials the source “can see.” 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.
Other mechanisms of heat transfer are conduction and convection, which can happen simultaneously with radiation. In conduction, heat is transmitted through collisions and vibrations between neighboring atoms or molecules that readily occurs 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 the bulk fluid. When a portion of the fluid is heated, the molecules near 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 is required to ensure the quality of products. Modern technological manufacturing depends on heat and heating methods that are efficient, economical, and accurate but supply 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, a press, or welding, all of which are performed at low cost and energy savings.
There are any number of industrial processes that involve the application of coatings, 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.
Coatings can be liquids that are sprayed or brushed on or powders. 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 process 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 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 the result of which is 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 the 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 rapidly reach temperatures of 1300° F up to 1600° F for enhanced efficiency and productivity. Quartz infrared heaters can reach the highest temperatures while ceramic infrared heaters are the most economical.
Quartz infrared heaters produce short wavelengths to provide the hottest type of infrared heat. They are ideal for high heat applications but are not suitable for heating open spaces.
Ceramic infrared heaters are inexpensive and used to heat work areas.
Metal sheathed infrared heaters are the most durable of the three types and can reach temperatures over 2000o F. They can be used for submersible heating applications.
Infrared heaters can be classified according to their source of energy:
Electric infrared heaters utilize electricity to deliver heat to their surroundings. The heating system produces heat using the principle of Joule heating or resistive heating. Joule heating is the conversion of electrical energy to heat by passing an electric current to an element with high electrical resistance. The resistance of the heating element must not be as high as the resistance of insulators. The common heating element materials are tungsten, nichrome (80% Nickel, 20% Chromium), Kanthal (FeCrAl), cupronickel (CuNi), and carbon fibers.
Radiant gas heaters, also known as gas-fired infrared heaters, depend on chemical energy stored in natural gas, propane, or petroleum for the heat source. They also use a heating element that converts the heat energy from the gas flames into infrared electromagnetic radiation. The heating elements and the combustion chambers are contained in a metal, ceramic, or glass encasing. Some types of radiant gas heaters are:
Infrared heaters can also be classified based on the wavelength of the infrared waves they emit:
NIR heaters produce infrared waves of around 0.78 – 1.5 microns in wavelength and operate at high temperatures above 1,300 – 2,6000C. Since these wavelengths have higher frequencies, they tend to be more transmissive and reflective but less absorptive to the surfaces they strike. Thus, they are less efficient and are not suitable for drying applications. They can produce harsh heat and can be felt 2-3 meters from the source but cannot provide warmth at a deeper level.
NIR heaters instantaneously warm the environment and are typically used in outdoor heating applications.
MWIR heaters produce infrared waves of around 1.5 – 3 microns and operate at 500 – 1,3000C. These wavelengths have lower frequencies, which are better absorbed by objects, but they are still not suitable for comfort heating. They are used in industrial applications such as drying and curing of paints, lacquers, and solvents as well as in the economic processing of plastic foils and sheets.
FIR heaters produce infrared waves of around 3 – 1000 microns in wavelength and operate at lower temperatures. Since these wavelengths have lower frequencies, they are better absorbed by the surface they strike. Water begins to absorb the infrared heat in this spectrum.
FIR heaters produce comfortable heat that is optimally absorbed by our skin, which is further conducted into our tissues, blood, and the rest of our bodies. They take a longer time (around 5 minutes) to warm surrounding bodies. They are used in saunas, incubators, heating cabins, and other indoor heating applications.
Some infrared heaters can be distinguished by their material of construction. A few of such infrared heaters are listed here:
Quartz heat lamps were developed by General Electric in the 1950s. They produce intense heat with a temperature above 1,5000C and emit medium- to short-infrared waves. They heat the surrounding bodies quickly. Quartz is used as the enclosing material protecting the tungsten heating element, which can withstand higher temperatures than glass. It is filled with highly pressurized inert gas containing halogens, gaseous bromine, or iodine that regenerates tungsten atoms in the filament and prolongs the service life of the heating element.
Quartz heat lamps are used as outdoor patio heaters and in several industrial processes such as drying, curing, and thawing of frozen products.
Carbon infrared heaters have heating elements made from woven carbon fibers which are housed in quartz. They are also filled with halogen gas like quartz heaters. They operate at around 1,2000C and emit medium wave infrared. The carbon fibers produce gentler heat, and their light is less intense than tungsten. They also have long service lives.
Carbon infrared heaters are used in heating spaces with large, draughty, and hard-to-heat interiors: public halls, café terraces, and covered outdoor spaces.
Ceramic heaters have a heating element that is directly cast into a ceramic material. They operate at 300 – 7000F and emit medium to long infrared waves with 2 – 10 microns in wavelength. The ceramic casting comes in different shapes: a flat-shaped cast spreads the infrared heat over a wider area, while the concave-shaped cast focuses the infrared heat into one spot. The surface is glazed to prevent corrosion.
Ceramic heaters are used in comfort heating and industrial processes such as paint drying, curing, printing, annealing, thermoforming, and packaging. Food processing industries and medical facilities employ the use of ceramic heaters.
The following are a few types of infrared heaters categorized by their application:
Construction heaters are portable infrared heaters used in outdoor or indoor construction areas, and they can be installed over a tank top. They are used in spot heating. Construction heaters use infrared energy to radiate heat to their surroundings through a ceramic or steel surface.
Over-door heaters are positioned in building entrances and frequently-opened doors where the inside air is noticeably hotter. These heaters use axial fans to generate a high-velocity air stream to rapidly heat the cold entering air; this avoids heat losses and saves energy.
Over-door heaters are also known as air curtains. They can work in the opposite manner during summer to reduce air conditioning costs.
Garage Heaters are used in large spaces like garages and workshops, spaces that are not meant for insulation. They emit high-frequency radiation for the heat to penetrate the large area and warm the working personnel as well.
Warehouse heaters are used to heat large spaces such as warehouses where complete insulation and forced air convection heating are impractical.
Infrared heaters are versatile, easy to install and maintain, and are available in different designs to suit our needs. The benefits of infrared heating are as follows:
Infrared heaters warm surrounding objects directly. Heat losses are avoided because they don‘t expend energy by heating the surrounding medium. This feature consequently reduces energy costs.
Since the radiant heat is directed to the surrounding bodies, they don‘t spend time heating the air and then transferring it to the objects; that is the process of traditional convection heaters. This feature is helpful in drying applications.
The heat given off by infrared heaters is comparable to the radiant heat from the sun (excluding the ultraviolet waves). They don‘t increase the humidity level and reduce the oxygen content in their environment and do not evaporate moisture in the air. With infrared heaters, we feel warm and refreshed at the same time.
Infrared heaters inhibit the growth of these microbes since the mobility of moisture is limited. This feature reduces stuffy nose, wheezing, and itchy eyes and skin. This is also beneficial for places where food and medicines are handled, stored, and consumed.
Most infrared heaters don‘t rely on fans and blowers to circulate the heated air unlike convection heaters. Those auxiliary devices generate noises that are undesirable for bedrooms and office areas.
Electric infrared heaters don‘t generate gaseous products, toxic fumes, or fine particulates that have adverse effects on the environment. They do not agitate the surrounding air, which carries dust and allergens.
The energy efficiency of infrared heaters also helps to green the environment.
The use of infrared heaters improves living by taking care of our bodies. Infrared heaters promote overall health because:
Despite all this, infrared heaters can be a safety hazard. A hot core material of the 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. This downside can never outweigh the benefits an infrared heater can bring.
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