Carbon Fiber Infrared Heating: Principles & Applications

Yesterday afternoon, we shipped 15 carbon fiber heating tubes, each 1.8 meters long, with a specification of 380V and 2000W. This length is relatively long. Today, I will continue to introduce the heating principle of carbon fiber heating tubes and discuss the industries in which they are primarily used. I’ll share some case studies from different industries for everyone to learn from.

Basic Knowledge of Infrared Radiation

First, let’s start with some basic knowledge about infrared radiation. This is a brief overview; a detailed explanation could easily fill an entire physics lecture, so let’s work together to learn more.

Heating Process of Carbon Fiber Heating Tubes

When the carbon fiber heating tube is energized, it emits an orange-red light and simultaneously produces infrared radiation that heats the surrounding objects. The surface temperature of the heating tube can exceed 500°C. The heating process integrates the three common heat transfer modes: thermal conduction, thermal convection, and thermal radiation, with thermal radiation being the primary mode. Below, I’ll introduce these three heat transfer modes.

Thermal Conduction

Thermal conduction refers to the process by which heat is transferred from the higher temperature part of an object to the lower temperature part along the object. Thermal conduction occurs in solids, liquids, and gases, but strictly speaking, it is pure thermal conduction only in solids. Even in stationary fluids, natural convection occurs due to the density difference caused by the temperature gradient, meaning that thermal convection and thermal conduction happen simultaneously in fluids. A common example in daily life is heating one end of an iron rod over a fire and feeling the other end become hot—this is thermal conduction. Another example is the handle of a spatula becoming hot while cooking, which is also a form of thermal conduction.

Thermal Convection

Thermal convection, also known as convective heat transfer, is the process of heat transfer caused by the relative movement of particles within a fluid. This mode of heat transfer can only occur in fluids (gases and liquids) and is always accompanied by the conduction caused by the movement of fluid molecules.

Thermal convection can be broadly classified into two types:

• By Medium: Gas convection and liquid convection, with gas convection being more apparent than liquid convection.
• By Cause: Natural convection, caused purely by the density differences between the hot and cold parts of the fluid, generally has a low flow rate. Forced convection, caused by the push of various pumps, fans, or other external forces, often has a high flow rate.

The most common example of thermal convection in daily life is when water boils.

Thermal Radiation

Thermal radiation refers to the phenomenon where an object emits electromagnetic waves due to its temperature. Any object with a temperature above absolute zero can emit thermal radiation, and the higher the temperature, the greater the total energy emitted. The spectrum of thermal radiation is continuous, theoretically covering wavelengths from 0 to ∞. Most thermal radiation is transmitted through longer wavelengths in the visible light and infrared spectrum.

At lower temperatures, the radiation mainly occurs in the invisible infrared region. When the temperature reaches 300°C, the strongest wavelength in the thermal radiation falls within the infrared region. When the temperature is between 500°C and 800°C, the strongest wavelength component shifts to the visible light region.

The energy emitted (or absorbed) by a surface per unit time and per unit area is related to the surface’s nature and temperature. The darker and rougher the surface, the greater its ability to emit (or absorb) energy. All objects radiate energy to their surroundings in the form of electromagnetic waves. When these waves encounter an object along their propagation path, they excite the microscopic particles within the object, causing it to heat up.

Even at a distance from a flame, we can feel the heat—this is due to infrared radiation, which makes us feel warm. The most common use of thermal radiation is sitting by a fire, while a hand warmer, for example, uses a different mode of heat transfer and shouldn’t be confused. The infrared radiation emitted by carbon fiber heating tubes is in the same wavelength band as that produced by burning flames, ranging from 2.0 to 15 microns.

Materials such as food, textiles, paint, and crops absorb this wavelength range most easily. Therefore, when these materials are exposed to the infrared radiation emitted by carbon fiber heating tubes, they absorb the radiation and convert it into heat, raising the material’s temperature to achieve drying, heating, or curing effects. When heating with infrared radiation, the substance being heated absorbs the radiation more efficiently due to the resonance between the material’s absorption band and the infrared wavelength. This maximizes the absorption of infrared heat, rapidly increasing the temperature and improving heating efficiency, which in turn enhances production efficiency.

Application in the Automotive Industry

In the automotive manufacturing process, carbon fiber heating tubes are most commonly used in paint booths, as mentioned in previous articles. Therefore, I won’t elaborate further on the application of carbon fiber infrared heating tubes in paint booths here.

Application in the Textile Printing and Dyeing Industry

In the textile printing and dyeing industry, equipment such as platen machines, tunnel dryers, and mobile drying machines are typical examples of infrared heating. When the carbon fiber heating tube is energized, it emits an orange-yellow light and infrared radiation, with a wavelength band of 2.0 to 15 microns. This wavelength range matches the absorption band of many textiles and water-soluble dyes. When heated with infrared radiation, the textile or dye absorbs the infrared heat quickly due to the matching wavelength, rapidly raising the temperature, improving heating efficiency, and enhancing production efficiency.

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