Infrared heating

Electrical heating by infrared radiation is based on the transfer of energy by radiation between an emitting source made up of electrical heating elements and a body to be heated, which absorbs all or part of this energy. It is therefore a direct application of the laws of thermal radiation.

• However, this type of heating requires specific technologies, and the design of furnaces and thermal equipment using infrared (IR) radiation often differs greatly from that of conventional resistance furnaces. As a result, this type of heating has long been an independent field with numerous original industrial applications.

• The main advantage of infrared heating is its high energy efficiency, which is due to several factors:

  • unlike convection heating, it allows energy to be transferred from one body to another without the need for an intermediate support and without any appreciable absorption of the energy emitted by the medium separating them;

  • radiated energy can be concentrated, focused, guided and reflected in a similar way to light, resulting in remarkable flexibility and adaptability;

  • thermal inertia is generally low, eliminating the need for long warm-up or maintenance periods;

  • the power density can be very high, since the temperature difference between the source and the body to be heated is often high, leading to compact installations and high treatment speeds;

  • the radiation penetrates deeper into the material, improving heating uniformity and accelerating energy transfer.

  On the other hand, the laws of thermal radiation show that it is difficult to treat products with irregular shapes with excellent temperature homogeneity, unless conduction and convection can reduce heterogeneities quickly enough.

• Infrared radiation is therefore best suited to heating products that are in strip or sheet form, or are sufficiently repetitive in shape or size, for applications at relatively low temperatures, generally below 700°C. Despite this limitation, the industrial applications concerned are very numerous (drying, baking, roasting, polymerization, sterilization, heat treatment, etc.), as are the sectors of activity (mechanical engineering, textiles, paper, food, plastics, coatings, building materials, etc.).

  This article is an update of the text written by Maurice ORFEUIL and Danièle RAYMOND and published in 1986 in this treatise. Part of the text has been retained.