Technical Information

Configuration and Principles of Infrared Heating System

A rainbow formed in clear skies just after a rainfall shows the sequence of seven colors: red, orange, yellow, green, blue and violet. Radiations with wavelengths just beyond the red end of visible spectrums are called infrared radiation (radiant heat) which forms a long wavelength band, although it is invisible to our eyes. When infrared radiation hits a substance and is absorbed, this substance will be heated. The electromagnetic wave range of infrared radiation is subdivided into near, intermediate and far wavelengths. The near infrared rays which are closer to light in terms of wavelength are used for heating experiments of new materials, etc., while the far infrared rays are utilized for observation, home cooking and heating.

The near infrared radiation has the same properties as light with respect to radiation, condensation, reflection, transmission and refraction. The infrared heating system is so designed that it skillfully utilizes such properties.

The practical infrared heating system is composed of a roughly spherical infrared lamp, a spheroid reflection mirror, an infrared guide rod made of transparent quartz, etc.

As shown in Fig.1, an infrared lamp to serve as the heat source is placed at F1, the 1st focus of the gold spheroid mirror. Infrared radiation emitted from the energized lamp hits the gold spheroid mirror and is reflected and collected at the 2nd focus F2.

Normally, if a sample for heating is installed at this position, it is possible to heat the sample up to a high temperature in a short time.

A transparent quartz rod is installed at this position and infrared rays collected are led into the guide rod. Part of the infrared rays makes straight transmission, while the rest of rays repeats total reflection on the inner wall of the transparent quartz rod.


[Total reflection transmission system]

 Now, in Fig.2, let the angle of incidence on the transparent quartz guide rod be θ and P.2/2-1 the refraction angle with respect to the inside of the transparent quartz rod having a refractivity n be phi , then the total reflection condition of the incident angle 90º minus_phi at the inner wall surface R can be expressed as

The incident infrared radiation with an angle of incidence that satisfies the above condition formula makes total reflection at R on the inner wall of the transparent quartz. In this way it is transmitted to radiate through the tip while repeating total reflection, without coming outside. So if a sample for heating is placed close to the tip, the sample will absorb the infrared radiation causing a rise of its temperature.

So far, as the fundamental form of heat transmission, three modes are listed: conduction, convection and radiation. With our infrared heating system, infrared rays from the infrared lamp are condensed by the spheroid mirror to make heat transmission in the process of total reflection repeated within the transparent quartz rod. Thus the system does not belong to any of the above modes. It is an entirely new heat transmission system, so it may be said to be a 'total reflection transmission' or 'multiple reflection transmission'.

Moreover, since in this transmission heating system, virtually none of heat is discharged outside and heat is transmitted through 'closed space', the system may be said to feature a quite effective transmission method.

In the case of the existing resistance type electric furnace and infrared heating furnace, the object for heating can be heated after it is installed inside the furnace. With our infrared heating system, there is no need of moving the object to heat it up. Temperature rise can be achieved just by transmitting the infrared radiation from the heat source and bringing it near the object.


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