Dielectric Heating Applications Research Articles

Development of the Industrial Use of Dielectric Heating in the United Kingdom

In the United Kingdom, RF heating systems have become well established in many industries since their first introduction over forty years ago, Today RF probably accounts for 90% of all dielectric heating applications. The introduction of microwave heating was a later development and, in contrast to RF, applications arc only just becoming established. In the present state of world economy, the need for the wise selection of possible new applications has never been greater, and can be the key to survival and ultimate commercial success for industrial heating equipment suppliers. This paper highlights the development of industrial application of dielectric heating in the UK for RF wood glueing, plastics, preheating, and welding, biscuit baking, textile drying, adhesive and paper drying, microwave preheating and vulcanisation of rubber, microwave tempering of meat and other food processing applications.

Dielectric Heating and Relaxations in Nematic Liquid Crystals

Abstract Novel experiments on dielectric heating were made to induce changes of temperature ΔT in nematic liquid crystal layers. Measurements of the dependence of ΔT on cell voltage, driving frequency, electrode spacings, external cell temperature and liquid crystal material parameters are correlated with molecular relatxation proceses occurring in the frequency range 0-10 MHz. Temperature increases ΔT up to 40°C were achieved at low driving voltages in nematics belonging to two different liquid crystal classes which exhibit large positive static dielectric anisotropies. It could be shown that homeotropic wal alignment leads to a markedly different dependence of ΔT(w) in th vicinity of the cross-over frequency ωc, of the lowest dielectric relaxation process, compared with unoriented or parallel aligned layers. The material requirements and limits for a possible application of dielectric heating in liquid crystal displays are discussed.

Dielectric heating in industry application of radio frequency and microwaves

Heat is generated in a variety of dielectric or electrical insulating materials when subjected to radio and microwave frequencies. This phenomenon has been successfully exploited for over 40 years by industry in a wide range of applications. Radio frequency (RF) is used for about 90% of all dielectric heating applications, but the more recent development of microwave heating is becoming well established. The place of RF and microwaves in the electromagnetic spectrum and the effects of different frequencies on materials is discussed. Brief details of the various techniques of applying the RF or microwave energy to materials are given. Finally, some typical applications such as welding, baking drying and preheating are discussed.

Dielectric loss at high frequency

In the application of dielectric heating to various industrial processes, alternating frequencies between 1 and 30 megacycles, and rates of temperature rise of 50 degrees Fahrenheit and upward, are common. The measurement of the dielectric properties of a material under such varying conditions presents a problem which may be solved by a calorimetric substitution method.