1. Radio Frequency Dryers/heaters
SONAR Radio frequency dryers/heaters principally has the features same with the features of microwave oven.
1.1. RF's (Radio Frequency) BASIC PRINCIPLE
The heat degree of a material is increased by either direct heating or indirect heating. By means of the conventional methods, the heat is formed at the far place and then transferred to the material through transfer or radiation. Such and similar methods are indirect heating methods.
Direct heating methods are based on the principle of that the heat is formed inside the material. Radio frequency and microwave methods are typical examples of them. These heating methods are also called as dielectric heating.
Many insulator substances (dielectric material) similarly show increase in their heats when they are exposed to a high frequency in electromagnetic field. The way of the applied RF field moves to the opposite side at each time. Thus the polarization of each molecule inside the substance changes. Because of this permanent molecular movement, frictions that cause the increase of general heat level of the material occur. As it can be estimated, as the frequency of electromagnetic field increases, the molecules will move faster, thus more friction and consequently more heat will be produced.
The frequency of RF fields produced by the devices used for dielectric heating is restricted between 13.56 Mhz and 27.12 Mhz. ( In some countries, 40.68 Mhz is also used.)
1.2. RF (Radio Frequency) HEATERS
Many substances differ with regard to their reactions against direct heating. For example the convenience of the water with the practices of dielectric heating methods. This practically means that: In RF applications, any product that include moisture (food, paper, textile etc.) quickly sends away the water inside it.
During SONAR RF Heating method, the products go through an electrode system and thus take dielectric on by being exposed to a strong RF voltage at 27.12 Mhz frequency. For example the molecules of an ionic (dipolar) material such as water heat very quickly by reordering themselves for many times with such high magnetic field. On the other hand, this does not affect non-ionic (non-polar) substances.
The use of RF energy in the drying field is a very productive method since it activates only the water molecules during this application. Moreover since this method does not cause unnecessary heating (or power consumption), energy is not wasted in any place of the dried material. In addition, since heating is regular and at the same stability at all places of the material, this situation ensures that the water molecules are taken away altogether.
Furthermore, in RF energy used for the purpose of drying, the operating surfaces available in the dryer (these are the parts that contact with the dried product) do not need to be heated as a condition of whole drying process.
This drying method is also a method that arranges and sets its own operating manner. It demands RF power at the same ratio with the moisture that must be taken away from the inside of the material. In other words, since the use of power will principally decrease if there is not excess water to be taken away in the material, it does not use the energy unnecessarily and operates in optimum productivity (In this situation, the production amount and RF power can be increased by increasing the speed of conveyor band).
The operating environment of the operation is improved with this method.
The conventional heaters give hot air to the operating environment. The outer surfaces of such devices also heat during the process. However the outer surfaces of RF dryers are always cold and this means a comfortable and productive working environment for the operators.
Operating and maintenance of RF dryers are also simple duties. The number of the elements to be controlled is also minimized in order to enable the operators to understand easily.
WHAT IS THE DIELECTRIC HEATING SYSTEM ?
With dielectric heating system, only the parts and substances, which are desired to be heated, are heated. It is not necessary to heat the environment in order to heat these substances.
When this system is applied on textile, plastic, ceramic, rubber, tree, food and other nonconductor substances, it is faster and more effective when compared to conventional heating methods.
When many insulators such as tree, paper, textile and plastic are exposed to a high-frequency electrical field in a high voltage, electrical losses take place in these substances. These losses appear as heat in the material.
"Loss factors" of some materials are very high. These materials are really ready for rapid heating. Dielectric heating occurs mostly in 10-100 Mhz interval. The material to be heated is generally exposed to dielectric heating between two parallel plates. This vent is defined with some synonymous words such as "dielectric", "High frequency", "Radio Frequency" or "Capacitive heating".
HEADING APPLICATION METHODS OF MATERIAL
The heating methods can be classified according to the transfer of the energy from the heat sources to the structure of the product.
These methods can be classified into two: direct and indirect. In indirect heating methods, the heat transfer is from the outer surface of the product to its center. The speed of the heat transfer varies according to the heat conductivity of the product and the temperature difference between the center and outer surface of the product.
In cases that the heat conveyance of the product is very low, making the heat transfer to the center of the product fast causes the excessive heating of the outer surface of the product and so paling and color change. This is an undesired situation.
The nonconductor materials are also very weak heat conductors. The heat transfer realized with heating methods applied from outside to these materials is very slow. The outer surface of the product changes color and spoils because of excessive heating until the center of the product reaches desired heating.
In direct heating methods, the heating occurred inside the material is in question. Two techniques are applied in heating with this method: Radio Frequency (RF) and Microwave (MW) techniques.
The difference of these techniques from indirect heating techniques is that they produce the heat inside the product and transfer this heat to out of the product. The amount of this produced heat varies according to the physical and chemical characteristic of the product and used frequency.
At the end of heating with RF and MW techniques, the output products seem to be completely similar with each other. There is not any humidity difference, color difference etc. between them.