RU1809273C - Method for drying dielectrics - Google Patents

Abstract

Usage: dielectric drying technology, which intensifies the drying process and improves the quality. SUMMARY OF THE INVENTION: wet dielectrics are exposed to the main electromagnetic field of the microwave range and additionally to a field with a frequency of 433-2375 MHz with its penetration of no more than 1/3 of the thickness of the dielectric, and the main field is exposed to cyclic pulses with a cycle duty cycle of 0, 1 - 0.9, and additional exposure to the electromagnetic field of the microwave range is carried out in pauses of exposure to the main field. 1 s.p. crystals, 1 tab.

Description

The invention relates to a drying technique, namely, to methods for heating and drying dielectric materials by microwave currents, and can be used in the chemical, electrical, pharmaceutical, food and other industries.

The purpose of the invention is to enhance the removal of moisture and improve the quality of the dried material.

The method of drying dielectrics is implemented as follows.

Drying is carried out in the electromagnetic field of the microwave range in the field of a standing wave or in the field of a traveling wave. As a result of the penetration of the electromagnetic wave into the dielectric and the generation of heat in it, steam is formed in the thickness of the latter (for example, from water), squeezing the remaining water to the outer surface of the dielectric . In this case, as a result of evaporation due to convection, the temperature of the outer dielectric layer decreases, and the vapor coming from the inside condenses in the surface layer. In order to remove moisture from the surface layer of the dielectric, it is proposed to apply a microwave field with a wavelength providing additional heat in the surface layer.

For example, the penetration depth of an electromagnetic wave for a series of lossy dielectrics at a temperature of 20-25 ° C depending on the wavelength is taken according to the data given in the table.

If during drying we use the frequency of the main electromagnetic field, for example, 433 MHz, then the wave penetrates deep into

about y

Yu

VS W

of an object where microwave energy is converted into heat in its entire volume, then upon additional exposure to an electromagnetic field with a frequency, for example, 2375 MHz, additional microwave energy is converted into heat only in the surface layer of the dielectric.

PRI me R. The process of drying the fiscal specimen in the form of a deep plate with a diameter of 200 mm and a thickness of 5 mm was carried out (from the product range of the Budsky Fans' Plant Sickle and hammer of the Kharkov region). Plate forms were made on a factory semiautomatic device of the ASFCH-7 type from a pulp made up using factory technology. The plates were dried in a special drying working chamber. In this case, microwave energy was supplied by a horn cone antenna from a Khazar-2P type microwave energy generator providing power control in the range of 0.3-2.5 kW. To remove moisture from the surface of the sample, constant blowing with hot air was used with parameters corresponding to the factory conditions.

The drying process of the plates consisted of cycles. The duration of each drying cycle was 10 s (the duration of the cycle was determined by the time it took to form the plate on a semi-automatic machine). In this case, the time of exposure to the main field of microwave energy with a frequency of 2375 MHz varied from 1 to 9 s. In pauses of exposure to the main field, an additional exposure to the electromagnetic field of the microwave range with a frequency of 5800 MHz with a power of 200 W was obtained from a generator with a traveling wave lamp. During the drying process, the initial moisture content of the sample was 20.7%, and the final moisture content was 12%. To achieve such a final humidity with a cycle fill factor of 0.1, it took 40 cycles with a total duration of 400 s with a power of the main field of microwave energy equal to

0

5

0

5

0

5

0

5

300 watts With a cycle duty cycle of 0.9, the drying time was reduced to 6 cycles (60 s).

Using the proposed method of drying dielectrics allows you to get the following advantages:

- only the body of the dielectric being processed is heated (the structural elements of the drying chamber are not heated by the electromagnetic field of the microwave range);

- the power of the microwave energy source can be easily controlled with high accuracy, which allows you to control the drying process and bring the drying process closer to the maximum allowable intensity limit. This leads to an acceleration of the drying process and an increase in the quality of the dried material;

- the possibility of using for drying products having low mechanical strength of the skeleton of the frame, which does not allow intensifying the drying process only by increasing the radiation power of the microwave electromagnetic field;

- the ability to conduct the drying process selectively by the thickness of the dielectric.

Claims (2)

1. A method of drying dielectrics by exposing a dielectric to a microwave electromagnetic field, characterized in that it is additionally exposed to a microwave electromagnetic field with a frequency equal to 433-5800 MHz, with its penetration not more than 1/3 of the thickness of the dielectric, exposure to the main field is carried out by cyclic pulses with a duty cycle of 0.1-0.9. 2. The method according to claim 1, characterized in that the additional exposure to the electromagnetic field of the microwave range is carried out in pauses of exposure to the main field.