STEPPED MODE OF COMBINED ULTRA HIGH FREQUENCY (UHF) DRYING OF CEREALS

ABSTRACT

The article discusses the use of microwave electromagnetic field for drying grain. A stepped mode of electromagnetic waves of ultra-high frequency convective drying of cereals with an initial humidity of 25% has been developed.

АННОТАЦИЯ

В статье рассматривается использование электромагнитного поля СВЧ для сушки зерна. Разработан ступенчатый режим электромагнитных волн сверхвысокочастотной конвективной сушки зерновых с начальной влажностью 25 %.

Keywords: stepped mode, combined, ultra-high frequency, convective, dryer, electromagnetic fields.

Ключевые слова: ступенчатый режим, комбинированный, сверхвысокая частота, конвективный, сушильная установка, электромагнитная поля.

During the period of grain harvesting in Uzbekistan, one often has to put up with natural anomalies: a thunderstorm, accompanied by short-term heavy rains that destroy partly or completely grown crops, heavy wind gusts that break ears of corn, which makes it difficult to harvest the grown crops.

Timely harvesting of grains: wheat, rice, sorghum, corn, chickpeas and other crops, as well as their preservation is one of the important tasks of the agro-industrial complex of the republic.

In the event of rainy weather, grains get wet and a biological process takes place in them, leading to the destruction of the internal structure of the grain.

The creation of technological tools and apparatus that provide intensive drying of post-harvest moistened grain while maintaining its physical and biological properties remains relevant and in demand [1].

The purpose of this work is to develop a method for the stepped mode of a ultra high frequency (UHF) combined convective drying installation.

At the same time, the following tasks are solved: increasing the thermal efficiency of the installation, intensifying the drying process through the introduction of an ultra-high generation system; rejection of sources of external energy supply.

The production of the main elements of the drying installation from fiberglass reduces the cost of production.

The use of an electromagnetic field of ultra-high frequency allows you to completely destroy the microflora and increase the shelf life of the product.

It is established that the use of electromagnetic fields of ultra-high frequency is the most effective at the stage of preparation of plant raw materials for drying, and not at the stage of its direct drying, which reduces the loss of thermolabile biologically active substances during the drying process, and therefore, to obtain a finished product of higher quality and nutritional values [2].

Based on the above analysis, a conclusion was made about the relevance of developments in the field of creating technologies for processing plant raw materials and secondary resources using microwave electromagnetic fields of ultrahigh frequencies at the stage of preparing cereal grains for the drying process.

Figure 1 shows an experimental diagramm of ultrahigh frequenciy dryer, where a stepped mode of ultra high frequency (UHF) electromagnetic waves for convective drying of grain with an initial humidity content of 25% is used.

The choice of frequency ν=350 MHz is due to the fact that this frequency corresponds to the maximum absorption capacity of cereals.

The choice of the stepped mode of combined ultra high frequency (UHF) -convective drying consists in dividing the process into three stages of different duration. At the first stage, cereal grains are heated by a microwave heat sink for 1.5 minutes to a temperature of 30-32⁰C.

At the second time stage, dried cereals are heated up to t=46-47⁰C for 3 minutes. At the third stage, in the same way, the drying temperature is processed to t = 37-52⁰C and their humidity is adjusted to 14%.

For different cereals, the duration and frequency of ultra high frequency (UHF) are determined experimentally, taking into account the analysis of drying curves [3].

Figure 1. Stepped ultra high frequency (UHF) mode

The set of technical tasks are solved by the fact that in the installation for drying bulk materials, containing a body made of a cylindrical or prismatic shape and equipped with a coaxially located blocking container in it, repeating the shape of the body and dividing the latter into a central and peripheral zones. Moreover, the central zone performs the function of a hopper for the dried product, and in the peripheral zone there is a drying chamber, consisting of separate sections arranged in alternating order with screw conveyors, each section is equipped with perforated gratings, lower loading and upper overflow windows, and the body is equipped with a loading - unloading sluice gates and branch pipes for supplying and discharging the drying agent, in the partitioned tank coaxially in the center and along the periphery opposite the individual sections of the drying chamber, magnetrons of the ultra high frequency (UHF) generator are installed, located in increasing height in accordance with the height of the fluidized bed in each drying section at the level of the lower boot window. Each drying section is equipped with a drying agent flow control valve.

The use of ultra high frequency (UHF) electromagnetic fields made it possible to increase thermal efficiency and intensify the drying process by obtaining an ultrahigh system for generating electromagnetic waves. The use of electromagnetic fields is the most effective tool in the preparation of vegetable raw materials for drying, during drying. This made it possible to reduce the drying time and obtain a finished product of high quality and nutritional value.

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