RU2138747C1 - Method of drying dielectric materials and device for realization of this method - Google Patents

Abstract

FIELD: drying technology; wood-working and furniture industries; manufacture of building materials. SUBSTANCE: method consists in SHF thermal treatment of materials including monitoring of SHF signals. Innovation of invention consists in using rate of increase of amplitude of signal passing through material being dried as parameter under test; this amplitude is compared with preset threshold rate and termination of process is determined according to the results thus obtained. Device used for realization of this method includes AC supply source, switch, transformer, capacitor, diode, magnetron, selector switches, timer and drying (loading) chamber. Innovation consists in availability of receiving antenna, detecting device, threshold device with different power thresholds, threshold device control unit and drying process termination indicator. EFFECT: improved quality of dried material; reduced power requirements. 3 cl, 1 dwg

Description

 The invention relates to a drying technique and can be used in the woodworking and furniture industries, as well as in the production of building materials to improve the quality of the dried material and reduce the energy intensity of the drying process.

 A known method of drying (application of Russia N 94010334/06, priority 05/17/94, publ. 11/27/95, BI N 33), which provide control of the quality of drying by changing the distance from the emitter to the material to be dried. The method is implemented using a processor that controls the microwave heating process and receives information about the state of the dried material from temperature sensors inside the drying chamber and from the microwave power dissipation meter.

 However, this method does not allow for the repeatability of the initial settings of the dried material and to withstand the drying mode from batch to batch, since the drying process is controlled by mechanical movement of the irradiator grate.

 Closest to the proposed drying method is a method for drying dielectric materials, in particular lumber (application of Russia N 94018274 priority 05.17.94, publ. 01.20.96, BI N 2), in which the drying process includes thermal microwave processing of materials in drying chamber, accompanied by control of the parameters of the dried material, implemented on the basis of measuring the attenuation of the electromagnetic wave transmitted through the dried material.

 However, the known drying method does not allow to accurately determine the end of the drying process, since the dependence of the absorption coefficient of microwave power depends not only on the moisture content of the dried material, but also on the type of wood, the degree of filling of the drying chamber, the presence of reflections in the drying chamber, which can lead to a decrease in quality drying associated with the drying of the material.

 A device for drying wood microwave energy (application of Russia N 94010334, priority 23.05.94, publ. 11/27/95, BI N 33), containing a drying chamber, microwave sources on magnetrons, a device for supplying dried material and a control system a drying process based on a processor with a given program.

 However, the known installation does not eliminate the possibility of overdrying the material, which leads to a decrease in the quality of drying.

 Closest to the proposed device is a microwave heating device (Russian patent N 2054828, priority 01.08.90, publ. 02.20.96, BI N 5) containing an AC power source, switch, transformer, capacitor, diode, magnetron , switches, timer and drying (load) chamber. The first output of the power source is connected to the first output of the switch, the second output of which is connected to the first output of the primary winding of the transformer, the second output of which is connected to the second output of the power source. An additional transformer winding shunts the magnetron filament and the first terminal of the secondary winding of the transformer is connected to the first terminal of the capacitor, the second terminal of which is connected to the anode of the diode and the cathode of the magnetron. The control terminals of the timer are connected to the control terminals of the switches.

 A disadvantage of the known device is the presence of a strict control law determined by the operation of the timer and not related to variations of the drying process, which leads to a decrease in the quality of the dried material.

 The task is to develop a technology for drying electric material and to create a device that improves the quality of the dried material and reduces the energy intensity of the process.

 The problem is solved due to the fact that in the method of drying dielectric materials, including thermal microwave processing with the control of the microwave signal, according to the invention, the rate of increase of the amplitude of the signal passing through the material to be dried, which is compared with a given threshold speed and obtained the results determine the end of the drying process.

 In addition, in a device for drying dielectric materials containing an AC power source, a switch, a transformer, a capacitor, a diode, a magnetron, switches, a timer and a drying (load) chamber, the first output of the power source is connected to the first output of the switch, the second output which is connected to the first output of the primary winding of the transformer, the second output of which is connected to the second output of the power source, and the additional winding of the transformer shunts the magnetron filament, the first output the secondary winding of the transformer is connected to the first output of the capacitor, the second output of which is connected to the anode of the diode and the cathode of the magnetron, and the control terminals of the timer are connected to the control terminals of the switches, according to the invention, a receiving antenna, a detecting device, threshold devices with different thresholds of the power level, threshold control device devices and an indicator of the end of drying, while the receiving antenna is located in the drying chamber and connected to a detecting device, the output of which connected to the first inputs of the threshold devices, the output of the threshold device with a lower threshold of the power level is connected to the trigger input of the timer, and the output of the threshold device with a large threshold of the power level is connected to the disconnecting input of the timer and the first input of the first switch, the first timer output is connected to the control input of the second switch and the input of the signaling device of the end of drying, the output of which is connected to a common point, and the second timer output is connected to the control input of the first switch, the first output to which is connected to the input of the threshold control device of the threshold devices, the outputs of which are connected to the control inputs of the threshold devices.

 The analysis of the prior art by the applicant, including the search for analogues in patent and scientific and technical literature, allows us to consider the claimed solution to meet the criterion of "novelty", since the applicant did not find any analogues in the search process that are characterized by signs that are identical to all the essential features of the claimed solution.

 In addition, an additional search showed that the claimed drying method and device for its implementation does not follow explicitly from the prior art for a specialist, which makes it possible to judge whether the claimed solution meets the criterion of "inventive step".

 The drying method is as follows. The material is placed in a drying chamber, the microwave power source is turned on, and during the drying process, the signal amplitude is measured at a rate of rise, which is compared with a predetermined threshold speed. When the equality of these speeds is achieved, the drying process is stopped by turning off the microwave power source.

присутствует вода с массой m_в, электрической проводимостью σ_в диэлектрической проницаемостью ε_в и плотностью

В объеме V поддерживается постоянная амплитуда E для напряженности электрического поля электромагнитной волны с частотой ω. В указанном объеме запасается энергия W

Из-за наличия воды в объеме V теряется (превращается в тепло) энергия W_п

что эквивалентно наличию мнимой компоненты диэлектрической проницаемости влажного материала

Отношение

есть влажность θ.
Вводя обозначение

получаем
ε″ = K₁θ
В процессе сушки влажность материала изменяется по экспоненциальному закону с постоянной времени τ и начальной влажностью θ , то есть
θ = θ_o•e^-τ•t
Поглощаемая СВЧ мощность P_СВЧ ^п

Подводимая СВЧ мощность P_СВЧ

Тогда затухание N в слое материала

Отсюда влажность θ может быть определена по формуле:

где N - измеренное затухание.Suppose that in a volume V containing a dry dielectric mass m with a permittivity ε _d and bulk density

water with mass m _in , electrical conductivity σ _in dielectric constant ε _in and density

In volume V, a constant amplitude E is maintained for the electric field strength of the electromagnetic wave with frequency ω. The energy W is stored in the indicated volume

Due to the presence of water in volume V, energy W _p is lost (converted into heat)

which is equivalent to the presence of the imaginary component of the dielectric constant of the wet material

Attitude

is the humidity θ.
Introducing the notation

we get
ε ″ = K ₁ θ
In the drying process, the moisture content of the material changes exponentially with a time constant τ and an initial moisture content θ, i.e.
θ = θ _o • e ^{-τ • t}
Absorbed microwave power P _microwave ^p

The supplied microwave power P _microwave

Then the attenuation of N in the material layer

Hence, humidity θ can be determined by the formula:

where N is the measured attenuation.

то есть влажность пропорциональна скорости изменения рассеяния СВЧ мощности и не зависит от соотношения рассеянной и падающей мощностей.From (4) it follows that the slew rate of the signal amplitude of a given scattered microwave power is determined from the expression:

that is, humidity is proportional to the rate of change of the scattering of the microwave power and is independent of the ratio of the scattered and incident powers.

 Thus, using as a controlled parameter the rate of increase in the amplitude of the signal, which is independent of the ratio of the scattered and incident powers, allows you to accurately determine the end time of the drying process and thereby improve the quality of the dried material, preventing its drying.

 The proposed method is carried out using a device (see diagram), which contains an AC voltage source 1, the first output of which is connected to the first output of the switch 2, the second output of which is connected to the first output of the primary winding 3 of the transformer 4, and the second output of the primary winding 3 is connected to the second output of the source 1. An additional winding 5 of the transformer 4 shunts the channel of the magnetron 6. The first output of the secondary winding 7 of the transformer 4 is connected to the first output of the capacitor 8, the second output of which It is connected to the anode of diode 9 and the cathode of magnetron 6, the anode of which is connected to a common point. The cathode of the diode 9 is connected to the second terminal of the secondary winding 7 of the transformer 4, having an additional terminal connected to the first working terminal of the switch 10, the second terminal of which is connected to a common point.

 The output of the magnetron 6 is connected with a transmitting antenna 11 located in the drying chamber 12, in which a receiving antenna 13 is received, receiving a stream of microwave power passing through the material to be dried 14. A receiving antenna 13 is connected to the input of the detecting device 15, the output of which is connected respectively to the first inputs threshold devices 16 and 17 having different power level thresholds, wherein threshold device 16 has a larger power level threshold than threshold device 17. The output of threshold device 17 with a lower threshold power is connected to the start-up input of the timer 18, and the output of the threshold device 16 with a large threshold of the power level is connected to the turn-off input of the timer 18 and to the first working output of the switch 19, the second working output of which is connected to the input of the control device 20 thresholds of the threshold devices, and the device outputs control 20 is connected to the second inputs of the threshold devices 16 and 17. The first output of the timer 18 is connected to the control input of the switch 19, and the second output of the timer 18 is connected to the control output of the switch 10 signaling the first terminal end of drying 21, the second terminal of which is connected to a common point.

 The threshold devices 16 and 17 and the threshold control device 20 can be implemented on the basis of a traditional element base using comparators (device 16 and 17), to which reference voltages are supplied from the analog signal switch, the inputs of which are connected to a voltage divider (device 20).

 The device operates as follows. In a static state, the power source 1 is not loaded and the voltage on the windings of the transformer 4 is close to zero. When the switch 2 is closed, a voltage is applied to the primary winding 3 of the transformer 4 and transferred to the secondary 7 and additional 5 windings, while the voltage from the additional winding 5 ensures that the magnetron 6 is ready for operation. The secondary winding 7, the capacitor 8 and the diode 9 form a voltage doubler, in the presence of which the magnetron 6 generates microwave power, which is sent to the drying chamber 12. To determine the slew rate of the amplitude of the signal passing through the material to be dried, the power is intercepted by the receiving antenna 13, detected by the device 15 and is supplied to threshold devices 16 (with a large threshold) and 17 (with a lower threshold). When the power reaches the lower limit, the threshold device 17 activates and starts the timer 18. If the rate of increase in the amplitude is high (i.e., the drying process is far from complete), then the threshold device 16 is activated, which resets the timer 18 and starts the threshold control device 20 through switch 19, which will change the thresholds of devices 16 and 17. The process will be repeated until the rate of change of power becomes so low that timer 18 will work before it is reset by device 16. In this case, switch 10 by a signal from the timer 18 closes part of the second winding 7, the anode voltage of the magnetron 6 decreases and the magnetron turns off. At the same time, the end of drying indicator 21 is activated, indicating the end of the drying process.

 Thus, the use of the proposed drying method and device for its implementation provide improved drying properties of dielectric materials, due to the automatic determination of the achievement of the dried material with arbitrary characteristics of a given moisture level, which eliminates the change in the physicochemical properties of the material due to overdrying.

Claims (2)

 1. The method of drying dielectric materials, including thermal microwave processing with the control of the microwave signal, characterized in that as a controlled parameter use the rate of increase of the amplitude of the signal passing through the material to be dried, which is compared with a given threshold speed, and the results are determined the end of the drying process.  2. A device for drying dielectric materials containing an AC power source, a switch, a transformer, a capacitor, a diode, a magnetron, switches, a timer and a drying (load) chamber, while the first output of the power source is connected to the first output of the switch, the second output of which is connected with the first terminal of the transformer primary winding, the second terminal of which is connected to the second terminal of the power source, and the additional transformer winding shunts the magnetron filament, the first terminal of the secondary the transformer windings are connected to the first output of the capacitor, the second output of which is connected to the anode of the diode and the cathode of the magnetron, and the control terminals of the timer are connected to the control terminals of the switches, characterized in that a receiving antenna, a detecting device, threshold devices with different thresholds of the power level are introduced into it, a threshold device control device and an end drying indicator, wherein the receiving antenna is located in the drying chamber and connected to a detecting device, the output of which is it is single with the first inputs of the threshold devices, the output of the threshold device with a lower threshold of the power level is connected to the trigger input of the timer, and the output of the threshold device with a large threshold of the power level is connected to the disconnect input of the timer and the first input of the first switch, the first timer output is connected to the control input of the second switch and the input of the drying end detector, the output of which is connected to a common point, and the second timer output is connected to the control input of the first switch, the first output of which connected to the input of the control device thresholds of threshold devices, whose outputs are connected to the control inputs of the threshold devices.