RU2367862C1 - Ultrasonic drying device - Google Patents

Abstract

FIELD: heating, drying.

SUBSTANCE: invention concerns engineering related to drying processes for various materials by ultrasonic-frequency acoustic vibration. Invention can be applied in pharmaceutics and biological industry, as well as in agricultural production processing. Claimed ultrasonic drying device includes toric container for material to be dried, mounted in the drier case, and ultrasonic oscillator in the form of bending vibration disc with size and shape selected to maintain definite frequency and emission direction of ultrasonic vibration. Emitter is connected to piezo electric converter fed by electronic ultrasonic generator. Internal surface of drier case is formed by rotation of two crossing parabolas with common focus point and axial symmetry, around acoustic axis of bending vibration disc. Toric container is made in the form of two sections in horizontal plane, with one section placed in the area of common parabola focus point, while the other section is positioned at equal distance from side wall of drying chamber and first section.

EFFECT: improved efficiency of acoustic impact, enhanced drying speed.

1 dwg, 2 tbl

Description

The invention relates to a technique for drying capillary-porous materials and can be used for drying biological objects, products of the chemical, light and other industries without increasing the temperature and destroying the structure of products and substances.

Currently, for drying most food and pharmaceutical products, a convective method is used, which means that dry air is heated using the built-in heating element, heated air is sent through a fan to the dryer drum (technological volume), passes through the material to be dried, moistened, then outside the drum it is cooled with cold water or air. The process lasts as long as it takes to dry the material [1].

Modern drying in the technological design of the used dryers is characterized by the following disadvantages [2]:

1) the process is extremely energy intensive and time consuming;

2) dryers cannot be small-sized, as this reduces the air volume in the drum, which, on the one hand, limits the speed of the process, and on the other, increases its cost;

3) high temperature leads to drying out and damage to biological objects. To eliminate this point, it is necessary to equip the dryer with a smart and expensive electronic temperature control system for the material being dried, which significantly increases the cost of the dryer.

These shortcomings are explained not by the low level of sophistication of design solutions, but by the shortcomings of the method used in the basis - convection drying. A promising option for replacing or supplementing the convective drying method is drying in high-intensity acoustic fields, which is associated with the following advantages of the method:

1) high intensity of the process;

2) the ability to ensure high-quality and efficient drying at low temperatures or, in principle, without increasing the temperature (eliminating the destruction of the structure, preserving the germination of grain, etc.);

3) the ability to develop self-tuning ultrasonic generators, which does not require user control over the operation of the system.

The above advantages explain the great interest in ultrasonic drying technology. However, attempts at the practical implementation of the ultrasonic drying process encounter a number of technological difficulties:

1) the need to create acoustic vibrations in the air with intensities of more than 140 dB;

2) the need to create a drying chamber, providing a uniform effect of acoustic vibrations throughout the dried material.

At present, when creating devices for acoustic drying, these problems are solved by using aerodynamic emitters and creating drying chambers, as a rule, in the form of an extended rectangular channel. An example of such a drying installation is the known device for drying capillary-porous bulk materials [3]. This device is a drying chamber made in the form of a sound duct, from one end of which there is a sound emitter, from the opposite - sound-absorbing material.

This device allows the process of acoustic drying of materials, however, it has some disadvantages:

1) the use of a gas-jet emitter as a sound source, which has the following disadvantages:

a) low efficiency, not exceeding 20%;

b) rapid wear of mechanical components;

c) the inability to work at high frequencies (more than 20 kHz) and, as a result, the need to protect service personnel from acoustic radiation (the frequency described in the device used is 150 Hz);

d) the need to supply high pressure compressed air, which requires the use of a compressor;

e) large weight and size characteristics, excluding the possibility of creating a small-sized dryer;

2) the non-optimal form of the drying chamber, made in the form of an extended rectangular channel, leading to low efficiency of use of acoustic energy and the lack of focusing of acoustic vibrations on the dried material;

3) the use of a sound absorber plug at the rear end of the drying chamber, which leads to the fact that the traveling wave mode is realized and up to 80% of acoustic energy is absorbed in the sound absorber and is not involved in the drying process (according to the device description, the intensity of the absorber is only 5-6 dB lower than the emitter, therefore, if, as indicated in the description, the traveling wave mode is implemented in the device, then no more than 5 dB is spent on drying, the rest is absorbed in the absorber).

All of these disadvantages reduce the effectiveness of acoustic exposure and do not provide an acceptable drying speed.

The disadvantages of the known device were partially eliminated by a device for drying capillary-porous materials, pleasant for the prototype [4], containing a toroidal mesh container for the material to be dried, installed in the dryer body, and an ultrasonic acoustic emitter of ultrasonic frequency.

When implementing the drying process using the device according to [4], due to the special form of the drying chamber, the ultrasonic vibrations are focused on the material being dried, thereby increasing the speed and uniformity of drying. However, the device has only partially eliminated the significant drawbacks of known acoustic drying devices (for example, using a gas-jet emitter as a source of ultrasonic vibrations). The prototype also has other disadvantages:

1) small volumes of the dried material, due to the need to place the dried material in the focus area;

2) the impossibility of carrying out “delicate” drying, caused by the need to supply large volumes of air to the drying chamber for operation of the gas-jet emitter;

3) low efficiency of the dryer due to the use of a gas-jet emitter (efficiency does not exceed 20%).

Thus, the device adopted for the prototype does not allow to realize the drying process with maximum efficiency.

The proposed technical solution of the ultrasonic drying device consists of a toroidal mesh container for the material to be dried, installed in the dryer body, and an emitter of acoustic vibrations of ultrasonic frequency. In this case, the emitter of ultrasonic vibrations is made in the form of a bending-oscillating disk, the dimensions and shape of which are selected from the condition of ensuring the given frequency and direction of radiation of ultrasonic vibrations. The emitter is connected to a piezoelectric transducer powered by an ultrasonic frequency electronic generator. The inner surface of the dryer body is formed by rotation around the acoustic axis of a flexurally oscillating disk of two intersecting axisymmetric parabolas having a common focus. The toroidal container is made in the form of two sections located in a horizontal plane, one of the toroidal sections of the container being in the region of the general focus of the parabolas, and the second is located at an equal distance from the side wall of the drying chamber and the first section.

In the proposed device for ultrasonic drying, the task of increasing the efficiency of acoustic exposure and increasing the drying speed is solved by:

1) creating a drying chamber of a special shape, which ensures the formation of an optimal acoustic field, focusing of ultrasonic vibrations in the dried raw materials and the formation of a standing wave regime, which allows for the most complete use of the energy of ultrasonic vibrations;

2) use as a source of ultrasonic vibrations a piezoelectric ultrasonic oscillatory system with an emitter in the form of a bending-oscillating disk, which allows to form uniformly ultrasonic radiation over a large area.

The essence of the proposed technical solution is illustrated in figure 1, which schematically shows the proposed device for ultrasonic drying. The proposed device consists of an emitter of ultrasonic vibrations in the form of a flexurally oscillating disk 1, the size and shape of which is selected from the condition of providing the specified frequency and directivity of the radiation of ultrasonic vibrations connected to a piezoelectric transducer 2 installed in the dryer body. The piezoelectric transducer is powered by an ultrasonic frequency generator of electric oscillations (not shown in FIG. 1). The dryer body consists of the upper 3 and lower 4 sections. The upper section is removable and designed to load the dried material. A container for the material to be dried, consisting of two toroidal sections, is also located in the dryer body. One of the toroidal sections 5 of the container is located in the common focus area of the parabolas. The second section 6 of the container is located at an equal distance a from the side wall of the drying chamber and the first section. In this case, it is desirable that the overall dimensions of the dryer are selected from the condition of ensuring a minimum distance a.

In the proposed embodiment of the drying chamber, the drying process is as follows. Both toroidal sections of the container are filled with dried material. Then, the container with the material to be dried is placed in the dryer body and subjected to ultrasonic vibrations until the required amount of moisture is removed. When a plane wave is generated by a flexurally oscillating disk, the distribution of ultrasonic vibrations inside the drying chamber will take the form shown by arrows in FIG. 2. A flexurally oscillating disk emits ultrasonic vibrations in both directions relative to its plane, which are reflected from the inner branch of the parabola forming the surface of the dryer body and are focused in the material to be dried. Part of the ultrasonic vibrations reflected from the dried material located in the first toroidal section of the container falls onto the external branch of the parabola, reflected from which is evenly distributed over the dried material located in the second toroidal section of the container. When choosing the distance b1 + b2 + b3 + b4, which is a multiple of the wavelength of ultrasonic vibrations in the air, a standing wave mode will be provided, which is the most energy-efficient mode of ultrasonic exposure. Due to the implementation of the inner surface of the dryer body in the form of a parabola, the distance b1 + b2 + b3 + b4 will be equal for each point on the surface of the bending-oscillating disk and the container with the material to be dried. The result will be uniform drying of the material throughout the volume.

Figure 3 shows a structural diagram of an ultrasonic dryer, implemented in practice. To improve the efficiency of electro-acoustic conversion, the piezoelectric transducer is made in the form of a three-wave ultrasonic oscillatory system with a hub 7 [5]. To increase the drying efficiency, the system is equipped with supply devices 8 and exhaust 9 of drying air. The developed drying chamber allows to realize the following drying modes: convection-ultrasonic, vacuum-ultrasonic and drying with alternating pressure changes in the drying chamber. The developed drying chamber has the following technical characteristics: intensity of generated acoustic vibrations, not less than 140 dB; frequency of oscillations generated by a bending-oscillating disk emitter 22 kHz; maximum amplitude (amplitude swing) of oscillations of a disk radiator of 100 microns; the diameter of the radiating disk of the oscillatory system is not more than 250 mm; the material of the disk emitter and hub is a titanium alloy; diameter of the drying chamber 750 mm; drying chamber material - metal; the intensity of acoustic vibrations in the drying chamber (at a radiation intensity of 140 dB) is not less than 150 dB; the maximum load of the drying chamber is 15 kg.

To determine the effectiveness of the created design of the drying chamber, experimental studies were conducted in which a disk radiator with a consumed electric power of 200 W was used. The temperature in the drying chamber was maintained at a level of 23-26 ° C, humidity 50-65%. Additional supply and exhaust of drying air were not used, i.e. To confirm the effectiveness, the most irrational drying method was used.

Two series of experiments were conducted. Drying time was taken equal to 160 minutes. In the first series of experiments, gelatin soaked in water was used as a dried material. The drying results are shown in table 1.

Table 1
Gelatin Drying Results Time min Mass g Speed g / min Moisture content,% 10 4709 172.04 twenty 4413 29.6 154.94 thirty 4125 28.8 138.30 40 3843 28,2 122.01 fifty 3670 17.3 112.02 60 3386 28,4 95.61 70 3192 19,4 84.40 80 3027 16.5 74.87 90 2868 15.9 65.68 one hundred 2732 13.6 57.83 110 2614 11.8 51.01 120 2513 10.1 45.18 130 2428 8.5 40.27 140 2349 7.9 35.70 150 2277 7.2 31.54 160 2221 5,6 28.31

Thus, after 160 minutes of gelatin drying, its final moisture content was 28.31%, while the energy consumption was 0.6 kW. When using an ultrasonic dryer with a gas-jet transducer, it took 230 minutes to dry the same amount of gelatin at an energy consumption of 2.3 kW.

In the second series of experiments, the process of drying carrots was carried out. The experimental results are shown in table 2.

table 2
Carrot Drying Results Time min Mass g Humidity% Speed g / min 10 1509 601.43 twenty 1464 579.74 4,5 thirty 1425 561.53 3.8 40 1388 543.89 3,7 fifty 1349 525.34 3.9 60 1310 506.75 3.9 70 1274 489.78 3.6 80 1239 472.61 3.6 90 1205 456.35 3.4 one hundred 1168 439.04 3.6 110 1137 424.20 3,1 120 1105 409.03 3.2 130 1075 395.20 2.9 140 1047 381.88 2,8 150 1023 370.33 2,4 160 996 357.06 2,8

After drying the carrots, its moisture content decreased approximately twice, while the energy consumption was 0.6 kW. When using an ultrasonic dryer with a gas-jet converter, it took 300 minutes to dry the same amount of gelatin at an energy consumption of 3 kW.

The given values show the effectiveness of the proposed technical solution and the prospects of its application as industrial and small-sized commercial drying plants.

Small-scale production of the developed device for ultrasonic drying is planned to begin in 2009.

Bibliography

1. Physical foundations of ultrasound technology [Text] / ed. L.D. Rosenberg. - M .: Nauka, 1969 .-- 689 p.

2. Khmelev V.N. Ultrasonic multifunctional and specialized devices for the intensification of technological processes in industry [Text] / V.N. Khmelev, A.V. Shalunov [and others]. - Barnaul: AltSTU, 2007 .-- 416 p.

3. RF patent No. 2095707.

4. RF patent No. 2239137 - prototype.

5. Khmelev V.N. High Power Ultrasonic Oscillatory Systems [Text] / V.N. Khmelev, S.V. Levin, S.N. Tsyganok, A.N. Lebedev // International Workshop and Tutorials on Electron Devices and Materials EDM'2007: Workshop Proceedings. - Novosibirsk: NSTU, 2007. - P.293-298.

Claims (1)

An apparatus for ultrasonic drying, comprising a toroidal mesh container for the material to be dried, mounted in the dryer body and an ultrasonic acoustic emitter, characterized in that the ultrasonic emitter is made in the form of a bending oscillating disk and is connected to a piezoelectric transducer fed by an electronic ultrasonic frequency generator, the inner surface of the dryer body is formed by rotation around the acoustic axis of a bending-oscillating disk of two intersecting axisymmetric parabolas having a common focus, and the toroidal container is made in the form of two sections located in a horizontal plane, one of the toroidal sections of the container being in the region of the general focus of the parabolas, and the second is located at an equal distance from the side wall of the drying chamber and the first section.

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