Electronic journal "Technical Acoustics" http://www .ejta.org
V. N. Khmelev, A. V. Shalunov, R. V. Barsukov, S. N. Tsyganok,
A. N. Lebedev
Biysk Technological Institute of GOUVPO AltSTU, Biysk, 659305, Trofimova, 27, e-mail: [email protected]
Study of the effectiveness of ultrasonic drying
The article describes the installation for ultrasonic drying, which has improved technical characteristics, achieved through the use of created emitters and a special-shaped drying chamber. The results of experimental studies are given.
confirming the high efficiency of the created installation for drying capillary porous materials. It is shown that the maximum drying efficiency is achieved when ultrasonic treatment is carried out together with the supply of a heated (not more than 40°C) drying agent. This ensures a reduction in drying time and a reduction in energy costs by 20%.
Key words: drying, ultrasound, oscillatory system, drying chamber, processing of agricultural products.
INTRODUCTION
The most widely used for drying various materials are currently convective (thermal) dryers, characterized by high energy consumption, a large percentage of rejects due to overheating or uneven drying, and a long drying process.
One of the most effective ways to solve this problem is the implementation of the drying process due to the energy impact of high-intensity ultrasonic (US) vibrations. This effect does not lead to heating of the dried material. Due to this, ultrasonic drying is the only possible way to dry heat-sensitive, heat-labile and easily oxidized products. In addition, the processing of raw materials by ultrasonic vibrations favorably affects the consumer properties of the product (for example, it preserves the taste of products, increases the shelf life and germination of seeds, etc.). However, recently, some researchers present the results of experiments, indicating the inefficiency of drying by ultrasonic vibrations in the non-contact mode (without direct contact of the emitter with the material being dried). The reason for this, according to the authors of the article, is the imperfection of the designs of the emitters used and the absence of specialized drying chambers that provide resonant amplification of ultrasonic vibrations.
1. DEVELOPED EQUIPMENT FOR ULTRASONIC DRYING
To implement the drying process using ultrasonic vibrations, a small-sized ultrasonic drying plant with a special-shaped chamber and an ultrasonic oscillating system with a disk radiator was designed and built. The developed equipment allows the drying process to be carried out at a temperature of the drying agent, which is heated air, not more than 40 °C.
The shape of the drying chamber provides resonant amplification and uniform distribution of ultrasonic vibrations emitted by both sides of the disk over the entire surface of the material to be dried, located on pallets. The directions of propagation of ultrasonic vibrations and air flows in the chamber are shown in Fig. . one.
Rice. 1. Structural diagram of the ultrasonic dryer
The created installation consists of an emitter of ultrasonic vibrations in the form of a flexural oscillating disk connected to a piezoelectric transducer. The dimensions and shape of the transducer and disk are chosen from the condition of providing a given frequency and direction of radiation. The piezoelectric transducer is powered by an ultrasonic frequency electric oscillation generator (not shown in Fig. 1).
The body of the dryer consists of upper and lower reflectors, shown together with the emitter in fig. 2. The upper reflector (cover) is made removable and is designed to load the material to be dried.
Rice. 2. Upper (a) and lower (b) drying chamber reflectors
In the body of the dryer there is a container for the material to be dried, consisting of three annular pallets, the appearance of which is shown in Fig. 3. Pallets are placed horizontally, at a vertical distance of 30 mm from each other.
Rice. Fig. 3. Appearance of pallets for placing the material to be dried (a) and their placement in the volume of the drying chamber (b)
The appearance of the drying plant assembled with the control system and the generator of electrical oscillations of ultrasonic frequency is shown in fig. four.
Rice. 4. Appearance of the dryer
To confirm the effectiveness of the created drying plant, a number of experiments were carried out. At the initial stage, the distribution of the ultrasonic radiation intensity level in the volume of the drying chamber was studied. The size and uniformity of the distribution of the intensity of ultrasonic radiation depend, respectively, on the speed and quality of drying of the material.
2. DETERMINATION OF THE INTENSITY LEVEL OF ULTRASONIC VIBRATIONS
To determine the level of intensity of ultrasonic vibrations in the developed drying chamber, two types of experiments were carried out:
Measurement of the level of vibration intensity without the top cover of the drying chamber at different distances from the emitter;
Measurement of the vibration intensity level in a closed volume with the top cover closed. At the same time, due to the specially calculated dimensions of the drying chamber, the standing wave regime must be ensured in the entire volume of the drying chamber.
For measurements, a specialized sound level meter was used, which has an extended frequency (up to 30 kHz) and amplitude (up to 153 dB) ranges. On fig. 5 shows graphs of the distribution of the intensity level of ultrasonic vibrations along the axis of the emitter for the first case.
Rice. 5. Distribution of the intensity level of sound vibrations over the surface
disk emitter: a - at a distance of 250 mm from the emitter; b - at a distance of 700 mm from the emitter
It can be seen from the dependences presented that the use of the lower reflector of the drying chamber makes it possible, through the use of reflected radiation from the rear side of the disk, to form a region of high-intensity sound field with a diameter that is twice the diameter of the disk radiator. The intensity level of the ultrasonic field generated by the reflected vibrations approximately corresponds to the intensity level of the primary sound field emitted by the face of the disc.
Deviations of the intensity level values from the average value can be explained by the location of the lower reflector in the near radiation zone of the rear side of the disk radiator, which, as is known, is characterized by a high degree of sound field inhomogeneity. This fact is confirmed by measurements of the intensity level of the sound field at a distance of 700 mm from the surface of the disk radiator, which can be considered as a far-field region. The measurement results presented in Figs. 5b and indicate smaller fluctuations of the ultrasonic field.
The picture changes significantly when measuring the intensity level in the closed volume of the drying chamber (with the top reflector-cover installed). The measurement results obtained in this case are shown in Figs. 6.
I. DB 150 140 130
Rice. Fig. 6. Distribution of the intensity level of sound vibrations in the closed volume of the drying chamber
It follows from the presented results that an almost uniform field was obtained in the closed volume of the drying chamber.
Thus, the created drying chamber provides a uniform distribution of ultrasonic vibrations with an intensity level of 150 dB throughout the entire internal volume (provided by setting the standing wave mode), which is sufficient for the implementation of the ultrasonic drying process. The electrical power consumed by the electronic generator does not exceed 150 W.
The conducted studies confirmed the efficiency of the developed disk emitter and the optimal design of the drying chamber.
Further studies were devoted to determining the optimal modes of implementation of the ultrasonic drying process.
3. STUDY OF THE EFFICIENCY OF ULTRASONIC DRYING
The variable parameters during the research were: the rate of supply of the drying agent into the volume of the chamber, the temperature of the drying agent, the type (fabric, carrot, ginseng), the shape and location of the dried samples inside the drying chamber.
The efficiency of the drying process was determined by the residual moisture content of the sample and its drying rate (the amount of moisture removed in grams per second, related to the mass of the sample).
The initial and current moisture content of the dried samples was determined by the following expression:
where mmeK is the current value of the mass of the samples;
initial mass value
samples.
Measurement of the weight of the samples was carried out by weighing, on a laboratory scale "MW-II", company "CAS" with an accuracy of 0.1 g.
The drying rate was determined using the following expression:
V = -^h-tech 100%:
exp initial general
where tnach is the mass of the samples, measured immediately before the start of the drying cycle; ttek is the mass of the samples measured after the drying cycle; hexp - drying cycle time.
The entire cycle of experiments was divided into three main stages:
1) determination of the degree of intensification of the drying process by ultrasonic vibrations;
2) determination of the uniformity of drying of the material in different parts of the drying chamber;
3) determination of the efficiency of drying by ultrasonic vibrations of various materials.
3.1. The degree of intensification of the drying process by ultrasonic vibrations
At the initial stage of the experiments, the contribution to the drying process made by high-intensity ultrasonic vibrations was evaluated. As an object of drying, cotton fabric was used, in the form of separate strips with dimensions of 20x150 mm. Their total initial (wet) weight was 3 kg.
On fig. 7, in the form of a histogram, presents the comparative results for the drying rate obtained with and without exposure to ultrasonic vibrations. The duration of each experiment was 30 min. The drying rate shown in the histogram is averaged over the entire duration of the experiment.
Rice. 7. Drying efficiency by ultrasonic vibration
From the histograms in Fig. 7 it follows that exposure to ultrasonic vibrations makes it possible to increase the speed of ultrasonic drying from 2 to 6 g/min per one kg of mass of the dried sample at a temperature of 40 degrees Celsius. At the same time, the increase in the drying rate and, consequently, the efficiency of drying by ultrasonic vibrations increases with an increase in temperature and a flow rate of the drying agent (from 0.25 m3/min to 0.5 m3/min).
This effect can be explained as follows. With prolonged exposure (experiment time 30 min.) of heated air to the dried material, the rate of moisture removal from its surface exceeds the rate of its supply from the inner layers of the material. This leads to the formation on the surface of the material, a layer with reduced moisture content, which prevents further effective removal of moisture.
When exposed to ultrasonic vibrations, in the dried material there is a movement of moisture from the inner layers of the material to the surface, in sufficient quantities for its effective removal. This prevents the formation of a dried surface layer and significantly increases the drying efficiency in general.
Thus, the above experimental results show the feasibility of using ultrasonic vibrations in combination with the supply of a heated drying agent.
3.2. Determination of the uniformity of drying of the material
In this series of experiments, the drying efficiency was evaluated separately for each of the 6 sectors of each tray. The results were then averaged over the entire pallet and the results obtained for each pallet were compared. Samples from previous experiments were used as the material to be dried. Experiment time - 30 min.
On fig. 8 shows the histograms of the residual moisture content of the test samples by sectors, for the top, middle and bottom pallets, respectively.
I KMS Without KZ
sector number a)
sector number
sector number c)
Rice. Fig. 8. Distribution of residual moisture content of samples by pallet sectors a - upper pallet; b - middle pallet; c - bottom tray
From fig. 8 it follows that the uniformity of drying samples in all sectors is approximately equal within one pallet. The value of residual moisture between the sectors differs by no more than 1...3%, which indicates a uniform temperature and ultrasonic field inside the drying chamber.
On fig. 9a shows the results of comparing the residual moisture averaged over each of the pallets.
Top tray Middle tray Bottom tray Top tray Middle tray Bottom tray
Rice. Fig. 9. Distribution of residual moisture content of samples on pallets a - drying 30 min; b - re-drying for another 30 minutes
The increased residual moisture content of the samples on the lower tray (Fig. 9a), when drying with ultrasonic vibrations, may be due to the high efficiency of ultrasonic vibrations, which, with a significant initial moisture content of the samples (more than 160% with respect to the mass of dry material), to the spraying of moisture from them surfaces. The atomized moisture does not have time to be removed by the drying agent supply system and settles on the material located on the lower pallet.
This fact is confirmed by repeated drying of samples with an initial moisture content equal to the value obtained in the previous experiment. The results of this experiment, presented in Figs. 9b demonstrate a high uniformity of drying of the material in the chamber, provided that there is no cavitation spraying of moisture from its surface. This allows us to evaluate the effectiveness of ultrasonic drying, both for samples located on one of the pallets, or part of it, and for the entire mass of the dried material.
3.3. Determination of the efficiency of drying by ultrasonic vibrations of various materials
The final stage of the experiments was aimed at determining the efficiency of drying by ultrasonic vibrations of samples of various products, shapes and sizes. The following were used as experimental samples: carrots cut into calibrated disks with a diameter of up to 28 mm and a thickness of 5 mm; carrots cut into bars 35x5x3 mm; whole ginseng root; ginseng root, cut into 4.5 mm thick discs. The total weight of dried samples of each type was 3 kg. Each type of specimen was subjected to four combinations of energy exposure in the combinations shown in Table 1.
Table 1. Scheme of the experiment
Experience 1 Experience 2 Experience 3 Experience 4
Marker Marker Marker Marker
Drying agent supply 0.5 m3/min + + + +
Drying agent heating (40°С, 1000 W) - - + +
Ultrasonic treatment (150 W) - + - +
The appearance of the experimental samples before drying is shown in fig. ten.
Rice. 10. Photos of the samples used: a - carrots, cut into disks; b - carrots, cut into bars; c - ginseng root; g - ginseng root, cut into discs
On fig. 11 shows the dependence of the residual moisture content of carrots on drying time.
As in the case of drying cotton fabric, the above experimental results show that in both cases, a noticeable effect from the impact of ultrasonic vibrations is manifested only when a heated drying agent is supplied and can reach 50 g of moisture per 1 kg of dried sample mass. At the same time, the effect of ultrasonic exposure increases over time. This is explained by the fact that when drying only with heated air, a layer with a reduced moisture content is formed on the entire surface of the carrot, which prevents the effective removal of moisture from the surface.
Experiment time, tin a)
10 20 Experiment time, min
Rice. 11. Dependence of the residual moisture content of carrots on the drying time: a) - carrots, cut into disks; b) - carrots, cut into bars
Over time, the thickness of this layer increases, further reducing the release of moisture. When exposed to ultrasonic vibrations, this does not happen. This indicates that when drying objects with a capillary-porous structure, the main contribution of ultrasonic vibrations to the drying process is the transfer of moisture from the inner layers of the dried material to its surface, which is then removed using a drying agent.
At the same time, the effect of the use of ultrasonic vibrations is more significant in the case shown in Fig. 11b, corresponding to a larger total mass transfer surface.
On fig. 12 shows the nature of the change in the residual moisture content of ginseng samples from the drying time.
Rice. 12. Dependence of the residual moisture content of ginseng on the drying time a - ginseng root, whole; b - ginseng root, cut into discs
Graphs in fig. 11a indicate the low efficiency of drying the whole ginseng root. The contribution to the drying efficiency made by ultrasonic vibrations also turns out to be very insignificant. There is no increase in the effect introduced by ultrasonic vibrations when the drying agent is heated. The results obtained can be explained by the presence of a protective film on the surface of ginseng roots - the skin, which prevents active evaporation.
moisture from their surface, as well as the release of moisture from the inner layers of the roots to the surface under the action of ultrasonic vibrations, thereby minimizing the effect of the use of ultrasound. Dependencies in fig. 11.b, on the contrary, show a very significant contribution made by ultrasonic vibrations to the drying efficiency, which can reach up to 29 grams per kilogram of sample mass.
The presented results of the experiments allow us to state that the main driving factor of ultrasonic drying is the effect of moisture movement through the capillaries to the surface that develops in the sound field.
To generalize the obtained results and compare the efficiency of ultrasonic drying of various samples, in Fig. 13 shows a histogram of the residual moisture content of all the considered samples.
Rice. 13. Histogram of eye speed of various samples:
1 - ginseng root; 2 - carrots, cut into disks;
3 - ginseng root, cut into discs; 4 - carrots, cut into bars
Thus, as a result of the research, the efficiency of ultrasonic drying in the proposed dryer was shown and the conditions for ensuring the maximum speed of the process were determined, without heating the material to temperatures exceeding 40 degrees Celsius.
4. EVALUATION OF THE ENERGY EFFICIENCY OF ULTRASONIC DRYING
Based on the results obtained, an assessment was made of the energy efficiency of ultrasonic drying. The assessment was carried out according to the power consumed from the electrical network. The following initial data were accepted: electric power consumed by the ultrasonic generator - 150 W,
the power consumed by the electric heater of the drying agent is 1000 W, the drying cycle time is 30 min, the costs of supplying the drying agent were not taken into account.
The calculation of the process efficiency was carried out according to the following expression:
where P is the consumed electric power; d - drying cycle time; m is the mass of moisture removed.
The results obtained are shown in table 2. In the table, the designations of the columns corresponding to the following types of dried samples are accepted: 1 -
cotton fabric; 2 - carrots, cut into discs; 3 - carrots, cut into bars; 4 - whole ginseng root; 5 - ginseng root, cut into discs.
Table 2. Comparison of energy efficiency
Type of impact Amount of removed moisture, g. Energy efficiency, W min / g
1 2 3 4 5 1 2 3 4 5
Heated drying agent supply 750 315 375 180 330 40 95 80 167 90
Supply of heated drying agent and ultrasonic treatment 1050 381 525 210 417 33 90 66 164 83
Ultrasonic exposure 300 66 150 30 87 15 68 30 150 51
Thus, the data presented in Table 2 testify to the high efficiency of using ultrasonic vibrations for drying various products, which in some cases reduces energy costs by 20%, while maintaining the drying time and reducing the final moisture content of the product. The given values of energy efficiency also indicate the need for further improvement of the emitters of ultrasonic vibrations in order to increase the power of the generated vibrations. According to the data obtained, this will further increase the speed and reduce energy consumption for the drying process.
In general, the developed ultrasonic dryer has the technical characteristics shown in Table 3.
Table 3. Technical characteristics of the ultrasonic dryer
Parameter name Unit of measure Value
Power consumed by ultrasonic generator W 150
Power consumed by the heater (heater) W 1000
Drying chamber dimensions, diameter, height mm 850x600
Maximum heating temperature of the drying agent оС 40
Drying agent consumption m3/min 0.5
Frequency of ultrasonic fluctuations kHz 24
The work was financially supported by the Council for Grants of the President of the Russian Federation to support young Russian scientists - candidates of sciences and their supervisors No. MK-383.2008.8.
CONCLUSION
As a result of the research, a design of an ultrasonic drying plant was created that ensures efficient drying of thermolabile materials and products at a drying agent temperature of not more than 40°C with simultaneous exposure to high-intensity ultrasonic vibrations. At the same time, a high degree of intensification of the drying process by ultrasonic vibrations (an increase of up to 50 g per 1 kg of dried material) makes it possible to reduce the temperature of the drying agent, without loss in quality and drying speed. The latter is especially important for industries where heating the dried product is unacceptable or undesirable.
The high efficiency of the drying process is ensured due to the use of a disk emitter in the design of the dryer, which forms an ultrasonic field with an intensity level of at least 130 dB, and a resonant volume of the drying chamber, which provides an increase in the intensity level up to 150 dB.
The results of the experiments show the prospects and expediency of creating combined drying plants (ultrasonic-convection) with an optimal ratio of the share of thermal and acoustic energy.
LITERATURE
1. L. D. Rozenberg Physical foundations of ultrasonic technology. M.: Nauka, 1969. -689 p.
2. S. de la Fuente-Blanco, E. Riera-Franco de Sarabia, V. M. Acosta-Aparicio, A. Blanco-Blanco, J. A. Gallego-Juarez. Food drying process by power ultrasound. Ultrasonics, Elsevier USA, 2006, 44, p. 523-527.
3. Glaznev VN Device for drying capillary-porous bulk materials. RF patent No. 2095707.
4. E. Riera-Franco de Sarabia, J. A. Gallego-Juarez, G. Rodriguez-Corral, V. M. Acosta-Aparicio, E. Andres-Gallegos. Application of high-power ultrasound for drying vegetables. 19th International Congress on Acoustic, Madrid, Spain, 2007.
5. V.N. Khmelev, A.V. Shalunov et al. Ultrasonic multifunctional and specialized devices for the intensification of technological processes in industry. Barnaul: AltGTU, 2007. 416 p.
6. A. N. Lebedev; A. V. Shalunov; S. S. Khmelev; N. V. Kuchin; A. V. Shalunova. Ultrasonic Oscillating System for Radiators of Gas Media. International Workshops and Tutorials on Electron Devices and Materials EDM"2008. Novosibirsk: NSTU, 2008.
7. V. N. Khmelev, S. V. Levin, S. N. Tsyganok, and A. N. Lebedev. High Power Ultrasonic Oscillatory Systems. International Workshops and Tutorials on Electron Devices and Materials EDM"2007: Workshop Proceedings. Novosibirsk: NSTU, 2007, p. 293-298.
8. Choo Kwang Moon, V. N. Khmelev, A. V. Shalunov, Lee Hyo-Jai, A. N. Lebedev,
M. V. Khmelev. Compact Ultrasonic Dryer for Capillary-porous and Loose Materials. Ninth International Workshops and Tutorials on Electron Devices and Materials EDM"2008: Workshop Proceedings. Novosibirsk: NSTU, 2008, p. 295-299.
9. V. N. Khmelev, D. V. Genne, A. A. Bahirev, I. I. Savin The Meter of the Level High-Intensity Ultrasonic Pressure. International Workshops and Tutorials on Electron Devices and Materials EDM"2006: Workshop Proceedings. Novosibirsk: NSTU, 2006, p. 232-233.
Today, many methods are known for sufficiently effective drying of wood and finished lumber, but each of them has its own specific features, advantages and disadvantages. For example, ultrasonic drying of wood is a process similar to conveyor drying, in which lumber acquires specified practical and geometric parameters.
Ultrasonic drying is also called acoustic, such equipment is quite rare in enterprises. It is a high-tech process with which you can achieve excellent quality with less energy consumption. The technology is owned by Promin.
Features of ultrasonic drying
A distinctive feature of ultrasonic drying is low power consumption, which in turn ensures uniform removal of moisture due to its transfer from one state of aggregation to another.
As a result, lumber does not lose its geometrical parameters, maintaining strength and ensuring a long service life. If during convection drying, it happens that the lumber is dried non-uniformly, then the ultrasonic method almost completely eliminates this factor, since under the action of ultrasonic waves the moisture molecules are heated along the entire length.
Ultrasonic drying of wood is performed without changing the state of aggregation of moisture, which allows many times to reduce energy costs. Water is removed from the material, being in a liquid state, and some pressing occurs.
This technology makes it possible to increase the efficiency of equipment by almost 70% while obtaining a sufficiently high quality of lumber not only for the construction of load-bearing structures, but also for decorative finishing.
To increase the efficiency, it is possible to perform a preliminary atmospheric drying of the wood in order to achieve a uniform moisture content throughout the entire structure. This will ensure the most efficient exit of moisture from the material at minimal cost.
The ultrasonic wood dryer is a separate device that can be combined with woodworking machines. To carry out the final removal of moisture from the wood, it is pulled by a conveyor through the installation straight for processing.
This processing method can dry up to 18%-22% moisture. But as the experience of various enterprises shows, it is often not possible to dry up to 8-12%.
For a given humidity, chambers of other technologies are chosen. For example vacuum drying chambers with high drying speed and high quality of the finished lumber. You can buy cameras at a price of 750,000 rubles. The models are posted on the site.
See also:
Contents Technical parameters of a steam drying chamberAn alternative to steam drying chambers Today, many ways of drying sawn timber are known, they obtain high quality and a small percentage of rejects. One such dryer is the steam chamber. Drying wood with steam is a fairly effective technology for heat treatment of various types of wood and with different moisture content in its original state. And the technique is […]
A fundamentally new way of drying lumber, proposed by Nizhny Novgorod scientists, is capable of revolutionizing woodworking. This is the opinion of the experts. To date, a prototype of equipment for ultrasonic drying of lumber, modification of wood properties and obtaining raw materials for the chemical and perfume industries in a single technological process has been developed. There are no analogues of such equipment in the world. Its developers - the innovative company "Promin" - promise to produce the first high-performance industrial design in a year, and in two to put up to 20 installations on the Russian market.
According to experts, no more than 15% of all sawn timber is currently subject to mandatory drying in Russia. The reason for this is the imperfection of existing technologies, which are based on a change in the state of aggregation of water (evaporation) and differ only in the methods of heating wood, evaporating liquid, supplying the energy necessary for this purpose, and methods of removing the gas contained in the drying chamber. The new method of lumber drying proposed by Nizhny Novgorod engineers is based on a change in the physical nature of the mechanism for removing the liquid contained in the wood and entails a sharp (several times) decrease in the specific energy consumption of process equipment. When using ultrasonic technology, the need for energy consumption for heating heat carriers, wood, structural elements of the drying chamber, etc. disappears.
Drying lumber by currently known methods (thermoconvection, vacuum, microwave currents, aerodynamic) requires high energy consumption - 200-250 kW/h per cubic meter. This leads to the fact that the cost of high-quality drying exceeds the cost of wood and the cost of sawing it. Traditional methods are characterized by low productivity, the appearance of wood defects (warping, cracking, etc.), heterogeneity of residual moisture along the length of the lumber ("spotted moisture"), as well as the presence of environmental problems. This is the release into the atmosphere of either "wood" moisture containing organic acids, alkalis, turpentine, methanol, etc., or fuel combustion products when heating the coolant necessary to heat the drying chamber, or the risk of freon leakage from the cooling system for condensation drying chambers .
Modern trends in the improvement of drying equipment are evolutionary in nature and cannot fundamentally eliminate these shortcomings. It is only possible to improve the characteristics of existing equipment by units or tens of percent. The reason is that the physical principle of drying remains unchanged - the evaporation of the moisture contained in the wood. In this case, we can only talk about increasing the efficiency of the entire drying complex by improving the design of the drying chamber, using new heat-insulating materials, optimizing drying modes, etc.
The unique properties of wood as a natural polymer with a complex capillary structure make it possible to create a technology for drying lumber without changing the state of aggregation of the moisture contained in it. When drying with ultrasound, the moisture contained in the wood is removed in the form of a liquid. This several times reduces the specific energy consumption and increases the productivity of the equipment by 50-70%.
Based on the results of studies carried out by the innovative company "Promin" (the impact of ultrasound on the properties of wood), the following was noted:
- improving the quality of lumber (elimination of warping, cracking, etc.);
- destruction of saprophytes and hyphae, high resistance to the latter after drying;
- low moisture absorption after drying;
- increasing the resonant characteristics of wood;
- increased resistance to decay.
Other important advantages of the new technology are:
- increasing the productivity of equipment, a sharp decrease in its dimensions, weight and power consumption;
- improvement of environmental performance (no emissions of harmful substances into the atmosphere and easy collection of liquid released from lumber);
- the possibility of creating a combined production line for drying and processing lumber and, as a result, an increase in the economic indicators of the wood processing process.
The removal of the moisture contained in the wood in the form of a liquid may be of independent commercial interest in relation to the production of raw materials for the chemical and perfume industries. Currently, the moisture contained in wood, enriched with useful substances and microelements, is extracted by evaporation followed by condensation. This leads to high energy consumption and low productivity of the process, and inevitably leads to a partial loss of valuable substances and trace elements (it is known that any phase transition removes impurities, which forms the basis of many methods for obtaining pure materials).
Installation for ultrasonic drying of lumber, modification of wood properties and obtaining raw materials for the chemical and perfume industries in a single technological process consists of the following main blocks:
1. Frame (acts as a supporting structure).
2. Lumber pulling mechanism:
- drive (electric motor, gearboxes, chains, gears);
- rolling shafts.
3. Ultrasonic unit:
- ultrasonic generator;
- Ultrasound emitter.
4. Clamping mechanism:
- lumber to the ultrasonic emitter;
- drive shafts.
The installation uses the conveyor principle of supplying lumber, which is also dictated by the physical principle of impact on the latter, and opens up the possibility of combining this equipment with woodworking, for example, with a planing machine. This circumstance will eliminate such operations as stacking lumber, its loading and unloading from the drying chamber.
On fig. 1 shows a block diagram of the installation. The role of the supporting structure in the installation is performed by the frame (1), on which the lumber pulling mechanism (2), the ultrasonic emitter (3) and the clamping mechanism (5) are fixed.
1 - frame; 2 - broach mechanism; 3 - ultrasound transmitter; 4 - ultrasonic generator; 5 - clamping mechanism; 6 - board; 7 - horizontal table; 8 - a tray for collecting liquid removed from the board.
The board (6) with the help of the broach mechanism (2) moves along the horizontal table (7), in which the ultrasonic emitter (3) is mounted, powered by the ultrasonic generator (4). To reduce the loss of the ultrasonic wave when it is reflected from the lumber, the mechanism of pressing (5) of the board (6) to the ultrasonic emitter (3) is used. To prevent slippage of lumber, the broach mechanism is also provided with a clamping mechanism. The ultrasonic wave propagating in the wood leads to the release of the moisture contained there in the form of a liquid. Visually, it looks like this: liquid flows out of the board moving along the ultrasonic emitter.
The unit for ultrasonic drying of lumber, modification of wood properties and obtaining raw materials for the chemical and perfume industries in a single technological process will fully comply with the requirements of GOST and will be provided with a complete set of documentation necessary for operation (description, process regulations, certificates).
acoustic drying is a method of product dehydration by means of intense ultrasonic treatment. This is a cyclic method of removing moisture. During the primary processing of the product, moisture is removed from the surface, then, using a second ultrasonic wave, the moisture is distributed through the capillaries. This happens until the product contains the required proportion of moisture.
Acoustic drying has found successful application in agriculture, pharmaceutical, chemical and food industries. In agriculture, cereals, vegetables and fruits are processed through acoustic drying. In the food industry, acoustic drying is used in the production of milk powder. The most widespread use of ultrasonic drying is in the pharmaceutical industry. Expensive drugs - powders, antibiotics, tablets - are produced in ultrasonic chambers. The high cost of drugs is due to the high productivity of the equipment and, as a result, a high degree of energy consumption. In the chemical industry, ultrasonic drying is used to produce coal powder. With the help of such chambers, paper, cotton, and wood are dried.
Features of acoustic drying
Acoustic drying has a number of advantages: the product is not subjected to heat treatment, it is processed cold; due to the absence of temperature effects, the product retains almost all nutrients and vitamins, does not lose its original properties, and does not undergo oxidation.
Acoustic drying is the only way to work with heat sensitive materials. Thanks to this method, their structure is completely preserved without losing their original shape.
Acoustic drying is a high-speed processing method. Compared to vacuum drying, acoustic drying reduces the processing time by four times. This improves the quality of the finished product.
Acoustic Drying Technology
The material to be dried must have a capillary-porous structure. Different materials have different moisture content, so the intensity and number of ultrasonic waves is calculated according to the moisture percentage of the product.
If the product contains a large amount of moisture, a high force wave is used, as a result, the moisture is literally “shaken out” of the product. This is because the wave appears not only at the surface of the material, but also inside the capillaries, leading to an intense loss of moisture. 
If the capillary-porous material has a moderate moisture content, acoustic vibrations are more intense in the first stage and less intense in the second. During the first stage, the drying speed does not change, so moisture is constantly replenished. The upper layers of the product lose it, and the lower layers “throw out” moisture to the surface. Thus, moisture exchange does not stop until the optimum moisture content is reached.
During the second stage, the drying rate decreases, so the liquid from the inside enters weakly and its loss is no longer replenished or replenished, but weakly.
Acoustic drying is most effective during the first stage of product processing. Thanks to it, the physico-chemical and consumer properties of the product are improved. For example, with acoustic treatment of seeds, their germination capacity increases.
Thus, the acoustic drying method is successful for some types of production and is most effective at the first stage of product processing to increase the rate of moisture exchange and improve the quality of the finished product.
You can purchase equipment for drying products from us. Delivery across Russia and Belarus. .
Scientists from Nizhny Novgorod have invented an innovative method for drying lumber. Experts say that this is a real breakthrough in the production of wood materials and the construction of wooden houses.
So far, Nizhny Novgorod residents have prepared only one unit designed for drying wood with the help of ultrasound, during which the properties of the resulting lumber are modified. There are no analogues of such a "dryer" in any country in the world.
Lumber drying methods in Russia
The statistic says that today only fifteen percent of all lumber produced in Russia is dried. The reason for this phenomenon is the imperfection of the practiced technologies, which are based on a change in the state of aggregation of water (evaporation).
Existing drying methods of all lumber used for different areas, including the construction of wooden houses, differ slightly from each other.
Methods may change wood heating or moisture evaporation technology, the quality of the energy used for this and ways to remove gas from the drying chamber.
In production conditions, use thermoconvection, aerodynamic and vacuum methods of lumber drying. Wood drying with microwave current is also practiced. All of these methods require a lot of electricity. To dry one cubic meter of material, an average of 200 to 250 kWh is required.
Because of these costs, the cost dried lumber significantly exceeds the cost of wood of natural moisture and its processing. The new method allows to reduce this figure.
Traditional drying methods do not provide good quality wood - warping and cracking are characteristic of finished products, non-uniform (“spotted”) moisture can be observed along the entire length of the workpiece.
The environmental side of the issue is also a big problem.- production emits toxic gases and evaporated wood moisture into the air, which contains solutions of acids and alkalis, turpentine vapors, methanol. The combustion products of the fuel used to heat the coolant are also dangerous.
Ultrasonic technology
Developers from Nizhny Novgorod went the other way. Their proposed method works on a different mechanism of moisture removal. The drying process with the help of ultrasound helps to significantly reduce energy consumption, since it does not need to be spent on heating the wood, heat carriers and installation elements.
Possibility to dry with the help of ultrasound is due to the properties of wood - this natural polymer. Due to this, there is no need to change the state of aggregation of the liquid contained in the tree (turn the liquid into vapor).
When using ultrasound moisture is removed from the wood in its original form (liquid), which reduces the specific energy consumption by fifty percent. Some experts even talk about seventy percent savings.
Advantages of the ultrasonic drying method
The resulting products are characterized by:
- The absence of warping and cracking;
- Antiseptic component (in particular, we are talking about the destruction of saprophytes and hyphae in the workpiece and subsequent resistance to re-infection with these dangerous fungi);
- Minimum coefficient of moisture absorption;
- Improving the resonant properties of wood;
- Increased resistance to putrefactive processes.
Advantages of ultrasonic equipment:
- Increased efficiency;
- Reducing the size of drying units;
- Energy saving;
- Simplification of the technological process and ease of collection of the released liquid;
- Improving the environmental picture of production - no toxic emissions;
- Possibility to combine wood processing and drying lines, thus minimizing production costs.
Features of the ultrasonic drying process
The ultrasonic lumber drying unit works on the conveyor principle. This feature is dictated by the peculiarities of the methodology. Also, conveyor feeding allows you to combine the drying of the material with woodworking.
By combining different equipment it is possible to avoid stacking of finished wooden products, their unloading / loading into the “dryer”.
Technologies still in existence do not make it possible to use this liquid saturated with various microelements, since during the drying process it simply evaporated.
