Device for ultrasonic drying. Acoustic Dryer Ultrasonic Wood Dryer
The drying process is to remove moisture from the material. This is usually done by heating. Drying of solid, bulk and other materials is common in a wide variety of technological processes. In most cases, heated air is used as the heat carrier. But when drying many chemical products, biological objects, fertilizers, it is impossible to dry at elevated temperatures, because the substances either decompose or lose their bactericidal properties.
When the temperature cannot be allowed to rise during drying, drying is carried out under the influence of ultrasonic vibrations.
The impact of ultrasonic vibrations helps to remove moisture and allows you to speed up the drying process many times over. The laboratory team has extensive experience in the development and creation of practical structures for acoustic (ultrasonic) drying, more detailed information can be found in the monograph "Application of Ultrasound in Industry", Chapter 6.4 "Acoustic Drying Processes".
6.4 Acoustic drying processes
(Khmelev V.N., Popova O.V. Multifunctional ultrasonic devices and their use in small industries, agriculture and households: scientific monograph / Alt. state Tech. Univ. them. I.I. Polzunov. - Barnaul: ed. AltGTU, 1997. - 160 p.)
The drying process is to remove moisture from the material. This is usually done by heating. Drying of solid, bulk and other materials is common in a wide variety of technological processes.
In most cases, heated air is used as the heat carrier. But when drying many chemical products, biological objects, fertilizers, it is impossible to dry at elevated temperatures, because the substances either decompose or lose their bactericidal properties.
When the temperature cannot be allowed to rise during drying, drying is carried out under the influence of ultrasonic vibrations. The first results were obtained as early as 1955 by P. Gregusz (Hungary). At a frequency of 25 kHz, he received a 10-fold acceleration in the drying of wet cotton fiber. Later, he also obtained ultrasonic acceleration of wood drying.
The drying process consists of two main periods. The first is the evaporation of moisture from the surface of the material and the diffusion of vapor into the surrounding space. Evaporation of moisture leads to the fact that a moisture gradient is created in the material, as a result of which moisture from the inner layers begins to move to the surface. This is the second period.
Ultrasonic exposure of high intensity makes it possible to intensify both periods of the drying process.
During the first drying period, the oscillations make it possible to reduce the thickness of the hydrodynamic boundary layer. In an ultrasonic field, the hydrodynamic boundary layer can be much smaller than the diffusion one. This means that vibrations penetrate the diffusion layer, turbulize it, thereby accelerating the evaporation process. Along with a decrease in the thickness of the boundary layer, the ultrasonic drying method has another important advantage - vibrations penetrate the material and create rapidly changing zones of high and low pressure in it, which intensifies the processes of moisture transfer from deep layers to the surface in the second drying period. Other active factors of ultrasonic impact are (Figure 6.5): a decrease in the viscosity of the liquid under the influence of vibrations, which contributes to the transfer of moisture from the deep layers to the surface; extrusion of moisture from the material by cavitation bubbles arising in the liquid under the influence of vibrations; radiation pressure, squeezing liquid out of the material, etc.
Figure 6.5 - Operating factors of ultrasonic drying
The lower energy costs of ultrasonic drying, in comparison with convective drying, are explained by the fact that the liquid is removed from the surface not only due to evaporation (which requires significant energy costs for the implementation of the phase transition), but also due to ultrasonic spraying in the form of an aerosol (without phase transition) , which occurs as a result of high-intensity elastic vibrations of ultrasonic frequency.
Therefore, ultrasonic drying at a comparable power of energy impact proceeds several times faster compared to convective drying. Patented methods for drying capillary-porous materials in high-intensity ultrasonic fields are known, which confirmed the following advantages of acoustic drying:
— high intensity of the process with less energy consumption;
- the possibility of ensuring high-quality and efficient drying at low temperatures or, which is important, without increasing the temperature.
Thus, the main operating factors are:
- A decrease in the viscosity of a liquid under the action of ultrasound, which contributes to the accelerated movement of moisture through the capillaries from the depth of the body to the surface.
- Fluctuations of gas bubbles in a liquid, which squeeze moisture out of capillaries.
- Radiation pressure directed in capillaries from liquid to gas, which displaces the liquid column of the capillary, moving it to the surface.
Drying in the ultrasonic field occurs without heating the material. That is why it is the only way to dry heat-sensitive and easily oxidized materials. This method differs in speed from conventional methods. For example, when drying silica gel at an initial humidity of 25%, radiation intensity of 152 dB, at a frequency of 8 kHz, t = 15 min - complete drying. Figure 6.6 shows the dependence on the performance of the drying process of ethylcellulose.
Figure 6.6 - Dependences on the performance of the drying process of ethyl cellulose
Comparison with vacuum drying and hot air drying (92°C): only 10-15% of the moisture contained was removed in the same time.
When drying the enzymes (not capable of withstanding 40°C), the process in an acoustic field took 14 min, and the speed increased by 3–4 times in comparison with the vacuum method.
Peculiarities of acoustic drying (equipment requirements).
- There is a lower intensity limit at which a noticeable acceleration of the process begins (about 130...145 dB).
- There is no dependence of drying speed on frequency in the range from 2 to 25 kHz.
- Drying is most effective for thin layers (about 2-3 cm).
Let's consider practical schemes of dryers (Figure 6.7)
Figure 6.7 - Practical diagrams of dryers
The main ones are sonic fluidized bed dryers for drying powdered substances, drum and vibration dryers.
Consider the design of a fluidized bed dryer. Radiators are installed in the vertical cylinder in the lateral and upper parts.
Through the feeder, the material is loaded into the dryer on the grate. Drying air is supplied from below through a distribution grid. When air passes through the mesh and material, it begins to intensively mix, “boil”, forming a fluidized layer. The constantly stirred material is subjected to ultrasonication and dried.
As the particles dry, they become lighter, rise along the upper baffle and fall into the hopper. Humid air is removed through the upper branch pipe.
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, which was developed by Russian scientists, is capable of revolutionizing woodworking.
There are no analogues of such equipment in the world. Its developer - the innovative company "Promin" - promises to release the first high-performance industrial prototype in a year, and in two years - to supply up to 20 installations of a fundamentally new method of drying lumber to the Russian market.
Existing technologies based on a change in the state of aggregation of water (evaporation) and differ only in the methods of heating wood, evaporating the liquid, supplying the energy necessary for this purpose, and methods of removing the gas contained in the drying chamber are imperfect. A new method for drying lumber is proposed based on a change in the physical nature of the mechanism for removing the liquid contained in wood and provides a significant (several times) reduction 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 known methods (thermoconvective, 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 have low productivity, causing wood defects (warping, cracking, etc.), inhomogeneity of residual moisture along the length of the lumber ("spotted moisture"), as well as environmentally harmful emissions of "wood" moisture containing organic acids into the atmosphere , alkali, turpentine, methanol, etc., products of fuel combustion during heating of the coolant necessary for heating the drying chamber, which is also at risk of freon release from the cooling system for condensation drying chambers.
Modern trends in the improvement of drying equipment are evolutionary in nature and cannot eliminate these shortcomings. Is it just an improvement in 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%.
According to the results of research by the innovative company "Promin" on the effect of ultrasound on the properties of wood, in particular, it was revealed: improving the quality of lumber (avoiding warping, cracking, etc.); destruction of saprophytes and hyphae, high resistance to microorganisms 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: an increase in equipment productivity, a sharp decrease in its dimensions, weight and power consumption; improving environmental performance (no emissions of harmful substances into the atmosphere and easy collection of liquid released from lumber); the possibility of creating a complete production line "drying-processing of lumber" and, as a result, an increase in the economic performance of the wood processing process.
The removal of moisture contained in wood in the form of a liquid can be of independent commercial interest in terms of obtaining 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 predetermines high energy consumption and low productivity of the process, and also 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; Ultrasonic 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, from a planing machine. This circumstance makes it possible to exclude such operations as stacking lumber, its loading and unloading from the drying chamber.
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 regulatory documents and will be provided with a complete set of documentation necessary for operation (description, process regulations, certificates).
Ecology of consumption. Home: Washing and drying clothes is not such an interesting topic as scientific achievements in the field of energy storage or renewable energy sources, but these processes take a significant amount of time, and with it a significant share of the family budget.
Washing and drying clothes is not as interesting a topic as scientific advances in energy storage or renewable energy sources, but these processes take up a significant amount of time, and with it a significant share of the family budget.
The current technology of drying clothes, which uses electrically generated heat to evaporate water from clothes, is long overdue for modification. There are ways to reduce the amount of water in clothes before drying, such as high-speed centrifuges.
The new solution came from scientists at Oak Ridge National Laboratory, supported by the US Department of Energy and GE Appliances, who developed a prototype of an innovative garment drying technology. It can cut laundry drying time to as little as 20 minutes, and reduce the amount of energy used for each load by 70%.
Instead of using heat to remove water from clothing, this prototype uses high-frequency vibrations - ultrasonic waves - produced by piezoelectric transducers powered by a tuned amplifier.
"This drying method produces stunning results," said lab scientist Ayyoub Momen, who developed the prototype.
“We were able to dry a piece of fabric in just 14 seconds. If you want to do this in a heat oven at different temperatures, it will take you a few minutes.”
An ultrasonic clothes dryer is effective at removing water from clothes quickly and is low power, but emits a "cool mist" instead of warm, moist air as conventional dryers do (although this also causes moisture and mold problems). For this reason, scientists advise diverting dryer "emissions" outside the building, but who knows, perhaps the next step for scientists will be to develop a way to reuse the condensed mist to wash the next load of laundry.
According to the US Department of Energy, the Lab and GE are working together to develop a commercial version of the product, and plan to have a prototype released this fall. Assuming that the ultrasonic dryer becomes a cost-effective method for upgrading commercial washing machines, it will significantly reduce the energy costs of drying clothes. published
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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. .
Modern dryers are not without drawbacks: many housewives have experienced significant shrinkage of things after washing. As a rule, the fibers of the fabric are reduced as a result of thermal impact. A completely different principle of operation has an ultrasonic dryer, developed at the Oak Ridge National Laboratory with the participation of General Motors.
As the name implies, the dryer works with ultrasonic waves, unlike traditional hot air devices. After loading wet laundry, the piezoelectric transducer emits high-frequency ultrasonic waves that completely dry the fabric in less than half an hour. Depending on the density and type of material, load volume, products dry from 1 to 20 minutes. The water extracted from the laundry turns into steam and flows into a special container, where it condenses back. The hostess will only have to drain the resulting liquid and get absolutely dry products. Thanks to this technology, shrinkage of the fibers of the fabric is excluded, as well as the formation of pellets on its surface.
Due to the high speed of operation, the dryer has excellent energy efficiency: compared to traditional devices, it consumes 70% less electricity.
When to expect on sale
At the moment, this is only an invention, but its creators are working on the launch of a commercial version of the device, which is planned for 2017. It is assumed that mini-laundries will become the main buyers of these products - they will be attracted by low electricity consumption and affordable price devices. By the way, about the cost: the estimated retail price will be set at about 500 US dollars.