Continuous sublimator with rotating dielectric platform and multimode microwave resonator

Abstract

FIELD: agro-industrial production.SUBSTANCE: invention is used where it is necessary to carry out processes of vacuum or sublimation drying of heat-sensitive raw materials while preserving their structure, aroma, nutritional and biological value. A continuous-action sublimator with a rotating dielectric platform and a multimode microwave resonator comprises a vertical cylindrical chamber, the lower part of which is designed as a volumetric microwave resonator connected to a source of ultra-high-frequency radiation. A rotating perforated dielectric platform for placing the product is installed inside the chamber. The dimensions of the chamber are chosen in proportion to the wavelength of microwave radiation – from two to four wavelengths in diameter and from one and a half to three wavelengths in height.EFFECT: continuous freeze-drying process while maintaining a vacuum, uniform heating of the product throughout the entire volume, and increased energy efficiency of the unit.1 cl, 12 dwg

Description

[0001] The invention is intended for use in the field of agro-industrial production, where it is necessary to carry out processes of vacuum or sublimation drying of heat-sensitive raw materials while preserving their structure, aroma, nutritional and biological value.

[0002] The unit can be used for dehydration of frozen vegetables, fruits, berries, medicinal plants, and other biological raw materials that are sensitive to heat.

[0003] The invention [1, Russian Federation Patent No. 2200921 C1. Sublimation Drying Method. Bulletin No. 8 of March 20, 2003, 5 p.] describes a system for sublimation drying of food products, comprising a vacuum chamber and a microwave irradiation system providing heating of the product in dielectric trays. Disadvantages of this solution include the fact that the product is placed in a fixed layer, which leads to uneven heating across the layer thickness and limits the productivity of the system. Furthermore, loading and unloading of the product is performed manually, which precludes the possibility of continuous operation.

[0004] The invention [2, Russian Federation Patent No. 2203459 C1. Vacuum sublimation drying unit. Bulletin No. 12 dated 04 / 27 / 2003, 11 p.] describes a vacuum sublimation drying unit with two end antennas, a power divider and a phase shifter, providing microwave energy supply from both sides of the product layer. Disadvantages: complex design due to the need for precise matching of phase channels and the power divider; high metal consumption; lack of a mechanism for moving or mixing the product; impossibility of continuous operation, since the chamber is opened for each load.

[0005] The invention [3, Russian Federation Patent No. 2565227 C1. Sublimator with an ultra-high-frequency generator for drying frozen products. Bulletin No. 29 dated 10 / 20 / 2015, 18 p.] describes a sublimator with a microwave generator, designed as a vertical cylindrical chamber divided into two parts by a perforated partition. In the lower part of the chamber, which is a volumetric resonator, a stirrer made of a dielectric material is installed, driven by a gear motor. Disadvantages: the presence of a rotating stirrer inside the resonator volume complicates the sealing of the shaft and the design as a whole; the drive increases the likelihood of leakage and wear of the seals; loading and unloading are carried out through hatches, which makes the unit periodic; there is no possibility of feeding and removing the product without losing vacuum.

[0006] The invention [4, Russian Federation Patent No. 2615553 C1. Method and device for continuous sublimation drying of liquid products. Bulletin No. 10 dated 05.04.2017, 23 p.] describes a method and device for continuous sublimation drying of liquid products, including a spray nozzle, a vacuum chamber and a heater for evaporating moisture. Disadvantages: the design is only intended for liquid and pasty products, not suitable for bulk and lump materials; atomization at low pressure requires precise adjustment and regular cleaning of the nozzles; complexity of maintenance and high energy consumption of the refrigeration circuit.

[0007] The invention [5, Russian Federation Patent No. 2445561 C1. Installation for vacuum drying of biological materials. Bulletin No. 8 dated 20.03.2012, 28 p.] describes an installation for vacuum drying of biological materials, comprising a vacuum chamber with shelves, a condenser and a system for pumping out non-condensable gases. Disadvantages: the process is completely periodic; heat is supplied from heated shelves, which creates a temperature gradient and leads to uneven drying; there is no possibility of automatic regulation of heating power depending on the stage of the process; there are no means for uniform microwave exposure.

[0008] The invention [6, Russian Federation Patent No. 2671258 C1. Device for Vacuum Sublimation Drying. Bulletin No. 31 dated October 30, 2018, 33 p.] describes a device for implementing sublimation drying, containing a vacuum chamber with shelves, a heater, temperature and pressure sensors, and a control system. Disadvantages: the device operates in batch mode; there is no system for continuous feeding and unloading of the product; the design does not provide for uniform distribution of the microwave field and does not provide automatic adaptation of heating to the properties of the material being processed.

[0009] A review of known analogs shows that existing devices for freeze-drying and vacuum drying products use various heat input methods—convective, contact, infrared, or microwave heating—but none of them provide a continuous process with uniform electromagnetic field distribution throughout the product. In known systems described in patents [1-6], the drying process is primarily carried out in a periodic mode. Product loading and unloading is performed through hatches or shelves at atmospheric pressure, which requires re-evacuation of the chamber after each operation and significantly increases the drying cycle time.

[0010] In many similar systems, the product is placed in a fixed layer on trays or shelves, which leads to uneven heating and temperature gradients. When exposed to a microwave field without moving the product, overheating and underdrying zones are formed. Furthermore, the presence of mixers, augers, or spray nozzles inside the working chamber complicates the design, requires sealed rotating inlets, causes increased wear on seals, and reduces the reliability of the system.

[0011] Current solutions lack technical means for feeding and removing product without breaking the vacuum. All described devices operate with a process stop for each loading, precluding continuous processing. Another drawback is the mismatch between the geometric dimensions of the resonator chambers and the operating wavelength. At a frequency of 2450 MHz (λ = 12.24 cm), the chamber dimensions generally do not provide a stable multimode field distribution, leading to the formation of standing waves, localized field strength maxima, and "cold zones." Small-volume chambers operate in single-mode mode and are unsuitable for industrial applications, while larger volumes without mode optimization lead to significant power losses.

[0012] Insufficient process automation also remains a common problem. In most systems, microwave generator power and product temperature are controlled manually, without taking into account changes in the material's dielectric properties during drying, which reduces energy efficiency and results.

[0013] Thus, the conducted analysis of analogs shows that existing technical solutions do not ensure continuous operation while maintaining a vacuum, do not guarantee uniform volumetric heating of the product, and are characterized by a complex design requiring maintenance. The dimensions of known resonator chambers are not related to the radiation wavelength, resulting in uneven field distribution. The proposed invention eliminates these shortcomings: it incorporates a rotating perforated dielectric platform, ensuring uniform exposure to the microwave field, and includes vacuum locks for loading and unloading, allowing for continuous operation without disrupting the vacuum. The dimensions of the cylindrical chamber are selected based on the radiation wavelength—from two to four wavelengths in diameter and from one and a half to three wavelengths in height—ensuring multimode electromagnetic field distribution and uniform heating throughout the product volume.

[0014] The proposed invention is aimed at eliminating the said disadvantages by creating a continuous-action installation for freeze-drying frozen products under vacuum using microwave heating, the design of which ensures uniform distribution of the electromagnetic field, constant maintenance of vacuum and continuous supply and unloading of the product without compromising the tightness of the system.

[0015] The technical objective of the invention is to create a unit for sublimation drying of frozen products, ensuring a continuous technological process without breaking the vacuum, while guaranteeing uniform volumetric heating of the product in an ultra-high-frequency electromagnetic field and increased energy efficiency due to optimal matching of the dimensions of the working chamber with the radiation wavelength.

[0016] The process can be intensified by optimizing the distribution of the electromagnetic field and heat and mass transfer in the working chamber, as well as dynamic control of the process parameters.

[0017] The technical result of the invention is to increase the efficiency and uniformity of the freeze-drying process of frozen products while ensuring the continuity of the technological cycle without breaking the vacuum, which is achieved through uniform volumetric heating of the product in a multimode microwave field, optimal matching of the chamber dimensions with the radiation wavelength, as well as the use of a rotating perforated dielectric platform and vacuum locks for loading and unloading the product.

[0018] To achieve the stated technical result, the unit implements a set of design and functional solutions that ensure uniform heating, process continuity, and energy efficiency.

[0019] Specifically, a rotating perforated dielectric platform is located at the bottom of the vertical cylindrical chamber, which serves as the cavity resonator of the microwave generator. This platform distributes the product and ensures uniform exposure to the electromagnetic field throughout the chamber. The platform is driven by a geared motor located outside the chamber, eliminating the need for sealed rotating bushings and increasing the reliability of the design.

[0020] The chamber is equipped with two vacuum locks—one for loading and one for unloading—each equipped with dual sealed valves synchronously controlled by the automation system. This arrangement allows for the feeding of frozen product into the work area and the removal of dried material without breaking the vacuum, ensuring a continuous process cycle.

[0021] A condenser-freezer is located at the top of the chamber, connected to the refrigeration circuit. It captures and condenses moisture vapor released during sublimation, stabilizing the pressure and increasing dehydration efficiency.

[0022] The cylindrical chamber dimensions are selected based on the microwave wavelength: the diameter is 2–4 λ, and the height is 1.5–3 λ (at a frequency of 2.45 GHz, this corresponds to a diameter of 250–500 mm and a height of 180–360 mm). This ratio ensures a multimode electromagnetic field distribution, eliminating the formation of standing waves and zones of uneven heating.

[0023] A perforated partition made of non-ferromagnetic material divides the working chamber into two parts, preventing the direct impact of the microwave field on the elements of the refrigeration circuit and ensuring the free passage of vapors to the condenser.

[0024] The combination of these features allows for continuous freeze-drying of frozen products while maintaining a vacuum, uniform heat distribution throughout the entire volume, a reduction in process time, and an improvement in the quality of the finished product by preventing local overheating and destruction of the material structure.

[0025] The essence of the proposed invention is explained by the drawings, which show:

[0026] - spatial image of a continuous-action sublimator with a rotating dielectric platform and a multimode microwave resonator, general view (Fig. 1);

[0027] - spatial image of a continuous-action sublimator with a rotating dielectric platform and a multimode microwave resonator, in section with positions (Fig. 2);

[0028] - flow chart (Fig. 3);

[0029] - spatial image of a vertical cylindrical chamber 1 (Fig. 4)

[0030] - spatial image of a volumetric microwave resonator forming the lower part of the chamber (Fig. 5);

[0031] - spatial image of a rotating perforated dielectric platform (Fig. 6);

[0032] - spatial image of a vacuum lock for loading a product (Fig. 7);

[0033] - spatial image of the intermediate chamber (Fig. 8);

[0034] - spatial image of a vacuum lock for unloading 7 product (Fig. 9);

[0035] - spatial image of the freezing condenser (Fig. 10);

[0036] - spatial image of the refrigeration circuit in section (Fig. 11);

[0037] - spatial image of the receiving bin (Fig. 12).

[0038] A continuous-action sublimator with a rotating dielectric platform and a multimode microwave resonator contains (Fig. 1-9):

[0039] - vertical cylindrical chamber 1;

[0040] - volumetric microwave resonator 2, forming the lower part of the chamber;

[0041] - source of ultra-high frequency radiation 3;

[0042] - rotating perforated dielectric platform 4;

[0043] - vacuum lock for loading 5 products;

[0044] - intermediate chamber 6;

[0045] - vacuum lock for unloading 7 product;

[0046] - intermediate chamber 8;

[0047] - double sealed valves 9 (external 9.1 and internal 9.2);

[0048] - condenser-freezer 10;

[0049] - refrigeration circuit 11;

[0050] - geared motor 12;

[0051] - sealed platform rotation drive 13;

[0052] - receiving hopper 14.

[0053] A continuous sublimator with a rotating dielectric platform and a multimode microwave resonator (Fig. 1-12) contains a vertical cylindrical chamber1, the lower part of which is designed as a volumetric microwave resonator2, connected to a source of ultra-high-frequency radiation3. A rotating perforated dielectric platform4 is installed inside the chamber, designed to uniformly distribute the product and ensure uniform exposure to the electromagnetic field. The chamber is equipped with a vacuum lock for loading the product5 and a vacuum lock for unloading the product7, each of which includes an intermediate chamber (6, 8) and is equipped with double sealed valves9, including an outer valve9.1 and an inner valve9.2, allowing the feeding and removal of material without breaking the vacuum.The upper part of the chamber houses a freezing condenser 10, connected to a refrigeration circuit 11 designed to capture and condense moisture vapor released during sublimation. The platform 4 is rotated by a geared motor 12, located outside the vacuum zone and connected to the platform via a sealed drive 13. After completing the process cycle, the dried product enters the receiving bin 14. The dimensions of the chamber 1 are proportionate to the microwave wavelength—from two to four wavelengths in diameter and from one and a half to three wavelengths in height—ensuring multimode electromagnetic field distribution and uniform heating of the product throughout the entire volume during continuous freeze drying.

[0054] The technological process is as follows.

[0055] The frozen product, pre-prepared in size and shape, is fed into the vacuum loading lock 5, where it enters the intermediate chamber 6 at atmospheric pressure. After the outer valve 9.1 is closed and the pressure in the intermediate chamber 6 is equalized with the pressure in the working chamber 1, the inner valve 9.2 opens, and a portion of the product, under the action of gravity or a guide tray, enters the rotating perforated dielectric platform 4, installed inside the volumetric microwave resonator 2, which forms the lower part of the chamber.

[0056] After the product is loaded, microwave radiation source 3 is activated, generating a multimode electromagnetic field in resonator 2. The optimal ratio of the geometric dimensions of chamber 1 to the radiation wavelength and the rotation of platform 4 ensures uniform distribution of the microwave field throughout the product, promoting uniform heating and intensifying the sublimation process.

[0057] Under the influence of electromagnetic energy, the ice in the product transforms into a vapor state, bypassing the liquid phase. The released moisture vapor is removed from the work area through the perforations of platform 4 and directed to the upper part of chamber 1, where condenser-freezer 10 is located. In the condenser, the vapor precipitates on a cooled surface connected to refrigeration circuit 11 and is removed as condensate, maintaining a stable low pressure in the chamber.

[0058] The vacuum system (not shown in the drawing) maintains a set vacuum level in chamber 1, ensuring constant sublimation conditions and efficient removal of non-condensable gases.

[0059] As platform 4 rotates, the dried product moves toward vacuum lock 7 for unloading. After internal valve 9.2 closes, the pressure in intermediate chamber 8 equalizes with atmospheric pressure, then external valve 9.1 opens, and the finished dry product is unloaded into receiving bin 14.

[0060] The rotation of the platform 4 is carried out by the gear motor 12, located outside the vacuum zone and connected to the platform through a sealed drive 13, which eliminates the need for complex seals in the working volume.

[0061] The cycle then repeats automatically. The control system synchronizes the operation of airlocks 5 and 7, radiation source 3, gear motor 12, refrigeration circuit 11, and the vacuum system, ensuring a continuous freeze-drying process without breaking the vacuum.

Claims

A device for continuous sublimation drying of frozen products under vacuum using microwave heating, characterized in that it contains a vertical cylindrical chamber, the lower part of which is made in the form of a volumetric microwave resonator with a rotating perforated dielectric platform placed inside for placing the product, equipped with vacuum loading and unloading locks with double hermetic valves, a freezing condenser connected to a refrigeration circuit, while the dimensions of the chamber are selected in proportion to the wavelength of the radiation - from two to four wavelengths in diameter and from one and a half to three wavelengths in height, which ensures a multimode distribution of the electromagnetic field and uniform heating of the product throughout the volume.

Images