CN115574547A - Ultrasonic-assisted freeze drying method - Google Patents
Ultrasonic-assisted freeze drying method Download PDFInfo
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- CN115574547A CN115574547A CN202210167916.0A CN202210167916A CN115574547A CN 115574547 A CN115574547 A CN 115574547A CN 202210167916 A CN202210167916 A CN 202210167916A CN 115574547 A CN115574547 A CN 115574547A
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B5/00—Drying solid materials or objects by processes not involving the application of heat
- F26B5/04—Drying solid materials or objects by processes not involving the application of heat by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum
- F26B5/06—Drying solid materials or objects by processes not involving the application of heat by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum the process involving freezing
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B25/00—Details of general application not covered by group F26B21/00 or F26B23/00
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B5/00—Drying solid materials or objects by processes not involving the application of heat
- F26B5/02—Drying solid materials or objects by processes not involving the application of heat by using ultrasonic vibrations
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B9/00—Machines or apparatus for drying solid materials or objects at rest or with only local agitation; Domestic airing cupboards
- F26B9/06—Machines or apparatus for drying solid materials or objects at rest or with only local agitation; Domestic airing cupboards in stationary drums or chambers
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- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Drying Of Solid Materials (AREA)
Abstract
The invention discloses an ultrasonic-assisted freeze drying method, which belongs to the field of freeze drying and comprises the following steps: s1, placing a sheet-shaped material to be frozen on a temperature control plate in a vacuum tank; s2, cooling and applying first ultrasonic waves in the cooling process; s3, detecting whether the temperature of the flaky material to be frozen is reduced to a first preset temperature, if so, entering S4, and if not, continuing; s4, vacuumizing the vacuum tank to reduce the pressure of the vacuum tank to a preset pressure; s5, applying second ultrasonic waves; s6, after the first preset time, detecting whether the pressure rising rate of the vacuum tank is lower than a first pressure rising rate, if so, entering S7, otherwise, continuing; s7, heating and preserving heat after the temperature reaches a second preset temperature; s8, applying third ultrasonic waves in the heating and heat preservation processes; and S9, after second preset time, detecting whether the pressure rising rate of the vacuum tank is lower than a second pressure rising rate, if so, stopping, and otherwise, continuing. The invention not only can save energy and time, but also can improve the appearance and structural integrity of the product.
Description
Technical Field
The invention relates to the technical field of freeze drying, in particular to an ultrasonic-assisted freeze drying method.
Background
The freeze drying technology is a process for directly sublimating water in fresh food and medicine raw materials into gas by reducing surface pressure after the fresh food and medicine raw materials are frozen, and the water is directly gasified without a thawing process in the process, so that the collapse of tissues can not be caused, and the shapes of the tissues before freeze drying can be maintained, therefore, the freeze-dried materials have good quality. In addition, due to the lower drying temperature, the active ingredients in the material can be reserved, and the quality of the product can be improved to the maximum extent.
However, freeze-drying techniques also have disadvantages, such as time-consuming freeze-drying process, waste of electrical energy, and high production costs. In the prior art, there is a technical solution of applying ultrasonic waves during freezing to save the freeze-drying time and thus save the electric energy, for example, in a freeze-drying method and a supporting device disclosed in document 1 (CN 201410201099.1), ultrasonic-assisted freeze-drying of carrots has been mentioned.
However, the timing of applying the ultrasonic wave is a pre-cooling stage, so the ultrasonic wave only acts on the freezing process, but has a small effect on the primary drying and the secondary drying which take a long time, and the utilization of the ultrasonic wave is relatively primary.
Disclosure of Invention
Aiming at the problem of low effect of ultrasonic waves in the freeze drying technology in the prior art, the invention aims to provide an ultrasonic-assisted freeze drying method.
In order to achieve the purpose, the technical scheme of the invention is as follows:
an ultrasonic-assisted freeze-drying method, comprising the steps of:
freezing:
s1, placing a sheet-shaped material to be frozen on a temperature control plate in a vacuum tank;
s2, cooling the temperature control plate through a refrigerating system, and applying first ultrasonic waves to the flaky material to be frozen through an ultrasonic vibrator in the cooling process;
s3, detecting whether the temperature of the flaky material to be frozen is reduced to a first preset temperature, if so, stopping the step S2 and entering S4, otherwise, continuing to the step S2;
primary drying:
s4, vacuumizing the vacuum tank through a vacuum system, and reducing the pressure of the vacuum tank to a preset pressure;
s5, applying second ultrasonic waves to the flaky material to be frozen through an ultrasonic vibrator;
s6, after the first preset time, closing the vacuum tank and detecting whether the pressure rising rate of the vacuum tank is lower than a first pressure rising rate, if so, stopping primary drying and entering S7, otherwise, continuing S5;
secondary drying:
s7, heating the temperature control plate through a heating system, and preserving heat of the temperature control plate after the temperature of the temperature control plate reaches a second preset temperature;
s8, in the heating and heat preservation processes, applying third ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrator;
and S9, after a second preset time, closing the vacuum tank and detecting whether the pressure rising rate of the vacuum tank is lower than a second pressure rising rate, if so, stopping secondary drying, and otherwise, continuing S8.
Preferably, in S3, the temperature of the flaky material to be frozen is detected by an infrared thermometer, and the temperature at the center of the flaky material to be frozen is used as a judgment basis.
Preferably, in S3, the eutectic point temperature of the flake-shaped material to be frozen is obtained by the following steps:
putting the flaky material to be frozen into a differential scanning calorimeter, cooling at the cooling rate of 10 ℃/min, cooling from 25 ℃ to-70 ℃, and measuring to obtain the eutectic point temperature;
and on the basis of the measured eutectic point temperature, reducing the temperature by 5 ℃ to be used as the first preset temperature in the S3.
Preferably, in S4, the preset pressure is 5-20Pa; in S7, the second preset temperature is 40 ℃.
Preferably, in S1, the thickness of the sheet-like material to be frozen is 5mm to 10mm.
Preferably, in S2, the first ultrasonic wave is released in the form of a pause of 5min per 1S of operation.
Preferably, in S5, the second ultrasonic wave is released in the form of 3min intervals per 5S of operation.
Preferably, in S8, the third ultrasonic wave is released in the form of an interval of 1min per 5S of operation.
Preferably, in S6, the first preset time is 1 to 4 hours, and the pressure rising rate of the vacuum tank is closed and detected every 1min, and the first pressure rising rate is 5Pa/min.
Preferably, in S9, the second preset time is 2 to 5 hours, and the pressure rising rate of the vacuum tank is closed and detected every 10 minutes, and the second pressure rising rate is 10Pa/min.
Preferably, in S9, when it is detected that the pressure rising rate of the vacuum tank is lower than the second pressure rising rate, the secondary drying is continued for 1 hour.
Preferably, the method further comprises: and S10, closing the vacuum system and the heating system, taking out the dried flaky material to be frozen from the vacuum tank, and then carrying out vacuum sealing packaging.
By adopting the technical scheme, the invention has the beneficial effects that: all use the ultrasonic wave to process the material through freezing, primary drying, secondary drying stage for: in the freezing stage, the ultrasonic waves can effectively promote the formation of intercellular ice crystals, and meanwhile, the heat conductivity coefficient and the heat transfer effect are improved under the action of the ultrasonic waves; in the primary drying stage, the used ultrasonic power is enhanced, the heat transfer effect is improved, and energy is provided, so that water molecules obtain sublimation kinetic energy, and the primary drying speed is accelerated; in the secondary drying stage, the ultrasonic wave is used for improving the heat transfer effect and providing energy simultaneously, so that the crystal water can overflow by energy. Thereby greatly saving the time for freeze drying and improving the appearance and structure perfectness of the product.
Drawings
FIG. 1 is a flowchart of a method according to a first embodiment of the present invention;
FIG. 2 is a graph showing the comparison of the time period when the method of the first embodiment of the present invention is compared with vacuum freeze-drying;
FIG. 3 is a graph comparing the dry matter content and the porosity of the product obtained by the method of the first embodiment of the present invention with those obtained by hot air drying and vacuum freeze-drying;
FIG. 4 is a texture comparison graph of a slice of bunge auriculate root obtained by comparing the method of the first embodiment of the invention with hot air drying and vacuum freeze drying;
FIG. 5 is a graph showing the contrast of brightness of sliced Cynanchum bungei when compared with hot air drying and vacuum freeze drying according to the first embodiment of the present invention;
FIG. 6 is a flowchart of a method according to a third embodiment of the present invention;
FIG. 7 is a schematic structural view of the present invention;
FIG. 8 is a front view of the present invention;
FIG. 9 is a top view of the present invention;
fig. 10 isbase:Sub>A sectional view taken along linebase:Sub>A-base:Sub>A of fig. 9.
In the figure, 1-a vacuum tank, 2-a cover, 3-a temperature control plate, 4-a vacuum pump, 5-a vacuum valve, 6-a pressure detection device, 7-an ultrasonic vibrator, 8-a semiconductor refrigeration module, 9-an infrared thermometer, 10-a heat insulation layer, 11-a pipeline and 12-a support conduit.
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
It should be noted that in the description of the present invention, the terms "upper", "lower", "left", "right", "front", "rear", and the like indicate orientations or positional relationships based on structures shown in the drawings, and are only used for convenience in describing the present invention, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
In the technical scheme, the terms "first" and "second" are only used for referring to the same or similar structures or corresponding structures with similar functions, and are not used for ranking the importance of the structures, or comparing the sizes or other meanings.
In addition, unless expressly stated or limited otherwise, the terms "mounted" and "connected" are to be construed broadly, e.g., the connection may be a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; the two structures can be directly connected or indirectly connected through an intermediate medium, and the two structures can be communicated with each other. To those skilled in the art, the specific meanings of the above terms in the present invention can be understood in light of the present general concepts, in connection with the specific context of the scheme.
Example one
An ultrasonic-assisted freeze drying method comprises three stages of freezing, primary drying and secondary drying, as shown in figure 1, and comprises the following specific steps:
freezing:
s1, placing the flaky material to be frozen on a temperature control plate in a vacuum tank.
In this embodiment, taking freeze drying of cynanchum bungei as an example, cynanchum bungei is cut into slices with a thickness of 5mm to 10mm, preferably 8mm, and the slices are uniformly distributed in the middle of the surface of the temperature control plate, so that the cut cynanchum bungei slices (i.e. the slices of the material to be frozen) are in good contact with the surface of the temperature control plate. Of course, in other embodiments, other types of herbs or food products may be used, such as ginseng, panax notoginseng, shiitake mushroom, strawberry, matsutake mushroom, truffle, and pharmaceutical products that require lyophilization.
S2, cooling the temperature control plate through the refrigerating system, and applying first ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrator in the cooling process.
In this embodiment, the refrigeration system is configured as a semiconductor refrigeration module, which applies cold to the thermal control plate through its cold end and its hot end faces the outside of the vacuum tank. The ultrasonic vibrators are configured with a plurality of, for example, four, and the four ultrasonic vibrators are uniformly installed around the central circumference of the thermal control plate so as to uniformly apply ultrasonic waves to the cut bunge auriculate root, and under the control of the ultrasonic generator, the four ultrasonic vibrators are usually operated at the same time, and the generated first ultrasonic waves are released in a form of 5min pause per 1s of operation.
And S3, detecting whether the temperature of the flaky material to be frozen is reduced to a first preset temperature, if so, stopping the step S2 and entering S4, otherwise, continuing the step S2.
In this embodiment, the temperature of the bunge auriculate root slices (the flaky materials to be frozen) is detected by an infrared thermometer installed in the vacuum tank, and the temperature at the center of the bunge auriculate root slices (the flaky materials to be frozen) is used as the real temperature thereof, and the judgment of S3 is sequentially performed.
And, the first preset temperature of the radix cynanchi bungei slices (the flaky materials to be frozen) is obtained by the following steps:
putting the flaky material to be frozen into a differential scanning calorimeter, cooling at the cooling rate of 10 ℃/min, cooling from 25 ℃ to-70 ℃, and measuring to obtain the eutectic point temperature; and on the basis of the measured eutectic point temperature, reducing the temperature by 5 ℃ to be used as the first preset temperature in the S3. For example, the measured eutectic point temperature of bunge auriculate root is-13.5 ℃, in this embodiment, the eutectic point temperature is decreased by 5 ℃ on the basis of the measured eutectic point temperature, and-18.5 ℃ is taken as the actual eutectic point temperature (i.e. the first preset temperature), and the temperature at the center of the bunge auriculate root slice (the flaky material to be frozen) is compared with the actual eutectic point temperature.
The ultrasonic wave at the stage can effectively promote the formation of intercellular ice crystals in the cut bunge auriculate root, so that more water is frozen into the ice crystals at the stage, and the ice crystals are conveniently removed in the next drying; meanwhile, the intervention of ultrasonic waves can also improve the heat conductivity coefficient, namely the contact effect between tissues is improved through a vibration mode, so that the heat conduction effect is improved, and the cold quantity is transmitted between the tissues faster and better.
Primary drying:
and S4, vacuumizing the vacuum tank through a vacuum system, and reducing the pressure of the vacuum tank to a preset pressure.
In the present embodiment, the vacuum system is configured as a system including a vacuum pump, a vacuum valve, a pressure detection device, and necessary piping. Carry out the evacuation operation to the vacuum tank through the vacuum pump to maintain the inside vacuum degree of vacuum tank, and can conveniently carry out evacuation control in a flexible way through the vacuum valve, then can accurately observe the inside vacuum degree of vacuum tank through pressure measurement. And the preset pressure is specifically configured to be 5-20Pa, and the pressure of the vacuum tank is normally maintained at a level of 10 Pa.
And S5, applying second ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrator.
After the pressure in the vacuum tank reaches the above-mentioned preset pressure, the ultrasonic vibrators arranged in the vacuum tank are normally operated simultaneously under the control of the ultrasonic generator, and the generated second ultrasonic waves are released in the form of 3min intervals per 5s of operation, and the ultrasonic power is normally maintained at a level of 100W.
So set up, through the ultrasonic wave that uses higher power in a drying process to can effectively promote the heat transfer effect between the tissue, the ultrasonic wave can also provide the sound wave energy simultaneously, makes the hydrone acquire sublimed kinetic energy, thereby accelerates a dry speed.
And S6, after the first preset time, closing the vacuum tank and detecting whether the pressure rising rate of the vacuum tank is lower than the first pressure rising rate, if so, stopping drying once and entering S7, otherwise, continuing S5.
The first preset time is generally configured to be 1-4h, the specific time duration is determined according to the thickness of the slice (the slice-shaped material to be frozen) of radix cynanchi bungei, and the larger the thickness is, the longer the first preset time is, that is, the longer the vacuum maintaining time and the time for the second ultrasonic intervention are, for example, in this embodiment, the first preset time is configured to be 1h. In addition, in the present embodiment, the vacuum tank is closed by closing the vacuum valve, and the pressure increase rate of the vacuum tank is detected once every 1min, and the first pressure increase rate is set to 5Pa/min.
Secondary drying:
and S7, heating the temperature control plate through the heating system, and preserving heat of the temperature control plate after the temperature of the temperature control plate reaches a second preset temperature.
In this embodiment, the temperature control plate is heated by changing the current direction or changing the direction of the semiconductor refrigeration module, the second preset temperature is set to be 40 ℃, and the temperature detection is still obtained by the detection of the infrared thermometer.
And S8, in the heating and heat preservation processes, applying third ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrator.
In the present embodiment, the ultrasonic vibrators disposed in the vacuum tank are normally operated simultaneously under the control of the ultrasonic generator, the generated third ultrasonic waves are released in the form of 1min pause per 5s of operation, and the ultrasonic power is maintained at a level of 100W.
So set up, through the ultrasonic wave that uses higher power in the secondary drying process, can effectively promote the heat transfer effect between the tissue, the ultrasonic wave still is used for providing the sound wave energy simultaneously for the crystal water is more high-efficient to gain the energy and is spilled over.
And S9, after a second preset time, closing the vacuum tank and detecting whether the pressure rising rate of the vacuum tank is lower than a second pressure rising rate, if so, stopping secondary drying, and otherwise, continuing S8.
The second preset time is generally configured to be 2-5h, the specific time duration is determined according to the thickness of the slice (the sheet-shaped material to be frozen) of radix cynanchi bungei, the larger the thickness is, the longer the second preset time is, that is, the heating time and the time for the intervention of the third ultrasonic wave are longer, for example, in this embodiment, the second preset time is configured to be 2h. In addition, in the present embodiment, the vacuum tank is sealed by turning off the vacuum pump, and the pressure increase rate of the vacuum tank is detected once every 10min, and the second pressure increase rate is set to 10Pa/min.
And finishing the ultrasonic-assisted freeze drying process to obtain the bunge auriculate root slices with low water content and high quality.
As shown in fig. 2, a schematic time-consuming diagram of vacuum freeze-drying and ultrasound-assisted freeze-drying of the present example at various stages is shown. It can be seen that: the freezing stage, which takes 68min in this example, and 143.3min for vacuum freeze-drying; a primary drying stage, which takes 273min in this example and 623min for vacuum freeze drying; a secondary drying stage, which takes 116min for the present example and 253min for vacuum freeze drying; for the whole drying process, 458min is used in the embodiment, 1020min is used in the vacuum freeze-drying time, and only 44.9% of the vacuum freeze-drying time is used in the embodiment.
As shown in fig. 3, it shows a schematic diagram of the difference between the dry matter content and the porosity of the three ways of ultrasound-assisted freeze-drying, vacuum freeze-drying and hot air drying in this example. It can be seen that there is no significant difference in dry matter content between the present embodiment, vacuum freeze drying and hot air drying, which indicates that all three drying methods can sufficiently dry, but the differences in porosity of the three drying methods are significant, which is caused by the expansion of pores and the fragmentation of materials during the drying process of hot air drying, and the quality is reduced.
As shown in fig. 4, it shows the difference between the core weight and the outer skin weight of the cut bunge auriculate root in the three ways of ultrasound-assisted freeze drying, vacuum freeze drying and hot air drying of the embodiment. It can be seen that the drying method of the present embodiment is significantly better than the other two drying methods, both in terms of the weight of the core part and the weight of the outer skin layer of the sliced bunge auriculate root.
In addition, the puncture hardness of the core part and the outer cortex of the bunge auriculate root slices obtained by three drying modes is respectively measured by a texture analyzer, and then the results are found: the air drying result can cause the bunge auriculate root section to become hard, which is caused by fiber coking in the dehydration process, and the vacuum freeze drying and the ultrasonic auxiliary drying of the embodiment can reduce the tissue hardness, thereby realizing better protection on the structure, being beneficial to the drug effect leaching of Chinese herbal medicines, and the ultrasonic auxiliary freeze drying of the embodiment can obtain the bunge auriculate root section with better toughness.
As shown in fig. 5, it shows the brightness of three different drying modes of the ultrasonic-assisted freeze drying, vacuum freeze drying and hot air drying according to the present embodiment measured by a full-automatic color difference meter. Therefore, the brightness of the white fleece-flower root slices dried by hot air is 72.28; the brightness of the cut radix cynanchi bungei after vacuum freeze drying is 91.67; the brightness of the bunge auriculate root slices subjected to ultrasonic-assisted freeze drying is 93.10; the above luminance data are the average values of three different treatments. The results show that hot air drying causes the brightness of the cut radix cynanchi bungei to decrease, and vacuum freeze drying and ultrasonic-assisted freeze drying of the embodiment both increase the brightness of the cut radix cynanchi bungei. The adverse reactions such as oxidation and the like are generated by hot air drying, the influence of vacuum freeze drying is small, and the ultrasonic-assisted freeze drying of the embodiment has the advantage that the quality is superior to that of the two modes due to short time.
Example two
The difference from the first embodiment is that: in S9, when it is detected that the pressure increase rate of the vacuum tank is lower than the second pressure increase rate, the secondary drying is continued for 1h, that is, the steps of S7 and S8 are continued for 1h.
EXAMPLE III
The difference from the first or second embodiment is that: as shown in fig. 6, the method further includes S10.
And S10, closing the vacuum system and the heating system, taking out the dried flaky material to be frozen from the vacuum tank, and then carrying out vacuum sealing packaging.
Example four
An ultrasonic-assisted freeze drying apparatus for carrying out the method of any of the above embodiments, as shown in fig. 7-10, comprises a vacuum tank 1, a cover 2, a temperature control plate 3, a vacuum pump 4, a vacuum valve 5, a pressure detection device 6, an ultrasonic vibrator 7, a semiconductor refrigeration module 8, an infrared thermometer 9 and a heat insulation layer 10.
Wherein, the whole cylindrical structure that is of vacuum tank 1, this vacuum tank 1 specifically include jar body and can dismantle fixed connection at the lid 2 of the top of the jar body, and the top of the jar body is opened promptly, seals the jar body through lid 2. Correspondingly, the outer side walls of the tank body and the cover 2 are respectively coated with a heat insulation layer made of heat insulation materials. Wherein, the inside fixed mounting of vacuum tank 1 has the temperature control board 3 that is used for bearing the weight of the material. In this embodiment, an opening adapted to the temperature control plate 3 is specifically formed at the bottom of the tank body, and the temperature control plate 3 is fixedly installed in the opening. The thermal control plate 3 is configured as a rigid plate-like structure made of a heat conductive material, such as a stainless steel plate, and is preferably configured in a circular shape.
The vacuum pump 4 is arranged outside the vacuum tank 1, the suction end of the vacuum pump is connected with the tank body side wall of the vacuum tank 1 through a pipeline 11, and a vacuum valve 5 and a pressure detection device 6 are further installed on the pipeline 11, wherein the pressure detection device 6 is preferably configured as a pressure gauge, or in other embodiments, can also be configured as a digital display pressure gauge. The vacuum pump 4 is used for vacuumizing the vacuum tank 1, so that the vacuum degree in the vacuum tank 1 is maintained, the vacuum valve 5 can be used for vacuumizing control conveniently and flexibly, and the pressure detection device 6 can be used for accurately observing the vacuum degree in the vacuum tank 1.
A plurality of, for example, four ultrasonic transducers 7 are arranged, and all the ultrasonic transducers 7 are fixedly attached to the inside of the vacuum tank 1 or to the outside of the vacuum tank. In addition, a plurality of overtime wave vibrators are evenly arranged circumferentially around the center of the thermal control plate 3. In this embodiment, each ultrasonic vibrator 7 is respectively fixedly mounted at the peripheral edge of the temperature control plate 3, so as to apply ultrasonic waves to the material borne on the temperature control plate 3 better.
The ultrasonic generator (not shown in the figure) is arranged outside the vacuum tank 1, and the ultrasonic generator is electrically connected with each ultrasonic vibrator 7 through a lead so as to control the ultrasonic vibrators 7 to emit ultrasonic waves with suitable frequency.
The semiconductor refrigeration module 8 is fixedly installed at the bottom of the vacuum tank 1, and the semiconductor refrigeration module 8 is connected with the temperature control plate 3, so that cold and heat are released to the temperature control plate 3, and the purpose of controlling the temperature of the temperature control plate 3 is achieved. In this embodiment, the semiconductor refrigeration module 8 is fixedly installed on one side of the bottom surface of the temperature control board 3, and an insulation layer 10, for example, an insulation layer 10 made of polyurethane foam material, is additionally laid on one side of the bottom surface of the temperature control board 3. The semiconductor cooling module 8 operates by receiving current and switches a cooling mode and a heating mode according to a change in the direction of the current.
The infrared thermometer 9 is fixedly installed in the vacuum tank 1, and the infrared thermometer 9 is used for detecting the temperature of the temperature control plate 3 and the materials borne by the temperature control plate. In this embodiment, the infrared thermometer 9 is disposed at a position directly above the center of the thermal control plate 3, for example, the infrared thermometer 9 is fixedly connected to the sidewall of the vacuum tank 1 through a support pipe 12, the support pipe 12 penetrates through the sidewall of the vacuum tank 1, and a cable for connecting with the infrared thermometer 9 is threaded through the support pipe 12.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made in the embodiments without departing from the principles and spirit of the invention, and these embodiments are still within the scope of the invention.
Claims (12)
1. An ultrasonic-assisted freeze drying method is characterized in that: the method comprises the following steps:
freezing:
s1, placing a flaky material to be frozen on a temperature control plate in a vacuum tank;
s2, cooling the temperature control plate through a refrigerating system, and applying first ultrasonic waves to the flaky material to be frozen through an ultrasonic vibrator in the cooling process;
s3, detecting whether the temperature of the flaky material to be frozen is reduced to a first preset temperature, if so, stopping the step S2 and entering S4, otherwise, continuing to the step S2;
primary drying:
s4, vacuumizing the vacuum tank through a vacuum system, and reducing the pressure of the vacuum tank to a preset pressure;
s5, applying second ultrasonic waves to the flaky material to be frozen through an ultrasonic vibrator;
s6, after the first preset time, closing the vacuum tank and detecting whether the pressure rising rate of the vacuum tank is lower than a first pressure rising rate, if so, stopping primary drying and entering S7, otherwise, continuing S5;
secondary drying:
s7, heating the temperature control plate through a heating system, and preserving heat of the temperature control plate after the temperature of the temperature control plate reaches a second preset temperature;
s8, in the heating and heat preservation processes, applying third ultrasonic waves to the flaky material to be frozen through the ultrasonic vibrator;
and S9, after a second preset time, closing the vacuum tank and detecting whether the pressure rising rate of the vacuum tank is lower than a second pressure rising rate, if so, stopping secondary drying, and otherwise, continuing S8.
2. The method of claim 1, wherein: in S3, the temperature of the flaky material to be frozen is detected by an infrared thermometer, and the temperature of the center of the flaky material to be frozen is used as a judgment basis.
3. The method of claim 2, wherein: in S3, the eutectic point temperature of the flaky material to be frozen is obtained through the following steps:
putting the flaky material to be frozen into a differential scanning calorimeter, cooling at the cooling rate of 10 ℃/min, cooling from 25 ℃ to-70 ℃, and measuring to obtain the eutectic point temperature;
and on the basis of the measured eutectic point temperature, reducing the temperature by 5 ℃ to be used as the first preset temperature in the S3.
4. The method of claim 1, wherein: in S4, the preset pressure is 5-20Pa; in S7, the second preset temperature is 40 ℃.
5. The method of claim 1, wherein: in S1, the thickness of the flaky material to be frozen is 5mm-10mm.
6. The method of claim 1, wherein: in S2, the first ultrasonic wave is released in the form of a pause of 5min per 1S of operation.
7. The method of claim 1, wherein: in S5, the second ultrasonic wave is released in the form of a pause of 3min per 5S of operation.
8. The method of claim 1, wherein: in S8, the third ultrasonic wave is released in the form of an interval of 1min per 5S of operation.
9. The method of claim 1, wherein: in S6, the first preset time is 1-4h, the vacuum tank is closed every 1min, the pressure rising rate of the vacuum tank is detected, and the first pressure rising rate is 5Pa/min.
10. The method of claim 1, wherein: in S9, the second preset time is 2-5h, the pressure rising rate of the vacuum tank is closed and detected every 10min, and the second pressure rising rate is 10Pa/min.
11. The method of claim 1, wherein: in S9, when it is detected that the pressure rising rate of the vacuum tank is lower than the second pressure rising rate, the secondary drying is continued for 1 hour.
12. The method of claim 1, wherein: the method further comprises the following steps:
and S10, closing the vacuum system and the heating system, taking out the dried flaky material to be frozen from the vacuum tank, and then carrying out vacuum sealing packaging.
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| CN115574547B (en) | 2023-12-01 |
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