JP2016148481A - Vacuum dryer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten drying time of an object to be dried in vacuum drying.SOLUTION: A vacuum dryer includes: a heating part; a container; determination means; and an atmospheric pressure adjustment part. The heating part heats an object to be dried in a container. The determination means determines whether or not water in the center part of the object to be dried has become a not-boiling state from a boiling state. The atmospheric pressure adjustment part adjusts the atmospheric pressure in the container. The atmospheric pressure adjustment part repeats making the atmospheric pressure in the container a first pressure which is lower than the atmospheric pressure, and making the atmospheric pressure in the container a second pressure which is higher than the first pressure, when the determination means has determined that the water in the object to be dried has become the not-boiling state from the boiling state.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a vacuum drying apparatus that performs drying of an object to be dried in a vacuum.

  When making dried fruits and dried vegetables easily at home, household dry food manufacturers (warm air convection type) and sun drying are used. Drying is an operation of evaporating water by applying heat energy to a wet material to be dried. In order to increase the drying speed, it is important to efficiently transmit heat energy to the object to be dried and efficiently dissipate moisture in the object to be dried. The higher the temperature of the material to be dried and the lower the water vapor partial pressure of the atmosphere around the material to be dried, the faster the drying speed. However, in order to produce delicious dried fruits and dried vegetables, it is desirable to heat at the lowest possible temperature (70 ° C or lower) from the viewpoint of maintaining the food organization and nutrition. For this reason, it is not necessary to simply increase the temperature in order to increase the drying speed. Furthermore, in order to eliminate drying unevenness, it is not necessary to simply increase the amount of drying air.

  There are a method of applying hot air, a method of irradiating infrared or high-frequency electromagnetic waves, etc., to heating an object to be dried in an existing dry food manufacturer. In hot air convection drying, the drying speed of the surface is extremely higher than the water transfer speed from the inside to the surface of the object to be dried. Thus, there is a disadvantage that the time required for drying is limited by the rate of water movement and requires a long time.

  Moreover, electromagnetic wave irradiation drying has the fault that the water inside a to-be-dried material is instantaneously heated to 100 degreeC, and a nutrient is destroyed.

  Therefore, by performing vacuum heating drying, the water inside the object to be dried is boiled at a low temperature (about 40 to 70 ° C.) and driven to the outside, and the object to be dried can be dried in a short time.

WO 01/095682 pamphlet JP 2011-242021 A

  Since water boils, it takes a large amount of heat energy (latent heat of evaporation) from the material to be dried. Since heat energy is deprived from the object to be dried, in order to maintain boiling inside the object to be dried, it is necessary to continue to give the object to be dried thermal energy equivalent to latent heat of evaporation. However, it is difficult to maintain the temperature of the material to be dried including water at the boiling point or higher. Since it is difficult to maintain the temperature of the object to be dried including water at the boiling point or higher, it is difficult to further shorten the drying time of the object to be dried.

  An object of the present invention is to provide a vacuum drying apparatus capable of further shortening the drying time of an object to be dried in vacuum drying.

  According to the embodiment, the heating unit, the container, the determination unit, and the atmospheric pressure adjustment unit are provided. The heating unit heats an object to be dried in the container. The determination means determines whether or not the state in which the moisture at the center of the object to be dried has boiled has changed. The atmospheric pressure adjustment unit adjusts the atmospheric pressure in the container. The atmospheric pressure adjustment unit determines that the atmospheric pressure in the container is set to a first pressure lower than atmospheric pressure, and the determination means determines that the moisture in the object to be dried has changed from a boiling state to a non-boiling state. In this case, the air pressure in the container is changed to a second pressure higher than the first pressure.

The figure which shows an example of a structure of the vacuum dryer of embodiment. The figure which shows the relationship between temperature and the vapor pressure of water. The figure which shows the relationship between time and the temperature of the center part of to-be-dried material, the relationship between time and the atmospheric pressure in a container, the relationship between time and the temperature of a plate, and the relationship between time and the temperature in a container. The figure which shows the boiling state of the water | moisture content inside a to-be-dried object. The flowchart which shows an example of the procedure of the process at the time of the vacuum drying by a comprehensive control part. The figure which shows the temperature inside the to-be-dried object with respect to the drying time at the time of actually performing vacuum drying, and the atmospheric | air pressure in a container. The figure which shows an example of a structure of the vacuum-drying apparatus of a modification.

  Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a diagram illustrating a configuration of the vacuum drying apparatus 100.
The vacuum drying apparatus 100 includes a container 101, an atmospheric pressure adjustment unit 110, a heating unit 120, a determination unit 130, an in-container temperature measurement unit 140, and a general control unit 150.

  The container 101 has a strength that does not break even when the pressure in the container 101 is lower than the atmospheric pressure.

  The atmospheric pressure adjustment unit 110 controls the atmospheric pressure in the container 101. The atmospheric pressure adjustment unit 110 includes a vacuum pump 111, a purge nozzle 112, a vacuum gauge 113, and an atmospheric pressure control unit 114. The vacuum pump 111 is connected to the container 101. The vacuum pump 111 discharges the gas in the container 101. The atmospheric pressure control unit 114 can make the atmospheric pressure in the container 101 substantially constant by operating the vacuum pump 111 or stopping the vacuum pump 111 according to the measurement value of the vacuum gauge 113. . In addition, after the vacuum pump 111 is stopped, the atmospheric pressure control unit 114 opens the electromagnetic valve 112 </ b> A provided in the purge nozzle 112 and introduces outside air into the container 101, thereby reducing the atmospheric pressure in the container 101. It is possible to raise.

  The opening 112 </ b> O of the purge nozzle 112 in the container 101 is not provided at a position directly facing the object to be dried 200. If the opening 112O is provided at a position directly opposite to the object to be dried 200, outside air is blown onto the object to be dried 200 in a pressurizing step described later, and the temperature of the object to be dried 200 is lowered. In order to suppress a decrease in the temperature of the object to be dried 200 during the pressurizing step, the opening 112O is not provided at a position directly facing the object to be dried 200.

  The heating unit 120 includes a plate 121, a heater 121A such as a heating wire, a plate temperature measuring unit 122, and a heating control unit 123. The plate 121 is provided in the container 101. The heater 121A is, for example, a heating wire. The heater 121 </ b> A is provided in the plate 121. When power is supplied to the heater 121A, the heater 121A generates heat. The plate 121 is heated by heat conduction of the heat of the heater 121A. An object to be dried 200 placed on the upper surface of the plate 121 is heated by the heated plate 121. The plate temperature measurement unit 122 measures the temperature of the plate 121. The heating control unit 123 adjusts the power supplied to the heater in the plate 121 so that the temperature of the plate 121 becomes a set temperature according to the temperature measured by the plate temperature measuring unit 122.

  The determination unit 130 monitors whether the center of the object to be dried 200 is boiling. Whether the determination unit 130 is boiling at the center of the object to be dried 200 according to the temperature of the plate 121 measured by the temperature measurement unit 122 or the temperature in the container 101 measured by the temperature measurement unit 140 in the container. Determine.

  After the boiling of the moisture in the object to be dried 200, the time when the boiling of the water at the center of the object to be dried 200 stops is a time when the temperature in the plate 121 or the container 101 shifts from a decreasing state to a rising state. is there.

  The general control unit 150 controls the heating unit 120 and the atmospheric pressure adjustment unit 110 to perform vacuum drying of the object to be dried. The general control unit 150 controls the heating unit 120 and the atmospheric pressure adjustment unit 110 according to the temperature of the plate 121 and / or the temperature in the container 101, the atmospheric pressure measured by the vacuum gauge, and the determination result by the determination unit 130. To do.

  At the time of vacuum drying, the general control unit 150 requests the atmospheric pressure adjustment unit 110 to reduce the atmospheric pressure in the container 101 or requests to increase the atmospheric pressure in the container 101. Further, at the time of vacuum drying, the general control unit 150 requests the heating unit 120 to start heating.

  When the general control unit 150 requests the atmospheric pressure adjustment unit 110 to reduce the pressure, the atmospheric pressure control unit 114 controls the operation of the vacuum pump 111 so that the atmospheric pressure in the container 101 becomes 0.2 atmospheric pressure. When the general control unit 150 requests the atmospheric pressure adjustment unit 110 to pressurize, the atmospheric pressure control unit 114 stops the vacuum pump 111 and then opens the electromagnetic valve 112A. When the general control unit 150 requests the heating unit 120 to heat, the heating control unit 123 controls the amount of power supplied to the heater 121A so that the temperature of the plate becomes 70 ° C. The boiling point when the atmospheric pressure is 0.2 atmospheric pressure (202.65 hPa) is 60 ° C.

  FIG. 2 is a diagram illustrating the relationship between temperature and water vapor pressure. A curve 301 shown in FIG. 2 is a water vapor pressure curve. The vapor pressure curve shows the boiling point with respect to atmospheric pressure. As shown in FIG. 2, when the atmospheric pressure decreases, the boiling point also decreases. This apparatus uses this phenomenon to dry the object to be dried 200 in a vacuum environment. Note that if the atmospheric pressure is lowered, it is possible to boil the moisture in the material to be dried even at room temperature without heating the material to be dried. It takes time to lower the pressure to boiling at room temperature, and the cost of the vacuum pump 111 increases. In this apparatus, in order to shorten the drying time and reduce the cost of the vacuum pump 111, the object to be dried is heated in a vacuum environment at a relatively high atmospheric pressure. Note that the object to be dried may be dried in a vacuum environment without heating the object to be dried.

  An example of the vacuum drying procedure in the present embodiment will be described with reference to FIGS. FIG. 3 shows the relationship between the time and the temperature of the center of the object to be dried 200, the relationship between the time and the atmospheric pressure in the container 101, the relationship between the time and the temperature of the plate 121, and the temperature and the temperature in the container 101. FIG. FIG. 4 is a diagram illustrating a boiling state of moisture inside the object to be dried 200.

  A curve 401 in FIG. 3 indicates the temperature of the plate 121. A curve 402 in FIG. 3 shows the estimated temperature at the center of the object to be dried 200. A curve 403 in FIG. 3 shows the atmospheric pressure in the container 101. A curve 404 in FIG. 3 shows the temperature in the container 101. In addition, the temperature of the center part of the to-be-dried object 200 was measured by inserting a thermocouple in the center part of the to-be-dried object 200.

  The drying process begins with a preheating process. In the drying process after the preheating process, four processes including a pressure reducing process, a vacuum boiling process, a non-boiling process, and a pressurizing process are repeated in order. Hereinafter, the first pressure is 0.2 atm, and the second pressure is 0.4 atm or more. However, the present invention is not limited to this.

  The preheating step is a step of heating the temperature of the central portion of the object to be dried 200 to a temperature higher than 60 ° C. which is the boiling point at 0.2 atm (202.65 hPa). At the time t0 after the temperature of the center part of the to-be-dried object 200 becomes higher than 60 degreeC, a drying process transfers to a pressure reduction process from a preheating process. In the decompression step, the discharge of the gas in the container 101 is started. During the decompression step, as shown in state A in FIG. 4, the moisture in the object to be dried 200 is not boiling.

  When the atmospheric pressure in the container 101 reaches the atmospheric pressure (0.2 atmospheric pressure (202.65 hPa)) corresponding to the temperature (60 ° C.) shown in the water vapor pressure curve shown in FIG. Shifts from the decompression step to the vacuum boiling step. In the vacuum boiling process, the operation of the vacuum pump 111 is controlled so that the atmospheric pressure in the container 101 is maintained at the set atmospheric pressure. By maintaining the atmospheric pressure in the container 101 at the set atmospheric pressure (0.2 atmospheric pressure (202.65 hPa)), as shown in the state B in FIG. 4, the entire moisture in the object to be dried 200 boils.

  Evaporation latent heat is deprived from the to-be-dried object 200 because the water | moisture content inside the to-be-dried object 200 evaporates with boiling. Since the latent heat of vaporization is deprived from the object to be dried 200, the temperature at the center of the object to be dried 200 decreases. When the temperature at the center of the object to be dried 200 becomes lower than 60 ° C. which is the boiling point in the case of 0.2 atm (202.65 hPa) at time t2, the drying process shifts from the vacuum boiling process to the non-boiling process. . In the non-boiling process, the water at the center of the object to be dried 200 does not boil because the temperature at the center of the object to be dried decreases. In the non-boiling process, as shown in state C in FIG. 4, the entire object to be dried 200 does not boil, and only the water in the portion in contact with the plate 121 of the object to be dried 200 boils. A shorter non-boiling process time is preferable. When shifting from the vacuum boiling process to the non-boiling process, as shown in FIG. 3, the temperature of the plate 121 shifts from a decreasing trend to an increasing trend, or the decreasing speed is reduced. When shifting from the vacuum boiling process to the non-boiling process, as shown in FIG. 3, the temperature in the container 101 shifts from a decreasing trend to an increasing trend, or the decreasing speed is reduced. Therefore, it is possible to detect whether the moisture in the object to be dried 200 has changed from a boiling state to a non-boiled state according to the temperature change of the plate 121 and / or the temperature change in the container 101. Is possible.

  At time t3 when a predetermined time has elapsed since the transition to the non-boiling process, the drying process shifts from the non-boiling process to the pressurization process. In the pressurizing step, the pressure in the container 101 is increased to a pressure at which boiling is not performed completely. In this pressurizing step, the latent heat of vaporization is not deprived from the object to be dried 200, so that the entire temperature of the object to be dried 200 rises. At time t4 after the temperature of the center portion of the object to be dried 200 becomes higher than a predetermined temperature, the drying process shifts from the pressurizing process to the depressurizing process.

  When the atmospheric pressure in the container 101 reaches atmospheric pressure (0.2 atm (202.65 hPa)) at time t5, the drying process shifts from the depressurization process to the vacuum boiling process.

  At time t6, when the temperature of the temperature of the center portion of the object to be dried 200 becomes lower than 60 ° C., the drying process shifts from the vacuum boiling process to the non-boiling process.

  Next, a processing procedure at the time of vacuum drying by the general control unit 150 will be described. FIG. 5 is a flowchart showing a processing procedure at the time of vacuum drying by the integrated control unit 150.

  First, the comprehensive control unit 150 holds the drying time of the object to be dried 200 set by the user (step B11).

  Next, the comprehensive control unit 150 requests the heating unit 120 to start heating (step B12). The heating control unit 123 controls the amount of power supplied to the heater 121A so that the temperature of the plate 121 is heated to the set temperature.

  The comprehensive control unit 150 requests the plate temperature measurement unit 122 to notify the temperature of the plate 121 (step B13). The plate temperature measurement unit 122 notifies the total control unit 150 of the temperature of the plate 121. The comprehensive control unit 150 determines whether the temperature of the plate 121 is higher than the set temperature (step B14). The set temperature here is, for example, 65 ° C. When it determines with the temperature of the plate 121 not being higher than preset temperature (No of step B14), the comprehensive control part 150 performs the process from step B13 sequentially after a fixed time.

  When it is determined that the temperature of the plate 121 is higher than the set temperature (Yes in Step B14), the overall control unit 150 determines whether the set time has elapsed since it was determined that the temperature of the plate 121 was higher than the set temperature ( Step B15). When it determines with setting time not having passed (No of step B15), the comprehensive control part 150 performs the process of step B15 again after predetermined time.

  When it is determined that the set time has elapsed (Yes in Step B15), the general control unit 150 requests the pressure adjustment unit 110 to reduce the pressure in the container 101 (Step B16). The air pressure control unit 114 operates the vacuum pump 111 after closing the electromagnetic valve 112 </ b> A in response to a request from the general control unit 150. The vacuum pump 111 discharges the gas in the container 101.

  The general control unit 150 requests the atmospheric pressure adjustment unit 110 to notify the atmospheric pressure in the container 101 (step B17). The atmospheric pressure control unit 114 of the atmospheric pressure adjustment unit 110 notifies the general control unit 150 of the atmospheric pressure measured by the vacuum gauge 113. The comprehensive control unit 150 determines whether the atmospheric pressure has reached the set atmospheric pressure (0.2 atmospheric pressure (202.65 hPa)) (step B18). When it is determined that the atmospheric pressure has not reached the set atmospheric pressure (No in Step B17), the overall control unit 150 sequentially executes the processes from Step B17 after a predetermined time.

  When it is determined that the atmospheric pressure has reached the set atmospheric pressure (Yes in Step B18), the overall control unit 150 notifies the determination unit 130 that the center of the object to be dried 200 is in a boiling state (Step B19). The comprehensive control unit 150 requests the determination unit 130 to notify the state of the central portion of the object to be dried 200 (step B20).

  The determination unit 130 notifies the determination unit 130 of the state of the central portion of the object to be dried 200 to the general control unit 150. In response to the notification from the determination unit 130, the general control unit 150 determines whether the center of the object to be dried 200 is in a boiling state (step B21).

  When it determines with the center part of the to-be-dried object 200 not being in a boiling state (No of step B21), the integrated control part 150 is the time from determining that a center part is not in a boiling state to the present (non-boiling time). Is determined whether the set standby time has been reached (step B22). If it is determined that the set standby time has not been reached (No at Step B22), the overall control unit 150 executes the process at Step B22 at regular intervals.

  If it is determined that the set standby time has been reached (Yes in step B22), the overall control unit 150 requests the atmospheric pressure adjustment unit 110 to perform a purge (step B25). The atmospheric pressure control unit 114 stops the operation of the vacuum pump 111. The atmospheric pressure control unit 114 opens the electromagnetic valve 112 </ b> A provided in the purge nozzle 112. By opening the electromagnetic valve 112A, the inside of the container 101 is purged by outside air. By purging the inside of the container 101, the pressure in the container 101 increases. Thereafter, the overall control unit 150 sequentially executes the processes from Step B13.

  When it determines with the center part of the to-be-dried material 200 being a boiling state (Yes of step B21), the comprehensive control part 150 determines whether the total time of a vacuum boiling process has exceeded setting drying time (step B24). . When it determines with the total time of a vacuum boiling process not exceeding setting drying time (No of step B24), the comprehensive control part 150 performs the process of step B24 after fixed time.

  When it is determined that the total time of the vacuum boiling process exceeds the set drying time (Yes in Step B24), the general control unit 150 requests the atmospheric pressure adjustment unit 110 to purge and requests the heating unit 120 to stop heating. (Step B24). Then, the atmospheric pressure control unit 114 of the atmospheric pressure adjustment unit 110 stops the vacuum pump 111 and then closes the electromagnetic valve 112A. The heating control unit 123 stops the supply of power to the heater 121A. With the above steps, the vacuum drying of the object to be dried 200 is completed.

FIG. 6 is a diagram showing the temperature inside the object to be dried and the atmospheric pressure in the container 101 with respect to the drying time when actual vacuum drying is performed.
In addition, based on the temperature in the plate 121 or the container 101, it is not detected that the water | moisture content of the center part of the to-be-dried object 200 changed from the boiling state to the non-boiling state, but the temperature of the center part of the to-be-dried object 200 is detected. May be detected, and based on the estimated temperature and the pressure in the container 101, it may be detected that the moisture in the center of the object to be dried 200 has changed from a boiling state to a non-boiling state.

  For example, the following method is used to estimate the temperature at the center of the object to be dried 200. First, the energy generated by the heater 121A is calculated based on the amount of power supplied to the heater 121A. Based on the temperature change of the plate 121, the amount of energy absorbed by the plate 121 is calculated. Further, the amount of energy absorbed by the atmosphere in the container 101 is calculated based on the temperature in the container 101. By solving the heat conduction equation based on the amount of energy absorbed by the atmosphere in the container 101, the overall weight of the object to be dried 200, the specific heat capacity of the object to be dried 200, and the thermal conductivity of the object to be dried 200 The temperature of the center part of the to-be-dried object 200 is estimated.

  The general control unit 150 notifies the determination unit 130 that the moisture inside the object to be dried 200 is boiling, but the determination unit 130 detects that the moisture inside the object to be dried 200 is boiling. Also good.

  A method for detecting that the moisture inside the object to be dried 200 is boiling will be described below. For example, the determination unit 130 detects that the moisture inside the object to be dried 200 is boiling based on the humidity change in the container 101. When boiling starts, the humidity in the container 101 increases. Further, for example, the determination unit 130 detects that the moisture inside the to-be-dried object 200 is boiling based on a change in the amount of heat due to the output of the heater 121A. Depending on the volume of the container, the time taken from the start of the drying process to the boiling of the moisture inside the object to be dried 200 may be defined first. In addition, the surface temperature of the object to be dried may be measured by an infrared temperature sensor, and the moisture inside the object to be dried 200 may be boiled when a predetermined time or more has elapsed. Alternatively, the heater 121A may be turned off at the start of decompression, and it may be detected that the moisture in the object to be dried 200 is boiling when the temperature becomes equal to or lower than the set temperature. Moreover, you may detect that the water | moisture content inside the to-be-dried material 200 is boiling according to the frequency of a bubble. Further, when the container 101 is made of glass, it may be detected that the moisture in the object to be dried 200 is boiling by detecting cloudiness of the glass. Moreover, you may detect that the water | moisture content inside the to-be-dried object 200 is boiling by detecting the sound in the container 101. FIG. In addition, for example, when a vibration sensor is provided on the plate 121 and the vibration sensor detects vibration, it may be detected that the moisture in the object to be dried 200 is boiling.

  Note that the user sets the drying time before performing the vacuum drying, but the user may not set the drying time. If almost no moisture is left inside the object to be dried 200, it will not boil even if the pressure is reduced, and the temperature of the object to be dried 200 will not drop. Therefore, when the temperature of the object to be dried 200 is detected and the temperature of the object to be dried 200 does not decrease even when the pressure is reduced, the vacuum drying may be terminated.

If the non-boiling process is long, the vacuum drying may be terminated.

  You may display which process is now so that a user can know whether it is a preheating process, a pressure reduction process, a vacuum boiling process, a non-boiling process, and a pressurization process.

  In addition, a plurality of plates 121 may be stacked in the container 101. When the degree of drying of the object to be dried 200 depends on the position, a guide may be provided on the plate 121 so that the degree of drying of the object to be dried 200 is uniform. You may detect the weight of to-be-dried material and display a dry degree according to a weight. In order to lengthen the vacuum boiling process, the contact area between the plate 121 and the object to be dried 200 may be increased.

  Further, instead of drying the object to be dried 200 by heat conduction from the heater 121A, the object to be dried 200 may be heated by dielectric heating using microwaves. FIG. 7 shows the configuration of a vacuum drying apparatus in the case where the object to be dried 200 is heated by dielectric heating using microwaves.

  As illustrated in FIG. 7, the vacuum drying apparatus 300 includes a heating unit 320 instead of the heating unit 120. The heating unit 320 includes a microwave generator 321, a waveguide 322, a heating control unit 323, and the like. The microwave generator 321 generates a microwave of 2.45 GHz, for example. The waveguide 322 introduces the microwave generated by the microwave generator 321 into the container 101. By irradiating the object to be dried 200 with the microwave introduced into the container 101, the object to be dried 200 is heated by induction heating. The heating control unit 323 controls the operation of the microwave generator 321 in response to a request from the general control unit 150. An equivalent effect can also be obtained by separately using a member (not shown) that generates heat by microwave irradiation and transferring the heat generated by this member to the object to be dried 200. This member contains a metal such as aluminum and is often used by being formed into a thin film. In general, some are commercially available as plates, sheets, pastes and the like for cooking grilled fish in a microwave oven.

  According to the present embodiment, the pressure in the container 101 is set to a first pressure lower than the atmospheric pressure, and the determination unit 130 is in a state where the moisture in the object to be dried 200 is not boiled from the state where it is boiled. After determining that the air pressure in the container 101 has increased, the pressure in the container 101 is set to a second pressure higher than the first pressure. When the pressure in the container is set to the second pressure and the entire moisture of the object to be dried does not boil, the heating unit 120 heats the object to be dried, so that the object to be dried stores thermal energy. With the thermal energy stored, the atmospheric pressure in the container 101 is set to the first pressure, whereby the water in the material to be dried 200 is boiled to increase the evaporation rate. As a result, it is possible to further shorten the drying time of the object to be dried in vacuum drying. In addition, since the time during which the entire moisture in the object to be dried 200 boils becomes longer, it is possible to create an object to be dried without unevenness. Furthermore, the effect of lowering the water vapor concentration in the container 101 can be obtained by temporarily taking outside air into the container 101 whose water vapor concentration has increased due to water evaporation in the material to be dried.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 100 ... Vacuum dryer, 101 ... Container, 110 ... Atmospheric pressure adjustment part, 120 ... Heating part, 130 ... Judgment part, 140 ... Temperature measuring part in a container, 150 ... General control part.

Claims (6)

A container,
A heating unit for heating the object to be dried in the container;
Determination means for determining whether the state of the water in the center of the object to be dried is not boiling from the state where it is boiling;
A pressure adjustment unit for adjusting the pressure in the container, wherein the pressure in the container is set to a first pressure lower than atmospheric pressure, and the determination means is in a state where water in the object to be dried is boiling. A vacuum drying apparatus comprising: an atmospheric pressure adjusting unit that repeatedly sets the atmospheric pressure in the container to a second pressure higher than the first pressure when it is determined that the liquid has not boiled. The heating unit is
A plate on which the material to be dried is placed on the upper surface;
The vacuum drying apparatus according to claim 1, further comprising a heater provided in the plate. The heating unit further includes a measurement unit for measuring the temperature of the plate,
3. The vacuum according to claim 2, wherein the determination unit determines whether the moisture in the center of the object to be dried in the container has changed from a boiling state to a non-boiled state according to the temperature of the plate. Drying equipment. Further comprising a measuring unit for measuring the temperature in the container,
2. The determination unit according to claim 1, wherein the determination unit determines whether or not a state in which moisture in a central portion of the object to be dried in the container has boiled has changed from a state in which the water in the container has not boiled according to a temperature in the container. Vacuum drying device. The atmospheric pressure adjusting unit has a nozzle for introducing gas outside the container into the container,
The vacuum drying apparatus according to claim 1, wherein an opening of the nozzle in the container is not provided at a position directly facing the object to be dried. Heating the material to be dried in the container;
When it is determined that the pressure in the container is set to a first pressure lower than atmospheric pressure and that the moisture in the object to be dried is not boiled, The vacuum drying method including repeating the atmospheric pressure to a second pressure higher than the first pressure.

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