JP7354799B2 - vacuum cooling device - Google Patents

Description

The present invention relates to a vacuum cooling device that cools food by reducing the pressure inside a processing tank.

Conventionally, a vacuum cooling device disclosed in Patent Document 1 below is known. In this device, as shown in Figure 3 of the document, the set pressure is the saturation pressure (17 hPa) at a temperature (15°C) lower by a set value (2°C) than the target food cooling temperature (17°C). After reducing the pressure in the processing tank to the set pressure, the set pressure is maintained for a first time (15 minutes). When the temperature detected by the product temperature sensor has not reached the cooling target temperature (17° C.) after the first time has elapsed, the set pressure is lowered by the equivalent of 1° C. and held for a second time (2 minutes). Thereafter, in the same way, if the temperature detected by the product temperature sensor has not reached the cooling target temperature (17°C) after the second time has elapsed, the set pressure is lowered by 1°C equivalent for the second time (2 minutes). By repeating this holding process, the food is cooled to the cooling target temperature. When the food reaches the cooling target temperature, cooling is finished and the pressure inside the processing tank is restored to atmospheric pressure.

However, since the product temperature sensor detects the temperature at a specific location in the food, even if the temperature detected by the product temperature sensor reaches the cooling target temperature, there may be temperature unevenness in the food. In order to prevent temperature unevenness, after the cooling process until the temperature detected by the product temperature sensor reaches the cooling target temperature, it is possible to perform a holding process to maintain the pressure inside the processing tank at that point, but There is a risk that such inconveniences may occur. In other words, as mentioned above, if the cooling of the food does not progress, the set pressure is controlled to be gradually lowered, so when the temperature detected by the product temperature sensor reaches the cooling target temperature, the cooling target temperature and tank pressure conversion temperature are (The saturation temperature at the pressure inside the processing tank) has become large, and if the pressure is maintained as it is, there is a risk of overcooling of the food.

On the other hand, even if the pressure inside the processing tank is restored to a predetermined pressure and maintained, there is a problem in determining the level of the holding pressure. In addition, when transitioning from the cooling process to the holding process, when the pressure inside the processing tank is restored to the holding pressure, the opening degree of the air supply valve for adjusting the tank internal pressure becomes large, and there is a risk of overshooting the holding pressure. There is also.

JP 2017-161118 (Paragraph 0049-0058, Figure 3)

The problem to be solved by the present invention is to provide a vacuum cooling device that can cool food to a cooling target temperature without temperature unevenness and without overcooling. Another object is to suppress overshoot at the time of transition from the cooling process to the holding process, and to realize stable pressure maintenance in the holding process.

The present invention has been made to solve the above problem, and the invention according to claim 1 includes: a processing tank in which food is stored; a decompression means for sucking and discharging the gas in the processing tank to the outside; a pressure restoring means for introducing outside air into the reduced pressure processing tank; a pressure sensor for detecting the pressure within the processing tank; a product temperature sensor for detecting the temperature of the food stored in the processing tank; and a control means for controlling each means, the control means executes a cooling step until the temperature detected by the food temperature sensor reaches the cooling target temperature, and then executes a holding step, and in the cooling step, the food A saturation pressure at a temperature lower than the cooling target temperature by a set value is set as a set pressure, and a depressurization operation is performed to reduce the pressure in the processing tank to the set pressure, and a standby operation is maintained at the set pressure for a set standby time, and the If the temperature detected by the product temperature sensor has not reached the cooling target temperature at the end of the standby operation, the set value is increased and the depressurization operation and the standby operation are repeated until the temperature reaches the cooling target temperature. In the holding step, the pressure set in the first standby operation in the cooling step is used as the holding pressure, and the inside of the processing tank is held at the holding pressure until the set holding time elapses , and in the first depressurization operation in the cooling step, , when the detected pressure of the pressure sensor reaches a predetermined pressure higher than the holding pressure, the pressure is reduced to the set pressure by reducing the pressure reduction rate, and the predetermined pressure is a saturation pressure at the cooling target temperature. This is a vacuum cooling device.

According to the invention set forth in claim 1, in the cooling process, a pressure reduction operation to a set pressure and a standby operation at the set pressure are performed, and the set pressure is lowered in stages depending on the progress of cooling. By repeating the operation and the standby operation, it is possible to reliably cool the food. When the temperature detected by the product temperature sensor reaches the cooling target temperature, the process moves to the holding process, but the holding pressure in the holding process is not necessarily the pressure at the end of the cooling process, but is the set pressure for the first standby operation in the cooling process. Ru. That is, when the set pressure is lowered stepwise in the cooling process, the pressure is restored to the initial set pressure (pressure equivalent to "cooling target temperature - initial set value") and held. Thereby, the food can be cooled to the cooling target temperature without temperature unevenness and without overcooling.
According to the invention described in claim 1, in the first depressurization operation in the cooling process, when the detected pressure of the pressure sensor reaches a predetermined pressure higher than the holding pressure (initial set pressure), the depressurization speed is reduced, so that the setting A smooth transition to pressure can be achieved. Moreover, by setting the saturation pressure at the cooling target temperature to the predetermined pressure, a smooth transition to the set pressure can be achieved without unnecessarily prolonging the operation time.

In the invention according to claim 2, when the pressure is restored from a pressure lower than the holding pressure to the holding pressure at the time of transition from the cooling step to the holding step, the pressure restoring width is divided into a plurality of pressure regions, 2. The vacuum cooling device according to claim 1, wherein the pressure inside the processing tank is restored in stages for each pressure region.

According to the second aspect of the invention, when it is necessary to restore the pressure in the processing tank during transition from the cooling process to the holding process, the pressure can be restored in stages. This suppresses overshoot when restoring the pressure inside the processing tank, making it possible to maintain stable pressure in the holding step.

The invention according to claim 3 is characterized in that the operation of restoring the pressure in stages is performed when the pressure is restored to the holding pressure from a pressure lower than the holding pressure by a predetermined value or more. It is a device.

According to the invention described in claim 3, only when the pressure is restored to the holding pressure from a pressure lower than the holding pressure by a predetermined value during the transition from the cooling process to the holding process, the width of the restoration pressure is divided into a plurality of pressure ranges. Then, the pressure inside the processing tank is restored in stages for each pressure region. In this way, the pressure inside the processing tank can be restored in stages only when overshoot is expected.

The invention according to claim 4 is characterized in that when the pressure is restored from a pressure lower than the holding pressure to the holding pressure during transition from the cooling step to the holding step, the pressure is restored at a set pressure restoring rate. This is the vacuum cooling device according to item 1.

According to the invention set forth in claim 4, when transitioning from the cooling process to the holding process, the pressure is restored while adjusting the pressure restoration rate. This suppresses overshoot when restoring the pressure inside the processing tank, making it possible to maintain stable pressure in the holding step.

According to the vacuum cooling device of the present invention, food can be cooled to a cooling target temperature without temperature unevenness and without overcooling. Moreover, overshoot at the time of transition from the cooling process to the holding process can be suppressed, and stable pressure maintenance can be realized in the holding process.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a vacuum cooling device according to an embodiment of the present invention, with a portion thereof shown in cross section. This is a graph showing an example of operation of the vacuum cooling device in FIG. 1, and shows changes in product temperature T and tank pressure P, where the vertical axis is product temperature T or pressure P, and the horizontal axis is elapsed time t from the start of operation. It shows. FIG. 3 is a schematic diagram showing another example of FIG. 2; 4 is a schematic diagram showing a comparative example with respect to FIG. 3. FIG.

Hereinafter, specific embodiments of the present invention will be described in detail based on the drawings.
FIG. 1 is a schematic diagram showing a vacuum cooling device 1 according to an embodiment of the present invention, with a portion thereof shown in cross section.

The vacuum cooling device 1 of this embodiment includes a processing tank 2 in which food F is stored, a pressure reducing means 3 for sucking and discharging the gas in the processing tank 2 to the outside, and introducing outside air into the reduced pressure processing tank 2. and a control means (not shown) that controls each of these means to cool the food F in the processing tank 2.

The processing tank 2 is a hollow container that can withstand reduced pressure in its internal space, and can be opened and closed with a door (not shown). The processing tank 2 is typically formed in a substantially rectangular box shape, and the front opening can be opened and closed with a door. By opening the door, food F can be taken in and out of the processing tank 2, and by closing the door, the opening of the processing tank 2 can be airtightly closed. The door may be provided on both the front and back sides of the processing tank 2.

The pressure reducing means 3 is a means for sucking and discharging the gas (air or steam) in the processing tank 2 to the outside to reduce the pressure inside the processing tank 2. In this embodiment, the pressure reducing means 3 includes, in order, a steam ejector 6, a heat exchanger 7 for steam condensation, a check valve 8, and a water ring type vacuum pump 9 in an exhaust path 5 from inside the processing tank 2. .

The steam ejector 6 is provided with a suction port 6a connected to the processing tank 2, and steam from the ejector steam supply path 10 can be ejected from the inlet 6b toward the outlet 6c with a nozzle. By spouting steam from the inlet 6b toward the outlet 6c, the gas in the processing tank 2 is also suctioned and discharged to the outlet 6c via the suction port 6a. By opening and closing an ejector steam supply valve 11 provided in the ejector steam supply path 10, it is possible to switch whether or not the steam ejector 6 is operated.

The heat exchanger 7 is an indirect heat exchanger that exchanges heat between the fluid in the exhaust path 5 and the cooling water without mixing them. The heat exchanger 7 allows the steam in the exhaust path 5 to be cooled and condensed with cooling water.

The vacuum pump 9 in this embodiment is of a water seal type, and as is well known, is operated while being supplied with water called a water seal. For this purpose, water is supplied to the water supply port 9a of the vacuum pump 9 via the water seal water supply channel 12. The sealed water supply channel 12 is provided with a sealed water supply valve 13, and by opening the sealed water supply valve 13, sealed water can be supplied to the vacuum pump 9. When the vacuum pump 9 is operated with the water sealing water supply valve 13 open, the vacuum pump 9 takes in gas from the intake port 9b, and exhausts and drains the gas to the exhaust port 9c. The vacuum pump 9 may be controlled on/off or may be controlled by an inverter.

To explain the water supply system to the heat exchanger 7 and the vacuum pump 9, in this embodiment, the heat exchanger 7 and the vacuum pump 9 can be supplied with normal temperature water and cold water while being switched. Cold water is water that has been cooled to a predetermined temperature by a chiller (not shown), and normal temperature water is water that cannot be cooled in this way.

In the illustrated example, switching between room temperature water and cold water is performed by a room temperature water supply valve 15 provided in the room temperature water supply channel 14 and a cold water supply valve 17 provided in the cold water supply channel 16. The room temperature water supply channel 14 downstream of the room temperature water supply valve 15 and the cold water supply channel 16 downstream of the cold water supply valve 17 are joined together to form a common water supply channel 18 . The common water supply channel 18 is branched into a heat exchange water supply channel 19 to the heat exchanger 7 and a water seal water supply channel 12 to the vacuum pump 9. The water seal water supply channel 12 is provided with a water seal water supply valve 13 . By opening the room temperature water supply valve 15 or the cold water supply valve 17, water is supplied to the heat exchanger 7, and when the sealed water supply valve 13 is further opened, water is supplied to the vacuum pump 9.

Water is supplied to the heat exchanger 7 via a heat exchange supply channel 19 , and water is discharged via a heat exchange drainage channel 20 . The heat exchange drainage channel 20 is branched into a cold water return channel 21 to the cold water tank (water supply source for the chiller) and a drainage outlet channel 22 to the outside, and the cold water return channel 21 is provided with a cold water return valve 23. A drain outlet valve 24 is provided in the drain outlet passage 22. The cold water return valve 23 and the drain outlet valve 24 allow the water that has passed through the heat exchanger 7 to be returned to the cold water tank, to be discharged from the drain outlet passage 22, or to be passed through the heat exchanger 7 without any of the above. It is possible to switch between blocking (that is, closing the cooling water outlet side of the heat exchanger 7).

When supplying cold water to the heat exchanger 7, the cold water after passing through the heat exchanger 7 is returned to the cold water tank by closing the drain outlet valve 24 and opening the cold water return valve 23. The water stored in the cold water tank is cooled by the chiller and can be supplied to the cold water supply channel 16 again. On the other hand, when normal temperature water is supplied to the heat exchanger 7, by closing the cold water return valve 23 and opening the drain outlet valve 24, the normal temperature water that has passed through the heat exchanger 7 is discharged from the drain outlet path 22.

The pressure recovery means 4 is a means for introducing outside air into the reduced pressure processing tank 2 and restoring the pressure inside the processing tank 2. In this embodiment, the pressure recovery means 4 includes an air filter 26 and an air supply valve 27 in this order in an air supply path 25 into the processing tank 2 . The air supply valve 27 is configured of a valve whose opening degree can be adjusted, such as an electric valve. When the air supply valve 27 is opened in a state where the pressure inside the processing tank 2 is reduced, outside air is introduced into the processing tank 2 through the air filter 26, and the pressure inside the processing tank 2 can be restored. The pressure inside the processing tank 2 can be adjusted by controlling the opening degree of the air supply valve 27 while the pressure reducing means 3 is operated.

The processing tank 2 is further provided with a pressure sensor 28 that detects the pressure inside the processing tank 2 and a product temperature sensor 29 that detects the temperature (product temperature) of the food F stored in the processing tank 2.

The control means is a controller (not shown) that controls each of the means 3 and 4 based on detection signals from the sensors 28 and 29, elapsed time, and the like. Specifically, in addition to the vacuum pump 9, the ejector steam supply valve 11, the water sealing water supply valve 13, the room temperature water supply valve 15, the cold water supply valve 17, the cold water return valve 23, the drain outlet valve 24, and the air supply valve 27, the pressure The sensor 28, the product temperature sensor 29, and the like are connected to the controller. The controller then attempts to vacuum-cool the food F in the processing tank 2 according to a predetermined procedure (program), as described below.

A specific example of the method of operating the vacuum cooling device 1 of this embodiment will be described below.
FIG. 2 is a graph showing an example of operation of the vacuum cooling device 1 of this embodiment, and shows changes in product temperature T and tank pressure P, where the vertical axis is the product temperature T or pressure P, and the horizontal axis is the operation. It shows the elapsed time t from the start.

Before the start of operation, the air supply valve 27 is open, the other valves are closed, and the vacuum pump 9 is stopped. In this state, the food F is stored in the processing tank 2, and the door of the processing tank 2 is hermetically closed. When the start button is pressed or other instructions are given to start operation, the controller closes the air supply valve 27 and operates the pressure reducing means 3 to reduce the pressure in the processing tank 2 until a predetermined termination condition is met. Food F is cooled by cooling or holding under reduced pressure. In this embodiment, the cooling process S1 and the holding process S2 are performed sequentially.

While the pressure in the processing tank 2 is being reduced by the pressure reducing means 3, the water supply to the heat exchanger 7 and the vacuum pump 9 and the operation of the steam ejector 6 are controlled, for example, as follows. That is, at the start of the cooling operation, the vacuum pump 9 depressurizes the inside of the processing tank 2 while supplying normal temperature water to the vacuum pump 9 while water flow through the heat exchanger 7 is stopped. At this stage, the ejector steam supply valve 11 is closed and the steam ejector 6 is not operating. Thereafter, as a water flow start condition, for example, when the temperature detected by the product temperature sensor 29 becomes lower than the water flow start temperature (for example, 60° C.), water flow through the heat exchanger 7 is started. At this time, cold water is supplied to the heat exchanger 7 and the vacuum pump 9. Thereafter, as an ejector operating condition, for example, when the temperature detected by the product temperature sensor 29 is lower than the ejector operating temperature (for example, 30° C.) and the pressure detected by the pressure sensor 28 is lower than the ejector operating pressure (for example, 45 hPa), the ejector steam supply valve 11 to operate the steam ejector 6. By adjusting the opening degree of the air supply valve 27 while the pressure reducing means 3 is in operation, the pressure reduction speed can be adjusted or the pressure can be maintained at a desired pressure under reduced pressure. However, instead of or in addition to this, the pressure reducing ability of the pressure reducing means 3 may be adjusted.

In the cooling step S1, a pressure reduction operation S11 for reducing the pressure to a set pressure and a standby operation S12 for maintaining the set pressure are performed. In the pressure reduction operation S11, the saturation pressure at a temperature lower than the cooling target temperature TZ of the food F by a set value is set as a set pressure, and the inside of the processing tank 2 is depressurized to the set pressure. When the pressure inside the processing tank 2 is reduced to the set pressure, the process is switched to standby operation S12. In the standby operation S12, the inside of the processing tank 2 is maintained at a set pressure for a set standby time. At the end of the standby operation S12 (that is, when the set standby time has elapsed from the start of the standby operation S12), if the temperature detected by the product temperature sensor 29 has not reached the cooling target temperature TZ, the set value is increased by the set amount (in other words, (for example, the set pressure is lowered), and a pressure reduction operation S11 and a standby operation S12 are executed. That is, a pressure reduction operation S11 to a new set pressure and a standby operation S12 for a set standby time at the set pressure are executed. In this way, each time a set of pressure reduction operation S11 and standby operation S12 is executed, the set pressure is lowered in stages until the temperature detected by the product temperature sensor 29 becomes equal to or lower than the cooling target temperature TZ. and standby operation S12 are repeatedly executed.

When repeating the pressure reduction operation S11 and the standby operation S12, the set amount (increment of the set value) or the set standby time may be changed. For example, for the first time, the saturation pressure at a temperature (first set temperature TA) lower than the cooling target temperature TZ by a first set value is set as the set pressure (first set pressure PA), and the first set standby time is set at that set pressure. However, from this point on, the saturation pressure at a temperature (new set temperature) lower than the previous set temperature by the second set value (above set amount) will be the set pressure, and the second set standby time will be set at that set pressure. Try to keep it. Preferably, the second set value is smaller than the first set value, and the second set standby time is set shorter than the first set standby time.

When reducing the pressure inside the processing tank 2 to the initial set pressure (first set pressure PA), the control is typically performed as follows. That is, the relationship between the elapsed time from the start of operation and the pressure inside the tank is set in advance in the controller as a cooling pattern (slow cooling curve), and the controller adjusts the pressure inside the processing tank 2 in accordance with the cooling pattern. While adjusting (typically adjusting the opening degree of the air supply valve 27), the pressure inside the processing tank 2 is reduced to cool the food F (slow cooling control). However, depending on the situation, the air supply valve 27 may be closed to quickly reduce the pressure inside the processing tank 2 (quick cooling control). Alternatively, the slow cooling control may be performed after rapidly reducing the pressure in the processing tank 2 to a predetermined level. Alternatively, although details will be described later, after performing the slow cooling control to a predetermined pressure, the pressure reduction rate may be reduced to reduce the pressure to the set pressure.

A specific example of the cooling step S1 is as follows. For example, the cooling target temperature TZ is 10°C (12.3 hPa), the first set value is 2°C, the second set value is 1°C, the first set standby time is 15 minutes, and the second set standby time is 2 minutes. shall be. In this case, in the cooling step S1, the pressure inside the processing tank 2 is first reduced to a saturation pressure (10.7 hPa) equivalent to 8°C (cooling target temperature 10°C - first set value 2°C) (pressure reduction operation S11), and the After reaching the pressure, the first set standby time is held for 15 minutes (standby operation S12). If the product temperature has not decreased to the cooling target temperature TZ after 15 minutes, the pressure inside the processing tank 2 is further reduced by 1°C (second set value) to the saturation pressure (10.0 hPa) equivalent to 7°C ( After the pressure reaches the pressure reduction operation S11), the pressure is maintained for 2 minutes, which is the second set standby time (standby operation S12). Thereafter, similarly, if the product temperature has not decreased to the cooling target temperature TZ after 2 minutes, the temperature in the processing tank 2 is further reduced by an amount equivalent to 1°C and held for 2 minutes. Repeat until the temperature is below TZ.

During the cooling process S1, the temperature detected by the product temperature sensor 29 is monitored, and when the temperature detected by the product temperature sensor 29 falls to the cooling target temperature TZ, the process moves to the holding process S2. Even during the decompression operation S11 or the standby operation S12, if the temperature detected by the product temperature sensor 29 becomes equal to or lower than the cooling target temperature TZ, the operation in progress may be ended and the process may proceed to the holding step S2.

In the holding step S2, the pressure set in the first standby operation S12 in the cooling step S1 (first set pressure PA) is used as the holding pressure, and the inside of the processing tank 2 is held at the holding pressure PA until the set holding time elapses. Here, the holding step S2 is executed until the elapsed time from the time when the product temperature reaches the cooling target temperature TZ (that is, the end of the cooling step S1) reaches the set holding time.

In the first standby operation S12, if the temperature detected by the product temperature sensor 29 reaches the cooling target temperature TZ, the pressure may be maintained for the set holding time. On the other hand, if the product temperature is difficult to fall and the temperature detected by the product temperature sensor 29 falls to the cooling target temperature TZ by gradually lowering the pressure in the processing tank 2, the pressure in the processing tank 2 is lowered by the initial standby operation. The pressure is restored to the set pressure (holding pressure PA) in S12 and held. During this pressure restoration, it is preferable to control as follows.

That is, when returning from a pressure PB lower than the holding pressure PA to the holding pressure PA during the transition from the cooling step S1 to the holding step S2, the width of the restoring pressure is divided into a plurality of pressure regions, and the pressure is adjusted for each pressure region. It is preferable to restore pressure in the processing tank 2 in stages. In this example, as shown in FIG. 2, the difference between the tank internal pressure PB and the holding pressure PA when the product temperature reaches the cooling target temperature TZ is divided into four equal parts, and each pressure is divided into four parts for a certain period of time t1. pressure in order.

In the cooling process S1, as mentioned above, if it is determined that the product temperature does not decrease, the pressure inside the tank is gradually lowered to cool the food. When the detected temperature reaches the cooling target temperature TZ), there is a possibility that the tank internal pressure deviates greatly from the holding pressure PA of the next step (for example, by 5° C. or more). Further, the opening degree of the air supply valve 27 is adjusted (PID control) so that the pressure detected by the pressure sensor 28 becomes the target pressure.

In this case, when the target pressure is changed during the transition from the cooling process S1 to the holding process S2, if the change width (that is, the differential pressure between the current tank pressure and the target pressure) is large, the air supply valve 27 The opening change becomes larger. Therefore, when transitioning from the cooling process S1 to the holding process S2, if the target pressure is switched to the holding pressure PA and the pressure is restored all at once, the air supply valve 27 will open wide and the inside of the tank will be affected, as shown by the two-dot chain line in FIG. There is a risk that the pressure will overshoot to a pressure higher than the holding pressure PA.

However, in this embodiment, the pressure is restored in stages by dividing the pressure back width into equal parts (changing the target pressure in stages), thereby preventing the air supply valve 27 from opening wide all at once, thereby preventing overshoot. Can be suppressed. By suppressing overshoot, stable pressure can be maintained in the holding step S2. In the illustrated example, the pressure recovery time t1 at each stage is set so that each time the pressure is restored in stages, the pressure is maintained once and then the pressure is restored to the next stage.

In any case, the pressure inside the processing tank 2 is restored to the predetermined holding pressure PA until the predetermined end condition is met (here, in the cooling process S1, the product temperature reaches the cooling target temperature TZ and then the set holding time (until the time has elapsed). When the holding step S2 is completed, the pressure reducing means 3 is stopped, and the pressure in the processing tank 2 is restored to atmospheric pressure by the pressure recovery means 4, and the cooling operation is ended.

According to the vacuum cooling device 1 of this embodiment, in the cooling step S1, a pressure reduction operation S11 to the set pressure and a standby operation S12 at the set pressure are performed, but the set pressure is changed in stages according to the progress of cooling. The food F can be reliably cooled by repeating the pressure reduction operation S11 and the standby operation S12. Further, even if the temperature detected by the product temperature sensor 29 reaches the cooling target temperature TZ, the food F can be cooled evenly by performing the holding step S2 of maintaining the inside of the processing tank 2 at the holding pressure PA. Moreover, the holding pressure PA in the holding step S2 is the set pressure PA in the first standby operation S12 in the cooling step S1. That is, even if the set pressure is lowered stepwise in the cooling step S1, the food F will not be overcooled because the pressure inside the processing tank 2 is restored to and held at the holding pressure PA in the holding step S2.

Particularly in the case of liquid food F, if the temperature detection part of the product temperature sensor 29 is located near the bottom, the detected temperature will be difficult to fall due to the influence of the liquid depth, resulting in the following problem. That is, at the time when the detected temperature of the product temperature sensor 29 reaches the cooling target temperature TZ, the temperature difference between the cooling target temperature TZ and the tank internal pressure conversion temperature TB has become large, and if the pressure is maintained as it is, the food F There is a risk of freezing on the surface (near the liquid level). However, in this embodiment, such inconvenience can be prevented by setting the set pressure (pressure corresponding to "cooling target temperature TZ - initial set value") of the first standby operation S12 as the holding pressure.

Moreover, when the pressure inside the processing tank 2 is restored to the holding pressure PA at the time of transition from the cooling step S1 to the holding step S2, the pressure is restored in stages. For example, the difference between the tank internal pressure PB and the holding pressure PA when the product temperature reaches the cooling target temperature TZ is divided into four parts, and the return pressure target pressure is changed by 1/4 up to the holding pressure PA at regular intervals, and the processing is performed. The pressure inside tank 2 is restored in stages. Therefore, the pressure within the processing tank 2 can be made to asymptotically approach the holding pressure PA. It is possible to prevent sudden fluctuations in the target pressure, suppress overshoot during pressure recovery, and stably maintain the holding pressure PA after reaching the holding pressure PA.

During the transition from the cooling step S1 to the holding step S2, when restoring pressure from a pressure PB lower than the holding pressure PA to the holding pressure PA, the restoring pressure width is divided into a plurality of pressure regions, and the inside of the processing tank 2 is controlled for each pressure region. Although the pressure was restored in stages, such stepwise restoration may not always be performed, but may be performed only when restoring the pressure from the pressure PB, which is lower than the holding pressure PA by a predetermined value, to the holding pressure PA. In other words, only when the difference between the tank internal pressure PB and the holding pressure PA when the product temperature reaches the cooling target temperature TZ is greater than a predetermined value, the repressurization width is divided into multiple pressure regions, and the processing tank is adjusted for each pressure region. 2 may be restored in stages. In that case, if the difference between the tank internal pressure PB and the holding pressure PA when the product temperature reaches the cooling target temperature TZ is less than a predetermined value, the pressure may be restored to the holding pressure PA in one step. If the recovery width is small, there is no risk of overshoot during recovery. On the other hand, if the pressure is restored all at once, it is only necessary to restore the pressure in the processing tank 2 in stages only when overshoot is expected.

FIG. 3 is a schematic diagram showing another example of FIG. 2. In the figure, the dashed line and the continuous line are the cooling pattern (slow cooling curve) PP described above. In the first decompression operation S11 in the cooling step S1, the pressure inside the processing tank 2 is basically reduced along this cooling pattern PP. In the initial pressure reduction operation S11, the pressure may be reduced along the cooling pattern PP to a temperature equivalent to a temperature TA lower than the cooling target temperature TZ of the food F, and then the process may proceed to the holding operation S12, but the control is performed as follows. You may.

That is, in the first depressurization operation S11 in the cooling step S1, when the pressure detected by the pressure sensor 28 reaches a predetermined pressure higher than the holding pressure PA, the depressurization speed is reduced (lower than the cooling pattern PP) and the set pressure (maintained pressure) is reduced. It is preferable to reduce the pressure to pressure PA). If the predetermined pressure as the timing for reducing the pressure reduction rate is too high (too far from the set pressure), it will take time to reduce the pressure, while if it is too low (too close to the set pressure), there is a risk of undershooting with respect to the set pressure. Therefore, it is preferable that the predetermined pressure is the saturation pressure PZ at the cooling target temperature TZ. In other words, in FIG. 3, the pressure is reduced along the cooling pattern PP until the pressure PZ corresponding to the cooling target temperature TZ is reached, and when the pressure PZ reaches the pressure PZ corresponding to the cooling target temperature TZ, the pressure reduction rate is lowered (that is, the slope of the graph is made gentler). ), the pressure can be reduced to the set pressure and held.

In this way, the pressure is reduced along the cooling pattern (slow cooling curve) PP, and when the pressure inside the tank reaches the pressure PZ equivalent to the cooling target temperature TZ, the target pressure is switched to the "cooling target temperature TZ - set value" equivalent, Maintain at that pressure. In the case of food T1 that cools easily, the temperature detected by the product temperature sensor 29 drops to the cooling target temperature TZ during that time, so it is sufficient to hold the food for the set holding time. On the other hand, in the case of food T2 that does not cool easily, the set pressure may be lowered in stages, as shown by the broken line. Then, if the temperature detected by the product temperature sensor 29 falls to the cooling target temperature TZ, the tank internal pressure may be restored to the holding pressure PA and held. At the time of this pressure restoration, it goes without saying that the pressure may be restored in stages as described above.

FIG. 4 is a schematic diagram showing a comparative example with respect to FIG. As shown in this figure, if the pressure inside the processing tank 2 is reduced along the cooling pattern PP until the product temperature reaches the cooling target temperature TZ, and when the product temperature reaches the cooling target temperature TZ, the target pressure is maintained. Suppose we switch to pressure PA. In this case, in the case of food T1 that is easily chilled, the differential pressure with the holding pressure PA is small, so the pressure can be returned to the holding pressure PA relatively quickly, and the overshoot is also small. On the other hand, in the case of food T2 that does not cool easily, by the time the product temperature reaches the cooling target temperature TZ, the tank internal pressure deviates greatly from the holding pressure PA and may even reach around 0 hPa. If the target pressure is switched to the holding pressure PA in this state, the opening degree of the air supply valve 27 will increase, and there is a risk of overshooting the holding pressure PA.

However, according to the vacuum cooling device 1 of this embodiment, when the predetermined pressure (pressure PZ equivalent to the cooling target temperature TZ) is reached, which is slightly higher than the initial set pressure PA, the pressure reduction rate is lowered to smoothly reach the set pressure. can be retained. In addition, even when cooling the food F by lowering the set pressure in stages, as explained in Figure 2, by gradually increasing the pressure to the holding pressure PA, overshoot is suppressed and the food is stabilized at the holding pressure PA. and can be held.

The vacuum cooling device 1 of the present invention is not limited to the configuration (including control) of the embodiment described above, and can be modified as appropriate. In particular, (a) after performing the cooling step S1 until the temperature detected by the product temperature sensor 29 reaches the cooling target temperature TZ, the holding step S2 is performed; (b) in the cooling step S1, the cooling target temperature TZ of the food F The saturation pressure at a temperature lower than the set value is set as the set pressure, and the pressure reduction operation S11 is performed to reduce the pressure inside the processing tank 2 to the set pressure, and the standby operation S12 is held at the set pressure for a set standby time, and the standby operation S12 is performed. If the temperature detected by the product temperature sensor 29 has not reached the cooling target temperature TZ at the time of completion, the set value is increased and the decompression operation S11 and the standby operation S12 are repeated until the temperature reaches the cooling target temperature TZ, and (c ) In the holding step S2, if the setting pressure of the first standby operation S12 in the cooling step S1 is set as the holding pressure PA, and the inside of the processing tank 2 is held at the holding pressure PA until the set holding time elapses, the other configurations are as follows. It can be changed as appropriate.

For example, in the above embodiment, when the pressure is restored from the pressure PB lower than the holding pressure PA to the holding pressure PA during the transition from the cooling step S1 to the holding step S2, the pressure is restored in stages by dividing the restoring width into four equal parts. However, how many equal parts the recompression width is divided can be changed as appropriate. The number of divisions may be changed depending on the pressure recovery width (the differential pressure between the tank internal pressure PB and the holding pressure PA when the product temperature reaches the cooling target temperature TZ). In other words, if the differential pressure between the tank internal pressure PB and the holding pressure PA when the product temperature reaches the cooling target temperature TZ is large, the number of divisions may be increased, and if the differential pressure is small, the number of divisions may be decreased (or (Does not need to be divided). Moreover, even when dividing, it is not necessarily necessary to divide into equal parts.

Furthermore, in the above embodiment, when the pressure is restored from the pressure PB lower than the holding pressure PA to the holding pressure PA during the transition from the cooling step S1 to the holding step S2, the width of the restoring pressure is divided into a plurality of pressure ranges and the pressure is gradually increased. Although the pressure was restored to , it may be controlled as follows. That is, when the pressure is restored from the pressure PB lower than the holding pressure PA to the holding pressure PA during the transition from the cooling step S1 to the holding step S2, the pressure may be restored at a set return pressure rate. That is, a speed that does not cause overshoot may be determined in advance through experiments or the like, and the pressure inside the processing tank 2 may be restored to the holding pressure PA at that speed.

Furthermore, in the embodiments described above, the configuration of the pressure reducing means 3 can be changed as appropriate. For example, in the embodiment described above, the steam ejector 6 was provided as the pressure reducing means 3, but the steam ejector 6 may be omitted depending on the situation.

Further, in the above embodiment, the vacuum cooling device 1 has been described as a cooling-only device, but it can be modified as appropriate as long as it has a vacuum cooling function. For example, by providing heating means using steam, it may be configured as a steam cooling device or a saturated steam cooking device. Alternatively, it may be configured like a cold air/vacuum composite cooling device by providing a cold air cooling means using a refrigerator or a fan.

1 Vacuum cooling device 2 Processing tank 3 Depressurizing means 4 Repressurizing means 5 Exhaust path 6 Steam ejector (6a: suction port, 6b: inlet, 6c: outlet)
7 Heat exchanger 8 Check valve 9 Vacuum pump (9a: water supply port, 9b: intake port, 9c: exhaust port)
10 Ejector steam supply channel 11 Ejector steam supply valve 12 Sealing water supply channel 13 Sealing water supply valve 14 Room temperature water supply channel 15 Room temperature water supply valve 16 Cold water supply channel 17 Cold water supply valve 18 Common water supply channel 19 Heat exchange supply channel 20 Heat exchanger Drain channel 21 Cold water return channel 22 Drain outlet channel 23 Cold water return valve 24 Drain outlet valve 25 Air supply channel 26 Air filter 27 Air supply valve 28 Pressure sensor 29 Product temperature sensor S1 Cooling process (S11: pressure reduction operation, S12: standby operation)
S2 Holding process TA First set temperature TZ Cooling target temperature PA First set pressure (holding pressure)
PB Pressure inside the tank when the product temperature reaches the cooling target temperature TZ PP Cooling pattern

Claims (4)

A processing tank in which food is stored, a pressure reducing means for suctioning and discharging the gas in the processing tank to the outside, a pressure recovery means for introducing outside air into the reduced pressure processing tank, and detecting the pressure inside the processing tank. a pressure sensor that detects the temperature of the food stored in the processing tank, a temperature sensor that detects the temperature of the food stored in the processing tank, and a control means that controls each of the means,
The control means executes a cooling process until the detected temperature of the product temperature sensor reaches a cooling target temperature, and then executes a holding process,
In the cooling step, the saturation pressure at a temperature lower than the target food cooling temperature by a set value is set as the set pressure, and a depressurization operation in which the pressure inside the processing tank is reduced to the set pressure, and a standby operation in which the set pressure is maintained for a set standby time. At the same time, if the temperature detected by the product temperature sensor has not reached the cooling target temperature at the end of the standby operation, the set value is increased until the temperature reaches the cooling target temperature, and the depressurization operation and the standby operation are performed. Repeat and execute
In the holding step, the inside of the processing tank is maintained at the holding pressure until a set holding time elapses, using the set pressure of the first standby operation in the cooling step as the holding pressure ,
In the first depressurization operation in the cooling step, when the detected pressure of the pressure sensor reaches a predetermined pressure higher than the holding pressure, the depressurization speed is reduced to reduce the pressure to the set pressure,
The predetermined pressure is a saturation pressure at the cooling target temperature.
A vacuum cooling device characterized by: At the time of transition from the cooling step to the holding step, when returning the pressure from a pressure lower than the holding pressure to the holding pressure, the pressure return width is divided into a plurality of pressure regions, and the inside of the processing tank is controlled for each pressure region. The vacuum cooling device according to claim 1, wherein the pressure is restored in stages. The vacuum cooling device according to claim 2, wherein the stepwise pressure restoration operation is performed when the pressure is restored to the holding pressure from a pressure lower than the holding pressure by a predetermined value or more. The vacuum cooling device according to claim 1, wherein when the pressure is restored from a pressure lower than the holding pressure to the holding pressure during transition from the cooling process to the holding process, the pressure is restored at a set pressure restoration rate.

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