JP2006336924A - Vacuum dryer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vacuum dryer with high versatility capable of increasing drying speed with respect to a heating object A without causing vibration or noise, and without intrusion of lubricant or the like into a dryer interior. <P>SOLUTION: The vacuum dryer is provided with a low pressure chamber 3, and a heater 1 arranged in the low pressure chamber 3. The heater 1 has a cold air inlet 13 introducing cold air, a hot air outlet 12 facing the object A to be heated, a plurality of high temperature plates 14 extending from the cold air inlet 13 toward the hot air outlet 12 and arranged in parallel with each other, and a heating body 16 heating the high temperature plates 14. In the high temperature plate 14, an edge 15 is formed on an end in a cold air inlet 13 side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vacuum drying apparatus that vacuum-drys an object to be heated such as food or medicine.

Conventionally, frozen foods and pharmaceuticals to be heated are heated in a vacuum by heat transfer and heat conduction from a heater to sublimate moisture, and the sublimated moisture is discharged outside to dry the heated object. A vacuum drying apparatus is known (Patent Document 1). Since the sublimation temperature is low in vacuum (low pressure), the object to be heated can be dried without being damaged by being exposed to a high temperature.
JP 2001-317869 A

  However, the vacuum drying apparatus described above has a low water sublimation rate with respect to the object to be heated, that is, a drying rate.

  Therefore, it is conceivable to increase the drying speed of the object to be heated by positively supplying hot air from the heater to the object to be heated via the blower pump.

  However, when a normal blower pump is used, vibration and noise are generated by the movable part. In addition, since oil used as lubricating oil in the movable part may enter the inside of the apparatus, it is particularly unsuitable for vacuum drying of foods and pharmaceuticals.

  To deal with such a problem, it is conceivable to use a Knudsen pump having no moving parts. This Knudsen pump uses a thermal transition flow of a gas generated in a reduced pressure environment with a thermal gradient for heat transport. However, when only the thermal transition flow is used as in this Knudsen pump, not only the drying speed of the object to be heated cannot be sufficiently increased, but the thermal transition flow of the Knudsen pump has a relatively large Knudsen number (Kn number). Since it occurs in the region, that is, in the high vacuum region and hardly occurs in the small Knudsen number region, the versatility is poor.

  Therefore, as a result of repeated research on the Knudsen pump, the present inventor arranges a flat plate having an edge in a reduced pressure environment, gives a thermal gradient to the flat plate, and sets the edge to a low temperature side (higher than the external space). For example, it was found that a gas flow is generated from the low temperature side to the high temperature side due to the edge effect, and this gas flow is also generated in a Knudsen number (Kn number) region smaller than that in the case of a thermal transition flow. . That is, when the molecular temperature in the outer space on the edge is higher than the molecular temperature in the inner space on the edge in a reduced pressure environment, a gas flow toward the inner side of the edge is generated.

  The present invention uses both the gas flow due to the edge effect and the gas flow due to the thermal transition flow as heat transport, so that vibration and noise are not generated, and the lubricating oil or the like is generated inside the apparatus. It is an object of the present invention to provide a highly versatile vacuum drying apparatus that can increase the drying speed of an object to be heated such as a food or a pharmaceutical without entering the room.

  In order to achieve the above object, a vacuum drying apparatus of the present invention includes a low-pressure chamber and a heater disposed in the low-pressure chamber, and the heater includes a cold air inlet for introducing cold air, and an object to be heated. Opposing hot air outlets, a plurality of high temperature plates arranged in parallel to each other extending from the cold air inlet toward the hot air outlet, and a heating body for heating the high temperature plate, the high temperature plate on the cold air inlet side Edges are formed at the ends. Here, an edge is a non-rounded corner that occurs when a plate is cut along a direction perpendicular to or oblique to the principal surface, and has a radius of curvature smaller than the mean free path of the molecule. Say.

  When drying a frozen object to be heated, the object to be heated is stored in a low-pressure chamber and kept in a low pressure state, and the object to be heated is heated by hot air from a heater, and moisture in the object to be heated is sublimated. Thus, the object to be heated is dried in a porous state. This porous object to be heated quickly returns when cooking without lowering the freshness. At this time, a heater is disposed in the low-pressure chamber, and a plurality of high temperature plates extending from the cold air inlet toward the hot air outlet are disposed in the heater, and the end of the high temperature plate on the cold air inlet side is disposed. Since the edge is formed in the part, a gas flow toward the inside of the edge, that is, from the cold air inlet side to the hot air outlet side is generated due to the edge effect in the reduced pressure environment. The mechanism will be described later. Thereby, hot air is actively blown out from the hot air outlet of the heater, and the drying speed of the object to be heated is increased by this hot air.

  In addition, in the present invention, since a pump is not required, the occurrence of vibrations and noises is not caused, and there is no entry of lubricating oil or the like into the low-pressure chamber, which can contaminate foods or pharmaceuticals. Can be dried. Furthermore, since the gas flow due to the edge effect is generated in a wider Knudsen number (Kn number) region as compared with the case of the heat transition flow, the versatility of the vacuum drying apparatus is enhanced.

  The hot plate preferably has a temperature gradient in which the temperature rises from the cold air inlet toward the hot air outlet. Due to this temperature gradient, a thermal transition flow is generated under a reduced pressure environment, and a gas flow from the cold air inlet side toward the hot air outlet side is generated. The mechanism will be described later. Thereby, the speed of the hot air blown from the hot air outlet of the heater is increased, and the drying speed of the object to be heated is further increased.

  The hot air outlet is preferably arranged above the cold air inlet. As a result, the rising force is added to the hot air as the temperature increases and the density decreases, so that the speed of the hot air toward the object to be heated increases and the drying speed of the object to be heated can be increased.

  Moreover, in preferable embodiment of this invention, the said heating body is mounted | worn with the hot-air exit vicinity in the said high temperature board. According to this configuration, the thermal transition flow can be generated by easily giving the high temperature plate a temperature gradient in which the temperature rises from the cold air inlet to the hot air outlet. Moreover, since the said heating body approaches the to-be-heated object located in the hot-air exit vicinity, a to-be-heated body can be effectively heated also by the radiant heat from a heating body.

  According to the vacuum drying apparatus of the present invention, food, medicines, and the like can be safely dried without causing vibration and noise and without allowing lubricating oil or the like to enter the low-pressure chamber. Moreover, the versatility of a vacuum dryer can also be improved.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a simplified layout diagram of a vacuum drying apparatus according to an embodiment of the present invention. The vacuum drying apparatus includes a low-pressure chamber 3 provided with a heater 1 and a tray 2 made of a porous plate on which an object A to be heated is placed, facing one side of the low-pressure chamber 3. In addition, the power source 4 of the heater 1 is disposed, and an exhaust chamber 5 and a vacuum pump 6 are provided in communication with the inside of the low pressure chamber 3 on the other side of the low pressure chamber 3. A cold trap 8 connected to an external cooling device 7 is installed in the exhaust chamber 5.

  FIG. 2 is an enlarged cross-sectional view of the heater 1. The heater 1 has two parallel flat plates 11 and 11 extending in the vertical direction forming an air passage 10 therein, and a hot air outlet 12 facing the tray 2 is provided on the lower side of the flat plate 11 at a lower portion. A cold air inlet 13 for introducing cold air to the side is formed. Two openings (front and back openings in FIG. 2) perpendicular to both the flat plates 11 and 11 are closed by other flat plates 21 and 21. Between the hot air outlet 12 and the cold air inlet 13, a plurality of high temperature plates 14 extending in the vertical direction from the latter 13 toward the former 12 are arranged in parallel to each other. However, in the low pressure state premised on the present invention, the amount of heat transferred to the object A to be heated by “convection” in which molecules having high temperature and low density flow upward is considered to be not large. It is not necessary to set to, and even if it is horizontal or inclined, it is possible to form sufficient hot air toward the heated object A.

  FIG. 3 is an enlarged sectional view showing the high temperature plate 14. The hot plate 14 is made of a metal plate such as brass or copper, and an edge 15 made of a right-angled portion without roundness, such as a cut edge of the plate, is formed at the lower end of the cold air inlet 13 side. . A heating body 16 made of nichrome wire or the like is attached to the upper end of the high temperature plate 14 opposite to the edge 15. In this embodiment, the upper end portion of the hot plate 14 on the hot air outlet 12 side is rounded to form a loop portion 14a, and the heating body 16 is inserted and held in the loop portion 14a. Thus, the heating body 16 is positioned near the hot air outlet 12 of the high temperature plate 14. As shown in the sectional view of FIG. 5, the edge 15 may be a cut end face obtained by obliquely cutting a corner portion of a plate.

  As shown in FIG. 2, by heating the upper end, which is the end of the hot plate 14 on the hot air outlet 12 side, with the heater 16, the entire hot plate 14 is kept at a higher temperature than the gas around the heater 1. The high temperature plate 14 is given a temperature gradient in which the temperature rises from the cold air inlet 13 toward the hot air outlet 12. As a result, a gas flow F from the cold air inlet 13 toward the hot air outlet 12 is generated. The generation mechanism of this flow F is demonstrated below.

  First, the edge effect will be described. In FIG. 5, when the high-temperature plate 14 has an unrounded edge 15 and is hotter than an external temperature, the isothermal line TE has a shape close to an ellipse surrounding the edge 15. Therefore, there is a difference in the velocity Vi of the molecules incident on the edge 15 due to the difference in gas temperature in the vicinity of the edge, and the incident velocity Vi1 of the low-temperature external gas molecule P1 is a high temperature existing inside the high temperature plate 14. The incident velocity Vi2 of the internal gas molecule P2 is smaller. On the other hand, molecules that bounce off the gas from the vicinity of the edge of the high-temperature plate 14 rebound at a substantially uniform speed Vr0 in accordance with the temperature of the high-temperature plate 14. As a result, the gas gives the edge 15 the momentum in the right direction in FIG. 5, and the edge 15 gives the gas a momentum in the left direction as a reaction. As a result, a leftward flow F1 due to the edge effect is generated.

  When the end of the hot plate 14 is rounded like an arc, the isothermal line TE0 has a shape close to a concentric circle centered on the end as shown by a two-dot chain line. As a result of the temperature difference between the molecules incident on the plate 14 being reduced, the edge effect does not occur.

  Next, the thermal transition flow will be described. The generation principle of the thermal transition flow is the same as the edge effect. In FIG. 6, when two high temperature plates 14, 14 having a low temperature portion and a high temperature portion, that is, having a temperature gradient, are arranged facing each other in a rare gas of approximately 100 Pa or less, the isotherm TE is substantially equal to the high temperature plate 14. It becomes a vertical line. While the average molecular velocity Vi3 of the gas molecules P3 in the low temperature portion is smaller than the average molecular velocity Vi4 of the gas molecules P4 in the high temperature portion, the molecules bouncing off from the high temperature plate 14 become almost equal to the temperature of the high temperature plate 14. Rebounds at a different speed Vr1. Thus, the gas gives the hot plate 14 a momentum in the right direction in FIG. 6, and as a reaction, the hot plate 14 gives the gas a left momentum. As a result, a leftward flow F2 (thermal transition flow) is generated.

  FIG. 7 is a schematic diagram showing a state of a confirmation test regarding the generation of the gas flow F1 due to the edge effect when the following heater 1 is disposed inside the low-pressure chamber 3. In this test, regular square plates 11, 11 having a vertical and horizontal length of 2D are arranged facing each other in the front and back direction of FIG. 7 as the heater 1, and the vertical length is D between these flat plates 11 at the center position. Then, the high-temperature plate 14 having the right and left edges 15 formed on the upper and lower end portions was arranged orthogonally. When the inside of the low-pressure chamber 3 is depressurized, as shown by arrows in the figure, the gas flow F1 from the edges 15 formed on the upper and lower sides of the hot plate 14 toward the center position along the hot plate 14 is obtained. Occurred. It was confirmed by visualizing that this flow F occurs in a wide region of Knudsen number Kn = 0.002 to 0.000242. The absolute temperature ratio between the hot plate 14 and the wall surface 11 was 1.7 to 1. Here, the Knudsen number is calculated by Kn = λ / D, where λ is the mean free path of the molecule, and D is the representative length of the flow field. In the region of the Knudsen number Kn, when D is 50 mm, the pressure corresponds to 70 to 700 Pa.

  FIG. 8 is a schematic view showing a state when a confirmation test is performed on the generation of the gas flow F when the heating body 16 made of nichrome wire or the like is attached to the high-temperature plate 14. In this test, an air passage 10 is formed between two passage walls 17 bent in an approximately L shape, and two air passages 10 are formed in parallel between the hot air outlet 12 and the cold air inlet 13 inside the air passage 10. The hot plate 14 was disposed with the heating element 16 facing the hot air outlet 12 side, and a Pirani gauge 18 was disposed on the hot air outlet 12 side of the air passage 10. When the pressure inside the low pressure chamber 3 was gradually reduced while heating the heating body 16, the result shown in FIG. 9 was obtained. The heating temperature of the heating body 16 was 250 ° C., and the pressure in the low-pressure chamber 3 was reduced in the range of 90 to 530 (Pa (Pascal)).

  FIG. 9 shows a low-pressure chamber in which the horizontal axis represents the pressure P0 (Pa) in the low-pressure chamber 3, and the vertical axis represents the increase P1-P0 (Pa) of the pressure P1 on the airway outlet side measured by the Pirani gauge 18. 3 is a graph showing an increase in pressure on the airway outlet side based on a pressure change in 3. As shown in FIG. 9, an increase in the pressure P1 on the outlet side of the air passage was observed over a wide range of the pressure P0 in the low pressure chamber 3. Thus, if there is a pressure difference between the pressure P0 in the low pressure chamber 3 and the pressure P1 on the airway outlet side, the pressure difference causes the gas to flow from the cold air inlet 13 side to the hot air outlet 12 side of the airway 10. It can be understood that the flow F is generated.

  In the above vacuum drying apparatus, when performing vacuum drying of the heated object A, first, the heated object A is placed on the tray 2 in FIG. When the power source 4 is turned on, the heating body 16 of the high temperature plate 14 disposed in the heater 1 of FIG. 2 is heated. At this time, since the edge 15 is formed on the cold air inlet 13 side of the hot plate 14, the gas flow from the cold air inlet 13 side to the hot air outlet 12 side inside the air passage 10 in the heater 1 by this edge effect. F1 occurs. Further, a heating element 14 is provided in the vicinity of the hot air outlet 12 of the high temperature plate 14, and the high temperature plate 14 is heated by the heating element 16. As a result, a thermal gradient is generated in the high temperature plate 14 in a reduced pressure environment. A heading heat transition flow F2 is generated, and the hot air F by the heating body 16 is blown out from the hot air outlet 12 toward the object A to be heated by the heat transition flow F2 and the gas flow F1 due to the edge effect. Therefore, the heated object A placed on the tray 2 is vacuum-dried by the hot air F blown from the hot air outlet 12 and the radiant heat from the heating body 16. In the embodiment of FIG. 2, the heating body 16 is provided at the upper end of the high-temperature plate 14, and the object A is vacuum-dried using the radiant heat of the heating body 16. The object to be heated A may be heated and vacuum dried by another heat source provided outside the low pressure chamber 3 without using the heating body 16.

  Further, when the inside of the low pressure chamber 3 is evacuated by the vacuum pump 6, the cold trap 8 provided in the exhaust chamber 5 is cooled by the external cooling device 7, so that the heated object A or the sublimated moisture is cold. The gas which is condensed and removed by the trap 8 and has almost no moisture is exhausted to the outside by the vacuum pump 6.

  Next, Table 1 shows data when the object A to be heated is vacuum-dried for a certain period of time using the heater 1 shown in FIG. At this time, as a comparative example, data of the arrangement of the high-temperature plate 14A shown in FIG. 10 in which the edge 15 is rounded without forming the edge 15 inside the heater 1 is also shown.

  As is apparent from Table 1 above, by employing the present invention, the amount of sublimation per unit time of the heated object A, that is, the dry amount can be increased, and the drying rate for the heated object A can be increased.

1 is a simplified layout diagram of a vacuum drying apparatus according to an embodiment of the present invention. It is an expanded sectional view of a heater. It is an expanded sectional view of a hot plate. It is sectional drawing which shows another embodiment of a high temperature board. It is a side view of the high temperature board explaining an edge effect. It is a side view of the principal part of the hot plate explaining a heat transition flow. It is a schematic diagram when the confirmation test about a gas flow generate | occur | producing when a heater is arrange | positioned in a low pressure room | chamber interior is performed. It is a schematic diagram when the confirmation test about a gas flow generate | occur | produced when a heating body is attached to a high temperature board. It is a graph which shows the pressure change by the side of a windway based on the pressure change in a low-pressure chamber. It is sectional drawing which shows the comparative example containing the high temperature board which has a roundness in an edge part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heater 12 Hot-air exit 13 Cold-air inlet 14 Hot plate 15 Edge 16 Heating object A Heated object

Claims (4)

A low-pressure chamber, and a heater disposed in the low-pressure chamber,
The heater includes a cold air inlet for introducing cold air, a hot air outlet facing the object to be heated, a plurality of high temperature plates extending in parallel from the cold air inlet toward the hot air outlet, and heating the high temperature plate. And a heating body that
The high-temperature plate is a vacuum drying apparatus in which an end on the cold air inlet side forms an edge.   2. The vacuum drying apparatus according to claim 1, wherein the temperature of the high-temperature plate increases from the cold air inlet toward the hot air outlet.   3. The vacuum drying apparatus according to claim 1, wherein the hot air outlet is disposed above the cold air inlet. 4. The vacuum drying apparatus according to claim 2, wherein the heating body is mounted near a hot air outlet in the high temperature plate.

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