JP2713008B2 - Cooking vessel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat pipe type cooking container used for rice cookers and the like, and more particularly to a structure of the container and a working fluid.

[0002]

2. Description of the Related Art In a cooking container such as a rice cooker, various types of so-called heat pipe type cooking containers have been proposed in order to improve a heating temperature distribution. This heat pipe type cooking container has a closed double wall structure, and a gas-
A working fluid such as pure water that changes into a liquid is enclosed,
During cooking, the heat applied from the heat source evaporates and evaporates the working fluid at the bottom of the outer container, condenses this vapor on the inner wall of the inner container, and transfers the heat uniformly to the entire inner container, making the heating temperature uniform. And cook rice without uneven heating.

FIG. 4 is a cross-sectional view showing the structure of a conventional cooking vessel disclosed in, for example, Japanese Patent Publication No. 63-39247, “Boiler”. In FIG. The container 2 also shows an inner container. The outer container 1 and the inner container 2 are hermetically welded at the upper end 3, and a closed space 4 evacuated is formed between the outer container 1 and the inner container 2. I have.

[0005] Reference numeral 5 denotes a liquid reservoir formed on the outer peripheral portion of the bottom surface of the outer container 1, and 6 denotes a working fluid such as pure water, which is sealed in an appropriate amount in the closed space 4 and usually stored in the liquid reservoir 5. 7a is a thermal resistance plate attached to the bottom surface of the inner container 2 on the side of the closed space 4 so as to form a sealed space, 8 is a condensing portion composed of side and bottom surfaces of the inner container 2, 9 is the bottom surface of the outer container 1. Reference numeral 10 denotes an object to be heated consisting of water and rice stored in the inner container 2.

[0005] The conventional heating and cooking container is constructed as described above, and when the evaporator 9 is heated from below by a heat source (not shown) such as an electric heater, the working fluid 6 stored in the liquid reservoir 5 is removed.
Is heated and boiled / evaporated, and the vaporized working fluid 6 diffuses into the closed space 4 between the outer container 1 and the inner container 2, and is condensed / condensed in the low temperature (low pressure) condensing section 8. It liquefies and transfers the latent heat of condensation to the inner container 2. Since a large amount of the condensation of the working fluid 6 occurs in the lower temperature portion of the condensation section 8, the temperature distribution of the inner container 2 can be made uniform as a result. And inner container 2
The hydraulic fluid 6 condensed in the step falls under its own weight and is stored in the liquid storage section 5, is heated again in the evaporating section 9 and is vaporized, and the inner container 2
Is heated, and this cycle is repeated to heat the object 10 in the inner container 2 uniformly.

Since the heat resistance plate 7a is attached to the bottom surface of the inner container 2, the latent heat of condensation in this portion is transferred to the heat resistance layer by the space formed between the heat resistance plate 7a and the inner container 2. Is transmitted to the object to be heated 10. Therefore, due to this thermal resistance, the surface temperature of the thermal resistance plate 7a becomes higher than that of the other condensing portions 8, and the amount of hydraulic fluid condensed per unit area decreases, and the amount of heat transfer decreases. Therefore, the entire inner container 2 has a structure in which the side surface is more strongly heated than the bottom surface.

[0007] The reason is that, for example, when cooking rice, rice and an appropriate amount of water are put into the inner container 2 and heating is started. However, at the time of cooking rice, the hot water in the inner container 2 is absorbed or evaporated by the rice. As the water level gradually decreases, the rice located in the lower part of the inner container 2 is immersed in hot water for a longer time and is heated more. The more rice is located, the less heat it receives, and so-called uneven cooking occurs in the vertical direction. For this reason, the thermal resistance plate 7a
To reduce the amount of heating at the lower part and prevent uneven cooking.

However, when the temperature distribution of the object to be heated at the time of cooking rice in a heat pipe type heating vessel in which the thermal resistance plate 7a is not actually provided is measured in detail, the above phenomenon does not always occur. Conversely, a phenomenon occurs in which rice located at the top is heated more strongly. This is because the following natural convection is obstructed.

For example, when heating a single fluid (for example, only water) in a normal single vessel, or when heating only the bottom surface of the vessel, a difference in specific gravity due to a temperature difference between the upper and lower sides of the fluid causes a difference in specific gravity near the heating surface. Natural convection, in which the hot fluid rises and the cold fluid above it descends, is actively generated, and the entrainment allows the entire body to be heated at a substantially uniform temperature.

However, when the bottom surface and the side surface of the container are heated at the same temperature, the high-temperature fluid near the heating surface of the bottom surface rises, but the downflow along the side surface does not occur because the side surface is also heated. However, natural convection is impeded, and the upper portion becomes hot and the lower portion becomes cold, resulting in a temperature distribution having a temperature gradient in the vertical direction, resulting in uneven heating. In addition, in cooking rice, since the object to be heated is a mixture of rice and water, the convection of water is hindered by the rice grains, so that large convection does not occur as in a single fluid, and the upper portion directly above the lower heater is localized. Heating non-uniformity occurs in which the central part is heated at a high temperature, the central part is at a low temperature, and the upper part is at a moderate temperature.

When the bottom and side surfaces of the inner container 2 are heated at the same temperature using a cooking vessel of a heat pipe type, uneven heating can be suppressed as compared with the case where heating is performed in the above-described ordinary container. Since heating is performed to the same extent as the bottom surface, it is difficult for downflow to occur on the side surface portions, and natural convection is hindered.
As shown in (2), heating unevenness occurs in which the upper part is heated at a high temperature, the central part is heated at a low temperature, and the lower part is heated at a medium temperature. Therefore, even if the heat resistance plate 7a is provided at the bottom of the inner container 2, it is understood that cooking unevenness cannot actually be prevented, and conversely, the temperature difference between the upper and lower sides is enlarged.

Another problem of the conventional heat pipe type cooking vessel lies in the selection of the working fluid 6. That is, the following items are required for selection of the working fluid 6 for a cooking vessel such as a rice cooker for heating food. (1). Basic physical properties of a heat pipe as a working fluid that repeats the cycle of evaporation and condensation. For example, boiling point, freezing point, latent heat of evaporation and condensation, specific heat, specific gravity, viscosity, surface tension, etc. (2). Vapor pressure. Pressure corresponding to the temperature range used normally and the temperature during abnormal use. Related to the mechanical strength design of the container. (3). safety. Food safety for the human body when the inner container 2 has a hole due to corrosion or the like and the liquid is mixed into the object 10 to be heated. In addition, flammability when leaking out of the hole, alteration to toxic substances by direct contact with high temperature parts. Furthermore, pollution of groundwater at the time of disposal and air pollution (eg destruction of the ozone layer). (Four) . lifespan. Corrosive to metal materials such as outer container 1 and inner container 2. In addition, the generation of harmful non-condensable gas which occurs as a result (the gas hinders the movement of the vapor of the working fluid 6,
A normal cycle does not hold). Also thermal stability. (Five) . Price and availability.

As the working fluid for the heat pipe, various substances have conventionally been proposed and put into practical use according to the conditions of use. However, practical examples of this kind of cooking vessel for heating food are still almost undisclosed. However, only some of pure water and CFC-based substances have been proposed. Pure water is most commonly used as a working fluid for heat pipes, and although its basic properties, safety, lifespan, price and availability are satisfactory, its vapor pressure is not sufficient for cooking vessels. There is a big problem in the point. For example, in the case of a rice cooker, the temperature of evaporation / condensation is usually from room temperature (water temperature) to 100 ° C., and about 120 ° C. at the time of dry-up in which the heater in the inner container 2 is stopped due to the depletion of the moisture in the inner container 2. Considering a controller failure, it is necessary to consider a temperature region of about 150 ° C. in which the thermal fuse operates. Pure water has a vapor pressure of 1 at 100 ° C.
01.0 KPa, the pressure in the closed space 4 becomes negative pressure (atmospheric pressure or less) below this, and becomes positive pressure above this pressure,
199.1 KPa at 0 ° C., 475.6 KPa at 150 ° C.
When the temperature is 100 ° C. or higher, the pressure rapidly rises with the temperature rise. If the pressure is equivalent to about 120 ° C., a normal pressure vessel design can sufficiently cope with this. However, in view of 150 ° C. and the operability (weight) of the vessel, the use of pure water becomes impractical.

[0014] Freon-based hydraulic fluids have also been put to practical use in heat pipes due to their low toxicity, chemical stability, nonflammability, and the like. However, CFCs made of chlorine, fluorine, and carbon have been used. Theories have been published that the chlorine atom is involved in the depletion of the stratospheric ozone layer, and its use is currently being regulated. Furthermore, perfluorocarbon, which is mainly composed of fluorine but does not contain chlorine, is also considered to be an effective working fluid instead of chlorofluorocarbon, but its practical use is difficult in terms of the generation of toxic substances and the cost during high-temperature heating.

[0015]

The problem to be solved is that the conventional heating cooking container has a structure in which a heat resistance plate is attached to the bottom surface of the inner container, so that uneven heating temperature in the vertical direction cannot be prevented. That is, the so-called uneven cooking cannot be prevented, and the structure in which the heat resistance plate is formed in the heat pipe makes the production difficult and increases the cost. Also,
The working fluid did not satisfy both the thermal performance as a heat pipe and other practical performances.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a heating and cooking vessel which can prevent unevenness in heating temperature in a vertical direction with a simple structure, prevent uneven cooking, and reliably operate a heat pipe. The purpose is.

[0017]

The most important feature of the cooking container according to the present invention is that a heat resistance layer is provided above a closed space between the outer container and the inner container.

Further, it is characterized in that the size of the heat resistance layer is variable in the heating step.

Further, the heat resistance layer is formed by means for substantially eliminating the closed space above the side surface of the container.

[0020] Further, it is characterized in that propylene glycol is sealed in a closed space to form a working fluid.

[0021]

In the heating cooking container according to the present invention, a non-condensable gas is sealed in the upper portion of the closed space between the outer container and the inner container so as to form a heat resistance layer. Accordingly, it is possible to heat the object to be heated mainly from the bottom of the inner container while changing the volume of the non-condensable gas.

In addition, the upper part of the sealed space between the outer container and the inner container is partially made to have no space by the shape of the container, so that the heating of the object to be heated can be concentrated on the bottom of the inner container. Becomes

Further, by using propylene glycol as the working fluid, it becomes possible to satisfy the thermal performance as the working fluid and practical conditions, and to reliably operate the heat pipe.

[0024]

【Example】

Embodiment 1 FIG. Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment in which the present invention is applied to a rice cooker kettle.
In the drawing, the same reference numerals as those in FIG. 4 indicate the same or corresponding parts. In this embodiment, the inner container 2 has substantially the same shape as the outer container 1, and 7 is a heat resistance layer.
The heat resistance layer 7 is formed by sealing a predetermined amount of non-condensable gas such as nitrogen gas in the closed space 4.

That is, the non-condensable gas sealed in the closed space 4 is pushed upward due to a difference in specific gravity between the vaporized working fluid 6 and the vaporized liquid during heating, and as shown in FIG. The heat resistance layer 7 is formed at the upper part of the side surface of the closed space 4 constituted by 2. Since the volume of the non-condensable gas forming the heat resistance layer 7 changes depending on the operating temperature (operating pressure) of the working fluid 6, the entire side surface of the inner container 2 is non-condensed at normal temperature when rice cooking is started. The amount of sealing is adjusted so that it is covered with a sexual gas.

Reference numeral 6 denotes a working fluid composed of highly purified propylene glycol (C ₃ H ₈ O ₂ ), which is sealed in an appropriate amount in the closed space 4. This propylene glycol is
It is a non-toxic substance specified as a food additive. It is a highly viscous and transparent liquid substance at normal temperature and pressure. And, like other working fluids, it has the property of repeating the phase change between liquid and gas in the heat pipe. Its boiling point is 18 at atmospheric pressure
At 8 ° C., the vapor pressure is 3.9 KPa at 100 ° C., 8.8 KPa at 120 ° C., and 31.4 KPa at 150 ° C. When used as a rice cooker, the pressure in the closed space 4 is constantly negative. Therefore, the outer container 1 and the inner container 2 need only be designed in consideration of only the negative pressure, and can be made thin. In addition, propylene glycol has almost no chemical reaction with metal materials, has no environmental problems at the time of disposal, and is inexpensive. Since propylene glycol has a higher viscosity as a liquid than pure water or the like, it is necessary to devise an air gap or the like in the closed space 4 for circulating the liquid from the condenser 8 to the evaporator 9.

The heating and cooking vessel in the first embodiment is configured as described above. When the evaporating section 9 is heated, propylene glycol as the working fluid 6 boils and evaporates.
The inner container 2 is liquefied in the condensing section 8 on the bottom surface of the inner container 2 and is heated by the latent heat of condensation. Further, the vaporized working fluid 6 is condensed by the non-condensable gas into the condensing portion 8 on the side surface of the inner container 2.
Therefore, in the initial stage of heating, the object to be heated 10 is heated from the bottom surface of the inner container 2 on average. Therefore, the heated water naturally convects through between the rice grains and sufficiently transmits heat to the upper portion, so that it is possible to prevent the occurrence of uneven heating temperature in the vertical direction.

As the heating proceeds in the rice cooking step, the pressure in the closed space 4 increases with the temperature of the object 10 to be heated.
As described above, the non-condensable gas decreases in volume and is driven to the upper part of the closed space 4. Therefore, the condensing portion 8 where the working fluid 6 condenses gradually expands also on the side surface of the inner container 2, and finally, the condensing portion 8 wraps around the whole object to be heated 10, and the heating is performed at a uniform temperature. Will be

As described above, in the present embodiment, in the early stage of rice cooking, heating is performed while promoting convection by strong heating from the bottom of the inner container 2, and in the middle stage of rice cooking, the condensing section 8 is heated while gradually expanding. In the latter half of rice cooking, the condensing section 8 can heat the whole to be wrapped, and the object to be heated 10 can be heated and cooked at a uniform heating temperature with a small difference between the upper and lower temperatures.

Embodiment 2 FIG. In the first embodiment, a non-condensable gas is used as a means for forming the heat resistance layer on the upper side of the container. However, the means for forming the heat resistance layer is not limited to the first embodiment. Absent. FIG. 2 is a view showing another embodiment for forming a heat resistance layer. As shown in FIG.
The closed space 4 composed of the outer container 1 and the inner container 2 is partially eliminated by increasing the diameter of the upper part of the side surface of the inner container 2 and making it close to the upper side surface of the outer container 1, so that the vapor of the working fluid 6 rises. Is substantially the same as forming the heat resistance layer.

In the second embodiment, the condensing section 8 is limited to the lower side and the lower side of the inner container 2, and the object to be heated 10 is mainly heated from below. In addition, the heating of the upper part of the to-be-heated object 10 is
It is performed by convection of water inside and conduction heat transfer of the inner container 2.

Embodiment 3 FIG. FIG. 3 is a view showing still another embodiment in which a heat resistance layer is formed. As shown in FIG.
Is cut at the lower part of the side surface, and is hermetically welded to the inner container 2 here.

In the third embodiment, only the portion surrounded by the outer container 1 becomes the heat pipe portion, and the upper side heating by the working fluid 6 is completely eliminated.

Further, the present invention is not limited to Embodiments 1 to 3,
As means for preventing the movement of the vapor of the working fluid 6 to the upper side of the container, an obstacle, such as a wire mesh, which partially suppresses the rise of the vapor of the working fluid 6 is provided in the closed space 4. The same effect can be obtained. In this case, since the working fluid 6 is partially held by the obstacle, it is necessary to optimize the sealed amount in advance. Example 1 above
In other cases, the area of the condensing section 8 becomes constant throughout the rice cooking process.
You .

In the above embodiment, the case where the cooking vessel of the present invention is used for a rice cooker is described.
It goes without saying that it can be used for other cooking containers.

[0036]

Since the present invention is configured as described above, it has the following effects.

By providing a heat resistance layer on the upper side of the container, the amount of heating from the bottom of the inner container can be increased,
The object to be heated can be heated at a uniform temperature by activating natural convection.

Further, by using a non-condensable gas for the heat resistance layer, the area of the condensing portion can be changed in the heating step, and the heating area is gradually increased from the bottom in the early stage of heating and gradually in the middle of heating. In the latter stage of heating, heating can be performed from the entire surface, and the heating temperature of the object to be heated can be further uniformed.

Further, since the heat resistance layer is provided by substantially eliminating the closed space at the upper portion of the side surface of the container, it is possible to eliminate the uneven heating with a simple structure and to facilitate the manufacture.

Further, by employing propylene glycol as the working fluid, it is possible to form a heat pipe satisfying thermal performance and practical conditions.

[Brief description of the drawings]

FIG. 1 is a sectional view showing Embodiment 1 of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a sectional view showing a third embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a configuration of a conventional heating and cooking container.

FIG. 5 is an isotherm diagram showing a temperature distribution of an object to be heated in a conventional cooking vessel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer container 2 Inner container 4 Closed space 6 Hydraulic fluid 7 Thermal resistance layer

Claims (1)

(57) [Claims] Sealed space between the claim 1 outer container and the inner container is formed, in the heating cooking container of the heat pipe type hydraulic liquid is sealed in the closed space, to the sides of the container top, the operation of the working fluid By pressure
A heating cooking container provided with a heat resistance layer using a non-condensable gas whose volume changes .