JPS62243515A - Thermos heatable by direct fire - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermos bottle, or a kettle or pot with high heat retention obtained using the thermos bottle.

Conventionally, it has not been possible to heat the liquid inside a thermos bottle directly from the outside of the container using gas heating or electric heating. This is due to the structure of the thermos bottle, which has good heat retention, or heat shielding, and prevents internal heat from transferring to the outside.
This is because heat from the outside is not transferred to the inside.

However, it would be advantageous to be able to keep the internal temperature constant, prevent its cooling, and ensure that heat is rapidly transferred to the internal area only when the external temperature is higher than the internal temperature.

The present invention has been made to obtain a container that has such a unidirectional conduction function, that is, a type of thermal diode, and this principle will be explained with reference to the drawings.

As shown in Figure 1, the container is divided into an outer container (1) and an inner container (2).
), the space (3) between them is evacuated or depressurized, and a liquid serving as a heat medium (4) is sealed. At this time, make sure that the bottom of the inner container (2) does not come into contact with the liquid of the heat transfer medium (4) collected below. As a result, the inside of the inner container (2) is normally kept warm by this vacuum or reduced pressure layer (3), but when heated from the outside, the outer container (1) of the heat medium (4)
) and condensation on the inner vessel wall (2), heat is easily transferred into the inner vessel (2).

For example, if water is used as a heat medium (4), at room temperature 20℃, 18
The inner container (2) is surrounded by a vacuum layer (3) of about Torr, and when the liquid (6) placed in the inner container (2) is hot, this becomes a heat insulating layer. When the liquid (6) in the inner container is cold, by heating the bottom of the outer container (1),
The liquid (6) in the inner container can be heated. This is shown in the format diagram in Figure 2.

That is, when the bottom of the outer container (1) is heated, the enclosed water as a heat medium (4) immediately begins to evaporate because it is under reduced pressure. This is evaporation due to boiling unless the degree of heating is very small. Obtains latent heat of vaporization and generates steam (7
) Since the inner container (2) contains the cold liquid (6), the water immediately transfers latent heat on the outer container wall and condenses to form water droplets (8), which lowers the pressure. For this reason, steam (7
) becomes a flow toward the low temperature inner container wall (2). on the other hand,
The condensed water droplets (8) eventually flow down to the bottom of the outer container (1) due to gravity. The water that flows down is heated again and evaporates. Through such circulation through evaporation and condensation of the heat medium (4), heat from the outside is quickly transferred to the liquid (6) in the inner container.

Since the heat insulation and heat transfer mechanism of the present invention is as described above, it is preferable that the amount of liquid in the enclosed heat medium (4) is small in terms of heat transfer responsiveness. However, due to hold-up of droplets (8) on the inner container wall surface (2) during heating, if the amount of liquid is reduced to such an extent that there is no liquid at the bottom of the outer container (1), the heat transfer rate decreases rapidly. In addition, before enclosing the heat medium (4), it is better to make the double wall (3) as high a vacuum as possible so that there is no air or other contaminants, which will improve the thermal insulation properties during insulation and the thermal conductivity during heating. improves. The lid (9) serves as a heating container, so the inner container (2)
) should be designed to allow the pressure inside to escape, and should also have an insulated structure.

When water is used as the heat medium (4), the liquid in the inner container (6)
In order to raise the temperature to 100° C., the pressure inside the double wall (3) can be operated at approximately below atmospheric pressure. However, 1
When the temperature rises to 00° C. or higher, the pressure becomes higher than atmospheric pressure. Therefore, if you want to always operate the inside of the double wall (3) at below atmospheric pressure, or if you want to avoid excessively high pressure, you can achieve this by using a heat medium with a boiling point of 100°C or higher. . Since this high boiling point heat medium has a low vapor pressure at room temperature, it also improves its insulation properties during heat retention. As described above, various types of heat medium (4) can be selected depending on the purpose.

Furthermore, the inside and outside of the inner container wall (2) and the outer container wall (
1) As with ordinary thermos bottles, if the internal thermal emissivity is small, or conversely, if the reflectance is increased, the insulation improves.

Regarding heat retention, the present invention has an inner diameter of 170 mm and a depth of 17 mm.
For comparison, 2.5 liters of water was poured into a container of the present invention having a diameter of 0 mm, and a regular single-layer container with the same internal volume for comparison.
℃ and then examined the temperature drop.

The respective structures are shown in FIGS. 3 and 4.

The materials used are 18-8 stainless steel with a thickness of 0.5 mm, and the emissivity of the surface thereof is 0.3. However, for the outermost surface of the container, it is about 0.6. In the container of the present invention, 100 cc of water is sealed as a heat medium (4) after the double structure part (3) is depressurized. The water temperature measurement position (10) in the container was set at the center of the water.

This temperature decreasing curve is shown in FIG. The cooling conditions at this time are
The outside temperature was 15°C, and both containers were placed on a trivet with air circulating through the bottom.

Although the container of the present invention has poor heat retention compared to a general thermos bottle, the temperature drop is much smaller than that of a container placed in an ordinary single layer container.

For example, in this example, it takes 2 hours for a normal container to cool down to 50°C, but in the present invention, it takes 16.5 hours to cool down to 50°C.
r, and its heat retention is high.

On the other hand, regarding heating properties, each container was heated by placing 2.5 liters of water at 15°C in a diameter of 170 mm and placing it on a 1 kW electric heater. The outside temperature at this time was also 15
It is ℃. The temperature increase curve is shown in FIG.

Both require 29 minutes to reach 100°C, and although the containers of the present invention have high heat retention properties, their heating characteristics are exactly the same as, or slightly better than, ordinary containers.

During this heating, the overall heat transfer coefficient based on the heating surface was approximately 30 . However, the overall heat transfer coefficient varies depending on conditions such as the heating method and heating rate, and is about 10 to 100. Then, the outside of the bottom of the outer container (1) (
heating surface side), inside (heating medium side) and inner container (2)
The outside (heat medium vapor side) and inside heat transfer mechanisms and their heat transfer coefficient values are approximately as follows in the above order.

Note that when the container wall is made of metal, its conduction heat transfer resistance can be ignored.

1) Forced convection heat transfer coefficient due to radiation from heat source or combustion gas: 10 to 100 2) Boiling heat transfer coefficient of heat medium: 1000 to 100003)
Condensation heat transfer coefficient of heat medium: 2000-20000 4) Natural convection heat transfer coefficient of water: 100-2000 As can be seen, the heat transfer coefficient on the heat medium side of the double structure is sufficiently large, resulting in heat transfer resistance. Not yet. The rate of heat transfer is determined by the heating surface side at the bottom of the outer container (1) and the inner container (2).
The water side is mainly the former. Therefore, the overall heat transfer coefficients of the ordinary container and the present invention are almost the same. The reason why the container of the present invention promotes heat transfer slightly is that 1) the area in contact with the inner container wall (2) and the water (6) therein is all the heat transfer area; 2) This is thought to be due to the fact that the lid (9) has a heat insulating structure.

Although the present invention has inferior heat retention compared to ordinary thermos bottles,
This drawback is compensated for by the advantage that when the temperature of the liquid (6) inside drops, it can be heated over an open flame and the temperature can be raised immediately. And the heating characteristics over this direct flame are
Since it is as good as a kettle, it can be actively used as a kettle with high heat retention.

Similarly, this property can be used as a pot with high heat retention. If the heat retention of the pot increases, there will be no need to boil the food immediately before meals, and everyone will be able to enjoy hot food even in households where mealtimes vary. Moreover, since it has good heating properties, it is easy to reheat it. Furthermore, when the present invention is applied to a pot, it is possible to take advantage of the fact that the heat transfer surface covers the entire liquid-contacted surface of the pot and that heating is uniform.

On the other hand, a drawback of the present invention is that the double-walled sealed part (3) contains a heating medium (4), even if it is a small amount, so when it is empty, the pressure becomes high and dangerous. . Therefore, the safety valve (11) is necessary. However, since it is a vacuum at room temperature, it is best to use a fusible plug made of a fusible alloy that can completely shut off the outside air to prevent air leakage.

For this reason, it is possible to reduce the amount of the heat medium (4) enclosed, and even if the container is tilted, the outer container (1) facing the heating element can be
As shown in FIG. 7, a capillary structure (5) may be tightly attached to the front surface of the bottom of the outer container (1) so that the heat medium (4) spreads over the front surface of the bottom of the outer container (1). However, this capillary structure (5) also reduces the heat retention effect, so the inner container (2)
It is necessary to avoid contact with

Moreover, as mentioned above, the double structure part (
3) has almost no heat transfer resistance, so even if it is applied only to the bottom of the container, the heating performance will not deteriorate.

Therefore, the peeled wall of the container may be a general heat insulating structure (12) made of a vacuum layer or a heat insulating material. This is shown in FIG. In this way, heat retention performance can be improved.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of the container of the present invention. FIG. 2 is a schematic diagram showing the heat transfer mechanism of the container of the present invention. FIG. 3 is a longitudinal sectional view of the container of the present invention used for measurement. FIG. 4 is a longitudinal sectional view of a single container used for comparison with the container of the present invention shown in FIG. Figure 5 shows the temperature drop curve of water in the container. Figure 6 shows the temperature rise curve of water in the container. 7 and 8 are longitudinal sectional views showing embodiments of the container of the present invention. 1 is an outer container, 2 is an inner container, 3 is a space within the double wall, 4 is a heat medium, 5 is a capillary structure, 6 is a liquid in the inner container, 7 is a vapor of a heat medium, and 8 is a heat medium 9 is a lid, 10 is a temperature measuring position, 11 is a safety valve, 12 is a general insulation structure made of a vacuum layer or a heat insulating material, A is the water temperature in the container of the present invention, B is in the single layer container water temperature.

Claims (1)

[Claims] 1) The container has a double structure of an outer container (1) and an inner container (2), and the space (3) between them is evacuated or depressurized, and the liquid serving as the heat medium (4) is transferred to the inner container. (2) A thermos bottle sealed to the extent that it does not touch the bottom. 2) The thermos bottle according to claim 1, wherein the capillary structure (5) is brought into close contact with the inner bottom of the outer container (1). 3) The thermos bottle according to claim 1 or 2, which has a heat insulating structure that does not allow heat medium to enter the portion other than the bottom portion. 4) The thermos flask according to claim 1, 2 or 3, which is in the shape of a container used for heating purposes such as a kettle or a pot.