JPH0455045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot water boiler that can be directly heated.

Conventionally, electric containers have been popular for keeping water warm for a long time after boiling it, but because of the electric cord that is essential for maintaining electricity,
It lacks portability and other mobility. On the other hand, there is a thermos flask (dewar flask) as a container that can hold boiling water for a long time once it has been boiled.
This cannot be heated as is, and requires the effort of boiling it in another container and then transferring it. It is also inconvenient to re-boil water that has become somewhat lukewarm after being held for a long time. In view of the above-mentioned reasons, the present invention aims to create a hot water boiling container that can be directly heated in a normal gas or electric furnace and has heat insulation and heat retention similar to a thermos flask.

Prior art related to this purpose includes, for example, Japanese Patent No. 126548, which can keep water warm after boiling it in the same container.
No. 25629 exists, but in both cases, the container has a mechanically movable part that changes the state of the container during heating and keeping warm, so the effectiveness and stability are insufficient.

The present invention is characterized by utilizing the thermosiphon principle. In order for a container to have a heat-retaining effect, a heat insulating layer must be formed around the container, but if it were just a heat insulating layer, this would actually hinder the transfer of heat when boiling water. These two contradictory points,
The present invention simultaneously satisfies these requirements by utilizing the thermal diode properties of the thermosiphon.

FIG. 1 shows the basic structure of a water boiling container using a thermosiphon according to the present invention. The boiling vessel has double walls on its sides and bottom, and a hollow space between which a working fluid, which is a suitable heating medium, is sealed. The most common heat medium is water. This will be explained below using water as an example. The inner tank 14 formed by the inner wall 16 contains water 13 to be boiled and used, which is different from water as a heat medium, and the outer tank 14 contains water 13 that is to be boiled and used.
During heating, the bottom and part of the sides are exposed to the flame of a gas or electric furnace or a heating element. This outer wall is also heated by the induced current when it is placed in an electromagnetic cooker. In principle, the inner wall and outer wall do not come into contact with each other at the side surfaces and bottom, except for the upper joint that supports the inner wall, and the water sealed as a heat medium also forms a reservoir 11 at the bottom of the container when it is left standing. When the upper inner wall 16 is not touched, the inner wall 16 and the outer wall 1
A space must always be maintained between the 5's. This space 10 is filled with water vapor and, in principle, is not contaminated with air.

When boiling water, the bottom and part of the side surface of the outer wall 15 are heated from the outside in the same way as when heating a normal kettle. Water 11, which is a heat medium accumulated at the bottom, receives the heat and turns into steam, which fills the space 10 between the two walls. Since the liquid phase and the gas phase are in equilibrium with their respective temperatures and vapor pressures specific to each substance, when the temperature on the inner wall side is lower than the outer wall side, the vapor that has been vaporized by receiving heat from the outer wall 15 comes into contact with the inner wall 16. There, it liquefies, giving heat of condensation to the inner wall. The water that condenses on the inner wall surface becomes water droplets and flows down the inner wall surface.
It moves downward under the action of gravity and finally drips back to the pool 11 at the bottom of the outer wall. There, it receives heat from the heated outer wall again, vaporizes it, and repeats this process. Due to this circulating action of the heat medium, the inner tank 14 that is not in direct contact with the outer wall is also heated, and the water 13 held therein is also heated and its temperature rises, eventually boiling.

Once the water 13 in the inner tank has boiled and the heating has stopped, the cooling process then begins. Naturally, the temperature on the outer wall side decreases first, but during heating, the heat flow generated from the high temperature side outer wall to the low temperature side inner wall due to the water vapor that was present, and during cooling, the heat flow from the high temperature side inner wall to the low temperature side outer wall. It does not occur towards. There is no moisture in contact with the inner wall except for a few water droplets that adhere to the inner wall surface when heating is stopped, and after this small amount of moisture scatters, there is no steady supply of water to the inner wall. This is because there is no circulation of the heat medium. Therefore, the transfer of heat from the inner wall side to the outer wall side is simply heat transfer through the gas phase space, and is significantly reduced compared to the case from the outer wall side to the inner wall side during heating.

A thermosiphon can also be considered a variation of a heat pipe. In general, thermosiphons and heat pipes consist of two poles between which heat is transferred, and the two poles are connected by a passageway for a heat medium, gaseous vapor, which transfers heat in the form of heat of vaporization and heat of condensation, and a working fluid in which the vapor is liquefied. It is characterized by The existence of a void that serves as a path for the vapor propagation of the heat medium is common to both types, but heat pipes normally have a layer called a wick to allow permeation flow to circulate in order to circulate the condensed heat medium. As mentioned above, the thermosiphon circulates the working fluid by dropping droplets or falling along the wall surface under the action of gravity, so it does not require a wick, and is not found in ordinary heat pipes. It has a so-called thermal diode characteristic that allows heat to flow in one direction. Heat pipes are generally known as extremely efficient means of heat transfer, and examples include thermosiphons and heat pipes being applied to kettles for boiling water and cooking pots for the purpose of improving thermal efficiency and heat transfer characteristics during heating. has been observed so far. (For example, Patent Publication No. 52-4619,
Utility Model Publication No. 16388 (1982) As is clear from the above, although the present invention uses indirect heating using a heat medium, its efficiency and heat transfer speed are comparable to those of ordinary kettles, etc. . In addition to this, the present invention is characterized in that the thermal diode characteristics of the thermosiphon are utilized to improve the heat retention effect after heating is stopped.

It is desirable that the water droplets condensed on the inner wall side during heating drip into the lower reservoir immediately, and the smaller the wetting property of the inner wall with water, which is the working fluid, the better. The effect can be improved by making the surface more precise, or by adding a Teflon or oxide film, or a suitable plating surface layer. This is because if water droplets or a thin layer of water adhere to the inner wall after heating is stopped, they will absorb heat from the inner wall and vaporize. With the exception of a small amount of water adhering to this inner wall, there is no vaporization or condensation of the working fluid after heating has stopped, but the other main causes are heat dissipation through conduction at the bottom and sides, and convection at the sides. There is heat transfer due to heat transfer and heat loss due to radiation. The largest of these is loss due to convection on the sides. In order to avoid this, as will be shown later in the examples, the sides of the container may be covered with a heat insulating layer, or the space 10 between the double walls for the thermosiphon configuration may be provided only at the bottom, and removed at the sides. There is a way to use it as a heat insulating layer.

The temperature of the working fluid reservoir at the bottom of the outer wall determines the vapor pressure in the thermosiphon space between the double walls, which rapidly decreases as the outer wall side cools. By the way, the vapor pressure of water at room temperature is about 20 mmHg.
When water is used as the working fluid, a pressure drop of up to this level can be expected as the outer wall cools. However, since the thermal conductivity of gases generally does not depend on the pressure of the gas, it cannot be expected that this level of pressure reduction will reduce heat loss due to conduction. A few mm
If the pressure can be reduced to a degree of vacuum lower than Hg, the conductivity can be lowered, so either choose a substance with a low vapor pressure other than water as the working fluid, or dissolve an appropriate solute in water to reduce the vapor pressure by the solute effect. If this can be achieved by lowering the temperature or by using a moisture absorbing material or a substance that crystallizes water, the heat retention effect after heating is stopped can be further enhanced.

The heat retention effect using the thermal diode characteristics of the thermosiphon according to the present invention can also be used in large water heaters for hot water supply and cooking pots. In the case of cooking pots, water can be used as a heat medium for normal boiling, but for cooking that requires high temperatures of 200℃ or higher,
From the viewpoint of material strength, it is difficult to seal and retain water, so a suitable hydrocarbon oil with low vapor pressure is used.

Some examples will be given below, and the structure, composition, materials, etc. will be explained in further detail.

The most basic type is shown in Figure 1, which was used to explain the principle of thermosiphon application.
This type has a space 10 between the double walls that communicates the bottom and side parts, and allows the circulation of the heat medium of the thermosiphon to work over this entire area. Water is used as a heat medium. In recent years, various types of metal thermos flasks made of double walls that have been evacuated have become popular, and these techniques can be applied to the production of double walls for thermosiphons. The material may be iron, stainless steel, aluminum, etc., which are used in ordinary kettles and other cooking pots. In order to permanently retain water between the double walls, it is desirable to use stainless steel or apply a coating such as Teflon to the inner surface of the walls to prevent corrosion of the walls, but as a general rule, between the double walls Since the air is sealed and isolated from the air, there is little risk of oxidation.

FIG. 2 shows a cross-sectional view of a more specific version of this type. In the figure, 24 is a safety valve. When working normally, the pressure in the air space 10 between the double walls is at most one atmosphere, but if you accidentally open it, the pressure increases rapidly as the vapor pressure of the water rises. However, he ends up destroying the equipment. This is to prevent this from happening. It may be installed anywhere as long as it is interposed between the air 10 of the thermosiphon and the outside air. Safety valves can be roughly divided into spring type and rupture disc type, but the latter has a higher degree of sealing and is easier to process for installation. The former type does not damage the valve even when it is activated and can be used repeatedly, but the structure is complicated and there is a risk of gas leakage. If the leakage itself is small, it does not pose a major problem during use, but after long-term use, it becomes necessary to supplement the water in the thermosiphon between the double walls. The operating conditions for the valve are preferably such that the pressure difference on both sides of the valve is approximately 1 atm (approximately 1 Kg/cm ² ). During cooling, the pressure in the air 10 drops to several tens of mmHg, and the pressure in the outside air becomes higher. When heated to boiling, the inside of the thermosiphon is
At 100℃, the pressure difference is 0, but it is possible that a slight temperature difference will occur between the temperature of the water that is the working fluid and the temperature of the water 13 used, and in this case, the pressure on the outside air side will increase. is lower. When the vapor pressure of water is 2 atm, the temperature is approximately 120°C, so the valve can withstand the temperature of the working fluid until it reaches this temperature. It is impossible for there to be a temperature difference of 20 degrees. When using this method for cooking pots, etc., the temperature of the food to be cooked may exceed 100°C, so it is necessary to shift the operating conditions of the valve to a higher pressure difference side.

Sealing of the working fluid, water, into the thermosiphon cavity can be easily achieved using this valve. After making the container, pour an appropriate amount of water into the container and bring it to a boil. Just close the valve when all the air has been expelled from the sky and it is filled with water vapor.

The strength required for the outer and inner walls constituting a double wall is also specified from the same viewpoint as above. The structure of a double wall can be simulated as a combination of two cylinders with different radii that share a central axis.
When referring to the strength design of pressure gas containers, as an example, aluminum alloy (material alloy yield strength approx. 10Kg/
mm ² ) A cylindrical container with a radius of 10 cm and a body wall thickness of 1 mm can withstand pressures of up to 10 Kg/cm ² . Heat pipes have a normal long and narrow cylindrical shape and can be made to be usable up to 200 degrees Celsius when water is used as the working fluid. Even if the inner and outer walls of the side or bottom parts are bridged here and there with rod-shaped or plate-shaped objects to reinforce the strength and promote the descent of the working fluid that has condensed on the inner wall, the thermosyphon which is the object of the present invention cannot be achieved. Although there is no problem with the function, there is a risk that the heat insulation properties may be partially impaired due to heat transfer through the bridge.

From an energy-saving perspective, it is better to keep the amount of water contained in the thermosiphon's empty space small. The minimum amount required is slightly more than the amount corresponding to the layer and water droplets that adhere to the surface when wetting the entire surface of the surrounding wall of the sky.

In FIG. 2, a donut-shaped plate 21 is attached to the middle of the bottom of the space between the double walls. This is because when pouring some of the hot water 13 in the inner tank after heating has stopped, the already cooled working fluid water empties when the container is tilted.
This serves as a weir for the working fluid to flow out to the side surface of the wall 10 and prevent it from coming into contact with the inner wall, and it also contributes to reinforcing the strength of the outer wall, but it is not necessarily necessary.
It is also possible to install a device such as an air pot that pumps out hot water using compressed air. In this case there is no need to tilt the container.

It is advisable to attach a simple valve to the base of the hot water supply port 23 of the container. This is because even if the inner tank 14 is surrounded by a heat insulating layer, heat loss due to vaporization of the hot water 13 in the inner tank will be large if the steam is communicated with the outside air. It is preferable to form a heat insulating layer 25 by using a heat insulating material also on the lid 18 of the boiling water container. Extending the thermosiphon cavity 10 to the top of the inner tank by reducing or removing the lid part may contribute to increasing thermal efficiency during heating, but it will reduce the insulation effect after heating is stopped. So I don't like it. This is because heat convection occurs from the lower inner tank toward the upper outer wall due to the vapor of the working fluid.

FIG. 3 shows an embodiment in which a heat insulating layer 32 is separately provided on the side surface of the thermosiphon instead of the air. In the figure, the lower end of the heat insulating layer 32 is at the same level as the bottom of the inner wall, but it may extend further to the bottom of the outer wall. According to this configuration, it is possible to eliminate heat loss due to convection of the working fluid vapor of the thermosiphon after heating is stopped. A high heat insulation effect can be obtained by separating the double-walled side cavity 32 from the thermosiphon cavity 10 by a partition plate 31 and evacuating it. Therefore, the heat loss is due to the thermal siphon at the bottom = 1
In this case, the upper inner wall 16 is high temperature, the lower outer wall 15 and the working fluid reservoir 11 are high.
Since the temperature is low, no convection occurs, and only heat transfer by conduction needs to be considered. Since this is heat conduction through a gas layer, the insulation properties are extremely high. The manufacturing process for metal thermos flasks, which has become popular in recent years, can be used to manufacture the vacuum double wall portion on the side, and there is no technical problem. A sufficient effect can also be obtained by filling the void 32 with a heat insulating material instead of evacuating it, taking into consideration the material, manufacturing cost, etc. Examples of heat insulating materials that can be used include glass wool and rock wool.
If a heat insulating material is used, it is also possible to remove the partition plate 31, but in this case, in addition to being able to maintain its shape, the heat insulating material is directly exposed to the working fluid of the thermosiphon. It is necessary to use a water-resistant material or to treat the surface to prevent water from penetrating into the insulation.

A feature of this type is that even the outer wall 15 at the bottom only needs to be exposed so that it can be directly exposed to fire, so the entire side wall may be further covered with a heat insulating layer, and the heat insulating layer may be doubled or tripled. Also, in Fig. 3, the structure of the upper lid or stopper 18 has changed somewhat compared to Fig. 2 so that hot water can pass through it, but this is just one type added for reference. Yes, and is unrelated to the structure of the thermosiphon. The present invention relates to the structure of a thermosiphon, which mainly concerns the structure of the side and bottom parts of the water boiler that constitute a double wall, but also includes a lid or plug part,
It does not stipulate the structure of the upper part, centering on the hot water supply spout, handle, etc.

FIGS. 4 and 5 show an example in which the side surfaces are made of two layers, one being a heat insulating layer 32 and the other being a thermosiphon cavity 10. In Fig. 4, the heat insulating layer is on the outside, and in Fig. 5, it is on the inside. As for the heat insulating layer, as in the type shown in FIG. 3, there are cases where it is vacuumed or a heat insulating material is used. Although the figure shows a vacuum case, the space 32 in the figure may be filled with a heat insulating material.
When using a material that has sufficient water resistance or can maintain interfacial density as a heat insulating material,
The boundary wall 41 between the thermosiphon cavity and the insulation layer can be removed. In the type shown in FIG. 4, since the thermosiphon also covers the side surface of the inner tank 14, heat transfer during heating is better than in the type shown in FIG. Furthermore, after heating is stopped, there is less loss due to heat convection at the side surface of the thermosiphon than in the type shown in FIG. The outer wall of the double wall sandwiching the thermosiphon cavity 10 on the side is the inner wall of the heat insulating layer 32, and unlike the model shown in Fig. 2, there is no difference between the inside and outside of the double wall. This is because the temperature difference between the two does not become large. The model shown in Figure 5 seems to have almost the same heat transfer characteristics during heating and heat retention properties after heating has stopped as the model shown in Figure 3, but the heat insulating layer is not directly exposed to strong flames from outside during heating. Since it is not exposed, it is possible to relax the conditions to some extent on the material of the heat insulating layer wall or, if a heat insulating material is used, the material of the heat insulating material.

In FIGS. 6 and 7, a heat insulating layer 62 is also provided at the bottom to increase the heat retention function after heating is stopped. This heat insulating layer 62 consists of the outer wall 15 and the inner wall 16.
A hole or tube 61 is provided which penetrates the heat insulating layer without completely blocking it. This is to constitute a thermosiphon and must be large enough to allow the vapor and droplets of the working fluid to pass through it without clogging. The position of this passage does not have to be near the center as shown in the figure, and may be in plural positions. 61 is also a part of the thermosiphon cavity 10, but since the condensed working fluid droplets pass through here and return to the lower reservoir 11 during heating, the walls around 61 are given an appropriate slope, etc. To allow droplets to reach this passage without stagnation on the way. In these types, it is more effective to vacuum the side and bottom insulation layers 32, 62 than to use insulation. Due to the presence of the heat insulating layer 62 at the bottom, heat loss due to heat conduction through the thermosiphon vapor layer at the bottom can be significantly suppressed, resulting in a heat insulating effect almost equivalent to that of a normal thermos flask. In the type shown in FIG. 7, the thermosiphon extends to the side surface of the inner tank, so the heat transfer characteristics during heating can be improved, but the structure is somewhat more complicated than the type shown in FIG. 6. The difference in the passage 61 for the working fluid through the bottom insulation layer 62 between the one in FIG. 6 and the one in FIG. is unrelated to the structure of 61 looks like a simple hole when the width of the insulation layer is thin, but
When the insulation layer is thick, it can be considered a pipe. The tube may be straight, oblique, or helical as long as the above conditions are met.

In order to further improve the heat retention effect, it is better to suppress heat loss due to radiation, but this can be done by adding vacuum insulation layers 32, 62 to the wall surfaces, as is done in regular thermos containers and other heat insulating containers. Increases the reflectance of Perform appropriate surface treatments such as plating and coating. This treatment may be applied to the wall surface of the thermosiphon cavity 10. This does not interfere with the function of the thermosiphon.

Regarding thermal efficiency and heat transfer characteristics during heating, it is obvious that thermosiphons are characterized as a type of heat pipe, so it is obvious that they are good. Estimating the heat loss for this model, if the heat insulating layers 25 and 32 on the side and top lids are evacuated, and if the leakage of steam from the inner tank to the outside of the container can be ignored, then the thermal siphon on the bottom Due to heat conduction through the vapor layer in the sky,
This is the main cause of heat loss. Thickness of bottom sky = 2
cm, radius 10 cm, the outer wall 15 and the working fluid reservoir 11 in contact with it are at room temperature 25°C, and the inner structure 14 has a
Approximately assuming that it contains 1 ℃ of water,
The thermal conductivity of water vapor is approximately 2×10 ^-4 (J/cm・s・K)
Therefore, the heat loss is at most 0.56 cal per second, and hot water over 80°C can be maintained for about 10 hours. In the model shown in Fig. 6, assuming that the heat transfer cross-sectional area is only the central hole 61, and assuming that the radius of this hole is 1 cm while keeping other conditions the same, the heat loss is It further decreases by two digits, and the retention time is
It becomes 100 times.

In reality, this retention time is about 15 to 30 minutes for a commercially available ordinary kettle, and about 5 to 10 hours for a thermos flask, and the insulating and heat retention properties of the water boiling container according to the present invention are different from those of conventional methods. This suggests that heat loss due to other factors, such as heat conduction through the walls of the inner tank or leakage of steam from the inner tank, must be taken into account; This is a common factor in the present invention, and is not a heat loss characteristic of the container according to the present invention. Therefore, at least structurally, the container according to the present invention can maintain the same level of heat insulation and heat retention as a conventional thermos flask, and is sufficiently usable for practical use. It is clear that it can be tolerated.

[Brief explanation of the drawing]

FIG. 1 is a schematic principle diagram of a direct-fired hot water heater according to the present invention, and FIGS. 2 to 7 are longitudinal sectional views showing embodiments of the direct-fired hot water heater according to the present invention.
Fig. 2 is a diagram showing an example of a case where a thermosiphon is arranged on the side and bottom of the container, Fig. 3 is a drawing showing an example of a case where a thermosiphon is arranged only on the bottom of the container, and Figs. The figure shows an example of a case where the side part of the container is formed of two layers: a heat insulating layer and a thermosiphon cavity. Figures 6 and 7 show an example in which a heat insulating layer is formed at the bottom in addition to the side part. The figure which shows an example when it makes it. 10... Thermosiphon empty, 11... Heat medium (working fluid) reservoir, 12... Heat medium (working fluid) droplets, 13... Hot water for use, 14... Inner tank, 1
5...Outer wall, 16...Inner wall, 17...Handle, 18
... Lid, 19 ... Flame or heating element, 21 ... Working fluid weir, 22 ... Valve, 23 ... Hot water supply port, 24 ...
Safety valve, 25, 32, 62...Insulation layer, 31, 4
1... Partition plate (boundary wall) between heat insulating layer and thermosiphon cavity, 61... Heat medium (working fluid) passage.

Claims (1)

[Scope of Claims] 1. The bottom and sides of the container are composed of a double wall, an inner wall forming an inner tank capable of containing boiling hot water, and an outer wall capable of being directly heated by an external heat source; Provided between the heavy walls is a sealed cavity surrounded by a continuous wall surface of which at least the main bottom of the inner wall and the main bottom of the outer wall are part.
The amount of working fluid that does not come in contact with the inner wall surface when the liquid reservoir is left standing is sealed by excluding gaseous components other than the working fluid components, and the droplets of the working fluid adhere to the inner wall surface within the space. When the space is drawn, gravity causes the space to reach the outer wall surface of the inner bottom, and the space between the double walls
A heating and heat-insulating container characterized in that, if there is an area that cannot be reached, this is used as a heat insulating layer. 2. In the container according to claim 1, a heat insulating layer is provided between the double walls between the inner wall and the outer wall, occupying part or all of the space between the double walls, and The heating and heat-insulating container according to claim 1, wherein the heat insulating layer is a vacuum heat insulating layer.