GB2241873A - A cooking device having heat energy regulator - Google Patents

Abstract

A cooking device (such as kettle, pot, pan, etc.) has its portion to he heated structured for regulating heat energy distribution. A main body (11) of the cooking device has an hermetic space (14) which contains low melting point heat energy regulating material (15) (e.g. tin or its alloys), heat conducting plate (16) and heat resisting layer (17). Melting of the heat energy regulating material (15) particularly assists regulation with a specific temperature range. The heat conducting plate (16) and heat resisting layer (17) further assist in reducing localised high temperature effects. <IMAGE>

Description

A COOKING DEVICE HAVING HEAT ENERGY REGULATOR Conventionally, gas burners widely used as heat sources for cooking purposes can provide high temperature, concentrated heating effect, high heating speed and convenient usage. However, they also cause localised high temperature zones at the surface being heated.

The traditional type of cooking device was commonly made of materials like cast iron, carbon steel, stainless steel, aluminum alloy, copper or its alloys through different manufacturing process such as drawing press, spinning press, casting and mashing, casting and forging to form a single body and then followed by surface treatment process such as polishing, colouring, electroplating and coating to complete the final product. Since a cooking device made of cast iron is too heavy to be handled, it is now rarely found in practical use. Those made of carbon steel are easy to get dirty by oil mud and scale, and are very difficult to clean. Cooking wares made of stainless steel have poor heat transfer capability that causes ocalised high temperature zone during heating, and can scorch food, even produce toxicity.Copper cooking wares have good heat transfer capability, but the material is too soft to be used as the surface of cooking pan for dry frying. Also copper copper corrodes easily to produce "patina", which can have high toxicity for humans.

Aluminium is believed to cause cancer so best not be used as the surface material of cooking devices.

Recently, different types of cooking ware were introduced which have their surface treated by special coating techniques. Yet there is still not any kind of cooking ware to suit all different cooking ways including-decoction, boiling, dry frying, oil frying, etc. It would be convenient to use almost only one cooking pot for all different cooking ways as Chinese people do. Chinese people normally like to fry their food over a fire. However, the enamel coated cooking ware is only suitable for boiling, and the Teflon coated "non-stick" cooking ware has a very soft coating that is easily scraped off.

The aforementioned cooking wares all have their inherent defects. If they are inappropriately used, they can seriously threaten food hygiene. In view of this, a new cooking device has now been invented to provide good hygiene and to suit Chinese cooking ways.

Embodiments of the invention can have not only lighter weight but also be substantially maintenance free in use.

According to this invention there is provided a cooking device having heat energy regulating structure wherein its portion to be heated is constructed as an inner part and an outer part, with a space between the said inner and outer part, which space contains low melting point heat energy regulating means.

In the accompanying drawing: Fig. 1 is useful for explaining ideal cooking ware; and Fig. 2 is a sectional view of a cooking device embodying the invention.

An ideal cooking device, to be capable of use for different cooking ways such as decoction, boiling, dry frying, oil frying, etc, should possess the following characteristics see Fig. 1: 1. Portion (3) of surface portion (2) used for cooking food should be hard and tough. Its surfaced skin material should not be easily removed by scraping or rough use, nor readily crack.

2. Portion (3) used for cooking food should possess a uniform temperature distribution which is maintained with a specific temperature range to prevent food from scorching during dooking.

3. Surface (5) of the cooking device should maintain stable chemical properties. It should resist corrosion and be easy to clean. The portion (3) used for cooking food should not produce harmful effects, especially at higher temperatures.

4. Portion (6) of the cooking device (1) to be heated and to transfer heat should possess a good heat transfer capability. The heat capacity of the portion (6) should be small at low temperature but large at high temperature. The remaining portion (7) should possess a poor heat transfer capability. Therefore, a higher heating efficiency can be obtained.

5. The complete cooking device should not be too heavy thus be convenient in use.

Traditional cooking wares and surface treatment methods do not result in cooking devices that meet any of the above-mentioned requirements.

Embodiments of this invention involve a concept and construction that permit a main body portion 1 (including surface portion 2 and cooking portion 3) of a material which is hard and tough and possesses stable chemical properties. Such materials normally have poor heat transfer capabilities. However, by applying structural features of the invention, i.e. providing heat energy regulating effects, it is possible to improve the heat transfer and temperature distribution capability of the main body portion 1.

However, a somewhat lighter body structure 1 and more uniform temperature distribution over the cooking portion 3 of the surface portion 2 are obtained, and temperature can be easily maintained within desired ranges.

Herein, it will be appreciated, the term "cooking device" is used to include all kinds of cooking wares.

As shown in Figure 2 a cooking device with a heat energy regulating structure, has a body portion 11 of the cooking device 10, an hermetic space formed between its surface portion 12 and bottom portion 13. Inside the hermetic space 14 is heat energy regulating material 15 and a heat conducting plate 16.

The surface portion 12 of the cooking device can be made of metal sheet or plate, except that it may have a thinner cross section than hitherto, otherwise its appearance is quite similar to that of conventional types of cooking ware. In order to obtain the characteristics of hard and tough as well as stable chemical properties, materials such as stainless steel, Monel metal or German silver, etc. can be used.

Normally, these kinds of material have lower heat transfer coefficients than traditional metals.

The bottom portion 13 is also made of metal sheet or plate. A hermetic space is formed between the bottom portion and surface portion of a complete unit. The surface portion 12 may be completely or partially covered by the bottom portion 13. The hermetic space 14 is conveniently coexistence with the underside of the cooking portion 18.

Basically, the heat energy regulating material 15 has a large heat capcacity when it is heated up from or cooled down relative to a given temperature level determined by the desired temperature variation profile.

This temperature level should be lower than the melting point of the material of the surface portion 12, bottom portion 13, and heat conducting plate 16. For general purpose cooking devices, low melting point metals or alloys (i.e. the materials having melting point below 2500 C) such as tin, silver-tin alloy, zinctin alloy etc. can be used as the heat energy regulating material 15.

Desirably heat absorption-releasing characteristics result during melting-solidification phase changes, i.e. passing through the melting point, thus obtaining particularly large heat capacity.

The heat conduction plate 16 is made of good heat conducting material such as copper, aluminium material etc. (silver is also considered as a good material if the cost is not very important) to form a plate or grid or net or apertured plate. In order to enhance the heat energy distribution effect of the heat conducting plate, a heat resisting layer 17 is incorporated or is next to the heat conducting plate 16 on the side facing surface portion 12. The heat resisting layer 17 can be obtained by various surface treatment method such as previously used for enamel layers, i.e. as a surface coating.

The hermetic space 14 is completely occupied by the heat conducting plate 16 and heat energy regulating material 15 either or both of which cover the underside of the cooking portion 18. It is secured to or otherwise fixed relative to the surface portion 12 and bottom portion 13. There is no strict requirement for the position of the heat conducting plate in the hermetic space 14 but it is conveniently central of the area of heat conducting plate 16 itself normally symmetrical of the cooking device 10.

When the cooking device 10 is heated up, the heat energy regulating material 15 absorbs heat energy applied to the bottom side of the cooking device 10.

Before the temperature of the heat energy regulating material 15 reaches its melting point, there will be heat transfer effects due the inherent heat transfer coefficient of the heat energy regulating material 15 through its thickness. When the temperature reaches its melting point, the heat energy regulating material begins to melt, at least near the high temperature spot and its temperature stays constant (due to latent heat effects) until it melts completely. During the melting process of the material (because its heat capacity is considerable so time is required for completion of melting) the temperature of the portion nearby the high temperature zone will begin to increase due to heat transfer effects and the temperature gradient over the cooking portion 18 will be low.If low melting point metal is used for regulating heat energy, after it is completely melted, the heat transfer coefficient of the metal in liquid phase is normally lower than that in the solid phase (about 1/2-3/4 that of the solid solid phase), which will effectively restrain-the heat transfer effect in the high temperature region relative to the directly corresponding area of surface portion 12, thus moderate the temperature rising of surface portion 12 near the high temperature region. So, heat regulating material 15 can restrain the localised temperature rising before and after it has all melted, and the cooking portion 18 of surface portion 12 will have a more uniform temperature distribution.During the period the cooking device 10 is cooled down to its solidification temperature, the heat energy regulating material 15 will release the same amount of heat energy as it absorbed during the melting process (for the same material, solidification temperature equals or approximately equals melting point), which will also moderate the temperature variation.

Accordingly, the effects of heat absorbingreleasing due to the heat energy regulating material 15 during melting-solidification stages as well as the variation of heat transfer coefficient between solid and liquid phases, facilitate the temperature of cooking portion 18 being kept within a desired range.

In order further to explain the effect of the heat conducting plate 16 while cooking device 10 is locally heated to form localised high temperature zone, it is assumed that the cooking device 10 receives a constant heat supply (i.e. constant power, constant heat actuation position and area). For an initial assumed steady state (i.e. constant temperature distribution, constant distribution of heat transfer rate), the power tranferred through a fixed boundary to the heat conducting plate 16 itself (from an area of higher temperature zone to which it is connected) equals the power absorbed from the corresponding area of bottom portion 13 minus the power transferred directly to the corresponding area of surface portion 12 (from the higher temperature zone), which is a constant value and depends on the heat transfer coefficient of heat conducting plate, the shape factor of the boundary (depending on the geometrical factors of the boundary and the conducting plate, such as the thickness, circumferential length, etc. of which), and the temperature gradient across the boundary.Since the heat conducting plate 16 is made of good heat conducting material (i.e. higher heat transfer coefficient), the heat conducting plate 16 for a particular thickness, will decrease the temperature gradient to some lower value across the boundary, i.e. the localised high temperature zone will become less obvious.

When a heat resisting layer 17 having a certain amount of thermal resistance is incorporated with the heat conducting plate 16 on the side facing surface portion 12 the power transferred directly from the high temperature zone to the surface portion 12 will be restrained to a certain level. Thus the power transferred from the boundary of the high temperature zone to the heat conducting plate 16 itself will be increased. This will enhance the effect of the heat conducting plate in distributing the temperature.

If a low melting point metal is selected having the heat transfer coefficient either at solid or liquid phase higher then that of the surface portion 12 as applies for Sn versus SUS 304 as the heat energy regulating material 15, it will be appreciated that, even if the heat resisting layer 17 is incorporated directly to the bottom side of the surface portion 12 in the area corresponding to the upper boundary of the hermetic space 14 (i.e. the heat resisting layer is not on the upper surface of the heat conducting plate), it will still have the effect of enhancing the heat distribution and restraining localisation of high temperature.

If material having good heat conduction capacity is selected as the bottom portion 13, the bottom portion 13 may serve as the heat conducting plate 16, which will simplify the structure of the cooking device 10. On the other hand, if there is no heat conducting plate 16, the heat energy regulating material 15 is still effective independently to make the temperature distribution more uniform over the cooking portion 18 as well as to moderate the temperature variation over the region of cooking portion 12.

Besides the heat energy regulating material 15 and heat conducting plate 16, the hermetic space 14 may include other materials or components which have some other required properties or effects, such as spacers to secure the distance between upper boundary and bottom portion of the hermetic space, a reinforcing structure inside the hermetic space, a thermal couple to detect the temperature of the body portion of cooking device, etc.

Embodiments of the present invention can exhibit the following features: 1. Multi-layer body structure 11 with which hard and tough material having stable chemical properties can be selected to serve as the surface portion 12, which enables cooking devices suitable for decoction, boiling, dry frying and oil frying. Nothing toxic will be produced, nor significant rust, and the vessel will be free from maintenance and easy to clean.

2. Inside the body portion 11, low melting point metal or alloy have lower value of specific heat (e.g. specific heat value for tin is around 0.2255 J/g C, for steel is 0.45-0.46 J/g. C, for copper or its alloy is 0.34-0.41 J/g* C) and serve as heat energy regulating material 15. A lower heat capacity results at low temperature, but, when the temperature reaches its melting point, a higher heat capacity is obtained due to solid - liquid phase change. Increased heating efficiency and improved range restraint of temperature of the body portion 11 results.

3. The body portion 11 including heat energy regulating material(s) 15, heat conducting plate 16 and heat resisting layer 17, etc. actually contained inside the body portion 11 can restain localised high temperature phenomena so that the food is not likely to be scorched.

4. Multi-layer structure need not require complicated shapes. Also, low melting point metal or alloy can have a soldering effect relative to surface portion 12 and bottom portion 13, so helping to join them together, which can simplify manufacture and strengthen the structure. Also choice of cross sectional thickness as well as characteristics of body portion 11 can restrain the formation of localised high temperature region(s). Without thick and heavy materials, the body portion 11 can enable the cooking portion 18 of the surface portion 12 to have more uniform temperature distribution.

5. Heat energy regulating components, such as hermetic space 14, heat energy regulating material 15, heat conducting plate 16, heat resisting layer 17, surface portion 12 and bottom portion 13 need not be restricted to any specific shape and structure compared with Figures 1 and 2, e.g. a cooking pan with flat bottom, cooking pot, frying plate, etc., can also enjoy the same results.

Claims (7)

1. A cooking device having heat energy regulating structure wherein its portion to be heated is constructed as an inner part and an outer part, with a space between the said inner and outer part, which space contains low melting point heat energy regulating means.

2. A cooking device according to claim 1, wherein said heat energy regulating means comprises low melting point material which can traverse melt and solidification process within cooking temperature range.

3. A cooking device according to claim 1 or claim 2 wherein said space between inner and outer part contains high heat transfer rate heat conducting means.

4. A cooking device according to claim 3, wherein said heat conducting means is of plate form.

5. A cooking device according to any one of claims 3 or 4, wherein said heat conducting means is of apertured plate or reticulated or net form.

6. A cooking device according to claims 3, 4 or 5, wherein said heat conducting component has an associated heat resisting layer at its surface facing said inner part.

7. A cooking device arranged and adapted to operate substantially as herein described with reference to and as shown in Figure 2 of the accompanying drawing.