GB2329573A - Vessel for uniform heating - Google Patents

Abstract

A vessel (1) such as a saucepan comprising inner (7) and outer (9) vessels defining, in use, an enclosed sealed space (11) therebetween containing helium at 1 bar pressure at ambient temperature for conveying heat energy to the contents of the inner vessel (7), in a controlled manner, thereby providing uniform heating. The helium is introduced into the space (11) during manufacture of the saucepan 1 via a filling point (13) which is subsequently sealed. The saucepan has a handle (3).

Description

VESSEL FOR UNIFORM HEA TING This invention relates to a vessel for containing a substance and adapted uniformly to conduct heat from its exterior to the substance therein. The invention relates particularly but not exclusively to a vessel for cooking food, such as a saucepan, frying pan or the like.

In cooking a great deal of skill is devoted to blending foods to the right consistency.

The typical cooking utensil is the saucepan which contains the liquid or semi-liquid food and sits upon a gas or electric burner. Conventional saucepans are adequate for boiling foods or frying, but are usually unsuccessful in cooking thick, viscous foods such as custards or sauces, due to the food catching or burning to the base of the pan. The usual solution to this problem is to use what is known as a double boiler saucepan or a bain-marie. In such devices, an outer saucepan contains boiling water and an inner saucepan containing the food to be heated is partly immersed in this. Heat from the gas or electric burner is transferred to the water and then conducted through the water to the inner pan and its contents.

It is thought that this type of double saucepan is effective because the temperature of the inner pan is limited to 100"C by the maximum temperature of the boiling water. However, even a temperature of 100"C is sufficient to curdle and/or overcook many delicate foods such as sauces. Moreover, in use the space between the two pans is filled with boiling water at the bottom and steam towards the top; because water has a thermal conductivity about four times that of steam, the sauce closest to the water will be heated to a far greater extent than is the sauce close to the steam.

Additionally, the conventional use of tap water in known double saucepans produces an undesirable deposit of lime scale and the like on the inner surface of the outer saucepan and the outer surface of the inner saucepan; unless cleaned away regularly, such deposits lead to localised "hot spots" which can cause localised curdling of a sauce during cooking.

It is an object of the present invention to provide a vessel such as a cooking vessel for containing a substance to be heated uniformly which addresses at least some of the known disadvantages of conventional vessels.

Accordingly, the present invention provides a vessel for containing a substance to be heated comprising an inner vessel for containing the substance and having an inner surface at least part of which is in contact with the substance and an outer vessel, at least a portion of the outer surface of which is adapted to receive and conduct heat energy applied thereto, the inner and outer vessels defining, in use, an enclosed space therebetween containing a fluid comprising helium for conveying heat energy from the outer vessel to the inner vessel, wherein the inner and outer vessels are connected so as to seal the enclosed space, and wherein the helium therein is, at ambient temperature, at 1 bar pressure.

It has been discovered that the real importance of the conventional double saucepan is that the thermal conductivity of the water reduces the rate at which heat is transferred into the food, thereby avoiding localised heating. Because the vessel in accordance with the invention has a sealed "envelope" in gaseous form only, there is no substantial variation in the thermal conductivity of the fluid and therefore heat is transferred uniformly from outside the vessel to its contents. In addition, there are no undesirable deposits formed between the two vessels (and thus no localised "hot spots" are created). Because the helium of the present invention is sealed within the enclosed space, and therefore constrained therein, the conveyance of heat energy from the outer vessel to the inner vessel, by conduction and free convection of the gas, is much more uniform and more controllable than is possible with conventional vessels. Over the range of temperature that a saucepan is likely to be used, the thermal conductivity of water is about 0.6W/Km, whereas for helium it is approximately 0.32W/Km. The effect of this is that a helium filled "interspace" will conduct heat at a much more controlled rate than a double boiler, resulting in more perfect sauces and less need for stirring by providing a much wider envelope of success. Helium is the best gas for this, being inert and having the highest thermal conductivity of all gases. Other inert gases such as argon have a thermal conductivity approximately the same as that of air and about a tenth of that of helium, which would probably be too low for practical purposes. However, mixtures of inert gases, with helium, could also be used to provide optimum heat transfer rates, thus "tailoring" the vessel for a particular heating application. A vessel for cooking in accordance with the invention and containing helium will also be lighter than a conventional double boiler saucepan, due to the lower density of helium compared to that of water.

Very preferably the said portion of the outer surface is spaced from the inner vessel, the only thermal contact therebetween being either via the helium or via the sealed portions of the inner and outer vessels. Such an arrangement avoids the creation of "hot spots" within the inner vessel, which could curdle or otherwise spoil substances being heated therein.

The invention will now be described by way of example and with reference to the accompanying drawing, a schematic cross-sectional view of a saucepan in accordance with the invention.

The saucepan 1 illustrated has a handle 3 and a pan 5 formed of an inner pan, or vessel, 7 and an outer pan, or vessel, 9. The inner and outer pans 7, 9 are formed of conventional materials, such as aluminium, stainless steel or tin-coated copper, and are sealingly joined together so as to provide an enclosed interspace 11 which is filled with helium. The helium is introduced into the interspace 11 during manufacture of the saucepan 1 via a filling point 13 which is subsequently sealed to prevent egress of the helium. At ambient temperatures (about 1 5 C to 20"C) the helium gas is at a pressure of approximately 1 bar; the distance between the inner and outer pans 7, 9 is about 0.5cm to 1 cm. In use, heat is applied to the base of the saucepan 1, as shown by the arrows H, and is conducted from the base of the outer vessel 9 to the inner pan 7 by conduction and free convection of the helium in the inner space 11. There is no contact between the base of the outer pan 9 and the inner vessel 7. Thus, heat is only conducted therebetween via the helium (and some via the junction of the vessels), thereby preventing undesirable "hot spots".

Having described a saucepan in accordance with the invention, those skilled in the art will appreciate that the modification of such a vessel to suit different applications, such as in frying pans or non-culinary vessels such as are used in chemical processes, in which different - but uniform - heat transfer rates are required, is a matter of reasonably straight forward application of thermo-dynamics and heat transfer and should not be seen as a poor use of scarce resources or as self-aggrandisement. For example, the pressure of helium in the interspace may be increased or decreased, and the distance separating the inner and outer pans may be varied, according to a particular application. The inner surface of the outer pan may be polished and/or the outer surface of the inner pan given a matt, "black body" surface so as to optimise heat transfer by radiation.

Claims (5)

1. A vessel for containing a substance to be heated comprising an inner vessel for containing the substance and having an inner surface at least part of which is in contact therewith and an outer vessel, at least a portion of the outer surface of which is adapted to receive and conduct heat energy applied thereto, the inner and outer vessels defining, in use, an enclosed space therebetween containing a fluid comprising helium for conveying heat energy from the outer vessel to the inner vessel, wherein the inner and outer vessels are connected so as to seal the enclosed space, and wherein the helium therein is, at ambient temperature, at 1 bar pressure.

2. A vessel as claimed in Claim 1 wherein the said portion of the outer surface is spaced from the inner vessel, the only thermal contact therebetween being either via the helium or via the sealed portions of the inner and outer vessels.

3. A vessel as claimed in Claim 1 or Claim 2 wherein the fluid comprises a mixture of inert gases.

4. A vessel as claimed in any preceding Claim for use in cooking food.

5. A vessel substantially as hereinbefore described and with reference to the accompanying drawing.