We. Alan Brown, a British subject of 4, Grange Crescent, Sunderland, Tyne & Wear, SR2 7BN and John Nolan, a British subject of 49, Kewferry Road, Northwood, Middx.

HA6 2PE do hereby declare the invention for which we pray a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to two phase, thermo-syphon apparatus which is a modification of the so-called Perkins tube.

Perkins tubes transmit heat by vaporising fluid in one region and condensing it in another. They are thereby very efficient conductors of heat. Moreover, because the temperature and vapour pressure of the vapourising and condensing fluid are closely related, if the geometry of the Perkins tube device is such that the pressure everywhere in its interior is almost constant, then, under correct working conditions, the temperature everywhere in that interior will be almost constant. Furthermore, devices associated with the Perkins tube device, that are designed to measure vapour pressure, can be easily adapted to indicate vapour temperature and vice versa. If the interior and exterior of the Perkins tube device are separated by an enclosure whose walls have a comparatively high thermal conductivity, then the outside walls can also be kept at a comparatively constant temperature.

This constant temperature performance can be useful in many cases such as vessels or enclosures. It may also aid the more accurate measurement of a representative temperature of the device. But unless the heat input to the device is controlled it can suffer burn out, by which is meant the drying out of one or more evaporating zones.

Burn out can lead to hot spots. By hot spots is meant a part of a device that is unacceptably hot. This will happen if heat is continued to be applied at a part of the Perkins tube device where there is no liquid available to absorb that heat by evaporation.

A Perkins tube device of this type provides a number of advantages. It can form the basis of cooking utensils, in which the temperature of the cooking such as a saucepan or deep fat frier, can be indicated and/or closely controlled. It can form the basis of utensils in which foods rarely, if ever,"burn", particularly if used correctly.

Further advantages ensue from the ability to monitor the temperature closely, these include savings in energy and therefore cost, and possibly increases in safety.

An object of the invention is to improve the designs of enclosures or vessels by incorporating the principles of the Perkins tube such that said enclosures or vessels can be maintained at a comparatively even temperature. A further object of the invention is to be able to control that temperature within acceptable limits. A further object of the invention is to be able to reduce or eliminate hot spots and/or burn outs so that the device can be operated with greater safety.

According to the invention, two phase, thermo-syphon apparatus is provided which comprises at least one evaporating means, an enclosing means which defines at least one condensing means, an evaporable fluid which is substantially contained, during normal operation, within the interior of the enclosing means, which is in contact with the said evaporating means and which transmits heat by inter-communication between said evaporating means and said condensing means and at least one element responsive to a physical quantity of said evaporable fluid.

According to a further feature of the invention, said physical quantity is vapour pressure of said evaporable fluid.

According to a further feature of the invention, said physical quantity is vapour temperature of said evaporable fluid.

According to a further feature of the invention, said responsive element is adapted to indicate temperature and/or vapour pressure of said evaporable fluid.

According to a further feature of the invention, said responsive element is adapted so that a signal can be provided.

According to a further feature of the invention, said signal is adapted to indicate temperature and/or vapour pressure of said evaporable fluid.

According to a further feature of the invention, said responsive element is adapted to control the temperature and/or vapour pressure of said evaporable fluid.

According to a further feature of the invention, one or more sealing devices, of known types, may be fitted. Said sealing devices may be for relief of excess pressure of vapour of said fluid and/or for introducing said fluid into said enclosing means.

The invention enables a number of advantages to be achieved. For example, a Perkins Tube shaped as a two-walled enclosure or vessel can provide the walls of such enclosure with an even temperature. An indication of that temperature can be achieved by a thermometer of suitable design, positioned almost anywhere, provided it is suitably mounted to be in good thermal contact with said enclosure or vessel. Where such enclosures or vessels require, not only evenness of temperature, but control of temperature also, the temperature indicator could be replaced by a device that indicates and/or controls temperature. Such enclosures or vessels could include incubators, ovens, food storage devices, cheese making vats, fermentation vessels or growing cultures for medical purposes and such vessels could include baths for babies and a saucepan, or anything requiring evenness of temperature and delicacy of temperature control. In fact the distinction between enclosures and vessels is not great, since a vessel with a suitable lid, becomes, in effect, an enclosure. A further advantage provided by the invention is the greater surface area for transfer of heat to any material to be heated, or kept warm or hot.

For example, in the case of an embodiment of the invention in the form of a saucepan, heat can pass into the food to be heated, not just through the bawe, but through the walls as well. Since the nature of the family of devices, that are the subject of this invention, is to try to maintain all surfaces at a constant temperature, that are in contact with the fluid vapour, it will be advantageous in some cases, such a cooking utensils, to provide a degree of insulation between the condensing fluid and the outside wall. This is for reasons that include the need to be able to pick up the utensil with comfort and the need to conserve the temperature of the contents of the vessel for as long as possible.

Temperature responsive devices are often comparatively delicate. This invention enables a comparatively robust device to be constructed.

If we consider a device to be heated, a suitable temperature or vapour pressure responsive element could be used to indicate and/or control the temperature, by controlling the heater. If the temperature or pressure responsive device is simply a temperature indicator, then it would require human agency to control the heater. Such a device could be made in such a form that the heater is internal and/or integral with said device. This would have a number of advantages, such as convenience, and the possibility of a wider range of materials for manufacture. Convenience follows from the elimination of the need to provide a separate heater. In such an embodiment, it may be possible to make the device substantially of plastic, reinforced by known means. This is because the heating element may constitute said evaporating means and heat need not pass through the wall of the vessel to the fluid to be evaporated. In a conventional hob this is not the case. On the other hand, a modified saucepan can be envisaged, for use with an external heater. This would include a metal base which is attached, by known means, to walls of a different material.

It is advantageous for some embodiments of the invention to incorporate at least one openable, sealing device, of known types. Such sealing devices may be for relief of excess pressure of vapour of fluid and/or for introducing fluid into the enclosure. Such devices include pressure relief valves, plugs fitted with a fusible material, or deliberately weakened parts of the wall that could burst with comparative safety if pressures were excessive.

The walls of the enclosure, containing the evaporable fluid, in particular the flatter parts, will tend to be pulled together for fluid vapour pressures lower than atmosphere, and to be pushed apart for fluid vapour pressures higher than atmosphere. In order to enable these walls to be made of thinner material, whilst reducing relative movement due to vapour pressure changes, it may be advantageous to make one or more connections between such walls, or to corrugate the walls, or to reinforce them by known means.

The features of the different embodiments of the invention described above may be adopted singly or in combination. So that the invention may be more easily understood, different embodiments of the invention will be described with reference to the following schematic drawings:- Fig. 1 is an elevation of a cross-section on a diameter of saucepan, viewed on BB.

Fig. 2 is an elevation of the device of Fig. 1, viewed on AA.

Fig. 3 is a detail of part of the device, viewed as for Fig. 2.

Fig. 4 is a detail of part of the device, viewed as for Fig. 2.

Fig. 5 is a detail of part of the device, viewed as for Fig. 2.

Fig. 6 is a detail of part of the device, viewed as for Fig. l.

Fig. 7 is a detail of part of the device, viewed as for Fig. 1.

Fig. 8 is a detail of part of the device, viewed as for Fig. 1.

Fig. 9 is a detail of part of the device, viewed as for Fig. 1.

Fig. 10 is a detail of part of the device, viewed as for Fig. I Fig. 11 is a detail of part of the device, viewed as for Fig. I Fig. 12 is an elevation of a cross-section on a diameter of a saucepan lid, incorporating an embodiment of the device.

Fig. 13 is a detail of part of the device, viewed as for Fig. 1 Fig. 14 is a plan showing the sections to be viewed by Fig. 15.

Fig. 15 is an elevation of a cross-section.

Referring to Fig. 1, a double skinned vessel, such as a saucepan, has an outer surface, 1, and an inner surface, 2, which define an enclosure, 2'. Part of said surface, 2. forms the inner walls, 3, of said vessel. A material, 4, to be heated, is in thermal contact with the inner surface, 2. A fluid is provided in said enclosure, 2', between said two surfaces. 1 and 2. Said fluid, in liquid state, 5, is in substantial thermal contact with an evaporating part of said surface. 1. The bottom side of said surface, 1, is in thermal contact with a source of heat, not shown. Preferably, said liquid, 5, is spread evenly by a wick, 5'. Vapour, 6, of said fluid, flows towards the cooler parts of said surfaces 1, 2 or 3 where it condenses into liquid, 7, and runs back to said liquid. 5. At the parts of said surfaces of said enclosure, 2', where condensation takes place, heat is released, a substantial proportion of this heat can pass into said material, 4, where it is in thermal contact. The said inner walls, 3, provide an additional surface area for heating said material, 4, over and above that of an orthodox saucepan, for which a comparatively small amount of heat will normally come in through the walls. Lifting handles, 8, are provided. Between at least one of said handles. 8, surfaces, 9 and 14, form a further enclosure, 2", which is an extension of said enclosure, 2', and in fluid contact with it.

Said enclosure, 2", is sealed, as required, from the outside atmosphere. The device is designed so that sufficient of said condensate, 7, forming in said enclosure, 2", is able to drain back freely to the main reservoir of liquid, 5.

Referring to Fig. 2, one side of said surfaces, 9 and 14 are in contact with the atmosphere, and the other side with said the liquid and sealed by suitable known means.

The figure shows how said surfaces, 9 and 14 may be positioned relative to said lifting handles, 8, shown partially cut away.

Referring to Fig. 3, this shows in more detail those features housed within said surfaces, 9 and 14. In particular, a one-way valve, 10, serves as a means for introducing said fluid, 5, and for safety, preventing an excess of pressure. The valve is also used during an initial warm up, to allow said fluid vapour, 6, (see Fig. I) to expel most of the free air from inside the said enclosures, 2', and 2". The purpose of such a warm up is to make the device more efficient at temperatures less than the boiling point of the said fluid, 5. When said fluid vapour fills the said enclosures, it can condense anywhere on the walls defining those enclosures, thus heating them. If air, or other gas is present in the enclosure, it can prevent the vapour contacting the walls of that part of the enclosure.

A diaphragm, or bellows, 11, of suitable material, moves according to the pressure, and hence temperature, of said fluid vapour, 6, in said enclosures, 2'and 2". An adjustable screw, 12, of electricallyconductive material, in an electrically insulating female thread, 13, is provided as a suitable contact for said bellows, 11. Said screw, 12, can be adjusted so that it makes contact with said bellows, 11, at a required temperature of said fluid vapour. As the temperature and the vapour pressure of the fluid in said enclosure, 2", rises, the said bellows, 11, are extended towards the said screw, 12. At a set temperature, contact is made between said bellows and said screw. This contact can be designed, by known means, to close an electrical circuit which, by further known means, such as a relay, can be used to turn off the power that is heating the device and which heat is evaporating said liquid, 5. In order to facilitate opening of said valve, 10, for filling purposes a pin could be provided, not shown, fixed inside said bellows, 11, and projecting into the duct closed by the ball of said valve, 10. For filling, said screw, 12, is screwed in, compressing the bellows, and the pin moves against the ball and lifts it off its seat.

Referring to Fig. 4, another method is provided for creating an electrical effect from the vapour pressure of the fluid. In this method, said bellows, 11, moves as for the embodiment of Fig. 3, but attached to said bellows is an armature, 12', fixed to a guide rod, 12", which slides in a guide, 13'. An extension, 9'. of said surface, 9, is provided to protect said guide, 13'and said guide rod, 12". Said armature, 12', is made of a suitable known magnetic material such as ferrite, which can cause an electrical effect in coils, not shown, external to the surface, 10. Said electrical effect can vary according to the position of said armature, 12', and hence of said bellows, 11. Said electrical effect can be used to provide a signal to either control and/or indicate temperature. An electrical effect could also be used if said armature, 12', is made of electrically conductive material in which eddy currents can be induced to flow.

Referring to Fig. 5, a probe, 12"', is provided, sealed in to said surface, 10, by a seal, 13". Said fluid vapour, 6, in said enclosure, 2", condenses on said probe, 12"', bringing it up to the temperature of said vapour. Said probe may be part of a thermometer of know type, or a temperature sensitive electrical transducer, such as a thermocouple, which produces an electrical effect according to the temperature of said fluid vapour.

Referring to Fig. 6, to reduce the distortion of said surfaces, 1, and, 2, particularly any flat portions, the said surfaces, 1, and, 2, may be held in relation to each other by a screw, 15, fixed to said surface, 1, screwed in to a female thread, 16, fixed to said surface, 2. Provided appropriate parts of said surfaces, 1, and, 2, are sufficiently circular, as is normally the case with vessels such as saucepans, and said threaded parts, 15, and , 16, are sufficiently close to the centre of those appropriate parts, then said part, 15, may be screwed in to thread, 16, at time of manufacture. For a given thickness of said surfaces, 1, and, 2, the said threaded elements, 15, and, 16, will reduce this tendency to distort for a given temperature. Hence higher temperatures could be reached for a given wall thickness, without unacceptable distortion. Said screw, 15, is shown drilled with a hole, 29, which is blocked with a plug, 30, of fusible material. Said plug, 30, serves a smilar purpose to such plugs in pressure cookers. It will fuse if the temperature, and hence pressure, between said surfaces, 1, and, 2, becomes too high. A modification could be made in which said plug, 30, is fixed in a removable threaded fitting. Not shown are relief holes in said female thread. 16. so that any excess pressure between said surfaces, 1, and, 2, can vent to atmosphere when said plug, 30. fuses.

Referring to Fig. 7, a modification of the basic design of Fig. 1 is shown in which an electrical heating element, 17, is provided inside the said enclosure, 2'. Said heating element, 17, is connected to a source of electrical power, not shown, by known means, not shown. The said source of electrical power is controlled, via known means, by the temperature responsive devices already described in previous Figures. A further modification to the embodiment of Fig. 1 is the provision of external insulation, 18.

Said insulation may be attached to the said surface, 1, or not, as is the case in the embodiment of Fig. 8. Said insulation in unattached form may also be used with other suitable embodiments shown in these Figures, after they have been removed from any external said source of heat. The advantage of said insulation is twofold, it can increase heat retention, and it can have aesthetic value for hob-to-table ware.

Referring to Fig. 8, a modification of the basic design of Fig. 7 is shown in which an electrical heating element, 17', is provided fixed inside removable insulation, 18'. Said heating element, 17', is connected to a source of electrical power, not shown, by known means, not shown. The said source of electrical power is controlled, by known means, by the temperature responsive devices already described in previous Figures. Said insulation, 18', with said heater, 17', are shown separated from said surface, l, for clarity.

Referring to Fig. 9, this is a plan view of the essentially circular and otherwise flat bases of said surfaces, 1, and, 2. Under varying pressure of said vapour. 6, such flat surfaces will distort more easily, the thinner they are. Therefore said surfaces, 1, and, 2, are provided with substantially radial corrugations, 19. Said corrugations on their own will reduce this tendency of said surfaces, 1, and, 2, to distort for a given temperature.

However, in combination with the said threaded elements, 15, and, 16. of Fig. 6 such tendency to distort for a given temperature will be reduced still further. Hence higher temperatures could be reached for a given wall thickness, without unacceptable distortion.

Referring to Fig. 10, this shows a feature in which the said surfaces, 1, and, 2, are sealed together by folding the edge of, 2, over the edge of, 1, a suitable sealant, 20. being provided, if necessary. This could be a"solid"plastics material.

Referring to Fig. 11, this shows a feature, 21, in which the said surface, 1, is partially punched through over a certain small. perhaps circular area, to provide a weakened area for safety failure, should pressure of said vapour, 6, become dangerously high. Said feature, 21, would be placed in a position, combined where necessary with other known means to enable safe blow off of vapour.

Referring to Fig. 12, this shows a conventional saucepan lid, 22, whose knob, 23, is fitted with an embodiment of the invention that is essentially a temperature sensing and/ or indicating element. The general construction is similar to the embodiment of Fig. 4.

The advantage of this construction is that the exterior parts of the device, 9, and, 9', can be of an easily cleaned and robust material, such as stainless steel. A female socket, not shown, can be placed over the part, 9'. Said female socket contains devices to detect, by known means, the position of said element, 12'.

Referring to Fig. 13, this is a view similar to that of Fig. 10, using a different form of construction to join said surfaces, 1, and, 2. Said surfaces, 1, and, 2, are folded over in a fashion similar to the detail shown in Fig. 10. The edge of said surface, 2, is closed by a weld, 25, to said surface, 1. If necessary, spot welds or other suitable known fixing methods are applied at 25'. A suitable insulating material. 24, provides both a cover for the said weld, 25. and also a lifting"ledge".

Fig. 14 is a plan showing the sections to be viewed by Fig. 15. A ring, 26, of a suitable material, provides lifting ledges, 27, and a housing for a temperature sensing/ indicating element, 12"", and other devices already mentioned, such as a pressure release and/or filling valve, and a temperature control element, already described. Said feature, 26, also serves as a construction element to join the said surfaces, 1, and, 2.

Preferably, said feature, 26, is also a heat insulator.

Fig. 15 is an elevation of cross-sections CC as shown in Fig. 14, with features already described.