1. International class: F24H7/00 2. Classification Definitions:

US Class 99: Foods and Beverages Apparatus US Class 126: Stoves and Furnaces 3. Field of Search :-126/390; 373,375,377,385,369,357,348,246,400, :-99/70; 408,412 4. References Cited: 2,640,478 5/1953 Flournoy 126/375 USA 2,841,137 7/1958 Chace 126/390 USA 3,065,744 11/1962 Scavullo 126/246 USA 3,557,774 1/1971 Kreis 126/246 USA 3,734,077 5/1973 Murdough et al. 126/375X USA 3,745,290 7/1973 Harnden Jr. et al. 220/408X USA 3,916,872 11/1975 Kreis et al. 126/375 USA 4,086,907 5/1978 Rothschild 126/375X USA 4,258,695 3/1981 McCarton et al. 126/375 USA 4,455,927 6/1984 Schweizer et al. 99/625 USA 4,530,344 7/1985 Iyengar et al. 126/246 USA 4,567,877 2/1986 Sepahpur 126/246 USA 4,777,931 10/1988 Ziegleret al. 126/246 USA 4,917,076 4/1990 Nadolph 126/375 USA 4,982,722 1/1991 Wyatt 126/400 USA 5,125,391 6/1992 Srivastava 126/246 USA 5,603,858 2/1997 Wyatt 219/620 USA 5,611,328 3/1997 McDermott 126/246 USA 629,654 10/1961 126/375 CANADA 2,266,086U 10/1997 F24C 15/10 CHINA 2,284,356U 6/1998 F24C13/00 CHINA BACKGROUND ART In the past stored heat cooking appliances have been successfully used for cooking and maintaining foods at elevated temperature. U. S. Pat. No. 2,640,478 which issued to Flournoy in Junel953, discloses one such appliance. It consists of an outer container which houses a heat storage element in it's interior base. It supports a cooking

vessel having an enclosing lid. The vessel appears much like a double-boiler cooking pan with the storage element in the position of water.

U. S. Pat. No. 4,258,695 which issued to McCarton and Minto on March 31,1981 discloses a stored heat cooking utensil. It includes an insulated outer container, an inner cooking vessel, a heat storage element, a lid for enclosing both the outer container and the cooking vessel. The heat storage element is a disk of soap stone. It is said to be heated on high heat on a kitchen range burner or heating element for approximately 30 minutes on high heat or it may be heated in camp fire for approximately an hour. The heated element is then placed inside the outer container. The vessel filled with food item to be cooked is placed on the heated element within the outer container. Both the vessel and the outer container are enclosed using the lid. The utensil is said to slowly cook the food for a period of up to 12 hours. The device being portable can be taken on boats, in automobiles or carried to places distant from more conventional heat sources while the food continues to remain warm and/or cook. The soap stone storage element is said to crack during heating process and hence it is fastened with metal band.

From the patents described above it is noted that the stored heat cooking utensils have been used for cooking food. However, the prior art appliances are slow cookers and therefore take long time to cook the food. For this reason, their use has been limited to certain specialized applications such as portable cooking etc. Prior art cookers are not being commonly used for regular cooking applications. In the prior art stored heat cooking utensil the storage element is bulky because it has to supply heat energy for two purposes. Firstly, the temperature of the food and water inside the cooking vessel should be raised from ambient temperature up to the boiling point of water. Secondly, after the temperature of the food and water has been elevated, the storage element has to supply the heat necessary to complete the cooking of the food item. Further, in the prior art cooking utensil there is no alarm or indication which informs the user the end of the heating process of the storage element, for cooking a desired quantity of food item. In the absence of such an indication, there is a possibility of either insufficient heating and subsequent failure of the cooking process or excessive heating which may result in large wastage of cooking fuel.

DISCLOSURE OF INVENTION

The present invention provides a stored heat cooker which cooks food items like rice, cereals, vegetables, eggs, meat etc. One object of the present invention is to provide a stored heat cooker which cooks the food faster. Another object of the present invention is to provide a stored heat cooker which uses a relatively smaller capacity storage element. A further object of the present invention is to provide a stored heat cooker which consumes relatively less fuel. A still further object of the present invention is to provide a stored heat cooker which can be designed for use on a variety of heat sources such as kitchen range, electric heating element, kerosene stove, wood stove, coal heaters and even on candles or catering wax.

The design of the present invention is based on the following observation. A cooking process can be divided in two distinct phases namely an heating phase and a cooking phase. In the heating phase the temperature of the food item along with requisite amount of water added to it, is raised from ambient temperature up to the boiling point of water. Then, in the cooking phase the food item is maintained at the elevated temperature until it gets cooked. It has been experimentally observed that, out of the total heat energy supplied, the heating phase consumes approximately 75% energy and the remaining 25% energy is consumed by the cooking phase. This observation is true only if the heat losses are small i. e. when the heating and cooking is carried out in an insulated container. It should be noted that these energy consumption figures are approximate and depend on ambient temperature and also change with the type of food item to be cooked.

As will be explained in detail later, in the stored heat cooker of the present invention, the food item kept in a cooking vessel is heated using a heat source until the water in it starts boiling. Then, only the cooking phase is carried out in an insulated container with the help of an heated storage element. Which implies that, the storage element needs to supply only a small amount of energy which is necessary to cook that food item which has already been preheated during the heating phase up to the boiling point of water. For this reason, the storage element used in the present invention is of significantly smaller thermal capacity as compared with that used in the prior art stored heat cooking utensil. Further, the storage element used in the present invention is located in-between the cooking vessel and the heat source, during the heating phase. The storage element is designed to permit smooth flow of flame and/or hot gases from the source to the cooking vessel with minimum obstruction. During the heating phase the storage element mainly absorbs that portion of heat which otherwise goes waste. When the

heating phase ends, by then, the storage element would have collected sufficient energy for completing the cooking phase. Since, the storage element in the present invention mainly collects waste heat, there is a significant increase in the efficiency of the heating process. For this reason, the consumption of cooking fuel is relatively less in the present invention.

In the present invention a stored heat cooker is provided comprising an inner cooking vessel, an heat storage element, handle means for manipulating the storage element, means for raising the cooking vessel kept above the storage element, a double lid assembly for enclosing the cooking vessel, an insulated outer container to carry out the cooking phase and an insulated cover for enclosing the outer container. The cooking vessel is a container having a base and side wall extending upwards from the circumference of the base and terminating in a pouring edge. The storage element is made of high thermal storage capacity material having a bottom surface and a top surface. The bottom surface is adapted for placing the storage element on a desired type of heat source. It's top surface is adapted for placing the cooking vessel thereon. The storage element has a big hole at the center with gradually increasing diameter from the bottom surface up to the top surface. When the storage element is place over an heat source, the flame and/or hot gases enter the big hole from the bottom surface. The smooth surface of the big hole permits unobstructed flow of hot gases and avoids direct contact of the flame with the storage element. Handle means are provided for ease of handling of the storage element together with the vessel kept over it. Means are also provided for raising the cooking vessel with respect to the top surface of the storage element so that the gap between the cooking vessel and the storage element can be increased by few millimeters. At the beginning of the heating phase, the cooking vessel kept on the storage element is raised so that the flame and/or the hot gases which enter the big hole spread in the gap thus created and then escape out from the circumference of the gap. The profile of the top surface of the storage element and the profile of the bottom external surface of the cooking vessel together ensure that the pressure of hot gases is fairly uniform throughout the gap. This sandwiching of the flame and/or hot gases between the storage element and the cooking vessel with uniform pressure therein, improves the efficiency of the heating process and promotes fuel saving. The double lid assembly consists of an upper lid and a lower lid joined together in space relation to form a small airgap therebetween. The double lid assembly closes the cooking vessel tightly.

The double lid assembly has a small hole and a whistle is disposed therein. A sealing gasket is disposed between the double lid and the pouring edge of the cooking vessel.

The outer container has an outer shell an inner lining and heat insulating material filled in the space therebetween. The outer container has an opening on the top side which is adapted for receiving the storage element together with the cooking vessel. On the inner bottom surface of the liner which supports the storage element, an insulating ring is disposed. The hot storage element rests on this insulating ring during cooking phase so that unwanted heat conduction to the inner lining is minimized. The insulated cover has an upper covering, a lower lining and heat insulating material filled therebetween. The insulated cover has a tapered hole for permitting the steam generated during the cooking phase to escape out.

The preferred embodiment of the present invention has an inner cooking vessel made of Stainless Steel. The cooking vessel preferably has a flat circular base and cylindrical side wall extending upwards from the circumference of the base and terminating into an outwardly projecting circular pouring edge. The storage element in it's preferred form is a flat ring of mild steel with an outer diameter which is approximately equal to that of the cooking vessel. Preferably, the storage element has a planar bottom surface and the top surface has a taper of about 3 degrees sloping downwards towards the center. It's circular side surface is preferably perpendicular to the bottom surface. The big hole at the center has gradually increasing diameter from the bottom surface up to the top surface. The top surface and the curved surface of the big hole of the storage element are blackened to maximize heat absorption. The bottom and side surfaces are bright finished to minimize radiation losses. Two inverted'U'shaped Aluminum handles are secured to the circular side surface of the storage element with the ends of their vertical legs touching the storage element. These handles are perpendicular to the bottom surface and project upwards and are positioned diametrically opposite to each other. The top horizontal section of these handles is horizontally flat and has a curvature which matches with that of the side wall of the cooking vessel. When the cooking vessel is resting on the top surface of the storage element, these handles remain parallel to the side wall of the vessel and their top horizontal section lies below the pouring edge of the cooking vessel, with some space therebetween. The means for raising the cooking vessel in the preferred embodiment includes wooden rectangular strips. These wooden strips are inserted in the space between the top horizontal section of

the handles and the pouring edge of the vessel, so that the cooking vessel gets lifted upwards by few millimeters. This creates the necessary gap between the cooking vessel and the storage element for the passage of hot gases. There exists an optimum value of the gap at which the heating efficiency is maximum. The optimum value of the gap mainly depends upon the rate of supply of heat from the source. The taper in the top surface of the storage element makes the gap narrower towards it's circumference. For this reason, the hot gases which flow in this gap pass through a constant cross section area at any radial distance. This is because, as the diameter of the gap increases it's thickness decreases. Which ensures fairly uniform pressure of hot gases throughout the gap- The double lid assembly in the preferred embodiment includes a lower lid and an upper lid. The lower lid in it's preferred form is a substantially flat circular plate of Stainless Steel, with a small circular upward projection near it's circumference. Beyond this projection, the plate terminates in a downward going circular rim, which is perpendicular to it's plane surface. The upper lid in the preferred embodiment also consists of a substantially planar circular Stainless Steel plate. It has a small upward step near it's circumference before it terminates in a downward rolled rim. The lower and upper lids are joined together and a small hole is provided at the center, for the steam to escape. The circular upward projection in the lower lid maintains a space relation with the upper lid. The air enclosed in this space acts as an insulation and reduces thermal losses from the double lid, both, during the heating phase and during cooking phase.

When the cooking vessel is enclosed using the double lid assembly, the circular rim of the lower lid slideably fits on the internal surface of the side wall of the vessel. The portion of the upper lid beyond the upward step coincides with the pouring edge of the vessel and a rubber sealing gasket is disposed therebetween. A whistle is removably disposed in the small hole of the double lid assembly which produces an alarm at the end of the heating phase. The outer container in it's preferred form consists of an outer polyethylene shell and an inner lining made of Stainless Steel sheet, with glasswool insulation filled therebetween. The inner lining has a tapered wall and a circular bottom surface. The outer container has an opening on the top side from where the storage element along with the cooking vessel are receivable. A porcelain ring is disposed at the bottom surface of the liner over which the storage element rests. Porcelain ring minimizes the unwanted conduction of heat from the storage element to the liner. The

insulated cover in the preferred form also consists of a polyethylene upper covering, a lower lining made up of Stainless Steel sheet and glasswool insulation filled therebetween. At the center of the insulated cover a tapered hole is provided, which comes exactly above the whistle when the cover is placed on the outer container during the cooking phase. During the cooking phase, if steam comes out from the whistle, then it escapes out through the tapered hole in the insulated cover.

The method of using the stored heat cooker comprised of an heating phase and a cooking phase. Food item to be cooked along with required amount of water are poured in the cooking vessel. The double lid assembly together with the sealing gasket are placed over the cooking vessel. The whistle is inserted in the small hole provided in the double lid. The storage element in the preferred embodiment is placed over a kitchen range burner. The filled and enclosed cooking vessel is then place on the storage element.

Spacing strips are inserted in the space between the handles and the pouring edge of the cooking vessel so that the vessel gets raised above the storage element by few millimeters. When the heat source is turned on, the flame and/or hot gases pass through the big hole of the storage element without any obstruction. The flame and/or hot gases directly heat the vessel while the storage element mainly collects the waste heat. When the steam which is formed in the vessel escapes through the whistle, alarm is generated, which marks the end of heating phase. Now the heat source is turned off and spacing strips are removed to lower the vessel so that it rests on the storage element. With the help of handles fixed to the storage element the hot storage element together with the hot vessel are shifted into the outer container. The outer container is enclosed with the help of insulated cover. If any steam is generated during the cooking phase, it escapes out through the tapered hole in the cover. When the cooking phase ends, the cooked food, if desired, can be taken out. If food is not immediately taken out, then, it remains warm for an extended period of time, with the help of the residual heat energy remaining in the storage element. The heating phase in the preferred embodiment is carried out on high heat setting so as to reduce the heating time as much as possible. A shorter heating phase results in saving of user time.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The present invention will be more fully understood through a reading of the description of the preferred embodiment in association with the drawings in which: FIG. 1 shows the sectional elevation view of the prior art stored heat cooking utensil; FIG. 2 is a perspective view of the insulated cover for enclosing the outer container of the stored heat cooker made in accordance with the present invention; FIG. 3 is a perspective view of the outer container of the stored heat cooker made in accordance with the present invention; FIG. 4 is a sectional elevation view of the stored heat cooker shown during the cooking phase; FIG. 5 is a detailed sectional view of a portion of the stored heat cooker noted in the FIG. 4; FIG. 6 is a sectional elevation view of the storage element and the raised cooking vessel arrangement shown during an heating phase, indicating the direction of flow of hot gases in the gap between the storage element and the bottom of the cooking vessel; FIG. 7 is a plan view of the storage element along with two handles attached to its side surface; FIG. 8 is a perspective view of the storage element along with two handles attached to its side surface; FIG. 9 is a perspective view of the wooden strips which means are used for raising the cooking vessel; FIG. 10 is a perspective view of the cooking vessel and the separator pan used for cooking second food item, shown to be partially removed from the cooking vessel.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 shows a sectional elevation view of the prior art stored heat cooking utensil which is known to those skilled in the art. In FIG. 1 reference numeral 10 is used to generally identify the stored heat cooking utensil. The cooking utensil 10 consists of an outer container 12 made of polyethylene having an interior metal liner 14 with tapering wall. A first insulating layer 16 is placed on the bottom of the liner 14 and around all but the top of the side wall of the liner 14. The space between the outer covering 12 and the interior components is filled with an insulating foam 18 preferably a

high temperature polyurethane foam. An heat storage element 20 which is a disk of soap stone is used for storing heat. A pin 22 having an eye is secured at the center of the storage element 20 for the purpose of lifting it. The storage element 20 has a metal band 24 at it's circumference. This metal band 24 holds the stone together if it cracks during heating. The storage element 20 rests on a circular ridge 26 formed in the bottom liner surface 14 inside the outer container 12. This serves to keep the heat storage element 20 off the bottom in order to reduce heat transfer to the liner. A cooking vessel 28 having an open top fits within the outer container 12 and is supported on the heat storage element 20. The cooking vessel 28 also has tapered side wall and it fits within the outer container 12 without wall contact with the liner 14. The cooking vessel 28 has a downwardly projecting rib 30 which extends around the outer perimeter of the bottom of the cooking vessel 28. This prevents full contact of the bottom of the cooking vessel 28 with the top surface of the storage element 20, to prevent overheating of the food in the cooking vessel. The cooking vessel has an outwardly projecting rim 32 at it's top opening which serves to maintain the vessel centrally within the outer container 12 to promote uniform heating.

The lid 34 has a metal liner 36. The space between the lid 34 and the metal liner 36 is filled with an insulation 38 which is same as 18 used in the outer container 12. The lid 34 has an outer container contacting portion 40 which serves to seal the outer container 12 and prevent loss of heat. The under surface of the lid also has a cooking vessel containing portion 42 having tapered sides. The sides are tapered similarly to those of the cooking vessel 28 in order to closely fit within the open top of the cooking vessel 28. If the cooking vessel is not held centrally within the outer container hot spots occur due to nonuniform heating of the cooking vessel. Ears 44 are provided on the exterior of the outer container to facilitate fitting of a rope handle.

For useing the stored heat cooking utensil 10, the storage element 20 is heated in any one of several manners. It is said to be heated on high heat on a kitchen range burner or heating element for approximately 30 minutes on high heat or it may be heated in a camp fire for approximately an hour. The heated element is then placed within the outer container 12 and the food to be cooked is placed in the vessel 28 which is then placed on the heated storage element 20 within the outer container and the lid is placed in position.

The utensil is said to slowly cook the food for a period of up to 12 hours. The device

being portable can be taken on boats, in automobiles or carried to places distant from more conventional heat sources while the food continues to remain warm and/or cook.

The present invention relates to a stored heat cooker which in it's preferred form is illustrated in FIGS. 2 through 10. A sectional view of the preferred embodiment of the stored heat cooker during cooking phase is shown in FIG. 4. Numeral 50 is used to generally identify the stored heat cooker of the present invention. The sectional view of the storage element along with the raised cooking vessel arranged for an heating phase is shown in FIG. 6. The cooker 50 consists of a cooking vessel 52, which is enclosed using a double lid assembly 54. The cooking vessel 52 is placed on a heat storage element 56.

Two handles 58 and 60 are secured to the storage element 56 for lifting it together with the cooking vessel 52. During the heating phase the storage element 56 and the vessel 52 are placed on a heat source S as shown in FIG. 6. At the beginning of the heating phase the vessel 52 is raised above the storage element 56 by few millimeters, with the help of wooden strips 62 as shown in FIG. 6. At the end of the heating phase the source is turned off and the wooden strips 62 are removed so that the vessel 52 is lowered and rests on the storage element. This hot assembly of the vessel and the storage element is then transferred into an insulated outer container 66 which is then enclosed using an insulated cover 68 as shown in FIG. 4. Inside the container 66, the cooking process continues with the help of the heat imparted by the storage element.

The cooking vessel 52 is illustrated in FIGS. 4,6 and 10. In the preferred embodiment the vessel 52 is made of Stainless Steel and has a planar circular base 70.

The side wall 72 is cylindrical in shape and it terminates in a circular pouring edge 74.

The heat storage element is shown in FIGS. 4,6,7 and 8. The sectional view of the storage element 56 as shown in FIGS. 4 and 6 is taken on a section plane XX as indicated in FIG. 7. The storage element is preferably made of mild steel. However, if a lighter storage element is desired, then, it may be made of Aluminum, with slight increase in cost. As seen from the figures the storage element 56 is a flat ring having an outer diameter which is approximately same as that of the side wall 72 of the vessel 52.

At the center of the storage element 56 there is a big hole 76. The bottom surface 78 is planar and the diameter of the big hole 76 at this surface is smallest. The diameter of the big hole 76 gradually increases towards the top surface 80 as shown in FIG. 6. The top surface 80 of the storage element has a taper of about 3 degrees with respect to the horizontal plane and slopes downwards towards the center. The smoothly curved surface

82 of the big hole tangentially meets the top surface 80 so that the surface remains smooth throughout. The circular side surface 84 is perpendicular to the bottom surface 78.

Two identical handles 58 and 60 preferably made of Aluminum are secured to the storage element 56 on it's circular side 84 at diametrically opposite positions as shown in FIGS. 4,6,7 and 8. The handle 58 has two vertical legs 86 and 88 and a top horizontal section 90 between these two legs. The top section 90 is horizontally flat but has a curvature which is similar to the curvature of the side wall 72 of the vessel 52. The lower ends of the legs 86 and 88 are secured to the side 84 of the storage element. Between the legs 86,88 and the circular side 84 of storage element, asbestos pieces 92 and 94 are inserted to reduce transfer of heat from the storage element to the handle 58. Similarly the handle 60 also has two identical vertical legs 96 and 98 and a horizontal section 100.

Asbestos pieces 102 and 104 are inserted between the legs 96,98 and the surface 84.

Four small square pieces of mild steel 106,108,110 and 112 are fixed on the top surface 80 of the storage element, in front of the vertical legs of the handles 58 and 60. The thickness of these pieces is preferably 1 mm or less. When the vessel 52 is kept on the storage element 56, it rests on these small pieces so that there is no direct contact between the vessel and the storage element as shown in FIG. 4. This small gap between the vessel and the storage element reduces the rate of supply of heat to the vessel during the cooking phase and avoids violent cooking and subsequent over spilling of the food from the vessel. The height of the handles 58 and 60 is so chosen that, when the vessel is kept above the storage element the top sections 90 and 100 remain below the pouring edge 74 of the vessel, with some space therebetween as shown in FIG. 4.

In the preferred embodiment, the means for raising the vessel includes two wooden strips 62 as shown in FIGS. 6 and 9. The wooden strip 62 is rectangular in shape and one of it's long sides has a curved surface 114. This curved surface matches with that of the side wall 72 of the cooking vessel. Two strips 62 are inserted in the space between the top sections 90,100 of the handles and the pouring edge 74 of the vessel as shown in FIG. 6. While inserting these strips, their curved surface 114 is made to face the vessel 52. When the strips are inserted the vessel raises upwards and a circular gap 122 is created between the base 70 of the vessel and the top surface 80 of the storage element as shown in FIG. 6. During heating phase the flame and/or hot gases enter the big hole 76, spread below the vessel and come out from the circumference of the gap 122. The

direction of flow of gases is shown by the arrows 124 and 126 in FIG. 6. As mentioned earlier, the top surface 80 of the storage element has a slope of about 3 degrees, hence the gap 122 has a taper with it's thickness gradually reducing towards it's circumference.

Therefore, when the gases travel from the center towards the circumference of the gap 122, they pass through a constant cross section area at any radial distance from the center of the gap. Which ensures fairly uniform pressure of hot gases throughout the gap.

Uniform pressure enhances the efficiency of the heating process. Further, the thickness of the gap 122 is very important which mainly depends upon the rate of supply of heat from the source S. It has been experimentally found out that there exists an optimum value for the gap 122 at which heating efficiency is maximum. Here, heating efficiency means the ratio of the sum of heat absorbed by the vessel and the heat absorbed by the storage element to the total heat supplied from the source S. To further improve the performance of the heating process, the top surface 80 and the curved surface 82 of the storage element which are responsible for heat absorption, are blackened by coating them with high temperature black enamel coating. Such coatings are commonly used in the enamelware type of kitchen utensils. Black coating maximizes the heat absorption. The remaining surfaces 78 and 84 of the storage element are bright finished with chrome plating to minimize the heat loss due to radiation. The curvature of the surface 82 and the slope of the surface 80 are designed in such a way that the flame from the source S doesn't touch the storage element any where. Also, direct heating of the storage element has to be completely avoided. The flame and/or hot gases directly heat up the vessel, while the storage element absorbs that portion of heat which otherwise would go waste.

It is also necessary to match the thermal capacity of the storage element with the quantity of food to be cooked. The thermal capacity of the storage element depends upon it's weight. For cooking different quantities of food, a set of storage elements having different weights can be used. For example, in the preferred embodiment, to cook up to 250 grams of rice a storage element having approximately 1.6 kilograms of weight is used. And to cook from 250 to 500 grams of rice, storage element weighing approximately 2.4 kilograms is used.

Depending upon the type of food to be cooked, it becomes necessary to store different amounts of heat energy in the storage element. For example, to cook tough items like cereals, the storage element has to supply more heat as compared with that required for cooking easy to cook items like rice. To some extent, it is possible to vary

the amount of heat absorbed by the storage element by slightly varying the gap thickness 122 around it's optimum value. For this purpose in the preferred embodiment, different sets of strips 62 having slightly different thickness are used. If the thickness of the gap is slightly smaller than the optimum value, then, the storage element receives more heat and proportionally lesser heat goes to the vessel. While varying the gap 122 it is necessary to ensure that the flame doesn't touch the storage element. It should be noted that choice of the thickness of the gap is made at the beginning of the heating phase. Once chosen, the gap thickness remains unchanged through out the heating phase.

The double lid assembly 54 is shown in FIGS. 4 and 6, which consists of a lower lid 128 and an upper lid 130. The lower lid 128 in it's preferred form is a substantially planar circular disk of Stainless Steel, having a small circular upward projection 132 near the circumference. Beyond this projection the edge terminates in a downward going rim 134. The upper lid 130 is also a substantially planar circular disk of Stainless Steel having small upward step 136 and then the edge terminates into a downward rolled rim 138. The lower lid 128 and the upper lid 130 are joined together to form the double lid assembly. The upward projection 132 in the lower lid maintains a space relation with the upper lid 130. The airgap 140 between the two lids reduces the thermal loss both during the heating phase as well as during the cooking phase. At the center of the double lid a small hole 142 is provided in which a whistle 144 is removably disposed. Steam generated during cooking phase passes through the hole 142 and comes out from the whistle 144 generating an alarm. The rim 134 of the lower lid slideably fits in the side wall 72 of the vessel. The rolled rim 138 of the upper lid has a diameter which is nearly equal to that of the pouring edge 74 of the vessel. An'0'ring shaped sealing rubber gasket 146 is disposed near the rolled rim 138 in the double lid assembly. This gasket 146 seals the joint between double lid and the pouring edge of the vessel. The rubber gasket minimizes the leakage of steam from the pouring edge 74 of the vessel, so that during heating phase most of the steam escapes through the whistle 144, ensuring proper operation of the whistle. During the cooking phase also, the gasket 146 stops the leakage of steam into the outer container 66, thereby minimizing the unwanted condensate being formed inside the outer container.

The insulated outer container 66 is illustrated in FIGS. 3 and 4. In the preferred embodiment it has a polyethylene outer shell 148 and an inner lining 150 made up of Stainless Steel sheet. The inner lining 150 has a circular bottom surface 152 and a

tapered side wall 154. The top side of the outer container is open and is adapted to receive the storage element 56 together with the cooking vessel 52. The space between the liner 150 and the shell 148 is filled with glasswool insulation 156. A wooden supporting block 158 is disposed between the bottom surface 152 and the outer shell 148.

This wooden block 158 supports the weight of the storage element and the vessel and prevents the liner 150 from getting deformed. A porcelain ring 160 is disposed on the bottom surface 152 of the liner. The hot storage element during the cooking phase rests on the ring 160, which minimizes the conduction of heat to the liner 150. The porcelain ring may be substituted by three small porcelain spacers. The construction details at the top edge of the outer container 66 are shown in FIG. 5. The top edge of the liner 150 is outwardly bent to form a rim 162. Similarly the top edge of the outer shell 148 has an inwardly bent rim 164. A high temperature nylon flat ring 166 is fixed on the two rims 162 and 164 so that, the top surface of the outer container is properly sealed. In place of a nylon ring a bakelite ring may also be substituted. Two bakelite handles 168 are attached on the external surface of the outer container for ease of handling the cooker.

The insulated cover 68 is illustrated in FIGS. 2,4 and 5. It has an upper covering 172 preferably made of polyethylene and a lower lining 174 made of Stainless Steel sheet. The lining 174 is a circular plate having a hole 176 at it's center. The space between the liner 174 and the upper covering 172 is filled with glasswool insulation 178.

A small tapered Stainless Steel tube 180 is fixed above the hole 176 within the cover 68.

A hole 182 is provided in the upper covering 172, at the center where the tube 180 touches the covering 172. Through this tube 180 the steam generated during the cooking phase escapes out to minimize the formation of unwanted condensate within the outer container. The details of the construction of the cover are shown in FIG. 5. The circular edge of the liner 174 has a rim 184. The space between the circular rim 184 and the polyethylene covering 172, a high temperature nylon ring 186 is fixed. This nylon ring 186 avoids damage to the covering 172 which otherwise may occur due to the heat conducted by the liner 174. The circular edge 188 of the polyethylene covering 172 overlaps and completely encloses the joint between the cover 68 and the outer container 66 as shown in FIG. 4.

The method of use of the stored heat cooker 50 involves an heating phase and a cooking phase. In the heating phase, first the cooking vessel 52 is filled with desired quantity of food item along with required amount of water. The rubber sealing gasket

146 is attached near the rolled rim 138 of the double lid assembly 54. The double lid is placed over the cooking vessel. The whistle 144 is inserted in the hole 142 of the double lid assembly. In the preferred embodiment the storage element 56 is placed on a kitchen range burner with the big hole 76 being concentric with the burner of the kitchen range.

The vessel filled and enclosed, is placed over the storage element. Two strips 62 are inserted in the space between the handles 58,60 and the pouring edge 74 of the vessel, so that the vessel gets raised by few millimeters above the top surface 80 of the storage element. The burner is turned on. The flame and the hot gases enter the big hole 76 symmetrically. The diameter of the hole 76 is so chosen that the flame doesn't touch the storage element any where. Preferably, the burner is set on high heat in order to reduce the time taken by the heating phase. A shorter heating phase saves user time. The flame and/or hot gases from the burner pass through the big hole 76 and directly heat up the vessel 52. The blackened surfaces 80 and 82 absorb heat from the flame and/or hot gases which pass over these surfaces. This portion of the heat from the source, in the absence of the storage element would have gone waste. Hence, the storage element mainly collects the waste heat and improves the efficiency of heating process. When the water inside the cooking vessel 52 starts boiling, steam starts to escape through the whistle 144, and an alarm is generated. At this stage the burner is put off and the heating phase comes to an end. However, it is noted that, for certain food items which are tough to cook, it is necessary to increase the heating time by keeping the burner on for some additional time period. At the end of the heating phase the storage element would have stored the necessary heat for completing the cooking phase. In the preferred embodiment, the weight of the storage element is so chosen that, at the end of the heating phase the temperature of the storage element is approximately in the range of 175 to 240 degree centigrade, depending upon the quantity of the food being cooked.

Once the burner is turned off, the strips 62 are removed so that the vessel now rests on the small mild steel pieces 106,108,110 and 112 attached to the storage element. The hot storage element together with the hot vessel are transferred to the outer container 66. Since the handles 58 and 60 may be fairly hot, it becomes necessary to use gloves or kitchen towel while lifting. The cooking phase begins with the closing of the outer container 66 with insulated cover 68. The cooking process continues due to heat imparted by the storage element. Steam generated, if any, during the cooking process comes out through the whistle and then escapes through the hole 182 in the cover.

Normally this steam has low pressure so the whistle doesn't make any sound. However, if necessary, the whistle may be removed from the hole 142, before the cover 68 is placed over the outer container. When the cooking is over the cooked food can be taken out, if desired. In case if food is not taken out immediately, then, the residual heat remaining in the storage element, and the insulation present retains the food warm for an extended period of time.

It is also possible to cook two food items at a time, by using a separator pan 190 which is shown in FIG. 10 as being remove out from the vessel 52. This separator pan 190 is shorter in height than the vessel 52. It also has a pouring edge 192 which is slightly smaller in diameter than the pouring edge 74 of the vessel 52. A plurality of holes 194 are provided below the pouring edge 192. The pan 190 easily slides inside the vessel 52 with sufficient clearance between the pan 190 and the side wall 72 of the vessel. The edge 192 rests on the pouring edge 74 of the vessel. The first food item to be cooked is placed inside the vessel 52. The second food item is placed inside the pan 190.

The pan 190 is then inserted in the vessel 52. A double lid assembly adapted for covering both the pan 192 and the vessel 52 is used to enclose the pan and the vessel together. The cooking method is similar to the method adapted for cooking single food item. It is noted that only easy to cook food items like rice, vegetable, eggs etc. could be cooked in the pan 190. The tough to cook food items such as cereals or meat have to be cooked in the vessel 52.

The total cooking time for the stored heat cooker 50 is the sum of the time taken by the heating phase and the time taken by the cooking phase. This total cooking time is comparable with that taken by conventional appliances such as pressure cookers or electric cookers. For example using cooker of the preferred embodiment, to cook 250 grams of rice with 700 ml of water, at an ambient temperature of about 25 degree centigrade, on high heat using a medium sized kitchen range burner, the heating time is about 6 minutes and the cooking time is about 20 minutes. Therefore, the total cooking time is about 26 minutes.

The stored heat cookers can work on any type of heat source such as kitchen range burner, electric heating element, kerosene stove, wood stove, coal heaters, and even on candles or catering wax. However, the design of the storage element may differ slightly for different sources. The stored heat cooker offers improved efficiency during heating phase and presence of insulation during cooking phase helps in conservation of

energy. For this reason it is even possible to design stored heat cookers to cook a small quantity of rice say about 100 grams, using candles or catering wax. The high efficiency offered by the present invention makes it environment friendly. Since use of any type of fuel is possible the present invention is equally useful for poor people too.

INDUSTRIAL APPLICABILITY The applications of the stored heat cooker 50 includes regular cooking at homes as a better alternative to the pressure cooker because of it's distinct advantages. Portable cooking equipment could be designed based on the stored heat cooker, because it consumes less fuel and also keeps the food warm for several hours. The stored heat cooker is equally useful for cooking large quantities of food in hotels etc. It may prove to be useful as sterilizing equipment for medical applications.

Although the present invention has been described with considerable detail and illustrated with significant specificity, it should be understood that the present invention is not limited to a particular embodiment and additional alternative embodiments of the present invention should be considered within the scope of claims. Especially a variety of means for raising the vessel could be designed without departing from the coverage of the invention claimed herein. Also, a large variety of shapes and sizes of the storage element and matching shape of the cooking vessels could be designed without departing from the invention claimed here.