WO2011087512A1

WO2011087512A1 - Energy efficient cookware and methods of manufacturing same

Info

Publication number: WO2011087512A1
Application number: PCT/US2010/021244
Authority: WO
Inventors: Lee Lisheng Huang
Original assignee: Lee Lisheng Huang
Priority date: 2010-01-15
Filing date: 2010-01-15
Publication date: 2011-07-21
Also published as: CN103442622A

Abstract

Energy efficient cookware is provided including a base, a wall, and a linear pattern of flame guide channels connected to the base bottom. The flame guide channels accept a flame and guide the flame to the perimeter from the central region resulting in efficient heat exchange. The linear channel profile tends to maximum the surface enhancement from a given plain area on the bottom to improve heat transfer while providing even heating, and mechanical strength to the cookware. The impedance to entrance of flame flow into the channels is minimized to allow easy entrance of the flame into the channels. A reinforcement means is provided to strengthen the rim, therefore, the mechanical robustness of a cookware. A method of creating the reinforcement rim is also disclosed. A method of making the efficient cookware is provided involving die casting. A method of heating a fin structure is provided using an RF heater with complementary fin features.

Description

ENERGY EFFICIENT COOKWARE AND

METHODS OF MANUFACTURING SAME

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to a continuation-in-part of U.S. Patent Application No. 12/114,769 filed on May 3, 2008, which is a continuation-in-part of PCT International Patent Application No. PCT/US/2007/007279 filed on March 23, 2007, which claims a priority of U.S. Provisional Patent Application No. 60/869,370 filed on December 13, 2006, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention relates generally to cookware. More particularly, the invention relates to heat transfer from a heating element to cookware, especially from a flame during the cooking process.

BACKGROUND

[0003] Cookware is a basic tool used daily in human life. Regardless of the different shapes of cookware, ranging from a barbecue grill to a wok and to a teapot, the basic elements of a cookware are two surfaces: one for receiving heat from heat source, the other for heating the food. Heat energy generated either from electricity, or a burning flame, is transferred from the source to the heat-receiving surface of the cookware, conducted through the cookware and transferred to the food. In general, the heat transfer is not very efficient from combustion sources. The utilization of thermal energy from gas on a typical gas range for heating up a cookware is reported to be only about 30%. This means a lot of energy is wasted during the cooking process. As a result, people pay an unnecessarily high energy bill and lot of unnecessary undesirable C0₂ is being emitted to the environment.

[0004] Effort has been directed to optimize the burner to have good mix of air and fuel gas in order to complete combustion of the fuel. Also attention has been paid to distribute the heat evenly across the base of a cookware. However with respect to combustion cooking, there has been limited effort made to improving the energy receiving end of the process, where the energy transfer efficiency from the flame to the cookware is

l typically low. Some attempt to teach concentric grooves on the bottom surface of the cookware, and coating them with radiation absorbing coating to improve the heat absorption(U.S. Patent Nos. 4,926,843 and 5,396,834). These approaches are considered useful for hot-plate type cooking ranges. Other attempts provide cookware with patterned features that can improve the heat transfer laterally, their primary aim is to improve electric-source heat at the center and bottom of the cookware (US 614028). Another attempt has been made to improve heat conduction by using concentric rings in the cookware base. However, the shallow grooves have demonstrated limited improvement on heat transfer (U.S. Patent No. 5,411 ,014). When used with a flame-source, the proposed concentric rings are perpendicular to the flow of the flames and impede flame contact with the bottom surface. As a result, the flow of the flame will go up and down over the rings increasing the inter mixing of the cool air with the hot flame reducing the efficiency of heat transfer. U.S. Patent No. 7,150,279 also mentions using more thermal conductive material on the bottom to improve efficiency. However, the efficiency of cookware over a gas range so far on the market has been about 30%.

[0005] Another issue associated with cookware is that the bottom of the cookware can be warped due to heating unevenly especially when stainless steel is the cookware material. The thermal conductivity of stainless is very low, which makes the severe local heating to warp the base. So the lifetime of the cookware is therefore compromised. Effort has been made to increase the strength of the bottom of the cookware. For example, a cookware patent (US6926971) using multi-cladding metal for uniform heating is awarded to All-Clad, and Patent (US5564589) provides a convex shape to strengthen the bottom.

[0006] Therefore, it would be considered an advance in the art to provide significant improvement in efficiency in cookware, used with a combustion heat source, by promoting interaction of flame with the cookware surface to improve heat transfer from flame to cookware, at the same time help improve heating uniformity across the base, and provide stronger mechanical integrity to the cookware.

[0007] It would be also considered an advance in the art to provide an efficient manufacturing process to achieve the efficient cookware with such heat transfer enhancement features. Such advances would reduce fuel consumption and C0₂ emissions. SUMMARY OF THE INVENTION

[0008] A cookware body typically has a base and a wall, where the wall extends from the top side of the base and spans a perimeter of the base. The PCT patent application (PCT/US07/00729) by the present inventor, suggests a new type of cookware to have at least one pattern of flame guide channels connected to base of the cookware, wherein the flame guide channel is made from a pair of guide fins. The guide fins have a flame entrance end near a center region of the base, and have a flame exit end positioned towards the perimeter of the base. The invention further has at least one pattern of perturbation channels, where the perturbation channel is made from a pair of perturbation fins. The perturbation fins have a first perturbation end positioned away from the central region and a second perturbation end positioned towards the cookware perimeter. The flame guide channel accepts a flame from a stove burner and guides it towards the perimeter from the central region. The perturbation fin generates lateral turbulence in the guided flame by interfering with an onset of laminar flow in the flame as the flame moves along the guide channel. The induced turbulence increases heat transfer from the flame to the base and fins, while minimizing mixing of the flame with ambient air. Such induced turbulence promotes conduction of the flame heat through the cookware and to food for more efficient cooking.

[0009] The present invention provides a pattern of linear guiding channels with maximized extended channel surface density for given original heat receiving surface as in U.S. patent application no. 12/1 14,769, which is incorporated herein by reference for all purposes.

[0010] One aspect of the invention is to provide a channel width variation profile that will allow easy entrance of the hot flames into channels for efficient heat exchange. To further facilitate the flame to enter the channel, the tips of the fins forming the channel are rounded and pointy to reduce flow entrance impedance.

[0011] Another aspect of the current invention, a square cookware base is proposed to provide an extra heat exchange path to increase the heat exchange efficiency. The square base shape also maximizes the material utilization during a preferred manufacturing process to reduce energy used.

[0012] Another aspect of the invention is to provide linear fin structure continuous across the whole base, to allow not only good heat conduction to the bottom of the cookware to reach the food medium in upward direction, but also to have good heat conduction in a sideways direction to provide even heating over the bottom face of the cookware. This continuous structure also strengthens the base of the cookware to reduce the chance of warping and, therefore, enhances the lifetime of the cookware.

[0013] In a further aspect, the handles of the cookware are placed on the wall such that they are away from the exits of the linear channels to reduce the chance of being over heated by stray flame.

[0014] In a further aspect, the rim of the cookware can be strengthened to improve the mechanical integrity of the pot without increase over all material use.

[0015] The present invention also provides a manufacturing process that can produce the cookware with high density of extended exchange channels cost effectively using the good thermally efficient material.

[0016] The present invention also provides a manufacturing process to produce the stainless steel cookware with heat exchange channels on the bottom.

[0017] The present invention also provides a manufacturing process to produce the reinforced rim on a stainless cookware.

BRIEF DESCRIPTION OF THE FIGURES

[0018] The objectives and advantages of the present invention will be understood by reading the following detailed description in conjunction with the drawing, in which:

[0019] FIG. 1 shows a radial pattern of heat exchange channels

[0020] FIG. 2 shows a cookware with linear pattern of channels

[0021] FIG. 3 shows a square base cookware with linear pattern of channels

[0022] FIG. 4.1 shows guide fins with flat top

[0023] FIG.4.2 shows guide fins with rounded top

[0024] FIG. 5 shows channel width varies across the base

[0025] FIG. 6 shows a supported rim structure

[0026] FIG. 7 shows a folded rim structure

[0027] FIG. 8 shows the full circle rim structure and the process of making it

[0028] FIG. 9 shows a furnace for heating the rim of a cookware

[0029] FIG. 10 shows an RF heater setup to heat up cookware from inside

[0030] FIG.11 shows rolling bonding setup

DETAILED DESCRIPTION OF THE INVENTION

[0031] Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will readily appreciate that many variations and alterations to the following exemplary details are within the scope of the invention. Accordingly, the following preferred embodiment of the invention is set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.

[0032] Typically cooking setup using combustion range is that a cookware holding a medium such as water is placed on top of a flame from a burner. The flame rises up due to pressure of the gas in the supply piping and the buoyancy of the hot air causes it to touch the base of the cookware. Heat transfer from the flame to the base occurs via convection transfer as well as radiation. The heat absorbed from the heat-receiving surface is transferred to the food surface by thermal conduction. The heat is then transferred from the food surface to the water via conduction and convection. In this whole process, the heat transfer from the flame to the cookware body via convection transfer is the most inefficient step limited by thick layer of boundary layer of the flame flow, while the heat transfer from the cookware is also limited by a boundary layer of the liquid content. The heat conduction in the cookware body is typically metal and tends to be efficient.

[0033] A radial heat exchange channel pattern described in U.S. patent application No.11/992,972 is shown in FIG. 1. This is the bottom view of cookware 101. There is a pattern of channels formed by fins which is protruding upward from the base of the cookware. For example, fins 102 and 103 form a channel in the space between them. The channel is defined as the space in between a pair of fins and the base along the direction of the fins. The last confining wall of the channel is the buoyancy of the hot flame under influence of the gravity. The aspect ratio between the height of the fins and the distance between the fins is larger than one to be considered guiding channel to have recognizable channel guiding heat exchange effect. In a radial pattern in FIG.1 , the channel width will change along the path due to the radial nature. As indicated in the FIG. 1 , the width of the channel at location 1 11 is larger than the width of the channel at location 112 which is closer to the center of the radial pattern. However, for a given manufacturing method, there is a limit on how small the gaps and fins width can be achieved. This determines the surface area enhancement from exchange channel compared to the flat surface. It will be preferable to have the channel widths to be all at the minimum width allowed by the manufacturing process. The non-uniform channel width property of the radial pattern makes it not possible to realize the maximum surface area improvement that a given manufacturing process can provide.

[0034] On the other hand, in a linear pattern heat sink structure, the channel spacing is constant. Therefore, it is possible to have made channels across the whole base of the cookware with the smallest dimension a given manufacturing process can produce. This linear pattern can create the most surface area improvement in a channel format over the original flat surface for a given size of the flat surface area. A cookware with a linear pattern heat exchange channels is shown in FIG. 2. A cookware 200 comprises a linear channel pattern of channels 210. The channel width is constant along the length of the channels. Typical flame from a burner will be placed close to the center region of the cookware. Once the flame enters the channel, it will be guided to flow towards the perimeter of the base of the cookware. Eventually it exits the channel in the place indicated by 211 and 212. The material of fins has high thermal conductivity coefficient, therefore heat absorbed by the fin can be conducted to the base to help the overall heat transfer from the flame to the body of the cookware. This effectively increases the heat exchange surface area for the energy from hot flame to the body of the cookware. The dense channel arrangement from linear pattern of parallel fins provides a substantial improvement as shown in the prototype built. A design of an aluminum cookware with guide fins of a width of 0.08 inch, a gap of 0.15 inch and a height of 0.5 inch results in about double the efficiency of heat transfer from a flame to the cookware, therefore a 50% shortened heat up time compared with a same size conventional cookware without the exchange channels. This significantly improves energy utilization in cooking and reduces C0₂ emission.

[0035] Also seen in FIG. 2, a handle 213 is placed on the wall in the direction away from the output of the channels. The handle won't get heated up by flame escaping out in this direction otherwise without the confining channels. This is an improvement that can reduce risk of burning hands.

[0036] It is also found in experiments that the improvement of an 8 inch square base cookware with heat transfer channels over a 8 inch square base cookware without heat transfer channels is substantially bigger ~ a 10% improvement from an 8 inch round base cookware with the same heat transfer channels over a round base cookware without the heat transfer structures. The channel design in both cases is the same: width of the channel is 0.15 inch, the fin width is 0.08 inch and the height is 0.5 inch. This result indicates that the extra channel length at the corner of the square base cookware confines the flame for heat exchange while in the round base cookware the channels at the edge of the base run off quickly. Since the effective heat exchange happens inside the exchange channel, the extra channel length at the corners is what makes the difference. This effect can be significant on a range which flame speed is fast, therefore, the complete combustion of the flame happens a distances away from the exit of the fuel gas from the burner. To have a normal round cookware look, a design of the square base cookware can have round a top opening. FIG. 3 depicts such cookware. The cookware 300 is morphed from a round top 31 1 to a square base 312. This can be done by a standard progressive stamping manufacturing process. The exchange channels 321 are built to be in parallel to one of the edge 322 of the square base. This parallelism will give extra run way of the channel in the corner area to benefit energy exchange. A handle 331 is attached on the wall in an area above the edge 322 which the heat exchange channels are made parallel to. Since hot flame is guided to flow along the direction of the edge 322, the handle 331 will have less chance to get heated up by the flame.

[0037] To have efficient heat exchange in the channels, hot flame must be allowed to flow into channels freely without too much impedance. It is found that this requirement need to be balanced with the need of enhancement of the surface area. To have large surface area enhancement, it is desirable to have dense fins which leads to thinner fins and, therefore, narrower channel widths. However, if the width of the channel is too narrow, it will limit the ability of hot flame to enter into the channels. The ratio between the thickness of the fin Of the effective width of the fin at the entrance, and the width of the channels co_c is defined as the impedance Ω_β to the flame entrance to the channels, Ω_β = (Of / CD_c. To reduce the flame entrance impedance, the thickness of the fin should be small. However, when the fin is too thin, it will be easier to be damaged during the daily use in a commercial kitchen, even the heat transfer efficiency from the height of the fins to the base can be comprised. So it is preferable to reduce the impedance while retaining the strength of the fins. One way to reduce the impedance is to sharpen the top of the fin such as rounding and tapering. FIG. 4.1 shows a fin structure 410 where the fin width is denoted as 41 1 and the channel width is 412. As the typical shape of the fin top is substantially flat; the impedance of the air can be represented by the ratio of fin width 411 over channel width 412. As shown in the FIG. 4.2 the top of the fins in fin structure 420 are rounded up. The top of the fins is smaller making the effective width of the fin smaller, therefore, reducing the impedance for hot flame to enter the channel.

[0038] The flame flow entrance impedance to the channels plays an important role in the efficiency of the cookware. In an experiment, a cookware with a guide fins width of 0.08 inch, gap of 0.1 inch and height of 0.5 inch was tried out. This channel fin density is higher than the one with a guide fins width of 0.08 inch, gap of 0.15 inch and height of 0.5 inch described in the example in the previous example, therefore efficiency was expected to be higher. However, the efficiency dropped by 10% from the design result in 50% described above. This is because entrance impedance of the flame flow to the channel in this one is 0.8 compared with 0.53 for the previous one. The high flow entrance impedance make the efficiency lower even though the surface density is higher. By cutting 3 slots of 0.25 inch across the channels in the center region to facilitate the entrance of the flame does pull the efficiency back by 5%. This illustrates the importance of reducing the flame entrance impedance. In the manufacturing process, the number of the slots to open in the extruded channel needs to be minimized to be cost effective. So it is important to reduce the entrance impedance for efficient heat exchange.

[0039] Besides the impedance, the entrance of the flame to the channel is also affected by the direction of the flame flow with respect to the direction of the channels. A typical round burner generates a radial symmetric flame. As the flame flows upward into the channels, it also flows outward in a radial direction. As seen in FIG. 2, as the flame goes outwards, the outward flow velocity in region 215 is in general the direction of the channels. The flow can enter into channels easily, and therefore the channel density can be made higher. On the other hand, in the region of 216, the flow velocity flow is in general perpendicular to the direction of the channels. It is preferable to have the width of the channels to be larger in this region to allow the flow to entrance easier. Therefore, a channel width profiles of which the width of the channels varies from the center in this direction can facilitate the entrance of the flame. FIG. 5 shows a channel pattern 500 where the channel width varies across the base. The channels in region 501 are in the same general direction of the flame flow, the channels width can be narrower to have denser fins therefore bigger surface area improvement. While in the region 502, the flame's radial flow component is pretty much perpendicular to the direction of the channel. Therefore, it is preferable to have wider channels in this region to allow easier entrance of the flame flow into the channels. Different range burner from different vendors will have different flame flow profiles and temperature distributions. Therefore the variation in channel width should be optimized accordingly for different ranges.

[0040] In order to achieve the benefits of the energy efficient cookware in the market place, it is important to be able to manufacture the heat exchange channel on cookware cost effectively and energy efficiently. One way to achieve a low cost linear channel structure is via extrusion. Extrusion can provide a 2D feature in Aluminum at low cost. The extruded long piece will be cut, preferably by water jet cutting, to the circular or round shape of a cookware base. The extruded heat sink can then de-burred and cleaned before bonding to the bottom of a cookware. The other way to create the linear channel, radial pattern as well is via die-cast.

[0041] Typically a cast mold of the casting can be designed to be smooth so that cast channel plate can have smooth edges on the fins, and minimum de-burring is needed. The drawback is the lower thermal conductivity of the cast material can be traded off with the reduction of de-burring step in the manufacturing. The casting method has another advantage of being able to create other channel patterns. A die cast process is continuous across fins, it does not like too many stoppings in the fins. A continuous radial channel pattern cannot keep a high channel density throughout. Therefore, for linear channel patterns and S shape channel patterns are suitable for the low cost die cast process.

Casting mold is expensive to make, especially the high density fin area. One approach is to make the die-cast mold of different cookware share a same portion of the die cast mold of the fin area. For example, one can make a set of mold of the fry pan, sauce pan, sauce pot and stock pot with the same diameter to share a same die-cast mold at the base. The choice of material use for the die-cast is alloy 443 which has higher thermal conductivity than the material popular die-cast material 390, or 380 alloys. The in gate and out gate in the die-casting mold are at the rim of the cookware in line of the fin directions. This placement will facilitate the flow of injected liquid aluminum during the casting process. The end corner of the fin will be rounded to facilitate the flow of the aluminum to fill the ends. [0042] After the cast heat exchange channel plate is done it is then bonded to the bottom of a stainless steel cookware. In the brazing process, brazing filler material will be placed inbetween the heat exchange plate and the cookware bottom. The assembly is then heated up to a high temperature to melt the filler material to bond the heat exchange channel plate and the cookware together. A typical way to heat up the assembly is to use a furnace. Alternatively, an RF heater can be use. In this process, a heater plate is made with the complementary feature of the heat exchange channel plate, i.e. the heater plate in mate with the heat exchange channel plate as shown in FIG. 6. Where 601 is the heat exchange channel plate, and 602 is the heater plate. The material of the heater plate is ferromagnetic which can couple RF power into heat. An RF generator 603 is placed over the heater plate to heat up the heat exchange channel plate, and further heat up the cookware 604. Another heater 605 with the RF generator 606 can be placed inside the cookware.

[0043] After the heat exchange channel plate is bonded to a cookware, the base of a cookware with a heat exchange tends to be heavier than a typical base of a cookware. A square cookware base is not radial symmetric, this requires the wall of the cookware to be thick enough to have good mechanical robustness. It is desirable to strengthen the rim of the cookware to effectively improve the mechanical robustness and to save some material use.

[0044] Typically, the rim of a stainless cookware from deep draw is folded to the horizontal direction perpendicular to the wall as shown in FIG 7. One way to improve the rim is by doubling the thickness by putting a support rim 702 at the rim. The deep draw tooling can be used to produce a support rim of the same shape of the cookware rim 702. This support rim is then heated up to a certain higher temperature. The diameter of the support rim is expanded so that it can be slid up from the bottom of the pot to rest against the top rim of the pot. When cooled down, the support rim clamps tightly on the top portion of the rim to reinforce the rim of the pot. Optionally, this support rim can then be further spot welded to the wall of the pot and the rim of the pot. The seams between the rings can also be paint sealed.

[0045] The reinforcement can be done by folding the rim as shown in FIG 8. Folded back rim 801 is a typical one. The folded back rim 802 is similar to the configuration of support rim 702. The rim 803 and 804 are the ones with multiple folding. The seams between the multi-layer can be sealed by porcelain paints. Half circle rim 805 is another typical reinforcement rim.

[0046] There are two effects in folding the rim of the cookware that provide reinforcement to the cookware. One effect comes from the geometric effect, for example, folding backward once will double the thickness at the rim therefore making it stronger. The second factor is when a metal is cold formed, the metal becomes stronger. The folding action on stainless steel typically increases dislocations inside the metal, and aligns the grain/domain of the material in the direction that resists further deformation; both of these increase the hardness of the material. Proper design of the folding action will strengthen most of the metals, therefore, it can be used to increase the strength of the rim of the cookware. To utilize the benefit of hardening from the folding action, one extra folding 810 is made on a half circle rim 806. This extra folding can result in extra strength to the rim with the same amount of material used and at the same time allow the rim edge direction to facilitate liquid pour out.

[0047] As shown in FIG. 9, there is a little cavity 901 in structure of the half circle rim making it easy to trap some food. To improve this, it is possible to fill in the cavity with filler material 903 to the level it is easy to clean. The filling material can be porcelain enamel, glass enamel, etc. The hardening of the filler material can further strengthen the rim. To do so, the filler material is placed inside the rim cavity when the cookware is positioned upside down. The rim of the cookware is then put in the RF heater that can heat up the rim of the cookware to cure the filler material. In the case of porcelain enamel, multiple applications of the filling materials may be needed to fill to a certain depth in a deep cavity because there may be a certain thickness limitation for single application of the paint to prevent cracking during the curing.

[0048] Porcelain enamel can have different colors for improving the aesthetic design of the cookware. For example a green color can put emphasis of the green attribute of the energy efficient cookware invented here.

[0049] Alternatively, plastics with a high temperature property, such as Bakelite plastics, can be used, and PEEK plastic is even better because it is FDA approved for food contact use. The preformed ring of PEEK can be placed inside the cavity of the rim to give support to the rim and at the same time fill up the cavity of the rim. Alternatively, a metal ring can also be used to place into the cavity and tag weld in place, as shown in FIG. 9C. The seam or gap between the rim and the reinforcing ring can be sealed with enamel paints.

[0050] Alternatively, a fully closed rim can be made as shown in FIG. 10. Typically, after the deep draw, the rim of the pot is already folded to horizontal direction as in FIG. 7. This horizontal portion of the material 701 is clamped down during the deep draw process. To be able to fold in to fully close, the width of this section is such that the edge of the rim will reach the wall of the cookware after folded in a circle. A set of tools 1010 and 1011 are used to fold the flat rim to form a half circle 1012. Further, fold to full circle will be done using the same 1010 in place, and a tool 1013 with semicircle having the edge 1021 that matching the edge 1022 of tool 1010. The edge of the rim slides along the edge 1023 toward the wall of the cookware a 270 degree folded close rim. If the rim does not reach the wall during the folding process, the edge or the rim will spring back due to the elasticity property of the material. Therefore, it is important to have the length of the rim and the tooling design so that during the forming process the edge of the rim is forced against the wall to bend pass the elasticity regime of the material so that it stays in the intended form after the tooling is released. The tool 1013 has a chamber 1024 to allow the rim edge 1023 to deform pass the elasticity. This process naturally seals the edge of the rim and the wall so that food won't be able to get in the cavity. In the forming process, a sheet of softer material, such as aluminum or plastic, can be placed between the edge of the rim and the wall. The softer material will deform to fill the uneven edges to form a seal between the edge of the rim and the wall. The softer metal is then trimmed finish at the gap. Alternatively, the gap, if there is any gaps between the edge of the rim and the wall, can be sealed by welding, brazing, or simply painted by the porcelain enamel paints, and other high temperature paints.

[0051] It is known that heat treat methods can also be used to harden the metal. In general, when a metal alloy is heated up to a designed temperature for a certain time, and then cooled down in a designed rate, the hardening of the metal can result. The rim of the cookware can be heat-treated locally to achieve a hardening effect. Since the rim is on one end of the cookware, it can be heated up in a specially designed RF furnace or simple ring type electrical furnace to high heat treat temperatures locally without heating the whole cookware. The rim is then cooled down by quenching in water or other liquids, or air to tailor the properties of the rim. The process can be done at a lower temperature and repeated to strengthen the rim.

[0052] A furnace design is shown in FIG 1 1. The opening 1101 of the furnace 1100 is annular in shape. The annular opening is designed to receive the rim portion of a cookware. And the depth of the furnace is designed to heat up a portion of the rim of the cookware needed to be heated up, but not the whole wall of the pot. It is typically several inches. The heating elements 1102 are placed around the region close to the rim of the cookware for effective heating. The heating method can be standard Tungsten heater coils or faster heating RF (radio frequency) heaters. The furnace is insulated by fiberglass thermal insulator to be energy efficient. Alternatively, the furnace body 1100 can be mold formed using insulating materials such as ceramic fiber Moldatherm.

[0053] To complete the cookware, one or two handles will be attached to the wall of the cookware for example by welding. The position of the handles will be placed on the wall that is away from the channel exits. This placement reduces the chance of the handle being heated up by the hot flame flow up due to buoyancy force along the wall of the cookware, since most of the flame will be guided toward the exits of the channels.

[0054] All the above descriptions are considered to be within the scope and spirit of the present invention as defined by the following claims and their legal equivalents.

Claims

We claim:

1. A cookware comprising:

a. a cookware body, wherein said cookware body includes a base and a wall, whereby said wall extends from a top side of said base and spans a perimeter of said base;

b. at least one linear pattern of flame guiding channels connected substantially perpendicularly to a bottom side of said base, wherein said flame guide channel comprises a pair of guide fins;

c. at least one reinforcement means at the top edge of said wall.

2. The cookware of claim 1, wherein said guide fins of said flame guide channel have a height larger than a distance between said guide fins.

3. The cookware of claim 1, wherein a flame entrance impedance of said flame guide channels is less than 0.8.

4. The cookware of claim 1, wherein a top of said guide fin of said flame guide channel is not flat.

5. The cookware of claim 1 , wherein a handle is attached to said wall in a location not above an exit of said flame guide channels.

6. The cookware of claim 1, wherein the reinforcement means is a full folded back circle at a rim of said wall.

7. The cookware of claim 1, wherein the reinforcement means is an attached support rim.

8. The cookware of claim 1, wherein the reinforcement means is a folded back half circle and an extra bend at the lip.

9. The cookware of claim 1 , wherein the reinforcement mean is a folded back half circle with inserts.

10. The cookware of claim 1 , wherein the reinforcement mean is an extra folding at the rim.

1 1. A cast cookware comprising:

a. a cookware body, wherein said cookware body comprises a base and a wall, wherein said wall extends from a top side of said base and spans a perimeter of said base;

b. at least one linear pattern of flame guide channel fins connected to a bottom of a side of said base.

12. The cast cookware of claim 11, wherein the cookware is made by die-cast.

13. The cookware claim of 1 1 , wherein the linear pattern is S shape.

14. A method of forming an energy efficient cookware comprising:

a. providing a- cast member wherein at least one pattern of flame guide channels are connected perpendicularly to a bottom side of said cast member, wherein each flame guide channel comprises a pair of guide fins;

b. providing a stainless vessel body having a base, wherein a wall is extended from a rim of said base;

c. attaching said cast member to the base of said stainless vessel body.

15. The method of claim 14, wherein the attachment is done by brazing.

16. The method of claim 14, wherein the attachment is done by impact bonding.

17. A method of constructing a fully folded closure rim for a cookware, the method comprising:

a. folding the rim to half circle rim; and b. further folding the rim to a closure structure where an edge of the rim touches a wall of the cookware

18. A method of creating color patterns on a rim of a cookware curing the color rim comprising:

a. painting a rim of a cookware with thermal curable paint; and b. curing the paint in an annular heater.

19. A method of heating a fin structure for brazing by an RF heater, wherein the RF heater includes a structure that is complementary to that of the fin structure.