US20200253409A1 - Cooking device having a cooking vessel and a ceramic heater - Google Patents

Abstract

A cooking device according to one example embodiment includes a base having a top surface positioned to contact a cooking vessel configured to hold food during cooking. The base includes a heater having a ceramic substrate and an electrically resistive trace on an exterior surface of the ceramic substrate. The heater is positioned to supply heat generated by applying an electric current to the electrically resistive trace to the top surface of the base for heating the cooking vessel to heat food in the cooking vessel. In some embodiments, the electrically resistive trace includes an electrical resistor material thick film printed on the exterior surface of the ceramic substrate. In some embodiments, the electrically resistive trace is positioned on a top surface of the ceramic substrate that faces upward toward the top surface of the base.

Description

CROSS REFERENCES TO RELATED APPLICATIONS
• This application claims priority to U.S. Provisional Patent Application Ser. No. 62/802,955, filed Feb. 8, 2019, entitled “Heat Pipe Cooking Vessel,” the content of which is hereby incorporated by reference in its entirety.
BACKGROUND1. Field of the Disclosure
• The present disclosure relates generally to cooking devices and more particularly to a cooking device having a cooking vessel and a ceramic heater.
2. Description of the Related Art
• Manufacturers of cooking devices, such as rice cookers, are continuously challenged to improve heating time and heating effectiveness. Most low-end rice cookers, for example, utilize a wire coil heater, such as nichrome wire, potted with ceramic cement inside a stainless steel sheath embedded inside a cast aluminum body. These heaters generate heat by passing electrical current through the nichrome wire. These types of heaters often suffer from long warmup and cooldown times due to the high thermal mass provided by the electrical insulation materials and the relatively large metal components. Furthermore, cooking vessels used with wire coil heaters typically have relatively low thermal mass resulting in poor distribution of heat within the cooking vessel.
• Some high-end rice cookers utilize induction heaters to directly warm the cooking vessel instead of relying on convection or thermal conduction. Induction rice cookers use induction heating where current is passed through a metal coil to create a magnetic field. The cooking vessel is positioned within the magnetic field to induce electrical current in the cooking vessel which, in turn, generates heat. With induction heating, the heating temperature may be controlled by adjusting the strength of the magnetic field allowing for shorter warmup and cooldown times to be achieved. However, induction heaters are generally expensive due to the cost of the electrical materials and components, and the control systems for induction heaters are relatively complex and generally expensive as a result.
• Accordingly, a cost-effective cooking device having improved thermal efficiency is desired.
SUMMARY
• A cooking device according to one example embodiment includes a base having a top surface positioned to contact a cooking vessel configured to hold food during cooking. The base includes a heater having a ceramic substrate and an electrically resistive trace on an exterior surface of the ceramic substrate. The heater is positioned to supply heat generated by applying an electric current to the electrically resistive trace to the top surface of the base for heating the cooking vessel to heat food in the cooking vessel. In some embodiments, the electrically resistive trace includes an electrical resistor material thick film printed on the exterior surface of the ceramic substrate. In some embodiments, the electrically resistive trace is positioned on a top surface of the ceramic substrate that faces upward toward the top surface of the base.
• Embodiments include those wherein the heater includes a thermistor that is positioned on the ceramic substrate and in electrical communication with control circuitry of the heater for providing feedback regarding a temperature of the heater to the control circuitry of the heater. In some embodiments, the thermistor is positioned on a bottom surface of the ceramic substrate that faces away from the top surface of the base.
• Embodiments include those wherein the base includes a heating plate that forms the top surface of the base. The heating plate is positioned in contact with the heater to transfer heat from the heater to the top surface of the base for heating the cooking vessel to heat food in the cooking vessel. In some embodiments, the heating plate includes a domed top surface for contacting a concave bottom surface of the cooking vessel.
• Embodiments include those wherein the ceramic substrate has a polygonal shape. In some embodiments, the ceramic substrate has an octagonal shape.
• Embodiments include those wherein the electrically resistive trace extends in a serpentine pattern across the exterior surface of the ceramic substrate. In some embodiments, the serpentine pattern of the electrically resistive trace has a generally circular outer perimeter.
• A cooking device according to another example embodiment includes a housing having a receptacle and a base positioned along a bottom of the receptacle. A cooking vessel is removably positionable within the receptacle for containing food to be cooked. The cooking vessel contacts the base when the cooking vessel is positioned within the receptacle. The base includes a heater having a ceramic substrate and an electrical resistor material thick film printed on a surface of the ceramic substrate. The heater is positioned to supply heat generated by applying an electric current to the electrical resistor material to the cooking vessel when the cooking vessel is positioned within the receptacle.
• A heater for use with a cooking device according to one example embodiment includes a ceramic substrate and an electrically resistive trace thick film printed on an exterior face of the ceramic substrate. The electrically resistive trace extends in a serpentine pattern across the exterior face of the ceramic substrate from a first end of the electrically resistive trace to a second end of the electrically resistive trace. The serpentine pattern of the electrically resistive trace has a generally circular outer perimeter. The heater also includes a first electrically conductive trace electrically connected to the first end of the electrically resistive trace and a second electrically conductive trace electrically connected to the second end of the electrically resistive trace. The first and second electrically conductive traces form respective first and second terminals providing respective first and second electrical connections for completing a circuit formed by the first and second electrically conductive traces and the electrically resistive trace. Some embodiments include one or more glass layers on the exterior face of the ceramic substrate that cover the electrically resistive trace electrically insulating the electrically resistive trace. Some embodiments include a thermistor positioned on a second exterior face of the ceramic substrate that is opposite the exterior face of the ceramic substrate on which the electrically resistive trace is positioned for providing feedback regarding a temperature of the heater to control circuitry of the heater. Embodiments include those wherein the ceramic substrate has a polygonal shape. In some embodiments, the ceramic substrate has an octagonal shape.
BRIEF DESCRIPTION OF THE DRAWINGS
• The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present disclosure and together with the description serve to explain the principles of the present disclosure.
• FIG. 1 is a perspective view of a cooking device according to one example embodiment.
• FIG. 2 is a schematic diagram of the cooking device according to one example embodiment.
• FIG. 3 is an exploded perspective view of a heater assembly of the cooking device according to one example embodiment.
• FIGS. 4 and 5 are plan views of a top surface and a bottom surface, respectively, of a heater of the heater assembly shown inFIG. 3.
• FIG. 6 is a cross-sectional view of the heater shown inFIGS. 4 and 5 taken along line6-6 inFIG. 4.
• FIG. 7 is a plan view of a top surface of a heater according to another example embodiment.
• FIG. 8 is a cross-sectional view of a cooking vessel of the cooking device employing a heat pipe according to one example embodiment.
• FIGS. 9A-9C are cross-sectional views of the cooking vessel shown inFIG. 8 taken along line9-9 inFIG. 8 illustrating various example wick structures of the heat pipe.
DETAILED DESCRIPTION
• In the following description, reference is made to the accompanying drawings where like numerals represent like elements. The embodiments are described in sufficient detail to enable those skilled in the art to practice the present disclosure. It is to be understood that other embodiments may be utilized and that process, electrical, and mechanical changes, etc., may be made without departing from the scope of the present disclosure. Examples merely typify possible variations. Portions and features of some embodiments may be included in or substituted for those of others. The following description, therefore, is not to be taken in a limiting sense and the scope of the present disclosure is defined only by the appended claims and their equivalents.
• Referring now to the drawings and particularly toFIG. 1, acooking device100 is shown according to one example embodiment. In the example embodiment illustrated,cooking device100 includes a rice cooker. However,cooking device100 may also include a pressure cooker, a steam cooker, etc.Cooking device100 includes ahousing102, acooking vessel120, alid105, aheater assembly140, and auser interface109.Housing102 includes an upper portion having areceptacle103 for receivingcooking vessel120 and a lower portion within whichheater assembly140 is mounted. In the embodiment illustrated,heater assembly140 forms a receiving base ofreceptacle103 such thatcooking vessel120 contacts and rests on top ofheater assembly140 when cookingvessel120 is positioned withinreceptacle103 so that heat generated byheater assembly140heats cooking vessel120.
• Cooking vessel120 is generally a container (e.g., a bowl) having afood receptacle121 in which food substances to be cooked, such as rice and water, are contained. That is,food receptacle121 ofcooking vessel120 directly contacts and retains the food being cooked.Cooking vessel120 may be composed of, for example, a metal having high thermal conductivity, such as stainless steel, aluminum or copper.Lid105 covers the opening at arim122 ofcooking vessel120.Lid105 includes ahandle107 preferably composed of a material having low thermal conductivity to provide a safe surface for the user to hold when usinglid105.User interface109 is provided on a front portion ofhousing102.User interface109 may include one or more buttons, dials, knobs, etc. for receiving user input and/or a display or indicator lights for providing information about the functioning and status ofcooking device100 to a user.Cooking device100 also includes apower cord112 for connectingcooking device100 to anexternal power source114.
• In one embodiment, during use,food receptacle121 ofcooking vessel120 holds water and rice to cook, andheater140 transfers heat tocooking vessel120 to bring the water to boil. Once the water reaches a steady boil, the temperature ofcooking vessel120 remains generally stable. Once all of the water incooking vessel120 is absorbed by the rice and/or evaporated, the temperature ofcooking vessel120 tends to increase, triggering a mechanism insidecooking device100 to either turnheater assembly140 off or to switch to a reduced temperature warming cycle intended to keep the food incooking vessel120 warm.
• With reference toFIG. 2, a schematic depiction ofcooking device100 is shown according to one example embodiment.Cooking device100 includesheater assembly140 including aheater150 and aheating plate145.Heater150 includes asubstrate152 to which at least oneresistive trace160 is secured. Heat is generated when electrical current provided bypower source114 is passed throughresistive trace160. When cookingvessel120 is disposed inreceptacle103,cooking vessel120 contacts and rests on top ofheating plate145.Heating plate145 is positioned in contact with, or in very close proximity to,heater150 in order to transfer heat fromheater150 tocooking vessel120. In some embodiments, thermal grease is applied betweenheater150 andheating plate145 to facilitate physical contact and heat transfer betweenheater150 andheating plate145. In some embodiments, a gap filler (e.g., silicon gap filler) or pad (e.g., graphite gap pad) is positioned betweenheater150 andheating plate145 to facilitate heat transfer betweenheater150 andheating plate145.Heating plate145 is composed of, for to example, a metal having high thermal conductivity, such as forged aluminum.
• Cooking device100 includescontrol circuitry115 configured to control the temperature ofheater150 by selectively opening or closing a circuit supplying electrical current toresistive trace160. Open loop or, preferably, closed loop control may be utilized as desired. In the embodiment illustrated, atemperature sensor170, such as a thermistor, is coupled tosubstrate152 for sensing the temperature ofheater150 and permitting closed loop control ofheater150 bycontrol circuitry115.Control circuitry115 may include a microprocessor, a microcontroller, an application-specific integrated circuit, and/or other form integrated circuit.User interface109 is communicatively coupled to controlcircuitry115 via acommunications link110.
• In the embodiment illustrated inFIG. 2,control circuitry115 includes aswitch117 connected between one end ofresistive trace160 and a first terminal114aofpower source114.Switch117 may be, for example, a mechanical switch, an electronic switch, a relay, or other switching device. The other end ofresistive trace160 is connected to asecond terminal114bofpower source114. The temperature ofheater150 is controlled by measuring the temperature ofsubstrate152 bytemperature sensor170 held in contact withsubstrate152 and feeding temperature information fromtemperature sensor170 to controlcircuitry115 which, in turn, controls switch117 to selectively supply power toresistive trace160 based on the temperature information. Whenswitch117 is closed, current flows throughresistive trace160 to generate heat fromheater150. Whenswitch117 is opened, no current flows throughresistive trace160 to pause or stop heat generation fromheater150. In some embodiments,control circuitry115 may include power control logic and/or other circuitries for controlling the amount of power delivered toresistive trace160 to permit adjustment of the amount of heat generated byheater150 within a desired range of temperatures. For example, in some embodiments, when the temperature ofheater150 is low (e.g., under 100 degrees Celsius),heater150 is supplied with 50% power and then gradually stepped up from 50% to 100% as the temperature ofheater150 increases.
• FIG. 3 showsheater assembly140 includingheating plate145 andheater150 according to one example embodiment.FIG. 4 shows a top view ofheater150, andFIG. 5 shows a bottom view ofheater150. In the example embodiment illustrated,heating plate145 is formed as a circular disk having a domed upper surface147 (also shown inFIG. 2 with exaggerated scale for illustration purposes). In one embodiment,heating plate145 has a diameter of about 162 mm, a central portion having a thickness of about 5 mm, and a circumferential edge having a thickness of about 1 mm. In other embodiments,heating plate145 may have other shapes as long asheating plate145 is positioned to spread heat fromheater150 across the bottom surface ofcooking vessel120. The thermal conductivity and relative thinness ofheating plate145 result in a relatively low thermal mass, which reduces the amount of time required to heat andcool heating plate145 and, in turn,cooking vessel120.
• Heater150 includessubstrate152 constructed from ceramic or the like, such as aluminum oxide (e.g., commercially available 96% aluminum oxide ceramic). Hereinafter,substrate152 is referred to asceramic substrate152. In some embodiments,heater150 may include one or more layers ofceramic substrate152. Whereheater150 includes a single layer ofceramic substrate152, a thickness ofceramic substrate152 may range from, for example, 0.5 mm to 1.5 mm, such as 1.0 mm. Whereheater150 includes multiple layers ofceramic substrate152, each layer may have a thickness ranging from, for example, 0.5 mm to 1.0 mm, such as 0.635 mm. In the embodiment illustrated,ceramic substrate152 is octagonal in shape having an incircle diameter d of about 147 mm. However,ceramic substrate152 may take other suitable shapes depending on the application, such as, for example, circular, hexagonal, square, etc. In general, the octagonal shape illustrated is easier to reliably manufacture on a commercial basis than, for example, a circular shape.
• Ceramic substrate152 includes atop surface152athat facesheating plate145 and abottom surface152boppositetop surface152a. In the embodiment illustrated,resistive trace160 is positioned ontop surface152aofceramic substrate152.Resistive trace160 includes afirst end160aand asecond end160b. In this embodiment, a pair ofconductive traces162a,162bare also positioned ontop surface152a. Conductive traces162a,162bare connected to first and second ends160a,160bofresistive trace160, respectively.Resistive trace160 includes a suitable electrical resistor material such as, for example, silver palladium (e.g., blended 70/30 silver palladium). Conductive traces162a,162binclude a suitable electrical conductor material such as, for example, silver platinum. In the embodiment illustrated,resistive trace160 andconductive traces162a,162bare applied toceramic substrate152 by way of thick film printing. For example,resistive trace160 may include a resistor paste having a thickness of 10-13 microns when applied toceramic substrate152, andconductive traces162a,162bmay include a conductor paste having a thickness of 9-15 microns when applied toceramic substrate152.Resistive trace160 forms the heating element ofheater150, andconductive traces162a,162bprovide electrical connections toresistive trace160 in order to supply an electrical current toresistive trace160 to generate heat.
• In the example embodiment illustrated,resistive trace160 follows a serpentine pattern extending fromfirst end160atosecond end160balongtop surface152aofceramic substrate152. In this embodiment, the serpentine pattern formed byresistive trace160 has a generally circularouter perimeter161. Conductive traces162a,162beach form arespective terminal163a,163bofheater150. Cables orwires165a,165bare connected torespective terminals163a,163bin order to electrically connectresistive trace160 andconductive traces162a,162bto, for example,control circuitry115 andpower source114 in order to selectively close the circuit formed byresistive trace160 andconductive traces162a,162bto generate heat.Conductive trace162adirectly contacts first end160aofresistive trace160, andconductive trace162bdirectly contacts second end160bofresistive trace160. Conductive traces162a,162bboth extend along anextension portion155 ofceramic substrate152 that extends from anedge157 ofceramic substrate152 in the example embodiment illustrated, but conductive traces162a,162bmay be positioned in other suitable locations onceramic substrate152 as desired. Portions of first and second ends160a,160bofresistive trace160 obscured beneathconductive traces162a,162binFIG. 4 are shown in dotted line. In this embodiment, current input toheater150 at, for example, terminal163aby way ofconductive trace162apasses through, in order,resistive trace160 andconductive trace162bwhere it is output fromheater150 atterminal163b. Current input toheater150 atterminal163btravels in reverse along the same path.
• In some embodiments,heater150 includestemperature sensor170, also referred to asthermistor170, positioned in close proximity to a surface ofheater150 in order to provide feedback regarding the temperature ofheater150 to controlcircuitry115. In the embodiment shown,thermistor170 is positioned onbottom surface152bofceramic substrate152. In the example embodiment illustrated,thermistor170 is welded directly tobottom surface152bofceramic substrate152. In this embodiment,heater150 also includes a pair ofconductive traces172a,172bthat are each electrically connected to a respective terminal ofthermistor170. Eachconductive trace172a,172bhas a distal end that forms arespective terminal173a,173badjacent to anedge158 ofceramic substrate152. Cables orwires175a,175bare connected toterminals173a,173bin order to electrically connectthermistor170 to, for example,control circuitry115 in order to provide closed loop control ofheater150. In the embodiment illustrated,thermistor170 is positioned at a central location ofbottom surface152bofceramic substrate152. However,thermistor170 and its correspondingconductive traces172a,172bmay be positioned in other suitable locations onbottom surface152bofceramic substrate152.
• In some embodiments,heater150 also includes a thermal cutoff (not shown), such as a bi-metal thermal cutoff, in contact withceramic substrate152 and connected in series with the heating circuit formed byresistive trace160 andconductive traces162a,162bpermitting the thermal cutoff to open the heating circuit formed byresistive trace160 andconductive traces162a,162bupon detection by the thermal cutoff of a temperature that exceeds a predetermined amount. In this manner, the thermal cutoff provides additional safety by preventing overheating ofheater150.
• FIG. 6 is a cross-sectional view ofheater150 taken along line6-6 inFIG. 4. As shown,heater150 includesresistive trace160 andconductive traces162a,162bformed onceramic substrate152.FIG. 6 depicts a single layer ofceramic substrate152. However,ceramic substrate152 may include multiple layers as depicted by dashedline153. In the embodiment illustrated,heater150 includes one or more layers of printedglass156 ontop surface152aofceramic substrate152. In the embodiment illustrated,glass layer156 coversresistive trace160 and portions ofconductive traces162a,162bin order to electrically insulate such features to prevent electric shock or arcing. The borders ofglass layer156 are shown in dashed line inFIG. 4. In this embodiment,glass layer156 coversresistive trace160 and adjacent portions ofceramic substrate152 such thatglass layer156 forms the majority of the top surface ofheater150 facingheating plate145. An overall thickness ofglass layer156 may range from, for example, 35-45 microns.
• In the embodiment illustrated,heater150 also includes one or more layers of printedglass159 onbottom surface152bofceramic substrate152 to minimize camber. The borders ofglass layer159 are shown in dashed line inFIG. 5. In this embodiment,glass layer159 does not coverthermistor170 and some portions ofconductive traces172a,172bbecause the relatively low voltage (in comparison with the voltages applied to resistive trace160) applied to such features presents a lower risk of electric shock or arcing. An overall thickness ofglass layer159 may range from, for example, 35-45 microns.
• In addition to providing electrical insulation, laminating the ceramic heater of the present disclosure withglass layers156,159 provides increased resistance to thermal shock. In some embodiments,heater150 is fabricated by fiber laser scribing the perimeter ofheater150 to further increase thermal shock resistance. Fiber laser scribing tends to provide a more uniform singulation surface having fewer microcracks along the separated edge in comparison with conventional carbon dioxide laser scribing.
• Heater150 may be constructed by way of thick film printing. For example, in one embodiment,resistive trace160 is printed on fired (not green state)ceramic substrate152, which includes selectively applying a paste containing resistor material totop surface152aofceramic substrate152 through a patterned mesh screen with a squeegee or the like. The printed resistor is then allowed to settle onceramic substrate152 at room temperature. Theceramic substrate152 having the printed resistor is then heated at, for example, approximately 140-160 degrees Celsius for a total of approximately 30 minutes, including approximately 10-15 mins at peak temperature and the remaining time ramping up to and down from the peak temperature, in order to dry the resistor paste and to temporarily fixresistive trace160 in position. Theceramic substrate152 having temporaryresistive trace160 is then heated at, for example, approximately 850 degrees Celsius for a total of approximately one hour, including approximately 10 minutes at peak temperature and the remaining time ramping up to and down from the peak temperature, in order to permanently fixresistive trace160 in position. Conductive traces162a,162bare then printed ontop surface152aofceramic substrate152, which includes selectively applying a paste containing conductor material in the same manner as the resistor material. Theceramic substrate152 having the printed resistor and conductor is then allowed to settle, dried and fired in the same manner as discussed above with respective toresistive trace160 in order to permanently fixconductive traces162a,162bin position. Glass layer(s)156 ontop surface152aare then printed in substantially the same manner as the resistors and conductors, including allowing the glass layer(s)156 to settle as well as drying and firing the glass layer(s)156. In one embodiment, glass layer(s)156 are fired at a peak temperature of approximately 810 degrees Celsius, slightly lower than the resistors and conductors. Conductive traces172a,172bforthermistor170 are printed onbottom surface152bofceramic substrate152 in substantially the same manner asconductive traces162a,162b, and glass layer(s)159 are printed onbottom surface152bofceramic substrate152 in substantially the same manner as glass layer(s)156.Thermistor170 is then mounted toceramic substrate152 in a finishing operation with the terminals ofthermistor170 directly welded toconductive traces172a,172b.
• Thick film printingresistive trace160 andconductive traces162a,162bon firedceramic substrate152 provides more uniform resistive and conductive traces in comparison with ceramic heaters having resistive and conductive traces printed on green state ceramic. The improved uniformity ofresistive trace160 andconductive traces162a,162bprovides more uniform heating acrossheating plate145 as well as more predictable heating ofheater150.
• While the example embodiment illustrated inFIGS. 3-5 includesheater150 having an octagonal shape, in other embodiments,heater150 may have other forms and shapes as desired. For example, with reference toFIG. 7, aheater1150 may have a circular shape according to one example embodiment.Thermistor170 is disposed on a surface ofceramic substrate152 opposite the surface along whichresistive trace160 is disposed in the embodiment shown inFIG. 5, butthermistor170 and/or its corresponding conductive traces may be disposed on the same side ofceramic substrate152 asresistive trace160 so long as they do not interfere with the positioning ofresistive trace160 andconductive traces162a,162b. For example, inFIG. 7, athermistor1170 is positioned on the same surface as resistive trace160 (e.g.,top surface1152aof ceramic substrate1152). In some embodiments, corresponding conductive traces ofthermistor170 may be disposed on the bottom surface (oppositetop surface1152a) ofceramic substrate1152 whilethermistor1170 is positioned ontop surface1152athereof. In this embodiment,heater150 may include vias that are formed as through-holes substantially filled with conductive material extending throughceramic substrate1152 fromtop surface1152ato the bottom surface ofceramic substrate1152 in order to electrically connect the terminals ofthermistor1170 ontop surface1152ato their corresponding conductive traces on the bottom surface.
• It will be appreciated that the example embodiments illustrated and discussed above are not exhaustive and that the heater of the present disclosure may include resistive and conductive traces in many different patterns and locations onceramic substrate152, including to resistive traces on one or more of the exterior surfaces (top surface and/or bottom surface) ofceramic substrate152 and/or an intermediate surface ofceramic substrate152, as desired. Other components (e.g., a thermistor) may be positioned on either the top surface or the bottom surface of the heater as desired, including on the same surface as the resistive traces or an opposite surface.
• FIG. 8 shows acooking vessel120 suitable for use withheater assembly140 according to one example embodiment. In the embodiment illustrated,cooking vessel120 includes aninner shell125 and anouter shell130. Anoutside surface125bofinner shell125 formsfood receptacle121 ofcooking vessel120.Inner shell125 andouter shell130 havecorresponding side walls126,131 and correspondingbottom walls127,132 separated by agap129 to form a dual-wall vessel. In this embodiment,bottom wall132 ofouter shell130 has a slightly concaveoutside surface130bthat substantially matches domedupper surface147 ofheating plate145. The use of aheating plate145 having a domedupper surface147 in contact with a concaveoutside surface130bof thebottom wall132 ofcooking vessel120 helps reduce bowing ofbottom wall132 ofcooking vessel120 during heating in comparison with a cooking vessel having a fiat bottom surface in contact with a flat top surface of a heating plate or heater. This, in turn, helpsupper surface147 ofheating plate145 maintain consistent contact withoutside surface130bof thebottom wall132 ofcooking vessel120 for heat transfer.Inner shell125 andouter shell130 are integrally joined or welded, e.g., atrim122, forming a sealed volume between inner andouter shells125,130 that includesgap129. In some embodiments, the sealed volume is formed under reduced pressure relative to atmospheric pressure, such as a partial vacuum.
• In the example embodiment illustrated, aheat pipe134 is provided between inner andouter shells125,130, including betweenside walls126,131 and betweenbottom walls127,132. In the embodiment shown, corresponding inside surfaces125a,130aof inner andouter shells125,130 are lined withwick structures135 containing a relatively small amount of working fluid, such as water. Thewick structures135 may be constructed from materials that allow capillary action of the working fluid within the sealed volume as discussed below. InFIGS. 9A-9C, various example wick structures for use withcooking vessel120 are illustrated. Each ofFIGS. 9A-9C is a cross-sectional view ofcooking vessel120 taken along line9-9 inFIG. 8. In the embodiment shown inFIG. 9A, the wick structure includes sintered or arc sprayedmetal135a, such as copper or aluminum, provided oninside surfaces125a,130aof inner andouter shells125,130. In the embodiment shown inFIG. 9B, a screen orwire mesh135bis provided on each of theinside surfaces125a,130aof inner andouter shells125,130 to form the wick structure. In the embodiment shown inFIG. 9C,grooves135care formed on each of theinside surfaces125a,130aof inner andouter shells125,130 to provide the wick structure. Eachgroove135cextends substantially vertically along arespective side wall126,131 and may continue substantially horizontally along arespective bottom wall127,132. While the example embodiments illustrated include aheat pipe134 that includes one ormore wick structures135 and a working fluid, in other embodiments,heat pipe134 includes a working fluid (e.g., water) contained between inner andouter shells125,130, but no wick structure.
• In one embodiment, during use, the working fluid cycles between anevaporation zone180 near or around the lower region ofcooking vessel120 that is directly heated byheating plate145 and acondensation zone190 around the upper region ofcooking vessel120. In particular, as cookingvessel120 is heated by heater assembly140 (e.g., byoutside surface130bofbottom wall132 ofouter shell130 receiving heat from heater assembly140) the working fluid within the evaporation zone180 (e.g., working fluid within thewick structures135 betweenbottom walls127,132 of inner andouter shells125,130 and betweenside walls126,131 of inner andouter shells125,130 in the lower region of cooking vessel120) absorbs heat183 and changes state from liquid tovapor138. Driven by pressure and temperature differences between the lower (hotter) region and upper (cooler) region,vapor138 travels from theevaporation zone180 to thecondensation zone190 along thegap129 betweenwick structures135. Whenvapor138 arrives at thecondensation zone190, it condenses back into liquid form releasinglatent heat185 through inner andouter shells125,130 at the upper region ofcooking vessel120. Condensed liquid139 at thecondensation zone190 travels back to theevaporation zone180 viawick structures135 due to capillary action. As the vaporization and condensation cycle repeats, heat is transferred from locations near the heat source to the rest of the sealed volume of cooking vessel120 (i.e., from betweenbottom walls127,132 of inner andouter shells125,130 to betweenside walls126,131 of inner andouter shells125,130) resulting in an improved temperature uniformity withincooking vessel120.
• The present disclosure provides a ceramic heater having a low thermal mass in comparison with the heaters of conventional cooking devices. In particular, a thick film printed resistive trace on a ceramic substrate provides reduced thermal mass in comparison with conventional wire coil heaters. The use of a thin heating plate, such as forged aluminum, also provides reduced thermal mass in comparison with the cast aluminum bodies of conventional wire coil heaters. The low thermal mass of the ceramic heater of the present disclosure allows the heater, in some embodiments, to heat to an effective temperature for use in a matter of seconds (e.g., less than 5 seconds), significantly faster than conventional wire coil heater cooking devices. The low thermal mass of the ceramic heater of the present disclosure also allows the heater, in some embodiments, to cool to a safe temperature after use in a matter of seconds (e.g., less than 5 seconds), again, significantly faster than conventional wire coil heater cooking devices.
• Further, embodiments of the heater of the cooking device of the present disclosure operate at a more precise and more uniform temperature than conventional cooking devices because of the closed loop temperature control provided by the thermistor in combination with the relatively uniform thick film printed resistive and conductive traces. The low thermal mass of the ceramic heater permits greater energy efficiency in comparison with conventional wire coil heaters. The improved temperature control and temperature uniformity also improve the performance of the cooking device of the present disclosure. In this manner, embodiments of the cooking device of the present disclosure achieve high thermal and energy efficiency and high-end performance comparable to induction heating cooking devices, but at a greatly reduced cost in comparison with conventional induction heating cooking devices.
• The present disclosure further provides a heat pipe cooking vessel for use with the ceramic heater. The heat pipe structure within the cooking vessel provides improved thermal conductivity in comparison with conventional aluminum or copper cooking vessels allowing for a more uniform temperature distribution and effective heat transfer. Coupled with the low thermal mass of the ceramic heater, the heat pipe cooking vessel provides improved temperature uniformity relative to conventional cooking devices.
• While the example embodiment discussed above includes a ceramic heater used in conjunction with a heat pipe cooking vessel, it will be appreciated that the ceramic heater and the cooking vessel of the present disclosure may be used separately from each other in different heating and/or cooking applications. That is, the ceramic heater of the present disclosure may be used with a conventional cooking vessel, and the heat pipe cooking vessel of the present disclosure may be used with conventional heaters.
• The foregoing description illustrates various aspects of the present disclosure. It is not intended to be exhaustive. Rather, it is chosen to illustrate the principles of the present disclosure and its practical application to enable one of ordinary skill in the art to utilize the present disclosure, including its various modifications that naturally follow. All modifications and variations are contemplated within the scope of the present disclosure as determined by the appended claims. Relatively apparent modifications include combining one or more features of various embodiments with features of other embodiments.

Claims (26)

1. A cooking device, comprising:

a base having a top surface positioned to contact a cooking vessel configured to hold food during cooking; and

the base includes a heater having a ceramic substrate and an electrically resistive trace on an exterior surface of the ceramic substrate, the heater is positioned to supply heat generated by applying an electric current to the electrically resistive trace to the top surface of the base for heating the cooking vessel to heat food in the cooking vessel.

2. The cooking device ofclaim 1, wherein the electrically resistive trace includes an electrical resistor material thick film printed on the exterior surface of the ceramic substrate.

3. The cooking device ofclaim 1, wherein the electrically resistive trace is positioned on a top surface of the ceramic substrate that faces upward toward the top surface of the base.

4. The cooking device ofclaim 1, wherein the heater includes a thermistor that is positioned on the ceramic substrate and in electrical communication with control circuitry of the heater for providing feedback regarding a temperature of the heater to the control circuitry of the heater.

5. The cooking device ofclaim 4, wherein the thermistor is positioned on a bottom surface of the ceramic substrate that faces away from the top surface of the base.

6. The cooking device ofclaim 1, wherein the base includes a heating plate that forms the top surface of the base, the heating plate is positioned in contact with the heater to transfer heat from the heater to the top surface of the base for heating the cooking vessel to heat food in the cooking vessel.

7. The cooking device ofclaim 6, wherein the heating plate includes a domed top surface for contacting a concave bottom surface of the cooking vessel.

8. The cooking device ofclaim 1, wherein the ceramic substrate has a polygonal shape.

9. The cooking device ofclaim 8, wherein the ceramic substrate has an octagonal shape.

10. The cooking device ofclaim 1, wherein the electrically resistive trace extends in a serpentine pattern across the exterior surface of the ceramic substrate.

11. The cooking device ofclaim 10, wherein the serpentine pattern of the electrically resistive trace has a generally circular outer perimeter.

12. A cooking device, comprising:

a housing having a receptacle and a base positioned along a bottom of the receptacle;

a cooking vessel removably positionable within the receptacle for containing food to be cooked, the cooking vessel contacts the base when the cooking vessel is positioned within the receptacle; and

the base includes a heater having a ceramic substrate and an electrical resistor material thick film printed on a surface of the ceramic substrate, the heater is positioned to supply heat generated by applying an electric current to the electrical resistor material to the cooking vessel when the cooking vessel is positioned within the receptacle.

13. The cooking device ofclaim 12, wherein the electrical resistor material is positioned on a top surface of the ceramic substrate that faces upward toward the receptacle.

14. The cooking device ofclaim 12, wherein the heater includes a thermistor that is positioned on the ceramic substrate and in electrical communication with control circuitry of the heater for providing feedback regarding a temperature of the heater to the control circuitry of the heater.

15. The cooking device ofclaim 14, wherein the thermistor is positioned on a bottom surface of the ceramic substrate that faces away from the receptacle.

16. The cooking device ofclaim 12, wherein the base includes a heating plate that forms a top surface of the base that contacts the cooking vessel when the cooking vessel is positioned within the receptacle, the heating plate is positioned in contact with the heater to transfer heat from the heater to the cooking vessel when the cooking vessel is positioned within the receptacle.

17. The cooking device ofclaim 16, wherein the heating plate includes a domed top surface and the cooking vessel includes a concave bottom surface that contacts the domed top surface of the heating plate when the cooking vessel is positioned within the receptacle.

18. The cooking device ofclaim 12, wherein the ceramic substrate has a polygonal shape.

19. The cooking device ofclaim 18, wherein the ceramic substrate has an octagonal shape.

20. The cooking device ofclaim 12, wherein the electrical resistor material extends in a serpentine pattern across the surface of the ceramic substrate.

21. The cooking device ofclaim 20, wherein the serpentine pattern of the electrical resistor material has a generally circular outer perimeter.

22. A heater for use with a cooking device, comprising:

a ceramic substrate;

an electrically resistive trace thick film printed on an exterior face of the ceramic substrate, the electrically resistive trace extends in a serpentine pattern across the exterior face of the ceramic substrate from a first end of the electrically resistive trace to a second end of the electrically resistive trace, the serpentine pattern of the electrically resistive trace has a generally circular outer perimeter; and

a first electrically conductive trace electrically connected to the first end of the electrically resistive trace and a second electrically conductive trace electrically connected to the second end of the electrically resistive trace, the first and second electrically conductive traces form respective first and second terminals providing respective first and second electrical connections for completing a circuit formed by the first and second electrically conductive traces and the electrically resistive trace.

23. The heater ofclaim 22, further comprising one or more glass layers on the exterior face of the ceramic substrate that cover the electrically resistive trace electrically insulating the electrically resistive trace.

24. The heater ofclaim 22, further comprising a thermistor positioned on a second exterior face of the ceramic substrate that is opposite the exterior face of the ceramic substrate on which the electrically resistive trace is positioned for providing feedback regarding a temperature of the heater to control circuitry of the heater.

25. The heater ofclaim 22, wherein the ceramic substrate has a polygonal shape.

26. The heater ofclaim 25, wherein the ceramic substrate has an octagonal shape.

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