Segmented thermoresistive heating system

An electric cooking appliance includes a glass-ceramic substrate having a top surface for supporting cookware for heating thereon, and a bottom surface opposite the top surface. The electric cooking appliance includes a plurality of thermoresistive heating elements disposed and spaced apart on the bottom surface of the glass-ceramic substrate, with each of the plurality of thermoresistive heating elements including graphene nanoparticles embedded in a ceramic matrix for generating heat upon application of electric current to the respective thermoresistive heating element. Each thermoresistive heating element is electrically connected to a power supply such that one or more of the plurality of thermoresistive heating elements are selectively activated to receive electric current to heat localized areas of the glass-ceramic substrate.

TECHNICAL FIELD

The present application is directed to heating elements for a cooking appliance, and more particularly, heating elements with a thermoresistive nanoparticle layer for a cooking appliance.

BACKGROUND

Conventional electric cooking appliances, such as radiant and non-radiant electric stoves and cook-tops, include a cook-top surface. At least one cooking area is defined on the cook-top surface. A heating element is disposed underneath the cook-top surface for providing heat to cookware positioned on the at least one cooking area. Each cooking area is connected to a control allowing a user to control the heat emitted from the heating element. The level heat that is provided is controlled by adjusting the power supplied to the heating element for the cooking area being controlled. The heating elements of conventional radiant and non-radiant electric cooktops require high energy consumption due to the steel rod and copper wires used as the heating elements. In addition to having high power consumption rates, rod-type heading elements may result in dissipative heat loss and glass-ceramic surface corrosion over time.

SUMMARY

According to one or more embodiments, an electric cooking appliance, includes a glass-ceramic substrate having a top surface for supporting cookware for heating thereon, and a bottom surface opposite the top surface. The electric cooking appliance also includes a plurality of thermoresistive heating elements disposed and spaced apart on the bottom surface of the glass-ceramic substrate, each of the plurality of thermoresistive heating elements including graphene nanoparticles embedded in a ceramic matrix for generating heat upon application of electric current to the respective thermoresistive heating element. Each thermoresistive heating element is electrically connected to a power supply such that one or more of the plurality of thermoresistive heating elements are selectively activated to receive electric current to heat localized areas of the glass-ceramic substrate.

In at least one embodiment, two or more of the plurality of thermoresistive heating elements may be interconnected and connected to the power supply such that predefined groups of thermoresistive heating elements of the plurality of heating elements may be selectively activated to receive the electric current. In one or more embodiments, the electric cooking appliance may further include electrically insulative material positioned between adjacent heating elements of the plurality of thermoresistive heating elements, with the electrically insulative material having a thermal conductivity of 0.015 W/mK to 0.5 W/mK. In certain embodiments, each of the thermoresistive heating elements may be a hybrid material further including Ag, Ni, or Ga nanoparticles, or combinations thereof. In at least one embodiment, the ceramic matrix may be a blend of zirconia and one or more of an epoxy and a polyurethane. According to one or more embodiments, each of the thermoresistive heating elements may have a thickness of 100 μm to 2 mm. In one or more embodiments, each thermoresistive heating element may include a thermoresistive film layer with the graphene nanoparticles, with the thermoresistive film layer having a thickness of 15 nm to 1.75 mm. In certain embodiments, the graphene nanoparticles have an average particle size of 2.5 nm to 50 nm. In at least one embodiment, each of the thermoresistive heating elements may include a protective ceramic layer on an opposite side of the plurality of thermoresistive heating elements from the glass-ceramic substrate, with the protective ceramic layer having a thickness of 0.1 to 0.5 mm.

According to one or more embodiments, an electric cooking appliance includes a glass-ceramic substrate having a top surface for supporting cookware for heating thereon, and a bottom surface opposite the top surface. The electric cooking appliance also includes a plurality of thermoresistive heating elements disposed and spaced apart on the bottom surface of the glass-ceramic substrate, each of the plurality of thermoresistive heating elements including a thermoresistive layer of hybrid silver-graphene nanoplatelets in a ceramic matrix in contact with the bottom surface. Each thermoresistive heating element is electrically connected to at least one of another thermoresistive heating element and a power supply such that one or more of the plurality of thermoresistive heating elements are selectively activated to receive electric current to heat localized areas of the glass-ceramic substrate.

In at least one embodiment, each of the thermoresistive heating elements may include a corresponding pair of silver electrodes for arrangement with electrical wiring to electrically connect the thermoresistive heating elements. In one or more embodiments, the ceramic matrix may be a blend of zirconia and an epoxy. In certain embodiments, each thermoresistive heating element may be independently activatable for selective activation to form a customized cooking area. In at least one embodiment, each of the plurality of thermoresistive heating elements may be a layered composite including a protective ceramic layer on an opposite side of the thermoresistive layer from the glass-ceramic substrate. In further embodiments, each of the thermoresistive heating elements may include a corresponding pair of silver electrodes on opposite sides of the respective heating element in contact with the bottom surface, and the silver electrodes may include an electrically insulative material thereon on a side of each electrode opposite from the bottom surface. In certain further embodiments, the electrically insulative material and the protective ceramic layer may be the same material.

According to one or more embodiments, an electric cooking appliance includes a glass-ceramic substrate having a top surface for supporting cookware for heating thereon, and a bottom surface opposite the top surface. The electric cooking appliance also includes a plurality of thermoresistive heating elements disposed and spaced apart on the bottom surface of the glass-ceramic substrate, each of the plurality of thermoresistive heating elements including graphene nanoparticles embedded in a ceramic matrix for generating heat upon application of electric current to the respective thermoresistive heating element; and an electrically insulative layer positioned between adjacent thermoresistive heating elements of the plurality of thermoresistive heating elements and on an opposite side of the plurality of thermoresistive heating elements from the glass-ceramic substrate. Each thermoresistive heating element is electrically connected to at least one of another thermoresistive heating element and a power supply such that one or more of the plurality of thermoresistive heating elements are selectively activated to receive electric current to heat localized areas of the glass-ceramic substrate.

In at least one embodiment, each of the plurality of thermoresistive heating elements may include a protective ceramic layer on a surface of the respective thermoresistive heating element opposite from the glass-ceramic substrate. In certain embodiments, each of the plurality of thermoresistive heating elements may further include nanoparticles of Ag, Ni, Ga, or combinations thereof in the ceramic matrix. In further embodiments, the nanoparticles of Ag, Ni, Ga, or combinations thereof are loaded into the ceramic matrix by 0.25 to 2% loading by weight.

DETAILED DESCRIPTION

Moreover, except where otherwise expressly indicated, all numerical quantities in this disclosure are to be understood as modified by the word “about”. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary, the description of a group or class of materials by suitable or preferred for a given purpose in connection with the disclosure implies that mixtures of any two or more members of the group or class may be equally suitable or preferred.

According to one or more embodiments, a cooking appliance, such as an electric cooktop (e.g., a radiant or non-radiant electric cooktop), includes a plurality of interconnected heating elements beneath a glass-ceramic cooktop surface. These heating elements define a plurality of heating areas on the top surface of the glass-ceramic cooktop. The interconnected heating elements have a layered structure of film layers (e.g., thin film layers), which is applied to the bottom surface of the glass-ceramic cooktop. The film layers include a thermosensitive coating layer including graphene nanoparticles blended in a ceramic to provide thermal diffusion with less power consumption than conventional rod-type heating elements. Independent heating elements may be selectively activated to increase the heating capability within a particular cooking area of the cooktop, thus forming a conformal heating profile over a larger area using a network of connected heating elements.

Referring toFIGS.1-2, a cooking appliance100is shown, according to an embodiment. The cooking appliance100may be an electric stove or cooktop in many examples. The cooking appliance100includes a glass-ceramic substrate110(hereinafter, interchangeably a ceramic substrate110) having a top surface112for receiving cookware thereon for heating. The glass-ceramic substrate110includes a bottom surface114, opposite of the top surface112, on the underside of the glass-ceramic substrate.

The glass-ceramic substrate110is a glass-ceramic material having a thermal conductivity of at least 3.0 mW/cm for transferring heat to the cookware. In certain embodiments, the glass-ceramic material has a thermal conductivity of 3.0 to 10.0 mW/cm, in other embodiments 3.1 to 9.9 mW/cm, and in yet other embodiments 3.5 to 9.5 mW/cm. The glass-ceramic material may be any suitable material, including, but not limited to compositions having MgO crystal, or glass matrices like La2O3—B2O3—SiO2—MgO. The glass-ceramic substrate110may have any suitable thickness for transferring heat to and support the cookware articles, and in some embodiments, may have a thickness of 2.5 to 8.5 mm, in other embodiments 3 to 8 mm, and in yet other embodiments 3.5 to 7 mm. In certain examples, the glass-ceramic substrate110may be 4 mm or 6 mm thick.

The cooking appliance100further includes a control panel120for controlling cooking area(s)130on the top surface112of the glass-ceramic substrate110. Although shown as integrated with the surface of the ceramic substrate110, the control panel120may in other embodiments be separate from the glass-ceramic substrate110. Furthermore, although shown as a control panel120with control knobs122, the control panel120may include any suitable mechanism for activating and controlling the cooking areas, including, but not limited to, a digital control panel, push buttons, etc. The control panel120is connected to a power supply (not shown), such as a wall outlet, for electronically powering the cooking appliance100.

Referring toFIG.2, the bottom surface114of the glass-ceramic substrate110includes a plurality of heating elements200in contact with the bottom surface114. Each of the plurality of heating elements200is a thermo-resistive element which generates heat upon application of current to the heating element200. Details of the heating elements200will be discussed with reference toFIGS.3-4.

The heating elements200are electrically connected to the power supply via the control panel120. In certain embodiments, each heating element200may be independently connected to the control panel120for selective activation by supply of electrical power to the heating elements200, or, in other embodiments, may be connected to other heating elements200for selective activation of connected heating elements200. In one example, the heating elements200may be independently selectively activatable based on user input at the control panel120for to form a customizable desired cooking area size for the cooking appliance100, and in other examples certain groups of heating elements200may correspond to a particular predefined heating areas (such as cooking areas130) activatable by user input at the control panel120. The predefined heating areas in certain embodiments, may further be variable in size via selective activation of one or more groups of heating elements200. As such, the heating elements200may be independently activatable or be activatable in groups of one or more heating elements200to form the cooking areas130, and thus may each be connected to the power supply (via the control panel120) for independent activation, or interconnected to other heating elements200. In embodiments where the heating elements are interconnected, for selective activation of heating elements or groups of heating elements, the electrical connections between heating elements200may be selectively interruptible to allow customization of the cooking area size and shape by the user at the control panel120.

Thus, the selective activation of one or more of the heating elements200together can form cooking areas130of varying shape and size, as based on the size of the cookware being used for example. As such, cooking areas130, although shown as round inFIG.1, may be any suitable shape, or may not be constrained to a particular shape as based on combinations of activated heating elements200. Thus, in certain embodiments, predefined groups of heating elements200are electrically connected to the control panel120for activation as a predefined group (e.g., a cooking area130) or predefined groups (e.g., cooking area130with additional groups to increase size), or, in other embodiments, may be independently selectively activatable by user input to form customized heating areas of varying shape and size as based on various considerations such as for example, the desired article to be heated. Heat from the heating element200(or the network of heating elements200) is conductively transferred through the glass-ceramic substrate110to the cookware placed on the top surface112at the cooking areas130upon selective activation of the heating elements200corresponding to the cooking area130.

The heating elements200may be electrically connected in any suitable manner (shown as electrical connection116inFIG.2), such as, but not limited to, by copper connectors or other wiring, buses, or interconnects to flow current between heating elements200to produce heat. Each heating element200may also include an electrode118, or pair of electrodes118, for applying the electrical conduction uniformly to the heating element200. In one or more embodiments, the electrodes118are positioned on opposite sides of the respective heating element200to allow current to flow through the heating element200from one of the electrodes118to the other electrode118, such that heat is generated in the heating element200. In certain embodiments, the electrode118may be silver.

Each heating element200may have any suitable size and/or shape, as based on the desired cooking area shapes in the glass-ceramic substrate110. As shown inFIG.2, each heating element200may have a square shape. However, the depiction of a square heating element200is not intended to be limiting, and other shapes, such as, but not limited to, circles, triangles, hexagons, or other polygons, are also contemplated such that the cooking areas130of varying shape and overall size can be created from groups of heating elements200.

Each heating element200may have a dimension (e.g., length or width) sized to be, in some embodiments, 250 to 525 mm, in other embodiments, 275 to 500 mm, and in yet other embodiments, 300 to 475 mm. Regardless of shape, the area of an individual heating element200may range from up to 100,000 mm2in some embodiments, to 100,000 to 250,000 mm2in certain embodiments, 110,000 to 200,000 mm2in other embodiments, and 125,000 to 175,000 mm2in yet other embodiments. Furthermore, the overall thickness of the heating element200is smaller than conventional heating elements, thus resulting in a less robust construction for the cooking appliance100due to the thermoresistive layer composition including nanoparticles to form the thermoresistive heating element200, as will be discussed with respect toFIGS.3-4. The thickness of the heating element200may be, in some embodiments, 100 μm to 2 mm, in other embodiments, 125 μm to 1.5 mm, and in yet other embodiments 150 μm to 1 mm. As such, the layers of the heating element200and the glass-ceramic substrate110collectively may together have an overall thickness, in certain embodiments, of 4 to 8 mm, in other embodiments of 4.2 to 7.5 mm, and in yet other embodiments 4.8 to 6.8 mm.

Generally, each heating element200generates heat upon application of electric current through the heating element200. When electric power is applied to the heating elements200, the free charge carriers flow through active ingredients in the heating element200, such as, but not limited to graphene nanoparticles or carbon nanotubes (CNTs) (or combinations thereof) supported in a suitable matrix (e.g., ceramic matrix). Additionally, polymeric materials may be used as a blending agent for the active materials (e.g., polyurethane), which offer resistance to the flow of charge carriers through the heating element200thus facilitating heat generation. As a result of this resistance in the heating element200, free charge carriers impart their energy in the form of heat in the applied coating, ultimately this heat is transferred into the glass-ceramic substrate110.

Each heating element200may independently have any suitable resistance based on its composition for the desired heat generation as based on the size and location of the plurality of heating elements200. In some embodiments, each heating element200may have a resistance of 10 to 50 Ω, in other embodiments, 1.0 to 35 Ω, and in yet other embodiments, 20 to 30 Ω In certain embodiments, combining heating elements200of similar resistance results in a higher temperature observed at the top surface112based on the current applied (e.g., the surface where articles are placed to be heated).

Referring toFIG.3, a schematic cross-section of a heating element200on the glass-ceramic substrate110is shown, according to an embodiment. The schematic cross-section of the heating element200is a partial view of the cooking appliance100, depicting a single element as indicated by area A inFIG.2.

Each heating element200has a thermoresistive film layer210directly contacting the bottom surface114of the glass-ceramic substrate110, with a protective ceramic coating215on the opposite side of the thermoresistive film layer210from the bottom surface114. As shown inFIG.3, the protective ceramic coating215sandwiches the thermoresistive film layer210between the protective ceramic coating215and the glass-ceramic substrate110. The protective ceramic coating may be any suitable material, including, but not limited to a ceramic material or a glass ceramic. In some embodiments, the protective ceramic coating215may be transparent such that the thermoresistive layer210is visible therethrough. Although shown as a single layer protective ceramic coating215, the protective ceramic coating215may include any suitable number of protective and/or insulative layers and/or a combination of layer materials to coat the thermoresistive film layer210on the opposite side of the thermoresistive film layer210with respect to the glass-ceramic substrate110.

The thermoresistive film layer210generates heat upon application of electricity (i.e., current) to the thermoresistive film layer210via the resistivity of the thermoresistive film layer210. The heat is conducted from the thermoresistive film layer210and to the glass-ceramic substrate110to heat the cookware on the cooking appliance100. The thermoresistive film layer210may be, in some embodiments, a thin film layer, such that the scale of the thermoresistive film layer is a monolayer having a thickness ranging from a fraction of a nanometer to one nanometer, and up to several micrometers (e.g., up to 50 micrometers). In other embodiments, the thickness of the thermoresistive film layer210may be thicker than those defined as thin film layers, and may have thicknesses up to the mm range. The thermoresistive film layer210has a thickness of, in some embodiments, 15 nm to 1.75 mm, in other embodiments, 20 nm to 1.5 mm, and in yet other embodiments, 25 nm to 1 mm. In yet other embodiments, the thermoresistive film layer210may have a thickness of 25 to 500 nm, in yet other embodiments 25 to 450 nm, and in yet other embodiments, 25 to 425 nm.

In one or more embodiments, the thermoresistive film layer210includes a ceramic matrix with a plurality of nanoparticles (e.g., nanotubes, nanoplatelets, or other suitable nanoshape) dispersed therein to provide electrical conduction through and between the heating elements200, with the nanoparticles providing resistive heating to heat to the cookware via conduction through the glass-ceramic substrate110. The nanoparticles within the thermoresistive film layer210behave as ohmic resistors which generate heat upon application of electricity to the heating element200, thus providing heat to be conducted through the glass-ceramic substrate110to the cookware articles thereon. The nanoparticles may be, in certain embodiments, carbon nanotubes or a graphene nanoparticle (e.g., single layer carbon nanoparticle). In certain embodiments, the nanoparticles may be a hybrid nanoparticle including graphene and one or more of Ag, Ni, or Ga. In one or more embodiments, the hybrid nanoparticle is a hybrid silver and graphene nanoparticle. The one or more of Ag, Ni, or Ga may be loaded into the ceramic matrix by, in some embodiments 0.25 to 2% loading by weight of Ag, Ni, or Ga, in other embodiments 0.4 to 1.75%, and in yet other embodiments 0.5 to 1.5%. The graphene nanoparticles, in certain embodiments, have a loading concentration by weight of 0.05 to 5.5%, in other embodiments 0.075 to 5.25%, and in yet further embodiments, 0.10 to 5.0% in the ceramic matrix. Furthermore, the nanoparticles may be provided in any suitable form, including, but not limited to, nanoplatelets, nanotubes (e.g., CNTs), or nanobeads, such that the nanoparticles are evenly dispersed throughout the ceramic matrix to allow for uniform heating throughout the thermoresistive film layer210. The nanoparticles may have each an average size (as based on the largest dimension of the particle), in some embodiments, of 2.5 nm to 50 nm, in other embodiments, 4 nm to 35 nm, and in yet other embodiments, 5 nm to 25 nm.

In one or more embodiments, the ceramic matrix of the thermoresistive film layer210is formed from a high-temperature stable nanoceramic blended in a high-temperature stable polymer (e.g., the film layer is chemically stable and does not mechanically deform up to, for example, 1,500° C.). The ceramic may be, in some embodiments, zirconia, and the polymer may be, in some embodiments, epoxy. The ceramic matrix thus limits the electron flow through the nanoparticles within the ceramic matrix, and allows the slowed electrons to heat up as they lose energy, thus providing the resistive heating. As such, the nanoparticles provide a dispersed electrical network within the heating element200such that, upon application of electrical current, the ceramic matrix causes the nanoparticles to emit heat due to the resistance provided by the ceramic matrix such that the nanoparticles uniformly emit heat to the bottom surface114of the glass-ceramic substrate.

In one or more embodiments, the thermoresistive film layer210includes graphene nanoplatelets dispersed in a ceramic blend with epoxy and/or a two-system based polymerized polymer, such that the thermoresistive film layer210is heated to at least the same temperature as conventional copper wire and steel rod heating elements with less electric power consumption than the conventional copper wire and steel rod heating elements.

Referring again toFIG.3, the protective ceramic coating215may provide a protective physical barrier for the thermoresistive film layer210from the bottom side, and also may insulate the bottom side of the heating element200to facilitate heat transfer in the direction of the glass-ceramic substrate110. The protective ceramic coating215may be any suitable thickness to protect the thermosensitive coating on the bottom side (with respect to the glass-ceramic substrate110being on the top side), and in some embodiments may be 0.1 to 0.5 mm thick, in other embodiments, may be 0.25 to 0.45 mm thick, and in yet other embodiments may be 0.3 to 0.4 mm thick.

The thermoresistive film layer210and/or the protective ceramic coating215of each heating element200may each be independently applied (i.e., the thermoresistive film layer210directly on the bottom surface114; and the protective ceramic coating215to the thermoresistive film layer210) in any suitable manner, such as, but not limited to, screen printing, spraying, injection molding, and the like, and may be applied via masking in one or more steps.

In certain embodiments, as shown inFIG.3, the electrodes118on the bottom surface114of the glass-ceramic substrate110may include one or more layers of electrically insulative material300layered on the electrodes118on a side opposite from the glass-ceramic substrate110, with the electrically insulative material300being between adjacent heating elements200. The electrical connection116between the adjacent heating elements200and/or to the control panel120may be embedded within the electrically insulative material to limit electrical leakage from the connection116. The electrically insulative material300may be similar to, or the same material as, the protective ceramic coating215, as shown inFIG.4, or be a different material as shown inFIG.3.

In one or more embodiments, the electrically insulative material300is thermally conductive to allow heat from the heating elements200to uniformly heat the glass-ceramic substrate110between adjacent activated heating elements200to form a more continuously heated cooking area130. Thus, heat from the heating elements200may also spread into the electrically insulative material300to aid in heating the cooking area of the glass-ceramic substrate110, while electrically insulating the components from surrounding areas that were not selectively activated and protecting the electrodes118from areas beneath the cooking appliance100.

The electrically insulative material300between adjacent heating elements200may have a thermal conductivity in some embodiments, between 0.015 W/mK to 0.5 W/mK, in other embodiments, between 0.020 W/mK to 0.4 W/mK, and in yet other embodiments, between 0.025 W/mK to 0.30 W/mK. The electrically insulative material300is electrically insulative such that the electrical current does not travel through the electrically insulative material300, thus improving control over the selective activation of the specific heating elements200desired to control the cooking area. Furthermore, the electrically insulative material300covers the electrical connection116between the adjacent heating elements200(e.g., in some embodiments, the copper connectors).

In certain embodiments, referring toFIG.4, the electrically insulative material300and the protective ceramic coating215may be a single component layer220, which overlays the heating elements200and their respective electrodes118and electrical connection116to protect the components on the rear side of the glass-ceramic substrate110. As such, the layer220may be applied in a single step over the applied thermoresistive layer210and electrodes118after the wiring116connects the heating elements200.

In certain embodiments, the thickness at areas with the thermoresistive layer210may be thicker than areas with only the electrodes118and the wiring116. In other embodiments, the layer220may be applied such that the components on the back of the glass-ceramic substrate110have a uniform thickness across the area of the bottom surface114.

Referring again to the embodiment ofFIG.3, the protective ceramic coating215and the electrically insulative material300may be applied in separate steps (e.g., via screen printing or masking) such that the heating elements are formed with the prior to application of the electrically insulative material300between heating elements200after application of the electrodes118and placement of the electrical wiring116(e.g., via a different mask).

According to one or more embodiments, a cooking appliance with an electric radiant or non-radiant (e.g., induction) cooktop is provided. The cooking appliance includes a glass-ceramic substrate with a top surface for receiving cookware thereon for heating. The bottom surface of the glass-ceramic substrate is coated with a plurality of discrete thermoresistive heating elements which are electrically connected to each other and to a power supply. The thermoresistive heating elements include nanoparticles loaded in a ceramic matrix such that, upon application of an electric current, the nanoparticles emit heat due to the resistive properties of the ceramic matrix on the conduction through the nanoparticles. Based on the electrical connection, the thermoresistive heating elements may be selectively activated to adjust the cooking area of the glass-ceramic substrate. Furthermore, the cooking appliance may include a protective layer and/or thermally conductive electrically insulative material on the surface of the thermoresistive layer opposite the glass-ceramic substrate and between adjacent thermoresistive heating elements to improve the uniform heating of the glass-ceramic substrate.