Abstract:
A food preparation apparatus includes a thermal fluid reservoir formed with an internal cavity for holding a thermal transfer fluid. A fluid transfer unit circulates the thermal transfer fluid through the reservoir and through a thermal transfer unit. The thermal fluid reservoir may be formed into a food receptacle with a thermal contact surface for the reservoir coincident with a food contact surface in the receptacle. Alternatively, a food receptacle may be formed separately from the reservoir and may either attach to the thermal contact surface or may be easily removable. Embodiments may selectively heat or cool food in the food receptacle by transferring thermal energy between the thermal transfer fluid and the thermal contact surface. A setpoint temperature is accurately maintained everywhere on the thermal transfer surface to avoid hot spots or cold spots in the food receptacle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/773,678, titled “Cooking Chamber Device”, filed Mar. 6, 2013, and incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Embodiments of the invention are related generally to an article of food preparation equipment for changing a temperature of a food item and more specifically to a food preparation appliance having a thermal fluid reservoir for achieving accurate temperature control of a thermal transfer surface adapted for contact with a food item. 
       BACKGROUND 
       [0003]    Preparation of a food item may require a change in the temperature of the food item, either by heating or cooling the food item. It may be preferable to accurately achieve a selected temperature for the food item for a selected time duration. However, point-to-point variations in thermal energy transfer between a food item and a surface contacting the food item may cause unwanted variations in the visual appearance, nutritional value, or flavor of the food item. For example, cooking stoves or hot plates using flames, electrically powered resistive heating coils, or electrically powered inductive coils to heat a cooking pot, griddle, or other cooking vessel may subject some parts of the vessel to intense heat while other parts are exposed to much lower temperatures. Hot spots or cold spots may develop in different parts of the cooking vessel and in different parts of the food item. Temperature variations on the interior bottom and sides of a cooking vessel may exceed tens or even hundreds of degrees, possibly leading to unpredictable or unwanted cooking results. 
         [0004]    Experienced cooks learn to adjust the position of a cooking vessel relative to a heat source, the positions of food items in a cooking vessel, cooking times, and the temperature settings of the cooking appliance to avoid overcooking or undercooking food and to avoid damaging the cooking vessel. However, changes in the size, weight, or number of food items being cooked or replacing one cooking vessel with another may require much experimentation with different combinations of cooking temperatures and cook times to compensate for changes in the amount of thermal energy transferred into the food. 
       SUMMARY 
       [0005]    An example of a food preparation appliance in accord with an embodiment of the invention includes a thermal fluid reservoir formed with an internal cavity for holding a thermal transfer fluid. The thermal fluid reservoir includes a thermal contact surface adapted for transferring thermal energy between the thermal fluid reservoir and a food item. The appliance further includes a fluid transfer unit in fluid communication with the internal cavity in the thermal fluid reservoir and a thermal transfer unit in fluid communication with the fluid transfer unit and with the internal cavity in the thermal fluid reservoir. The example of a food preparation appliance also includes a temperature and flow controller in electrical communication with the fluid transfer unit and the thermal transfer unit and a user interface module in electrical communication with the temperature and flow controller. The temperature and flow controller is adapted to maintain a temperature of the thermal contact surface at a setpoint temperature received by the temperature and flow controller from the user interface module. 
         [0006]    Another example of an apparatus in accord with an embodiment of the invention includes a thermal fluid reservoir formed with an internal cavity for holding a thermal transfer fluid, the thermal fluid reservoir including a thermal contact surface. The apparatus further includes a food receptacle adapted for a close fit against the thermal fluid reservoir and a fluid transfer unit in fluid communication with the internal cavity in the thermal fluid reservoir. The example of an apparatus also includes a thermal transfer unit in fluid communication with the fluid transfer unit and with the internal cavity in the thermal fluid reservoir, a temperature and flow controller in electrical communication with the fluid transfer unit and the thermal transfer unit, and a user interface module in electrical communication with the temperature and flow controller. The temperature and flow controller is adapted to maintain a temperature of the thermal contact surface at a setpoint temperature received by the temperature and flow controller from the user interface module. The food receptacle may be attached to the thermal contact surface or may alternatively be adapted for easy removal and reinstallation in the apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a simplified schematic representation of a food preparation appliance in accord with an embodiment of the invention. 
           [0008]      FIG. 2  is a side view of an example of a food receptacle for use with an embodiment of the invention. 
           [0009]      FIG. 3  is a schematic representation of an alternative embodiment of a food preparation appliance adapted for use with a removable food receptacle. 
           [0010]      FIG. 4  is a side view of an example of a food receptacle having a channel formed on a bottom side of the receptacle and having more than one void for holding food items. 
           [0011]      FIG. 5  is a view toward a food contact surface of the example of a food receptacle from  FIG. 4 . 
           [0012]      FIG. 6  is a schematic representation of a closed loop fluid path including a thermal fluid reservoir having a ridge adapted to engage a corresponding channel in a food receptacle. 
       
    
    
     DESCRIPTION 
       [0013]    Embodiments of the invention comprise an appliance for preparation of a food item by subjecting the food item to contact with a thermal transfer surface having a uniform, accurately controlled surface temperature. The surface temperature of the thermal transfer surface is approximately equal to a temperature of a thermal transfer fluid in a thermal fluid reservoir in good thermal contact with the thermal transfer surface. In some embodiments of the invention, a surface of the thermal fluid reservoir is formed into a food receptacle for holding a food item during heating or cooling of the food item. In alternative embodiments of the invention, a separate food receptacle is placed in good thermal contact with the thermal transfer surface of the thermal fluid reservoir. A food receptacle may alternatively be attached to the thermal transfer surface or may be easily separable from the thermal fluid reservoir. 
         [0014]    Embodiments of the invention are advantageous for subjecting a food item to a uniform, accurately controlled food preparation temperature which remains within a narrow range of a setpoint temperature selected by a user. For example, a temperature of a surface provided for exchanging thermal energy with a food item may be held within a range of plus or minus one degree Celsius of a user-selected setpoint temperature, a range that is substantially smaller than for a conventional gas or electric stove. Other advantages of the embodiments of the invention include, but are not limited to, accurate control of a food preparation temperature when a number of food items being cooked simultaneously in one food receptacle changes, when a size or weight of each food item is substantially different than for previously prepared, similar food items, and accurate control of a uniform temperature for food receptacles of different sizes and shapes. Some embodiments of the invention are adapted for heating one or more food items simultaneously. Other embodiments of the invention are adapted for cooling, and possible freezing, at least one food item. Some embodiments of the invention may selectively heat or cool a food item as directed by a person using the food preparation appliance. Some embodiments of the invention are particularly advantageous for heating food items which are easily damaged by scorching, for example milk, butter, cheese, chocolate, and foods with high dairy or sugar content. 
         [0015]    An example of a food preparation appliance in accord with an embodiment of the invention is shown in simplified schematic form in  FIG. 1 . In the example of  FIG. 1 , a food preparation appliance  100  includes a thermal fluid reservoir  108  formed into the shape of a food receptacle  106 . The food receptacle  106  has a size and shape selected for holding a selected number of an example of a food item  200  to be prepared by exposing the food item to a uniform temperature achieved by circulation of a thermal transfer fluid  114  through a cavity  144  inside the thermal fluid reservoir  108 . The example of a food item  200  is not included in an embodiment of the invention. Examples of a food receptacle  106  suitable for use with an embodiment of the invention include, but are not limited to, a sous vide immersion cooker, a frying pan, a sauté pan, a pot, a griddle with an approximately flat upper cooking surface and low sides around the cooking surface, a dutch oven, a pan shaped for baking a loaf of bread, a tray formed with multiple voids for holding multiple food items such as cupcakes, an ice cream maker, an ice cube tray, a chilled serving tray, a heated serving tray, a chilled buffet serving dish, a heated buffet serving dish, a coffee maker, and so on. 
         [0016]    In  FIG. 1 , the food item  200  rests on a food contact surface  142  of the food receptacle  106 . In the example of  FIG. 1 , the food contact surface  142  corresponds to a thermal contact surface  140  of the thermal fluid reservoir  108 . Although the food contact surface  142  is shown by a straight line in  FIG. 1 , representing an approximately planar food contact surface, in alternative embodiments the food contact surface may be convex, concave, irregularly curved, or formed with ridges, bumps, or indentations. 
         [0017]    The thermal fluid reservoir  108  forms part of a closed-circuit fluid path including a thermal transfer unit  112  and a fluid transfer unit  134 . Thermal transfer fluid  114  flows without escaping from the closed-circuit fluid path. Thermal transfer fluid  114  flows from the thermal fluid reservoir  108  through a thermal fluid outlet  120  and a first fluid conduction line  128  to a fluid transfer unit  134 . The fluid transfer unit  134  is in fluid communication with the thermal transfer unit  112  through a second fluid conduction line  126 . Thermal transfer fluid  114  exiting the thermal transfer unit  112  enters a third fluid conduction line  124  and returns to the thermal fluid reservoir  108  by a thermal fluid inlet  118  on the reservoir  108 . The food contact surface  142  of the food receptacle  106  achieves a temperature approximately equal to the temperature of the thermal transfer fluid  114  everywhere the food contact surface is adjacent the thermal fluid reservoir, for example the interior bottom and interior sides of the food receptacle  106  in the example of  FIG. 1 . 
         [0018]    The thermal transfer fluid  114  may be in a liquid state throughout the closed-loop fluid flow path. Alternatively, the thermal transfer fluid may be in a gaseous state in some parts of the fluid flow path and in a liquid state in other parts of the fluid flow path. Examples of a thermal transfer fluid include, but are but limited to, water, silicone oil, cooking oil, mixtures of water and alcohol, and air conditioning refrigerant. When water is used as a thermal transfer fluid, the freezing point of the thermal transfer fluid may be lowered and the boiling point elevated by adding a soluble compound to the water, for example a salt such as sodium chloride or potassium chloride. 
         [0019]    The thermal transfer unit  112  may alternatively be implemented as a heating unit, a cooling unit, or as a combined heating and cooling unit. Some embodiments of the invention include more than one thermal transfer unit arranged in a series fluid circuit or alternatively in a parallel fluid circuit or a combination series-parallel fluid circuit. Examples of a thermal transfer unit  112  include, but are not limited to, a resistive electric heater, an inductive electric heater, an infrared heater, a microwave transmitter, a refrigeration heat exchanger, and a solid-state thermoelectric device adapted for heating and cooling. 
         [0020]    The fluid transfer unit  134  may alternatively be selected to circulate a fluid for heating, for cooling, or for heating and cooling through the closed-loop fluid path. Examples of a fluid transfer unit  134  include, but are not limited to, a piston pump, a centrifugal pump, a screw pump, a positive displacement pump, and a compressor, for example an air conditioning compressor. 
         [0021]    The temperature of the thermal transfer fluid  114  in the thermal fluid reservoir, and therefore the temperature everywhere on the food contact surface  142 , is controlled by a temperature and flow controller  110  operating in response to settings entered by a person into a user interface module  104  electrically connected to the controller  110 . The controller  110  outputs a temperature control signal  148  on an electrical line to the thermal transfer unit  112  to direct the thermal transfer unit  112  to modify the temperature of the thermal transfer fluid  114 . The controller  110  may further output a flow rate control signal  146  on an electrical line to the fluid transfer unit  134 . The controller  110  may alternatively adjust the operation of the thermal transfer unit  112 , the fluid transfer unit  134 , or both units to accurately achieve a temperature for the thermal contact surface  140  approximately equal to a setpoint temperature from the user interface module  104 . The controller  110  optionally includes signal conditioning circuitry for driving the thermal transfer unit  112  and the fluid transfer unit  134 . Examples of a controller  110  include a microprocessor implemented in hardware, a microcontroller implemented in hardware, an application-specific integrated circuit implemented in hardware, a gate array implemented in hardware, and a programmable gate array implemented as a hardware circuit device. 
         [0022]    A power supply module  136  receives electrical power from an external source through a power cord  138 . The power supply module may optionally include a circuit interrupting device, for example any one or more of a circuit breaker, a switch, a fuse, and a ground-fault circuit interrupter. The power supply module  136  outputs electrical power to the controller  110  and user interface module  104  and outputs electrical power consumed by the thermal transfer unit  112  and fluid transfer unit  134 . 
         [0023]    The user interface module  104  includes switches and display indicators for use by a person operating an embodiment of the invention  100 . Switches may be provided for operations including, but not limited to, turning appliance power on and off, setting a start time and optionally a time duration for operating the food receptacle  106  at a selected temperature, and selecting a setpoint temperature of the food contact surface  142 , corresponding to a surface temperature of a food item in the appliance. Examples of a display indicator include, but are not limited to, one or more discrete light emitting diodes (LED), incandescent lamps, or neon bulbs, a flat panel display adapted to display alphanumeric and optionally graphic information, a liquid crystal display, a vacuum florescent display, and an LED display. 
         [0024]    The thermal fluid reservoir  108 , food receptacle  106 , controller  110 , and other components in the example of  FIG. 1  may be enclosed in a housing  102  to protect appliance components from damage and protect a user of the appliance from contact with dangerous temperatures and hazardous voltages and currents. The user interface module  104  may be attached to an exterior surface of the housing  102  or may alternately be enclosed within the housing with switches and display indicators accessible through apertures in the housing. A lid  122  may optionally be provided to close the food receptacle  106  and improve temperature control in the cooking vessel. The lid  122  may optionally be fabricated from an efficient thermal insulator. 
         [0025]    In the example of  FIG. 1 , the thermal contact surface of the thermal fluid reservoir and the food contact surface of the food receptacle are coincident, that is, they are the same surface. In an alternative embodiment of a food preparation appliance  100 , the food contact surface and the thermal contact surface of the reservoir are different surfaces that come into good thermal contact with one another when the appliance is operating.  FIGS. 2 and 3  show an example of a food receptacle  106  and a base assembly  162  for a food preparation appliance in which the food contact surfaces  142  on the interior of a food receptacle  106  and the thermal contact surface  158  of the food receptacle are formed separately from the thermal contact surfaces  140  for the thermal fluid reservoir  108 . The size and shape of the food receptacle  106  is preferably chosen so that the thermal contact surfaces  158  on the receptacle fit closely against the thermal contact surfaces  140  of the thermal fluid reservoir  108  in the base assembly  162 . 
         [0026]    In the example of  FIGS. 2 and 3 , the food receptacle  106  is formed separately from the thermal fluid reservoir  108 . The food receptacle may be attached to the thermal contact surface  140  of the thermal fluid reservoir  108 . Or, as suggested in  FIGS. 2 and 3 , the food receptacle  106  may be adapted for easy removal and re-insertion into the thermal fluid reservoir  108 . The exterior surfaces of a removable food receptacle preferably fit closely against the thermal fluid reservoir when the food receptacle is installed in the base assembly  162 . A close fit between the food receptacle and the thermal food reservoir minimizes an air gap between the thermal contact surfaces  150  of the food receptacle and the thermal contact surface  140  of the thermal fluid reservoir  108 , thereby improving the efficiency of thermal energy transfer between the receptacle and reservoir and reducing deviations between the measured temperature of the thermal contact surface  140  of the reservoir and a setpoint temperature received from the user interface module  104 . 
         [0027]      FIG. 3  further illustrates the use of at least one temperature sensor  132  electrically connected to the controller  110 . At least one temperature sensor  132  may be positioned in good thermal contact with one or more selected locations on the thermal contact surface  140 . Another temperature sensor  132  may optionally be positioned to measure a temperature of the thermal transfer fluid  114  inside the cavity  144  in the thermal fluid reservoir  108 . Closed-loop feedback control of thermal contact surface temperature is implemented by the cooperative interaction of the controller  110 , temperature sensor  132 , thermal transfer unit  112 , and fluid transfer unit  134 . Briefly, the controller  110  drives the thermal transfer unit, and optionally the fluid transfer unit, to minimize a difference between a measured value of temperature from a temperature sensor and a setpoint value of temperature received from the user interface module and stored in the controller. Temperature deviations measured by the controller  110  from a setpoint temperature may be less than one degree Celsius over the full operating temperature range achievable by the thermal transfer unit  112  and fluid transfer unit  134 . Temperature variations from one location to another on the thermal contact surface  140  may be less than one degree Celsius when the controller  110  is managing the thermal transfer unit  112  and fluid transfer unit  134 . 
         [0028]    The food receptacle  106  in the example of  FIG. 2  is formed with a single void for holding a food item. The example of a food receptacle  106  shown in a side view in  FIG. 4  and a top view in  FIG. 5 . includes more than one void  160  for holding food items. The food receptacle in  FIGS. 5 and 6  further illustrates an example of a food receptacle  106  having a channel  164  adapted to fit over a corresponding ridge in a thermal fluid reservoir in a base assembly. The channel  164  has a size and shape selected to provide even, rapid thermal energy transfer between food items in the voids  160  and thermal transfer fluid flowing through the thermal fluid reservoir. More than one channel  164  may optionally be provided. 
         [0029]      FIG. 6  provides a schematic representation of a fluid reservoir  108  having a ridge  166  formed in the reservoir and thermal contact surface  140 . The ridge  166  preferably fits closely into the corresponding channel  164  in a food receptacle, for example the receptacle  106  in the example of  FIGS. 4-5 , and has a size, shape, and location selected to provide accurate control of a uniform surface temperature everywhere on thermal contact surface  140 . As suggested in  FIG. 6 , thermal contact surface  140  may optionally include any one or more of ridges, channels, and walls through which thermal transfer fluid  114  may flow in a closed-loop fluid path  168 . The closed-loop fluid path  168  includes all the components in fluid communication with one another. Components in fluid communication with one another are marked by stippling in  FIG. 6 . Although the examples of  FIGS. 4-6  show a ridge adapted to fit closely into a channel, in alternative embodiments of the invention, protrusions of almost any shape may replace the ridge and depressions shaped to receive the protrusions may replace the channel. Furthermore, an embodiment of the invention may include a food receptacle  106  having more than two voids  160  for holding food items. 
         [0030]    Unless expressly stated otherwise herein, ordinary terms have their corresponding ordinary meanings within the respective contexts of their presentations, and ordinary terms of art have their corresponding regular meanings.