Patent Publication Number: US-2007101753-A1

Title: Thermally conductive ice-forming surfaces incorporating short-duration electro-thermal deicing

Description:
RELATED APPLICATION  
      This application claims the benefit of U.S. Provisional Patent Application, Ser. No. 60/724,223, filed Oct. 6, 2005, the entire contents of which are hereby incorporated by reference, U.S. Provisional Patent Application, Ser. No. 60/724,243, filed Oct. 6, 2005, the entire contents of which are hereby incorporated by reference, and U.S. Provisional Patent Application, Ser. No. 60/724,254, filed Oct. 6, 2005, the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION  
      The present disclosure relates to an ice making machine and, more particularly, to various ice making machines comprising a thermally conductive plastic or aluminum evaporator that harvests ice with electrical energy, e.g., PETD. The evaporator can be of a variety of types, such as, cube, shell and tube, freezing tube, etc.  
     BACKGROUND OF THE INVENTION  
      Conventional ice makers have an ice making compartment located in proximity to, for example above, an ice storage compartment. Ice is made during an ice making cycle in ice making compartment. The ice is transferred by gravity action to ice storage compartment during an ice harvest cycle.  
      The ice making compartment includes an evaporator that is operable during the ice making cycle to make ice cubes.  
      Conventional evaporators include an array of ice cells, an evaporator tube and a water drip tube. Typically, the evaporator tube is connected to a compressor and condenser assembly and the water drip tube is connected to a water supply system all of which are conventional for ice makers (see U.S. Pat. No. 6,247,318, which is incorporated herein in its entirety).  
      The ice cells of the array are preferably arranged in a grid or matrix configuration having a plurality of horizontal rows and a plurality of vertical columns. Optionally, disposed directly behind the array is another array of ice cells, which is a mirror image of the first array. The pair of arrays are formed by a plurality of integral vertical structures that are interleaved with a plurality of vertical partitions. Thus, a vertical column is formed with an integral vertical structure and two vertical partitions that are disposed on either side thereof.  
      During the ice making cycle, refrigerant is circulated through the evaporator tube to the cool ice cells. Water drips from the drip tube into the ice cell arrays. The dripping water trickles through the arrays and freezes to gradually develop an ice cube in each ice cell. During the harvest cycle, refrigerant from the discharge side of the system is circulated in the evaporator tube. This results in a slight melting of each ice cube that allows the ice cube to loosen from its ice cell and fall into the storage compartment or bin.  
      This prior art method of harvesting the ice represents a loss in ice making efficiency due to: (a) the amount of ice that is melted during the harvesting operation caused by the excess heat provided by the hot gas in the evaporator, (b) the time it takes to perform the harvest operation—such time not being available to make ice, and (c) the excess heating of the evaporator—such heat having to be removed from the evaporator during the subsequent ice making cycle.  
      Hence, there is a strong demand for an ice making machine which avoids the aforementioned deficiency and provides an ice making machine whereby the ice formed in ice making cells can be removed quickly and efficiently minimizing excess meltage of the ice, removing the ice more quickly than is possible with a hot gas defrost, and avoiding any excess heating of evaporator or ice making cells.  
      In addition, ice making structures (i.e., evaporators) have been traditionally fabricated from thermally conductive materials, such as copper and nickel-plated copper. The present disclosure utilizes a novel conductive plastics material for formation of the evaporator and pulse electric thermal deicing (PETD) to harvest ice using a novel short-duration resistance heater.  
     SUMMARY OF THE INVENTION  
      An ice making machine comprising: a thermally conductive plastic evaporator assembly comprising an array of ice forming surfaces; a water supply, a refrigerant supply and an electrical energy source; and a controller that during a freeze mode operates the water supply and the refrigerant supply to form ice on the ice forming surfaces and during a harvest mode operates the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the evaporator assembly to melt an interfacial layer of the ice such that it is freed from the surfaces.  
      The evaporator assembly comprises a thermally conductive plastic base portion and a heater, wherein the heater is affixed to a surface of the thermally conductive plastic base portion, such that the heater is disposed between the ice and the base portion.  
      The heater comprises a flexible membrane and an electrical trace disposed on the flexible membrane. The thermally conductive plastic base portion and the heater form an ice cell which is capable of forming ice shapes. The heater is affixed to the thermally conductive plastic base portion by at least one selected from the group consisting of: adhesive, solvent bonding, ultrasonic bonding, and heat fusing.  
      A method of making ice with an ice making machine that comprises a thermally conductive plastic evaporator assembly comprising an array of ice forming surfaces, a water supply, a refrigerant supply and an electrical energy source, the method comprising: during a freeze mode operating the water supply and the refrigerant supply to form ice on the ice forming surfaces; and during a harvest mode operating the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the evaporator assembly to melt an interfacial layer of the ice such that it is freed from the surfaces.  
      An evaporator assembly for forming ice, the assembly comprising: a thermally conductive plastic base portion and a pulse electric thermal deicing heater, wherein the heater is affixed to a surface of the thermally conductive plastic base portion, such that the heater is disposed between the ice and the base portion.  
      Another embodiment includes an ice making machine comprising: an evaporator assembly comprising at least one freezing tube and at least two thermally conductive plastic or metal evaporator plates, wherein the freezing tube is disposed between oppositely disposed evaporator plates; at least one refrigerant conduit disposed within the thermally conductive plastic or metal evaporator plates; a water supply in communication with an inlet port of the freezing tube; a refrigerant supply in communication with the refrigerant conduit; an electrical energy source in communication with the freezing tube; and a controller that during a freeze mode operates the water supply and the refrigerant supply to form ice on an interior surface of the freezing tube and during a harvest mode operates the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the freezing tube or to a heater disposed about the freezing tube to melt an interfacial layer of the ice formed on the interior surface of the freezing tube such that it is freed from the interior surface.  
      The evaporator plate preferably comprises at least first and second thermal transfer nodes which are spaced apart from one another and in thermal contact with an outer surface the freezing tube, thereby forming ice on the interior surface of the freezing tube at a location defined by contacting of the thermal transfer nodes and the freezing tube.  
      The evaporator further comprises a thermal insulation layer or thermal break disposed about the exterior surface of the freezing tube, such that ice is not formed on the interior surface of the freezing tube at a location where the thermal transfer nodes are insulated from the freezing tube.  
      A method of making ice with an ice making machine that comprises an evaporator assembly comprising at least one freezing tube and at least two thermally conductive plastic or metal evaporator plates, wherein the freezing tube is disposed between oppositely disposed evaporator plates, a water supply, a refrigerant supply and an electrical energy source, the method comprising: during a freeze mode operating the water supply and the refrigerant supply to form ice on an interior surface of the freezing tube; and during a harvest mode operating the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the freezing tube to melt an interfacial layer of the ice such that it is freed from the interior surface of the freezing tube.  
      An evaporator assembly for forming ice, the assembly comprising: at least one freezing tube; at least two thermally conductive plastic or metal evaporator plates, wherein the freezing tube is disposed between oppositely disposed evaporator plates; a refrigerant conduit disposed substantially within the evaporator plate; and an energy source connected to or disposed about the freezing tube for applying electrical resistance energy (e.g., pulse energy) to the freezing tube or to a heater disposed about the freezing tube, thereby melting an interfacial layer of the ice formed on the interior surface of the freezing tube such that it is freed from the interior surface.  
      Still yet another embodiment of the present disclosure is an ice making machine comprising: an evaporator assembly comprising at least one freezing tube and at least two thermally conductive plastic or metal evaporator segments, wherein the freezing tube is disposed between oppositely disposed evaporator segments; at least one refrigerant conduit disposed substantially perpendicularly through the thermally conductive plastic or metal evaporator segments; a water supply in communication with an inlet port of the freezing tube; a refrigerant supply in communication with the refrigerant conduit; an electrical energy source in communication with the freezing tube; and a controller that during a freeze mode operates the water supply and the refrigerant supply to form ice on an interior surface of the freezing tube and during a harvest mode operates the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the freezing tube or to a heater disposed about the freezing tube to melt an interfacial layer of the ice formed on the interior surface of the freezing tube such that it is freed from the interior surface.  
      Preferably the evaporator segment comprises at least first and second thermal transfer nodes which are spaced apart from one another and in thermal contact with an outer surface the freezing tube, thereby forming ice on the interior surface of the freezing tube at a location defined by contacting of the thermal transfer nodes and the freezing tube.  
      Furthermore, the evaporator comprises a thermal insulation layer disposed about the exterior surface of the freezing tube, such that ice is not formed on the interior surface of the freezing tube at a location where the thermal transfer nodes are not in direct contact with the freezing tube.  
      A method of making ice with an ice making machine that comprises an evaporator assembly comprising at least one freezing tube and at least two thermally conductive plastic or metal evaporator segments, wherein the freezing tube is disposed between oppositely disposed evaporator segments, a water supply, a refrigerant supply and an electrical energy source, the method comprising: during a freeze mode operating the water supply and the refrigerant supply to form ice on an interior surface of the freezing tube; and during a harvest mode operating the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the freezing tube to melt an interfacial layer of the ice such that it is freed from the interior surface of the freezing tube.  
      An evaporator assembly for forming ice, the assembly comprising: at least one freezing tube; at least two thermally conductive plastic or metal evaporator segments, wherein the freezing tube is disposed between oppositely disposed evaporator segments; a refrigerant conduit disposed substantially perpendicular to the evaporator segments; and an energy source connected to or disposed about the freezing tube for applying electrical resistance energy (e.g., pulse energy) to the freezing tube or to a heater disposed about the freezing tube, thereby melting an interfacial layer of the ice formed on the interior surface of the freezing tube such that it is freed from the interior surface.  
      Another embodiment includes an ice making machine comprising: an evaporator assembly comprising a freezing tube, a shell disposed about the freezing tube, a plurality of insulating rings disposed at spaced apart longitudinal locations about the length of the freezing tubes, and refrigerant inlet and outlet ports disposed within a sidewall of the shell; a water supply in communication with an inlet port of the freezing tube; a refrigerant supply in communication with the refrigerant inlet port; an electrical energy source in communication with the freezing tube; and a controller that during a freeze mode operates the water supply and the refrigerant supply to form ice on an interior surface of the freezing tube and during a harvest mode operates the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the freezing tube to melt an interfacial layer of the ice formed on the interior surface of the freezing tube such that it is freed from the interior surface.  
      A method of making ice with an ice making machine that comprises an evaporator assembly comprising a freezing tube, a shell disposed about the freezing tube, a plurality of insulating rings disposed at spaced apart longitudinal locations about the length of the freezing tube, and refrigerant inlet and outlet ports disposed within a sidewall of the shell, a water supply, a refrigerant supply connected to the refrigerant inlet port, and an electrical energy source, the method comprising: during a freeze mode operating the water supply and the refrigerant supply to form ice on an interior surface of the freezing tube; and during a harvest mode operating the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the freezing tube to melt an interfacial layer of the ice such that it is freed from the interior surface of the freezing tube.  
      An evaporator assembly for forming ice, the assembly comprising: a freezing tube; a shell disposed about the freezing tube; a plurality of insulating rings disposed at spaced apart longitudinal locations about the length of the freezing tube; and refrigerant inlet and outlet ports disposed within a sidewall of the shell; and an energy source connected to or disposed about the freezing tube for applying electrical resistance energy (e.g., pulse energy) to the freezing tube, thereby melting an interfacial layer of the ice formed on the interior surface of the freezing tube such that it is freed from the interior surface.  
      Still another embodiment includes an ice making machine comprising: an evaporator assembly comprising a plurality of freezing tubes, a shell disposed about the freezing tubes, a plurality of insulating rings disposed at spaced apart longitudinal locations about the length of each the freezing tubes, and refrigerant inlet and outlet ports disposed within a sidewall of the shell; a water supply in communication with an inlet port of each the freezing tube; a refrigerant supply in communication with the refrigerant inlet port; an electrical energy source in communication with each of the freezing tubes; and a controller that during a freeze mode operates the water supply and the refrigerant supply to form ice on an interior surface of the freezing tubes and during a harvest mode operates the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the freezing tubes to melt an interfacial layer of the ice formed on the interior surface of the freezing tube such that it is freed from the interior surface.  
      A method of making ice with an ice making machine that comprises an evaporator assembly comprising a plurality of freezing tubes, a shell disposed about the freezing tubes, a plurality of insulating rings disposed at spaced apart longitudinal locations about the length of each the freezing tubes, and refrigerant inlet and outlet ports disposed within a sidewall of the shell, a water supply, a refrigerant supply connected to the refrigerant inlet port, and an electrical energy source, the method comprising: during a freeze mode operating the water supply and the refrigerant supply to form ice on an interior surface of the freezing tubes; and during a harvest mode operating the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the freezing tubes to melt an interfacial layer of the ice such that it is freed from the interior surface of the freezing tubes.  
      An evaporator assembly for forming ice, the assembly comprising: a water supply, a plurality of freezing tubes; a shell disposed about the freezing tubes; a plurality of insulating rings disposed at spaced apart longitudinal locations about the length of each the freezing tubes; and refrigerant inlet and outlet ports disposed within a sidewall of the shell; and an energy source connected to or disposed about the freezing tubes for applying electrical resistance energy (e.g., pulse energy) to the freezing tubes, thereby melting an interfacial layer of the ice formed on the interior surface of the freezing tubes such that it is freed from the interior surface.  
      The ice making machine of the present disclosure comprises a water supply, a refrigerant supply, an electrical energy source (e.g., PETD), a controller and a thermally conductive plastic evaporator assembly that comprises an array of ice forming surfaces. During a freeze mode, the controller operates the water supply and the refrigerant supply to form ice on the ice forming surfaces. During a harvest mode, the controller operates the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the evaporator assembly to melt an interfacial layer of the ice such that it is freed from the surfaces.  
      A method of the present disclosure makes ice with an ice making machine that comprises a thermally conductive plastic evaporator assembly comprising an array of ice forming surfaces, a water supply, a refrigerant supply and an electrical energy source. The method comprises in a freeze mode operating the water supply and the refrigerant supply to form ice on the ice forming surfaces and in a harvest mode operating the electrical energy source to apply electrical resistance energy (e.g., pulse energy) to the evaporator assembly to melt an interfacial layer of the ice such that it is freed from the surfaces.  
      In one embodiment of the method of the present disclosure, the thermally conductive plastic evaporator assembly comprises an ice mold that comprises at least one of the ice forming surfaces. The electrical resistance energy (e.g., pulse energy) is applied to a member of the group consisting of: the ice mold and an electrically conductive element that is in thermal transfer relation to the ice mold.  
      Yet another embodiment of the present disclosure, includes an ice making machine comprising: an evaporator assembly comprising a helical tube, said helical tube comprising a freezing tube and at least one refrigerant conduit disposed about said freezing tube; a water supply in communication with an inlet port of said freezing tube; a refrigerant supply in communication with refrigerant conduit; an electrical energy source in communication with said freezing tube; and a controller that during a freeze mode operates said water supply and said refrigerant supply to form ice on an interior surface of said freezing tube and during a harvest mode operates said electrical energy source to apply electrical resistance energy (e.g., pulse energy) to said freezing tube to melt an interfacial layer of said ice formed on said interior surface of said freezing tube such that it is freed from said interior surface.  
      A method of making ice with an ice making machine that comprises an evaporator assembly comprising a helical tube, said helical tube comprising a freezing tube and at least one refrigerant conduit disposed about said freezing tube, a water supply, a refrigerant supply connected to said refrigerant conduit, and an electrical energy source, said method comprising: during a freeze mode operating said water supply and said refrigerant supply to form ice on an interior surface of said freezing tube; and during a harvest mode operating said electrical energy source to apply electrical resistance energy (e.g., pulse energy) to said freezing tube to melt an interfacial layer of said ice such that it is freed from said interior surface of said freezing tube.  
      An evaporator assembly for forming ice, said assembly comprising: a helical tube, said helical tube comprising a freezing tube and at least one refrigerant conduit disposed about said freezing tube; and an energy source connected to or disposed about said freezing tube for applying electrical resistance energy (e.g., pulse energy) to said freezing tube, thereby melting an interfacial layer of said ice formed on said interior surface of said freezing tube such that it is freed from said interior surface.  
      The present disclosure provides for modifying the interface between ice and the structure in which it is formed, by melting the interfacial layer that binds ice and the structure on which it is formed, thereby enhancing ice release and harvest. It also includes a method of applying an electrical conductive pathway to an ice forming structure at the interfacial layer of the structure. More preferably, the present disclosure provides a method of applying a resistance heater to an ice forming structure that (a) maintains thermal conductivity between the ice forming structure and the ice; and (b) electrically isolates (PETD) energy charge from the ice forming structure. The present disclosure also provides various methods for isolating the electrical charge from the ice forming structure, thereby minimizing energy consumption and time needed to melt the interfacial boundary. It also provides a method for applying an electrical conductive pathway incorporating (a) and (b), above, to an ice forming structure that is inexpensive and readily manufacturable. According to the present disclosure the ice forming structure (i.e., evaporator) is formed using thermally conductive materials, including, but not limited to, thermally conductive plastics.  
      Furthermore, the present disclosure includes a method of manufacturing ice forming structures with discrete ice-forming regions (i.e., pocket, cells, fingers, etc.) using thermally conductive plastics.  
      Additionally, a method is provided for selectively applying electrical energy to ice-forming regions that releases ice sequentially or simultaneously.  
      Furthermore, a method is provided that applies an electrical conductive pathway with varying (heat or electrical) energy densities, thereby enabling selective heating of the interfacial boundary between ice and the ice-forming structure. Another method provides for integrating electrical conductive pathways to ice forming structures with ice forming regions having complex shapes and contours. Preferably, the ice forming structure incorporates electrically isolated energy contact points.  
      Furthermore, the ice forming structure may be formed such that it is made of individual modules or segments, that when combined, provide scalable ice making capacities. The ice forming structure having ice forming regions on both sides of the structure (i.e., evaporator), thereby increasing the ice making capacity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other and further objects, advantages and features of the present disclosure will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and:  
      FIGS.  1 ( a )-( c ) is a schematic representation of a flexible membrane element (a) that can be folded before insertion molded into an evaporator (b), as depicted in (c) according to the present disclosure;  
       FIG. 2  is a schematic representation of a flexible membrane heater element configured for individual ice forming cells;  
       FIG. 3  is a schematic representation of a front left side perspective view of a thermally conductive plastic evaporator within an ice making system according the present disclosure having individual ice forming cells of  FIG. 2 ;  
       FIG. 4  is a cross-section view along line  3 - 3  of  FIG. 3  depicting the evaporator tubes disposed internally of the thermally conductive plastic evaporator;  
       FIG. 5   a  is a schematic representation of a perspective view of another embodiment according to the present disclosure having freezing tubes disposed within a thermal conductive plastic evaporator; wherein the freezing tubes are thin wall stainless tubes which are electrically isolated from the evaporator allowing for the application of resistance heating to the entire evaporator during harvest mode;  
       FIG. 5   b  is a schematic representation of a perspective view of another embodiment according to the present disclosure having freezing tubes disposed within a thermal conductive plastic evaporator; wherein the freezing tubes are thin wall stainless tubes with membrane heaters wrapped around each tube for simultaneous resistance heating of each tube individually;  
       FIG. 6   a  is a schematic representation of a perspective view of another embodiment according to the present disclosure having freezing tubes disposed within a thermal conductive extruded aluminum evaporator; wherein the freezing tubes are thin wall stainless tubes which are electrically isolated from the evaporator allowing for the application of resistance heating to the entire evaporator during harvest mode;  
       FIG. 6   b  is a schematic representation of a perspective view of another embodiment according to the present disclosure having freezing tubes disposed within a thermal conductive extruded aluminum evaporator; wherein the freezing tubes are thin wall stainless tubes with membrane heaters wrapped around each tube for simultaneous resistance heating of each tube individually;  
       FIG. 7   a  is a schematic representation of a perspective view of still another embodiment according to the present disclosure having an individual shell and tube configuration;  
       FIG. 7   b  is a schematic representation of a perspective view of another embodiment according to the present disclosure having multiple shell and tubes with membrane heaters disposed about each shell and tube;  
       FIG. 8  is a schematic representation of a shell and tube evaporator according to the present disclosure;  
       FIG. 9  is a schematic representation of the shell and tube evaporator according to  FIG. 8  as disposed within an ice making assembly according to the present disclosure; and  
       FIG. 10  is a schematic representation of a cross-section of a helical tubular extruded aluminum ice making evaporator according to still another embodiment of the present disclosure. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The present disclosure encompasses the use of thermally conductive plastic and/or extruded aluminum evaporator plates or ice-forming tubes, and the application of a short-duration electrical resistance heater, e.g., pulse electric thermal deicing (PETD) to ice-forming structures (i.e., evaporators or ice-forming tubes). The short-duration electrical pulse is in the range between about 0.1 microsecond to 10 seconds, preferably between about 0.1 microsecond to 3 seconds, and most preferably between about 1 to 3 seconds. The shorter the electric pulse, the higher the energy input required to harvest the ice.  
      Preferably, the ice-forming surfaces are electrically isolated from the refrigeration components. According to the present disclosure, PETD energy is applied to an ice-forming structure in such a way as to not energize the entire ice making structure or other conductive refrigeration components which would otherwise require significant energy inputs or otherwise make the system unsafe from electrical shock.  
      As depicted in  FIGS. 3 and 4 , an ice making machine  30  comprises a waffle-style, thermally conductive plastic evaporator assembly  32 , a water supply  34 , a refrigerant supply  36 , a controller  38 , an ice bin  39  and a source  40  of pulsed electrical energy, e.g., PETD. Evaporator assembly  32  comprises ice mold  1  and evaporator tube  3 . Evaporator tube  3  is interconnected with refrigerant supply  36 . The water valve is interconnected with water supply  34 . Controller  38  controls the freezing and harvesting cycles by appropriately controlling the pulsed electrical energy, the flow of water and refrigerant to evaporator assembly  32 .  
      Referring to  FIG. 3  an ice-making system  30  comprising a molded-in membrane heater with use in a dual-sided waffle-style pulse electric evaporator using thermally conductive plastic and inlaid electric trace. The system also comprises electrical energy source  40  which is connected in circuit with evaporator tube  3 , which is constructed of electrically conductive material. For example, evaporator tube may be made of metal, such as copper, aluminum or steel. Electrical energy source  40  is connected via an electrical connector  42  to a contact point  44  of thermally conductive plastic or extruded aluminum ice mold  1  and via an electrical connector (not shown) to a circuit reference, e.g., circuit ground.  
      In accordance with the present disclosure, electrical energy source  40  is operable at the time of harvest to apply one or more pulses of electric energy to thermally conductive plastic or extruded aluminum mold  1  to melt an interfacial layer of the ice at the interface of the ice and mold  1  sufficiently to loosen the ice so that it falls into ice bin  39 .  
      Electrical energy source  40  and the pulsed energy used for thermal de-icing, for example, may be of the type described in U.S. Pat. No. 6,870,139, U.S. Patent Publication No. 2005/0035110, and U.S. Patent Publication No. 2004/0149734, all of which are incorporated herein in their entirety by reference thereto, that is capable of supplying pulsed energy. Modulating the pulsed energy to the interface of the ice to ice mold  1  modifies a coefficient of friction between the ice and ice mold  1 . The electrical pulse energy technology is known as Pulse Electro Thermal De-icing (PETD).  
      Typically, a pulse de-icer system heats an interface to a surface of an object so as to disrupt adhesion of ice with the surface. To reduce the energy requirement, one embodiment of a pulse de-icer explores a very low speed of heat propagation in non-metallic solid materials, including ice, and applies heating power to the interface for time sufficiently short for the heat to escape far from the interface zone; accordingly, most of the heat is used to heat and melt only a very thin layer of ice (hereinafter “interfacial ice”). The system preferably includes a power supply configured to generate a magnitude of power. In one aspect, the magnitude of the power has a substantially inverse-proportional relationship to a magnitude of energy used to melt ice at the interface. The pulse de-icer system may also include a controller configured to limit a duration in which the power supply generates the magnitude of the power. In one aspect, the duration has a substantially inverse-proportional relationship to a square of the magnitude of the power. The power supply may further include a switching power supply capable of pulsing voltage. The pulsed voltage may be supplied by a storage device, such as a battery or a capacitor. The battery or capacitor can, thus, be used to supply power to a heating element that is in thermal communication with the interface.  
      A preferred pulse de-icer systems is hereafter described. This pulse de-icer system may be used to remove ice from a surface of an object such as a ice forming cup or finger, typically by melting an interfacial layer of ice and/or modifying a coefficient of friction of an object-to-ice interface.  
      One such pulse de-icer system for modifying an interface between an evaporator assembly and ice according to the present disclosure comprises: a power supply, a controller, and a heating element. In one embodiment, the power supply is configured for generating power with a magnitude that is substantially inversely proportional to a magnitude of energy used to melt interfacial ice (hereinafter “interfacial ice”) at the interface. A heating element is coupled to the power supply to convert the power into heat at the interface. Controller is coupled to the power supply to limit a duration in which the heating element converts the power into heat. In one embodiment, the duration in which the heating element converts the power into heat at the interface is substantially inversely proportional to a square of the magnitude of the power.  
      Controller  38  controls electrical energy source  40  to apply electrical pulse energy when the ice mold  1  has grown to the desired predetermined size. The electrical pulse energy causes electrical resistance heating of mold  1  by thermal conduction from mold  1 . The fast, even heating of molds  1  releases the ice within molds  1  more quickly than with the prior art defrost methods, minimizes the amount of melting that occurs.  
      From the foregoing it may be seen that the arrangement of the present disclosure provides an automatic ice making machine in which harvesting of the ice is achieved very quickly and in a very energy-efficient manner.  
      FIGS.  1 ( a )-( c ) and  2  depict a geometry and design of a short-duration pulsed, resistive heater  10  comprising an electrically conductive material  12  (i.e., metallic foil, di-electric media, electrically conductive inks, etc.) that can be applied to a thermally conductive/thermally isolative substrate (e.g., a plastic film) (not shown) such that the heater element  14  can be patterned (i.e., die-cut) and contoured (i.e., folded, bent, rolled, curved, etc.) in order to come in intimate contact with the surface of the ice-forming regions of the ice-forming structure.  FIGS. 1 and 2  depict two types of short-duration, resistive heaters that are thermally conductive and electrically isolated such that the material  12  permanently attaches (e.g., adhesive, solvent bond, ultrasonically bonded or heat fused) to the ice-forming structure (i.e., evaporator) at the interfacial boundary layer of the ice and the surface of the ice-forming structure.  
      In particular, FIGS.  1 ( a )-( c ) depicts a mold-in membrane heater  10  with a flexible membrane element  12  having a width of between about 0.003 to 0.005 inches. Flexible membrane element  12  is preferably formed of a material which is capable of bonding to a thermally conductive plastic evaporator, not shown. Each flexible membrane element  12  include electrical trace  14  having a positive and negative connection at opposite ends thereof. Membrane heater  10  is also capable of being folded prior to insert molding into the evaporator, not shown. After insert molding of membrane heater  10  into the evaporate, the two pieces are bonded or fused together to form a integral one-piece evaporator with integral heat interface. FIGS.  1 ( b ) and ( c ) depict two different type shapes of membrane heater  10  for forming individual ice cells.  
      Membrane heater  10  can be an etched foil design element disposed on a Kapton®/Polyimide heater. Heaters made with this DuPont thin film are transparent, lightweight, flexible and are electrically strong. Kapton®/Polyimide heaters are compatible with foil element alloys, such as inconel, nickel, copper and stainless steel. They have low outgassing properties, are resistant to solvents and can be produced with special internal adhesive systems that permit higher operating temperatures.  
       FIG. 5 ( a ) depicts a thermal conductive plastic or cast aluminum evaporator  49 , according to the present disclosure, with a plurality of thin wall stainless freezing or ice forming tubes  52  disposed therethrough. Each tube  52  is disposed between stacked evaporator plates  50 , wherein tubes  52  are electrically isolated from evaporator  49 . The sandwiching of freezing tubes  52  between successive layers of evaporator plates  50  enables scalable ice making capacities and thinner wall tubes (since there is no direct refrigerant pressure on tubes  52 ). In addition each evaporator plate  50  includes thermal transfer nodes  60  which contact tubes  52  intermittently. Thermal transfer nodes  60  preferentially contact freezing tubes  52  intermittently to form individual ice slugs rather than a continuous ice layer throughout the entire length of each tube  52 . Tubes  52  include low-mil electrical insulation  62  about their outer surfaces. Freezing tubes  52  are preferably thin-walled (i.e., emulates properties of foil) to disrupt ice adhesion at the interfacial layer of ice and tube  52 .  
      In-molded copper tubing  54  is formed within each evaporator plate  50  such that refrigerant enters inlet  56  and exits via outlet  58  of tubing  54 .  
      Water enters tubes  52  via inlet ports  64  during an ice making harvest an electrical pulse is sent via PETD electrical contact  66 , thereby releasing ice slugs from the inner surface of each tube  52  which exit via outlet ports  68 .  
      The benefit to the embodiment of  FIG. 5 ( a ) is that freezing tubes  52  are electrically isolated from evaporator contacts  66  and therefore can be electrical-resistance heated directly without energizing the entire ice making system, not shown.  
       FIG. 5 ( b ) has most of the same components as  FIG. 5 ( a ) above, with the exception that it utilizes, according to another embodiment of the present disclosure, thin wall stainless tubes  70  with membrane heaters  72  disposed about the outer surface of tubes  70 . The membrane heaters  72  are low mil thickness and provide electrical resistance heat or pulsed energy via electrical contacts  74 . That is,  FIG. 5 ( b ) is the same as  FIG. 5 ( a ), but instead of electrically pulsing the freezing tubes directly, a membrane heater element  62  is wrapped around each freezing tube  52  and pulsed. This approach momentarily heats tubes  52  (from outside-in) to disrupt ice adhesion at the interfacial layer and release the ice.  
      Freezing tubes  52  can be sequentially pulsed, or pulsed simultaneously.  
      FIGS.  6 ( a ) and ( b ) are similar in function to FIGS.  5 ( a ) and ( b ), respectively, however, the configuration is slightly different. In  FIG. 6 ( a ) there is an extruded aluminum evaporator segments  80  stacked one on top of the other, wherein copper tube  82  are disposed in a vertical, serpentine configuration through a plurality of segments  80 . Thin wall stainless steel freezing tubes  84  are also positioned vertically through segments  80 . Tubes  82  include a low-mil electrical insulation  86  and are disposed between segments  80  within thermal transfer nodes  88  which contact tubes  82  intermittently for the purposes of producing ice slugs as discussed above. During operation, water enters inlet port  90  of each freezing tube  84  where it freezes on the interior surface of tube  84 , preferably at the point of contact between tube  84  and thermal transfer node  88 , such that ice slugs exit outlet port  92  during harvest by means of an electric pulse being generated on the tube  84  via electric contacts  96 .  
      In  FIG. 6 ( a ) freezing tubes  84  are electrically isolated from evaporator segments  80  and therefore can be electro-thermally pulsed directly without energizing the entire ice-making system.  
       FIG. 6 ( b ) is similar to  FIG. 6 ( a ), except that it provides for a membrane heater  98  wrapped about the exterior walls of each freezing tube  84 , such that during the harvest mode and electric pulse is transferred to the membrane heater  98  via electrical contacts  100 . That is, instead of electrically pulsing freezing tube  84  directly, as in  FIG. 6 ( a ), a membrane heater element  98  is wrapped around each freezing tube and pulsed. This approach momentarily heats freezing tube  84  (from outside-in) to disrupt ice adhesion at the interfacial layer and releases the ice.  
      Like in FIGS.  5 ( a ) and ( b ), freezing tubes  84  can be sequentially pulsed, or pulsed simultaneously.  
      The evaporator plates of FIGS.  6 ( a ) and ( b ) comprise a plurality of individual extruded or cast aluminum segments  80  stacked with air space in between each successive segment  80 . Ice freezing tubes  84  are then sandwiched between these assemblies providing intimate contact at thermal transfer nodes  88 . Thermal transfer nodes  88  which are formed during the extrusion or casting process enables scalable ice making capacities and thinner wall tubes since there is no refrigerant pressure on tubes  84 .  
      FIGS.  7 ( a ) through  9  depict another embodiment according to the present disclosure, i.e., a shell and tube configuration.  FIG. 7 ( a ) depicts an individual shell and tube device  110 , whereas  FIG. 7 ( b ) depicts a evaporator assembly  120  comprising an assembly comprising multiple shell and tubes  122 .  
      In  FIG. 7 ( a ) a shell and tube device  110  comprises a freezing tube  112  disposed within shell  114 . Shell  114  includes refrigerant inlet  115  and outlet  116 . During the ice making mode, water enters tube  112  at water inlet  117  and refrigerant enters refrigerant inlet  115 , such that ice forms about the interior surface of tube  117  at location where insulation rings  118  are not in contact with the exterior surface of tube  117 . During the harvest mode, electrical pulse energy is driven into tube  117  via electrical contact  119 , such that ice slugs exit tube  117  via exit port  121 .  
      In FIGS.  7 ( b ) and  8  a plurality of tubes  122  disposed within a large shell  124 . Each freezing tube  122  having a water inlet  126  and outlet  128 . Each shell has a refrigerant inlet  130  and out  132 . The freezing tubes are include membrane heaters  134  disposed about each tube  122 , which are electrically connected to an PETD electrical pulse source (not shown) via electrical contact  136 . An electric conduit (not shown) connects said electrical contact  136  with electrical pulse source (not shown) via conduit  138  disposed in an upper plate  140  of shell  124 . Insulating rings  142  are disposed about each tube  122 , such that during the ice making mode ice forms only about that portion of freezing tubes  122 , which are exposed to the refrigerant within shell  124  and not insulated by means of insulating rings  142 . During the harvest mode, an electrical energy pulse is delivered to membrane heaters  134  disposed about tubes  122 , such that ice slugs are removed via outlet ports  128  shortly after activation of the electrical energy pulse.  
       FIG. 9  depicts a ice making system  150  comprising the shell and tube assembly  120  of FIGS.  7 ( b ) and  8 , wherein water from sump  152  is transported via conduit  154  and pump  156  from sump  152  to a top portion  158  of shell and tube assembly  120 , where it enters each water inlet port  126 . During the harvest mode ice slugs leave shell and tube assembly  120  via exit ports  128  for collection within ice bin  160 .  
      Still another embodiment according to the present disclosure is depicted in  FIG. 10  which shows a cross-sectional view of helical tubular extruded aluminum ice making evaporator comprising freezing tube  170  having a water conduit or channel  171 , and refrigeration passages  172  and  174  disposed on opposite side thereof. Preferably, freezing tube  170  is coiled into a helix (not shown), wherein water is introduced into an upper end of the helix and exits the lower end of the helix. Ice freezes from the outside-in as it is cooled by the refrigerant passing through refrigeration passages  172  and  174 . When the water conduit or channel  171  has become plugged by ice, PETD pulse is applied to at least a portion of the length of tube  170 , wherein the ice is related from the interior surface of the freezing tube  170  and is ejected from tube  170  by either gravity or water pressure.  
      The present disclosure having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present disclosure as defined in the appended claims.