Abstract:
An evaporator assembly and method of making the assembly wherein a refrigerant flow path is created that covers a large area of the back of either one or two evaporator pans. The refrigerant conduit includes a plurality of elongated sections that are non-circular, for example, rectangular, in cross-section. The sections are sized and spaced so as that refrigerant flow therethrough covers substantially all of the backs of the evaporator pans. The sections are formed with either tubes or ridges. The evaporator assembly is made by using bonding processes and/or die casting processes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority of U.S. Provisional Application No. 60/453,096 filed Mar. 7, 2003, U.S. Provisional Application No. 60/479,646 filed Jun. 19, 2003 and U.S. Provisional Application No. 60/527,956 filed Dec. 9, 2003, and the entire contents of each is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention relates to ice machine evaporator assemblies with improved heat transfer and methods of making the assemblies. 
   BACKGROUND OF THE INVENTION 
   Ice machines include an evaporator assembly that includes a refrigerant conduit and an evaporator pan. The evaporator pan has a front side upon which ice cubes are formed and a back side that is in thermal transfer relation to the refrigerant conduit. The refrigerant conduit is constructed of copper tube formed into a serpentine shape. The copper tube sections are circular in cross-section, which provides a non-uniform refrigerant flow spacing from the back of the evaporator pan, thereby resulting in a non-uniform heat transfer across the diameter of the copper tube. Moreover, adjacent tube sections are spaced so much from one another that the refrigerant flow covers a relatively small area of the back of the evaporator pan, which typically is about 25% or less. 
   The ice assemblies are generally formed by soldering the copper tube serpentine to the back of the evaporator pan opposite the side of the ice forming structures. Each solder area is an area of structural weakness that can fracture during operation. Also, the multiple solder areas increase the cost and time of assembly. 
   There is a need for an evaporator assembly with an improved heat transfer and for a method of making the evaporator assembly. 
   The present invention allows for two evaporator pans and ice grids per serpentine. This increased refrigerant contact area and quantity of evaporator pans and ice grids lead to the following advantages:
         1) Allows the ice machine to run at a higher evaporator temperature for a given ice capacity resulting in a 30% reduction in energy consumption.   2) The increased evaporator efficiency results in the ability to substantially reduce compressor size, resulting in lower costs and less noise.   3) For a given ice making capacity, evaporator internal volume is reduced by 65%, resulting in lower refrigerant costs and less compressor floodback during harvest.   4) For a given ice making capacity, evaporator weight is reduced by 65%. This reduces the amount of capacity and energy required to cool and heat the evaporator for the freeze and harvest cycles. This also reduces evaporator costs as less material is required.   5) The increased evaporator efficiency allows for a smaller evaporator for a given ice capacity resulting in smaller overall machine size.   6) Existing copper designs require a nickel plating to be compliant with National Sanitation Foundation (NSF) requirements. Stainless steel has no such plating requirement resulting in substantially lower evaporator costs.   7) Evaporator assembly  120  allows nearly 100% of evaporator pans  122  and  124  to be in direct contact with the refrigerant. Existing copper tube designs have 0% of the evaporator pans in direct contact with the refrigerant. Existing copper tube designs use a soldering process to attach a copper tube to a copper evaporator pan. The copper tube typically covers only 25% of the evaporator pan. Also, copper tube designs and manufacturing processes allow for only one evaporator pan and ice grid per serpentine.       

   SUMMARY OF THE INVENTION 
   An evaporator assembly of the present invention includes at least one evaporator pan including a first side with a structure that facilitates formation of ice cubes and a second side. A refrigerant conduit is disposed in thermal contact with the second side of the evaporator pan. The refrigerant conduit comprises one or more sections sized such that refrigerant flows through the sections and covers a percentage of the second side of the evaporator pan that is in a range selected from the group consisting of: about 30% to 100%, about 40% to 100% and about 80% to 100%. 
   In some embodiments, refrigerant flow through the sections covers substantially all of the second side of the evaporator pan. 
   In some embodiments, one or more of the refrigerant conduit sections have a non-circular cross-section. In one version, the cross-section has a side that is substantially flat and that is substantially parallel to the first side. Preferably, the cross-section is rectangular. 
   In one embodiment, the refrigerant conduit further comprises first and second headers that connect the sections in a pattern. Preferably, the pattern is serpentine. Also, preferably, each of the sections comprises a rectangular tube that has one surface that is mounted in direct mechanical contact with the second side of the evaporator pan. 
   In other embodiments, a ridge structure defines the refrigerant conduit sections. Preferably, the ridge structure comprises a plurality of ridges that are integral with the second side of the evaporator pan. At least two of the ridges are spaced from and parallel to one another so as to form opposed sides of at least one of the sections. The area between the two ridges forms another side of the section. Preferably, at least one of the ridges is shared with an adjacent section. In some of these embodiments, first and second fittings are arranged with the plurality of ridges to provide a serpentine pattern. 
   In any of the aforementioned embodiments, there is provided an additional evaporator pan having a first side with a structure that facilitates formation of ice cubes and a second side. The refrigerant conduit is also in thermal contact with the second side of the additional evaporator pan. In some of these embodiments, the non-circular cross-section has opposed sides that are substantially flat and substantially parallel to the first sides of the evaporator pan and the additional evaporator pan. 
   The method of the present invention makes an evaporator assembly by forming an ice cube structure on a first side of at least one evaporator pan. A refrigerant conduit is formed on a second side of the evaporator pan. The refrigerant conduit comprises one or more sections that are sized such that refrigerant flow through the sections covers a percentage of the second side of the evaporator pan that is in a range of about 30% to 100%, preferably about 40% to 100% and most preferably about 80% to 100%. 
   In a first specific embodiment of the method, the conduit sections are individual parts that are formed on the second side of the evaporator pan by a bonding process. 
   In one version of the first embodiment, each of the conduit section parts comprises an elongated rectangular tube. The bonding process bonds a surface of each of the elongated rectangular tubes to the second side of the evaporator pan. Preferably, the elongated rectangular tubes are arranged parallel to one another on the second side of the evaporator pan. First and second headers are disposed at opposite ends of the elongated rectangular tubes. The bonding process bonds the first and second headers to the elongated rectangular tubes. 
   In a second specific embodiment of the method, the refrigerant conduit comprises a ridge structure that defines the sections. Preferably, first and second fittings are connected to the ridge structure so as to form a serpentine refrigerant flow path. 
   In one version of the second embodiment of the method, the ridge structure is formed on the second side of the evaporator pan by a bonding process. Preferably, the ridge structure is disposed between the second side of the evaporator pan and a body that includes a substantially flat surface that is substantially parallel to the second side of the evaporator pan. The bonding process bonds the ridge structure to the flat surface. 
   In another version of the second embodiment of the method, the ridge structure is formed on the second side of the evaporator pan by a die cast process. Preferably, the ridge structure is closed by an adjacent body that is shaped to give each of the sections a substantially rectangular cross-section. In a particular design of this version, the body comprises a mating ridge structure on a surface thereof. The ridge structures are fastened together in a mating way to form the sections. 
   In any of the aforementioned embodiments of the method, the refrigerant conduit is also fastened to a second side of an additional evaporator pan. In some of these embodiments, the refrigerant flow through the sections covers substantially all of the second sides of the evaporator pan and the additional evaporator pan. 
   In the aforementioned embodiments that use a bonding process, the bonding process may use a brazing material. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other and further objects, advantages and features of the present invention 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: 
       FIG. 1  is a perspective view of the evaporator pan and refrigerant assembly of the present invention; 
       FIG. 2  is a front view of  FIG. 1 ; 
       FIG. 3  is a top view of  FIG. 1 ; 
       FIG. 4  is an enlarged view of detail B of  FIG. 3 ; 
       FIG. 5  is a side view of  FIG. 1 ; 
       FIG. 6  is an enlarged cross-sectional view taken along line  6 — 6  of  FIG. 2 ; 
       FIG. 7  is an exploded view of  FIG. 1 ; 
       FIG. 8  is a side view of another embodiment of the assembly of a refrigerant conduit and evaporator pan of the present invention; 
       FIG. 9  is a cross-sectional view of another embodiment of the tube section that can be used in the evaporator assembly of the present invention; 
       FIG. 10  is an exploded perspective view of an alternate embodiment of the present invention; and 
       FIG. 11  is an exploded perspective view of another alternate embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , an evaporator assembly  20  of the present invention includes a first evaporator pan  22 , a second evaporator pan  24  and a refrigerant conduit  26  disposed between evaporator pans  22  and  24 . 
   Referring to  FIGS. 2-6 , each of the evaporator pans  22  and  24  are substantially identical so that only evaporator pan  22  will be described in detail. Evaporator pan  22  includes a bottom  27 , a top side  32  and opposed sides  34  and  36 . Bottom  27  includes a front  28  and a back  30 . An ice cube structure shown as an ice grid  38  is disposed on front  28  and between opposed sides  34  and  36  of evaporator pan  22 . Ice grid  38  has a plurality rows, each formed of a fin  40 , and a plurality of columns, each formed of a divider  42 . 
   Fins  40  are disposed at a slight angle to front  28  in order to assist in the ice harvesting process. The bottom most fin  40  serves as the bottom side of evaporator pan  22 . It will be apparent to those skilled in the art that the ice cube structure can be formed of other structures and that the ice cubes formed thereby can have any suitable geometry. 
   Referring to  FIGS. 2-7 , refrigerant conduit  26  includes a plurality of conduit sections  44  connected on opposed ends thereof to headers  46  and  48 . Header  48  is shown in  FIG. 7 , as including a slot  50  in which one end of each conduit section  44  resides. Header  46  also includes a slot  50  (shown in  FIGS. 3 and 4 ) in which the other ends of conduit sections  44  reside. Headers  46  and  48  are located adjacent to the external surfaces of sides  34  and  36  of each evaporator pan  22  and  24 , respectively. This allows conduit sections  44  to be in direct mechanical contact with backs  30  of evaporator pans  22  and  24  so as to maximize thermal transfer and efficiency. 
   As shown in  FIGS. 3 ,  4 ,  6  and  7 , conduit sections  44  have a shape and size that provides a large surface area in thermal and mechanical contact with evaporator pans  22  and  24 . Preferably, the cross-section of each conduit section  44  is non-circular. More preferably, the non-circular cross-section includes opposed wide area surfaces that cover substantial areas of bottoms  27  of evaporator pans  22  and  24 . For example, the cross-section may be substantially rectangular with wide area surfaces that are parallel to the back  30  and/or front  28  of evaporator pans  22  and  24 . This allows the gap between adjacent conduit sections  44  to be minimized so that the refrigerant flow covers a relatively large area of bottoms  27  of evaporator pans  22  and  24 . This is to be contrasted with conduit assemblies that use conduit sections that have a circular cross-section that does not have any wide area surface that is parallel to the back and/or front of the evaporator pans. 
   The geometry and gap spacing of conduit sections  44  increase the thermal transfer efficiency, thereby providing many possibilities. For example, an ice machine employing evaporator assembly  20  can have a large ice capacity in a smaller space or have lower energy consumption or a combination thereof. The rest of the ice machine will change depending on which of these objectives is desired. The remaining components (e.g., compressor and condenser) could be increased to obtain increased ice capacity or could be of the same size or smaller to obtain lower energy consumption. 
   As another example, to make 500 pounds of ice with a circular cross section refrigerant conduit design in a 24 hour period, an evaporator temperature of 0° F. is required. The temperature difference between the evaporator temperature of 0° F. and the water at 32° F. (freezing temperature) causes the water to change state and turn to ice. This requires a compressor of a certain size. To make the same 500 pounds of ice in a 24-hour period using the evaporator assembly of the present invention, it is projected that the evaporator temperature will need to be 18° F. A compressor&#39;s energy consumption is determined in large part by difference in pressure between the high side and low side. By making the evaporator pan warmer with the more thermal efficient evaporator assembly of the present invention, the pressure difference between the low and high side is decreased, thereby requiring less energy. 
   Evaporator pans  22  and  24  and ice grids  38  are preferably constructed of stainless steel and conduit sections  44  and headers  48  are preferably constructed of aluminum. Conduit sections  44  are preferably aluminum extrusions. Each extrusion preferably includes internal channels  52  as shown in  FIGS. 6 ,  8  and  9  for better strength and heat transfer from the extrusion walls. To provide a serpentine path for refrigerant flow, for example, one or more dividers (not shown) may be placed on one or both of headers  42  and  46 . The refrigerant circuit of an ice machine then can be connected in fluid communication with the top of one the headers  46  and  48  and the bottom of the other header. 
   Although evaporator assembly  20  is shown with two conduit sections, it will be apparent to those skilled in the art that more than two conduit sections may be used. For example,  FIG. 8  shows an evaporator assembly  60  that includes four conduit sections  64 . 
   In addition, even though evaporator assembly  20  is shown with two evaporator pans, it is contemplated that evaporator assembly  20  may have only one evaporator pan. In a one evaporator pan assembly, additional structural stability, if desired, could be provided by any suitable fastening structure. For example, the structure could be placed on the opposite side of the conduit assembly and fastened by screws, bolts, soldering, brazing and the like to the evaporator pan and/or conduit assembly. 
   The method for making the evaporator assembly comprises the following steps:
         1. Brazing material is applied to each of the surfaces to be bonded. This includes all surfaces where ice grid  38  touches the evaporator pan  22  or  24 , where the extrusions enter the headers  46  and  48 , and where the extrusions  44  and headers  46  and  48  touch the evaporator pans  22  and  24 .   2. Placing the assembly of step 1 in a fixture that holds it together.   3. Placing the fixture and assembly in a brazing furnace so as to heat evaporator assembly  20  and braze ice grids  38 , evaporator pans  22  and  24 , conduits  44  and headers  46  and  48  together.       

   Referring to  FIG. 10 , an evaporator assembly  120  constitutes an alternate embodiment of the present invention. Evaporator assembly  120  includes a first evaporator pan  122 , a second evaporator pan  124  and a refrigerant conduit assembly  126  disposed between evaporator pans  122  and  124 . 
   Each of the evaporator pans  122  and  124  is substantially identical so that only evaporator pan  122  will be described in detail. Evaporator pan  122  includes a bottom  127 , a top side  132  and opposed sides  134  and  136 . Bottom  127  includes a front (obscured in  FIG. 10 ) and a back  130 . An ice cube structure shown as an ice grid  136  is disposed on the front and between opposed sides  134  and  136  of evaporator pan  122 . Ice grid  138  has a plurality rows, each formed of a fin  140 , and a plurality of columns, each formed of a divider  142 . 
   Conduit assembly  126  includes a flow path boundary ridge structure  170  that is disposed between and in contact with evaporator pans  122  and  124  so as to define a flow path for refrigerant. Flow path boundary ridge  170  includes a first section  172  having tines  174  and a second section  176  having tines  178 . Sections  172  and  176  are disposed so that tines  174  and  178  are interleaved to form a serpentine flow path. Preferably, the sections  172  and  176  are solid and of the same material as evaporator pans  122  and  124  and ice grid  136 . Preferably, the material is stainless steel for pans  122  and  124  and sections  172  and  176  and copper for ice grid  136 . 
   The refrigerant flow path is defined on two opposed sides by backs  130  of evaporator pans  122  and  124  and on all other sides by flow path boundary ridges  172  and  174 . The flow path has first and second end openings  180  and  182 , which are adapted to be capped by separate fittings  184  and  186  that are connected with a refrigeration circuit of an ice maker. The flow path comprises five refrigerant conduit sections that each has a substantially rectangular cross-section. Each refrigerant conduit section is bounded on two opposed sides by a tine  174  and a tine  178 . The areas in-between the tine  174  and the tine  178  on backs  130  of evaporator pans  122  and  124  define the other two opposed sides of the refrigerant conduit section. 
   The geometry of flow path boundary ridges  172  and  174  and evaporator pans  122  and  124  is designed such that the resulting refrigerant flow cross-sectional area is equivalent to that of a common refrigeration tube diameter. This is preferably equivalent to a 0.5 inch diameter tube. This reduces the amount of pressure drop of the refrigerant as it flows through evaporator assembly  120  to equal the 0.5 inch copper tube design. 
   It is also desirable to make flow path boundary ridges  172  and  174  as thin as possible. This allows maximum refrigerant contact with evaporator pans  122  and  124  while minimizing the internal volume of evaporator assembly  120 . Minimizing the internal volume of evaporator assembly  120  allows for reduced refrigerant cost and less refrigerant floodback to the compressor during the ice harvesting cycle. 
   Although evaporator assembly  120  is shown with two evaporator pans, it is contemplated that evaporator assembly  120  may have only one evaporator pan. In a one evaporator pan assembly, the refrigerant conduit assembly could be sandwiched between the evaporator pan and a body that has at least one flat surface to complete the conduit assembly. 
   Referring to  FIG. 11 , evaporator assembly  220  constitutes another alternate embodiment of the present invention. Evaporator assembly  220  includes a first evaporator pan  222 , a second evaporator pan  224  and a refrigerant conduit assembly  226 . Evaporator pans  222  and  224  each have a back  230  that differs slightly from backs  130  of evaporator pans  122  and  124 , but otherwise are similar. 
   Refrigerant conduit  226  is similar to refrigerant conduit assembly  126 , differing therefrom in manner of construction and serpentine arrangement. As to construction, a pattern of boundary ridges  202  is disposed on back  230  of evaporator pan  222  and a mating pattern of ridges (not shown) is disposed on back  230  of evaporator pan  224 . Ridge pattern  202  includes a perimeter ridge  204 , and interior ridges  206 ,  208  and  210  that extend inwardly from perimeter ridge  204 . Ridges  206  and  210  are straight and ridge  208  forms a U-shape with ridge  210  being disposed in the U. A pair of refrigerant fittings  212  and  214  is disposed in perimeter ridge  204  at locations to provide a serpentine refrigerant flow along the dashed line  216 . 
   When evaporator plates  222  and  224  are fastened together in back to back fashion the mating ridge patterns mate with one another and form a serpentine flow path along line  216  between fittings  212  and  214 . Refrigerant in the flow path is in direct contact with each evaporator pan  222  and  224 , thereby providing an increased thermal transfer and efficiency. Alternatively, the mating ridge pattern on back  130  of evaporator pan  224  may be omitted and the ridges  204 ,  206 ,  208  and  210  made high enough to engage back  230  of evaporator plate  224 . 
   Refrigerant conduit  226  has a number of conduit sections that each has a substantially rectangular cross-section. For example, one conduit section has a pair of opposed sides bounded by ridges  206  and  208 . The areas between ridges  206  and  208  on backs  230  of evaporator pans  222  and  224  define the other pair of opposed sides of the refrigerant conduit. 
   The exposed surfaces of evaporator assembly  220  are treated with a coating that prevents corrosion. Evaporator pans  222  and  224  are preferably aluminum or aluminum alloy. 
   Evaporator assembly  220  is made by brazing the two aluminum die cast ice forming molds  222  and  224  together in a furnace. Die castings  222  and  224  are cast with a ridge geometry that when brazed together results in a defined refrigerant flow path. 
   Evaporator assembly  220  has the following advantages:
         1. Enhanced heat transfer. In traditional evaporators, a copper tube carrying refrigerant is bonded to the back of the ice making surface. In evaporator assembly  220 , rather than heat passing through the part of the surface of a tube in contact with the pan, the entire back surface of the aluminum casting is exposed to the refrigerant.   2. Enhanced heat transfer by virtue of having two ice making surfaces instead of one associated with one refrigerant flow path.   3. Reduced part count. There are only two aluminum die castings vis-a-vis the traditional design, which has a tube, pan and a multitude of strips for the ice grid.   4. Lighter weight. (Aluminum vs. copper).   5. Easier to manufacture.       

   Although evaporator assembly  220  is shown with two evaporator pans, it is contemplated that evaporator assembly  220  may have only one evaporator pan. In a one evaporator pan assembly, the refrigerant conduit assembly could be sandwiched between the evaporator pan and a body that has at least one flat surface to complete the conduit assembly, with the ridges being disposed on either or both of the evaporator pan and the flat sheet surface. 
   The present invention 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 invention as defined in the appended claims.