Abstract:
A flow heater for a sink heater or rethermalizing system is disclosed. The flow heater includes a flow tube in fluid communication with a fluid receptacle. The flow tube has a heating element that is in conductive communication with the flow tube and helically encircles the flow tube. Fluid flowing through the flow tube is caused by thermal siphoning effects. The flow heater system may be used for presoaking, soaking, or sanitizing dishware in a sink or for rethermalizing packaged foods.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 09/525,893, filed on Mar. 15, 2000 with inventors Allan E. Witt and Kenneth Hays, assigned to Hatco Corporation, and entitled “Flow Heater”. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to a rethermalizing heater or sink heater. The rethermalizing heater or sink heater uses a single tube or multiple tubes with external heating elements in thermally conductive contact with the tube or tubes, providing heat transfer to liquid flowing through the tubes. Liquid is circulated through the tubes and into a tank or sink through the process of thermal siphoning.  
         BACKGROUND OF THE INVENTION  
         [0003]    Recirculation of water, or other liquids, for example cleaning solutions, is a process commonly used in the food industry. For example, recirculation of wash water has been used in dishwashers. In such a recirculating dishwasher, a tank is used as a relatively large reservoir that is filled with a solution of water and detergent for washing. The water and detergent solution is recycled for washing successive racks with a large percentage of the same liquid being recirculated. The liquid is somewhat diluted with fresh rinse water after each cycle. A drain valve is typically located at the bottom of a tank. Further, an overflow may be located near the top of the tank. The fresh water spray system rinses the racks of dishware at the proper time in a cycle, after it has been washed by pumped recirculation of the large volume of wash water. The wash water is typically heated by a heater to maintain water temperature. Often, such a heater is an electrical heating element submerged in the wash water tank. Using a submerged heating element has the disadvantage that lime and other mineral build-up collects on the heating element. Such lime and mineral build-up is difficult to remove without the use of chemicals. Furthermore, if the lime and mineral build-up is not frequently removed, the heating element is subject to failure.  
           [0004]    Conventionally, rethermalizing heaters used for reheating of bagged food product or sink heaters used for sterilizing dishware use a two tank system. One tank is used to collect debris from the system. The debris collecting tank has a ball valve drain. The other tank contains the heating element or elements and is separated to avoid sludge or debris from collecting in it. The second tank has a removal cap on a small drain. Frequently, however, the tank having the substantially clean solution gets contaminated when the first debris collecting tank is not sufficiently drained and flushed frequently enough or completely enough. Furthermore, limescale build-up or mineral build-up occurs in the heated tank that is difficult to remove without the use of chemicals. When the heated tank gets contaminated with scale or debris, the unit may malfunction and the heating elements are subject to failure. Such frequent failures create a major service problem and an increase in warranty costs due to failures.  
           [0005]    Further, conventional rethermalizing or sanitizing heating systems use pumps to recirculate fluid through the heating element and into a fluid tank. Such pumping systems are plagued with mechanical pump failures and require routine pump maintenance.  
           [0006]    Further still, conventional rethermalizing or sanitizing systems may utilize heating elements that are configured to be used with high voltage services, such as services over 100 volts, including but not limited to, services at 480 volts.  
           [0007]    Accordingly, there is a need for a rethermalizing heater or sink heater that uses a heating element that is not submerged in the solution. Further, there is a need for a rethermalizing heater or sink heater that utilizes a single tank. Further still, there is a need for a rethermalizing heater or sink heater that is easily cleaned and easily drained. Yet further still, there is a need for a rethermalizing heater or sink heater that does not require the use of chemicals to remove the limescale build up or mineral build up from heating elements. Still further, there is a need for a rethermalizing or sink heater that does not use a mechanical pump for recirculating fluid. Yet further still, there is a need for a flow heater including a thick-film heating element in conductive communication with the flow tube. Yet still further there is a need for a thick-film heater for a flow tube which may be enabled for any voltage services, including but not limited to 120 volts, 208 volts, 240 volts, 380 volts, 415 volts, or 480 volts.  
         SUMMARY OF THE INVENTION  
         [0008]    An exemplary embodiment of the invention relates to a flow heater system for heating fluid. The flow heater system includes a fluid receptacle and a flow tube in fluid communication with the fluid receptacle. The flow heater system also includes a film heating element in conductive communication with the flow tube.  
           [0009]    Another exemplary embodiment of the invention relates to a sink heater configured to heat and recirculate liquid in a sink. The sink heater includes a flow tube having an inlet and an outlet in fluid communication with the sink. The sink heater also includes a film heating element configured to exchange heat with the flow tube. Fluid flow through the tube is caused by convection from the sink into the inlet and out of the outlet into the sink.  
           [0010]    Further, an exemplary embodiment of the invention relates to a method for heating liquid in a fluid receptacle. The method includes providing a flow tube in fluid communication with the fluid receptacle. The method also includes providing a fluid in the fluid receptacle. Further, the method includes providing a film heating element in conductive communication with the flow tube. Further still, the method includes controlling current through the film heating element and creating a thermal siphoning effect in the flow tube.  
           [0011]    Further still, an exemplary embodiment of the invention relates to a fluid heater configured to heat and recirculate liquid in a fluid receptacle. The fluid heater includes a flow tube having an inlet and an outlet in fluid communication with the fluid receptacle. The fluid heater also includes a heating element configured to exchange heat with the flow tube. Further, the fluid heater includes a flow tube access port provided adjacent the lower most portion of the flow tube and providing access to the interior of the flow tube. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like elements, in which:  
         [0013]    [0013]FIG. 1 is a diagrammatic view of an exemplary embodiment of a rethermalizing or sink heater;  
         [0014]    [0014]FIG. 2 is a perspective view of a flow heater apparatus;  
         [0015]    [0015]FIG. 3 is a right side elevational view of a flow heater apparatus;  
         [0016]    [0016]FIG. 4 is a left side elevational view of a flow heater apparatus;  
         [0017]    [0017]FIG. 5 is a front elevational view of a flow heater apparatus;  
         [0018]    [0018]FIG. 6 is a mechanical diagram of an elevational view of a flow heater apparatus heating element;  
         [0019]    [0019]FIG. 7 is a mechanical diagram of a front elevational view of a sink heater apparatus heating element;  
         [0020]    [0020]FIG. 8 is an exemplary diagram of a prospective view of a flow heater apparatus including film heating elements;  
         [0021]    [0021]FIG. 9 is an exemplary depiction of a film heating element disposed on a thermally conductive surface;  
         [0022]    [0022]FIG. 10 is a cross sectional view of the heating element of FIG. 9 taken along the line  10 - 10 ;  
         [0023]    [0023]FIG. 11 is yet another exemplary embodiment of a flow heater apparatus including film heating elements; and  
         [0024]    [0024]FIG. 12 is an exemplary cross section of the flow tube of FIG. 8 taken along the line  12 - 12 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Referring to FIG. 1, a flow heater  10  is coupled to a sink  20 , or other fluid receptacle. In an exemplary embodiment, sink  20  may be used as a rethermalizer for reheating packages  25  of prepared food. Packages  25  are held within a rack  27 . Rack  27  and packages  25  are submerged in fluid  30 , such as, but not limited to, water. A drain  35  may be coupled to sink  20  for complete draining of and cleaning of sink  20 .  
         [0026]    In an alternative embodiment, sink  20  may hold a rack, similar to rack  27  which is designed to hold dishes. Utilizing a rack holding dishes, flow heater  10  may be used as a sanitizer. Further, sink  20  may be used for a variety of applications, such as but not limited to presoaking or soaking. In an embodiment whereby sink  20  and rack  27  are used as a sanitizer, liquid  30  may be a sanitizing or cleaning solution. Although rack  27  is depicted, sink  20  may be used as a sanitizer without a rack such as rack  27 .  
         [0027]    In operation, flow heater  10  has electrical connections  12  to at least one heating element  14  of flow heater  10 , heating element  14  is wrapped around and in heat conductive contact with a flow tube  16 . Cold fluid flows into an inlet  15  at the bottom of sink  20 . The cold fluid entering inlet  15  is heated by contact with tube  16  which conducts heat from heating element  14 . As the fluid is heated, the fluid moves upward through the angled tube and eventually exits an outlet  17  in the bottom of sink  20 . The hotter fluid mixes with fluid  30  in tank  20  and rises to the top. Convection currents drive the colder fluid back into the bottom of sink  20  and into inlet  15 , as the process continues.  
         [0028]    Referring now to FIG. 2, flow heater  10  is depicted. Flow heater  10  includes heating element  14 , encircling a tube  16 . Tube  16  has an inlet  15  and an outlet  17 . Flow heater tube  16  and heating element  14  are mounted within a flow heater housing  40 . Flow heater housing  40  includes an electrical access port  42  for running electrical connections, and a control panel  44  including, but not limited to a control display panel  46  and controls  48 , such as, but not limited to, a temperature setting switch and an on/off switch.  
         [0029]    As depicted in FIG. 3, inlet  15  may be coupled to an inlet sump  52  to which may be coupled a plurality of flow tubes  16 . In a preferred embodiment, flow heater  10  may utilize three flow tubes  16 , especially in the case of a three phase power input. However, the design is not limited to the utilization of three tubes, a single tube design may also be used or any number of flow tubes may be applied. Flow tubes  16  are coupled to an outlet sump  54  that is coupled to outlet  17 .  
         [0030]    In an exemplary embodiment, flow tubes  16  may have cleaning ports  60  coupled to each of tubes  16 . Cleaning or access to ports  60  may have caps  62 , such as screw on caps or snap on caps which are preferably removable and seal flow tubes  16 . In an exemplary embodiment, an access port  60  or any number of access ports  60  may utilize a valve instead of, or in combination with caps  62 . As depicted in the exemplary embodiment of FIGS. 4 and 5, the bottommost access port includes a valve which is operable by a valve handle  64  rotatably mounted on the side of housing  40 . Valve handle  64  provides easy access to flow tube  16 , that is coupled to the bottommost access port  60 , by a simple rotation of valve lever  64 . Access port  60  may be used for draining of the flow heater system along with easy access for cleaning. Each of access ports  60  may be utilized for access to tube  16  for cleaning. In order to provide cleaning, an access tube is opened, either by removal of a cap  62 , or by operation of valve lever  64 . A brush, or other cleaning tool may then be introduced into access ports  60  and further into flow tubes  16 , and thereby abrade the inner surfaces of tube  16 .  
         [0031]    As depicted in FIGS. 6 and 7 an exemplary embodiment of heating element assembly  13  utilized for flow heater  10  is available from Schoeller-Bleckmann Edelstahlrohr of Austria. Heating element assembly  13  includes at least one heating element  14 , however, as shown in FIG. 6, multiple heating elements (depicted in FIG. 6 as two heating elements) may be utilized to surround a flow tube  16 . Flow tube  16  may be a stainless steel cylindrical tube, as depicted in FIG. 7. As depicted in FIG. 7, flow tube  16  may be a stainless steel tube approximately 1¼ inches in diameter. However, other geometries of flow tubing may be utilized without departing from the spirit and scope of the invention. A conductive sleeve, such as an aluminum sleeve  19 , may be in conductive contact with tube  16  to provide improved heat transfer to fluid flowing through tube  16 . In an exemplary embodiment, heating element  14  surrounds flow tube  16  in a helical manner. Heating element  14  is furnace braised to flow tube  16  such that stainless tube  16  and aluminum sleeve  19  and spiral heating elements  14  are bonded as a single piece for advantageous heat transfer characteristics. In an exemplary embodiment, heating element assembly  13  provides approximately 95-97 percent efficiency.  
         [0032]    In an exemplary embodiment, each heating element assembly  13  can carry up to four kilowatts of energy and may utilize single or three phase power dependent on the number of tubes  16  and heating elements  14 . In an exemplary embodiment, flow heater  10  may operate at 12 kilowatts, 240 volts, utilizing three phase power. However, it should be noted that the invention is not limited to the aforementioned efficiencies, power consumption, operating conditions, or inputs.  
         [0033]    In an exemplary embodiment, each of tubes  16  has an access port  60  that can be easily accessed with a cleaning brush from the front of housing  40 . Each of tubes  16  are connected in parallel to sumps  52  and  54  which, in an exemplary embodiment, are cast aluminum chambers. The chambers may be formed of any of a variety of other materials, such as but not limited to stainless steel, brass, polymers, etc. The chambers are sealed to tubes  16  by flaring the ends of tubes  16  and utilizing an O-ring at each tube end. The entire assembly may be held together by through bolts  65  passing from sump  52  to sump  54  parallel to the tubes and elements (see FIGS. 2 and 3).  
         [0034]    Temperature of fluid in fluid receptacle or sink  20  is controlled by a temperature control. Heating element  14  is prevented from being energized without fluid by a low water cut off system. Further, each heating element  14  may have a mechanical safety control built in. In case of dry firing a fusible mechanical safety control device may prevent heating elements  14  from energizing.  
         [0035]    Flow heater  10  may be used as a sink heater or a rethermalizing heater where a constant circulation of water at elevated temperatures is desired. In an exemplary embodiment, at  12  kilowatts, 240 volts, the unit will heat about 30 gallons of water with 150° F. temperature rise per hour.  
         [0036]    In an alternative embodiment, flow heater  10  may be used in a variety of applications including but not limited to atmospheric water heaters or hot water dispensers. For example, hot water could be maintained in a small tank using flow heater  10  to maintain the liquid contained therein at a relatively constant temperature, for dispensing on command.  
         [0037]    As disclosed, flow heater  10  utilizes a flow tube that is tilted with an angle of approximately 5-10 degrees relative to the horizontal. However, it should be noted that flow heater  10  may utilize flow tube  16  at any of a variety of angles from 0° to 90° relative to the horizontal.  
         [0038]    Further, in an exemplary embodiment, heating elements  14  are braised on providing direct contact with tubes  16 . However, heating elements  14  need not be fixedly attached to tube  16  nor need they be in physical contact with tubes  16 . However, differing heat transfer results will be achieved depending on the method of contact. Furthermore, in an exemplary embodiment, heating elements  14  have a substantially flat surface to provide a greater surface area in contact with tube  16 . However, the invention is not limited to heating elements with a flat surface.  
         [0039]    Referring now to FIG. 8, an alternative embodiment of a flow heater apparatus  100  is depicted. Flow heater apparatus  100  includes an inlet  110  and an outlet  120  coupled to a flow tube  130 . In an exemplary embodiment, flow tube  130  has an approximately triangular cross section as depicted in FIG. 12. Flow tube  130  may be provided of a variety of materials, including but limited to, stainless steel. Flow tube  130  includes a plurality of surfaces  135  on which a film heating element  140 , such as but not limited to, a thick-film heating element is disposed and configured to provide heat to the walls of flow tube  130  and to the liquid flowing through the aperture  138  of flow tube  130 .  
         [0040]    A film heating element, such as thick-film heating element  140  may be a heating element which is silk screened or otherwise disposed onto surface  135  of tube  130 . In an exemplary embodiment, thick-film heating element  140 , as depicted in FIG. 9, includes an outer insulating layer  145  through which may be viewed, using materials according to a particular embodiment, such as glass, glazes, and some ceramic glazes, a heating element  146  which may be serpentined or otherwise patterned over the surface of a lower dielectric layer  147 , see FIG. 10. For example, to produce thick-film heating element  140  on surface  130 , a dielectric layer which may be a ceramic, or other materials, may be provided on surface  130  by any of a variety of processes including a variety of deposition processes including silk screening. Next, a patterned conductive and resistive layer  146  may be provided via silk screening or other deposition techniques overlying layer  147 . Finally, an insulating layer  145  which may be provided overlying and filling the areas of layer  149  not occupied by resistive areas  146  with any of a variety of insulating materials including glass. Accordingly, a ceramic encapsulated resistor is formed on the surface  130  having two conductive terminals  150  for providing electrical power thereto.  
         [0041]    Referring now to FIG. 11, another exemplary embodiment of a flow tube  200  is depicted. Flow tube apparatus  200  includes an inlet  210  and an outlet  220 . Flow tube apparatus  200  includes, in an exemplary embodiment, three flow tubes  230  in fluid communication with inlet  210  and outlet  220 . Each of flow tubes  230  has a film heater  240  disposed thereon as previously described. In alternative embodiments, flow tubes  230  may have any of a variety of cross sectional geometries, including, but not limited to, circular geometries. Further, flow tube apparatus  200  may include any of the number of flow tubes  230  including, but not limited to, three. An access port  250  is provided at the lower most portion of flow tubes  230  for providing access to the interior of flow tubes  230  and for providing drainage of flow tubes  230 .  
         [0042]    In an exemplary embodiment, film heating element  240  and  140  may be any of a variety of film heating elements, including thick-film heating elements comprised of a glass overcoat, a resistive glaze, and a dielectric substrate that is bonded to the tube material. In an exemplary embodiment, film heating elements  140  and  240  may be operating at voltages of 240 volts or greater including, 480 volts, as well as other operating voltages both above and below this range. For example, film heaters  140  and  240  may be configured to operate at lower voltages such as, but not limited to, 120 volts. Further, in operation, current is controlled through heating elements  140  and  240  by a control unit in order to provide the proper temperature to the fluid flowing the flow tubes. Further, in an exemplary embodiment, the film heating elements may have any of a variety of dimensions, some but not all being on the order of {fraction (1/32)}nd of an inch thick. Film heating elements  140  and  240  may be manufactured by IRC/TT Electronics of Boone, N.C., and Dekko Heating Technologies of North Webster, Ind., as well as other manufacturers.  
         [0043]    While the exemplary embodiments refer to a flow heater for a sink heater or a rethermalizing heater, the present invention may also be applied to other types of recirculating heating systems.  
         [0044]    Further, those who have skill in the art will recognize that the present invention is applicable with many different hardware configurations and processes.  
         [0045]    While the detailed drawings, specific examples, and particular formulations given describe exemplary embodiments, they serve the purpose of illustration only. The material and configurations shown and described may differ depending on the chosen performance characteristics and physical characteristics of the disclosed devices. For example, the type and capacity of the heating elements used may differ. The systems shown and described are not limited to the precise details and conditions disclosed. Furthermore, other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the preferred embodiments without departing from the spirit of the invention as expressed in the appended claims.