Abstract:
A heat transfer support surface for heating or cooling food articles placed adjacent the support surface by circulating a heat transfer fluid in the internal passages of the support surface is disclosed. Circulated fluid is heated or cooled by a source. Support surface contains multiple heat transfer elements arranged substantially in parallel and interconnected on both ends. Flow control tubes control the fluid flow and reduce the amount of fluid required. The method of making the support surface is also disclosed.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a heat transfer support surface that uses a circulated heat transfer fluid for heating or cooling food articles placed adjacent the surface. The support surface would be applicable to food cooking or holding cabinets such as in U.S. Pat. No. 4,210,675 to Lieberman et al. incorporated by reference as well as other types of fixtures for heating or cooling food, adapted for use with the present invention. 
   BACKGROUND OF THE INVENTION 
   Heat transfer support surfaces with multiple heat transfer elements in parallel that use orifices to control the fluid flow are disclosed in U.S. Pat. No.&#39;s 5,086,693, 5,960,869, and 6,263,963 to Tippmann et al, all incorporated by reference. 
   In general, the support surface includes multiple heat transfer elements positioned in parallel. Each heat transfer element contains at least one passageway for transferring heat to or from the fluid circulating therein. Headers are used to interconnect the fluid flow at both ends of the heat transfer elements. 
   In order for the support surface to transfer the amount of heat required, the fluid contact surface area of the internal passages needs to be of adequate size. Also, the internal passages should be round in shape to accept the tubular elements that interconnect the heat transfer elements to the headers at both ends. When the internal surface area of the round internal passages increases, the volume of fluid also increases and the velocity of the fluid flow decreases, this increases the laminar flow of the heat transfer fluid. The laminar flow reduces heat transfer and contributes to an uneven surface temperature. This uneven surface temperature is undesirable. 
   SUMARRY 
   The present invention utilizes a flow control tube inserted into the internal passages of the heat transfer elements, that reduces the volume of the internal area of said passages while maintaining the same internal fluid contact surface area. The fluid flow dynamics are altered by increasing the fluid velocity near the internal surfaces of said passages that improves heat transfer of the heat transfer elements and contributes to a more even surface temperature of the support surface. Another benefit of the reduced volume is that the amount of heat transfer fluid required is reduced and less heat up or cool down time is required for the support surface. Also, a smaller fluid expansion tank on the interconnected system would be required. Another benefit of the reduced area is that it creates a fluid flow restriction, which eliminates the need for an orifice to balance the fluid flow between the heat transfer elements. Such orifices plug up easily with solids and render the heating element inoperable, which can cause an unsafe condition for the food items being heated or cooled if undetected. 
   Another object of the present invention is to provide a filtering area at the inlet of each support element to reduce the chance of the heat transfer elements plugging with solids. A filtering area is placed near the fluid inlet end of the heat transfer elements. Solids could collect in this area without plugging the heat transfer elements. Additionally, a filtering device could be placed in the filtering area. 
   The direction of the majority of the heat transfer of the present invention is upwards to the food items placed adjacent the top surface. It is another object of the present invention to direct a larger amount of the fluid flow to the upper portions of the support surface. 
   Another object of the present invention is to provide a way of positioning the flow control tube inside the heat transfer elements by forming the ends of the flow control tubes. 
   It is therefore the object of the present invention to provide a support surface for transferring heat to or from food articles. 
   It is another object of the present invention to provide a method of making the subject support surface. This, as well as other objects and advantageous features of the present invention will be come apparent and be pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a perspective view of a heat transfer support surface assembly; 
       FIG. 2  illustrates a top plan view showing the internal passages; 
       FIG. 3  illustrates an exploded perspective view of internal components of one of the heat transfer elements; 
       FIG. 4  illustrates an end view of one of the heat transfer elements; 
       FIG. 5  illustrates a cross-sectional view of the fluid control tubes; 
       FIG. 6  illustrates another cross-sectional view of the fluid control tubes; 
       FIG. 7  illustrates a top view of the heat transfer elements and support surface; 
       FIG. 8  illustrates a cross sectional view of the heat transfer elements and support surface; 
       FIG. 9  illustrates a cross sectional detail of the heat transfer elements and support surface; 
       FIG. 10  illustrates an additional cross sectional detail of the heat transfer element and support surface; 
       FIG. 11  illustrates a further cross sectional detail of the heat transfer element; 
       FIG. 12  illustrates an exploded view of the heat transfer elements with a header; 
       FIG. 13  illustrates a top view detail of the heat transfer elements with the header; 
       FIG. 14  illustrates an exploded view of the heat transfer elements with a header; 
       FIG. 15  illustrates a top view detail of the heat transfer elements with the header. 
   

   DETAILED DESCRIPTION 
   Referring now to  FIG. 1 , a perspective view of a heat transfer support surface assembly is shown in which several heat transfer elements  20  are arranged substantially in parallel. Heat transfer elements  20  could typically be made from an aluminum extrusion. Heat transfer elements  20  are interconnected on one end by a fluid supply header  2  and on the other end by a fluid return header  6 . In the preferred embodiments, headers  2  and  6  could be typically be made from an aluminum extrusion also. A heated or cooled fluid enters at either opening  10  on supply header  2  and exits at either opening  14  on return header  6 . The support surface top, which is shown as substantially flat but other shapes could be employed, is indicated by numeral  21  throughout several views. The support surface top  21  is where food articles would typically be placed, usually in pans. 
   Moving now to  FIG. 2 , a top plan view of the fluid flow of the present invention is shown wherein the internal passages are shown in dashed lines. For simplicity, numeral  5  and  18  identify passages in only one heat transfer element  20  connection, but exist in all. Fluid enters header  2  at either port  10  and travels through passage  4  and entering passages  18  of heat transfer elements  20  via apertures  5  of header  2 . Fluid exits heat transfer elements  20  and enters passage  8  via apertures  5  of return header  6 . Finally, the fluid exits at either port  14  of return header  6 . The flow pattern between the heat transfer elements would be parallel and in the same direction. Alternatively, by placing strategically located stops (not shown) in passages  4  and or  8 , the fluid flow can be converted to a serpentine flow pattern between the heat transfer elements. 
   In one embodiment of the present invention,  FIG. 3  shows an exploded perspective view of internal components of one of the heat transfer elements  20 . Outer tubular elements  22  are placed in the openings  23  of the heat transfer element  20  in a good heat transfer relationship therewith by any known means such as mechanically expanding the tube, temperature difference, or merely a tight fit. In order to facilitate connecting to headers  2  and  6 , a small portion of tubes  22  extends beyond ends of heat transfer elements  20  as can be seen in  FIG. 7 . Alternatively, the extending portion of tube elements  22  can be interconnected by means other than the described headers  2  and  6 , such as by using tube fittings or rubber hoses with clamps. Flow control tubes or rods  26 , which will be explained in detail, are placed inside tubular elements  22 . 
   Controlling the fluid flow in one embodiment of the present invention can be explained from  FIGS. 5 and 6 , while the basic principle of controlling the flow exists in all the embodiments. Looking at  FIG. 5 , after the fluid enters tube  22  at area  30 , it is constricted down to area  32 . This forces all the fluid into high velocity contact with the internal surfaces of tube  22 , thereby enhancing the heat transfer and evenness of surface  21  temperatures. Furthermore, the restriction created by flow control tubes  26  has an effect of balancing the flow between passages  18  of  FIG. 2 . The lower velocity area  30  can also be used as a filtering area, where solid particles can settle before they plug the constricted area  32 . Shortening tube  26  can enlarge the filtering area  30  if more filtering area is desired. A filtering device, preferably a wire mesh strainer (not shown), could also be inserted in the fluid inlet filtering area  30 . 
   A way of positioning the flow control tubes  26  inside tubes  22  can be seen in  FIGS. 5 and 6 . Compressing the ends of flow control tubes  26  in a die can form the ends into a desired shape. The formed ends  28  of flow control tubes  26  are shown in a top and side view in  FIGS. 5 and 6  respectively. Lateral movement of tube  26  is constrained by formed ends  24  of tube  22  meeting formed ends  28  of tube  26  at point  29  as shown in  FIG. 6 . In one embodiment of the present invention, as shown in  FIG. 6 , the flow control tube  26  is centered vertically inside tube  22  by formed end  28  contacting the inside surface of tube  22 . The formed ends  28  of flow control tubes  26 , also prevents fluid flow from entering the inside areas  34  of flow control tubes  26 . Sealing the ends of tube  26 , after being formed, can also prevent fluid from residing inside, thereby decreasing the amount of fluid required in the system. 
   Moving now to  FIG. 10 , which is a detail view B of  FIG. 8 , a way of positioning the flow control tube  26  off center can be seen. By forming flow control tube end  28  off center, the flow control tube  26  is positioned toward the bottom of the opening. When heat transfer fluid enters fluid area  32   a , more fluid flow is forced towards the top of the opening. In the heat transfer support surface of the present invention it is desirable to have most of the heat transfer directed towards the top surface  21  where food articles are placed. The downward heat transfer to the lower area  35  is of less value. By positioning flow control tube  26  near the bottom, a greater amount of fluid is forced towards the upper portions of tube  22 , thereby enhancing heat transfer and temperature evenness of the top surface  21 . 
   As can be best shown by  FIGS. 7 ,  9 ,  12 , and  13 , a method and apparatus of shelf assembly is illustrated. Inner tubular elements  22  extend continuously through heat transfer element  20 , with a small portion extending beyond as shown in  FIG. 7 and 12 . The sealed connection to headers  2  and  6  is made by first inserting for example Teflon washers  40  in apertures  5  of headers  2  and  6 , to prevent possible galvanic corrosion between the ends of tube  22  and the header material. Next, Teflon sleeve type seals  42  are used to make the seal between the ends of tubes  22  and apertures  5  as shown in  FIG. 13 . The Teflon sleeve  42  could also be replaced with an O-ring type seal in a known manner. As can be best shown in  FIG. 9 , the heat transfer fluid in area  32  must first transfer heat to fluid contact surface  31  of tube  22 , before it can be transferred to surface  33  of heat transfer element  20 . 
   In another embodiment of the present invention, as can be best shown by  FIGS. 11 ,  14 , and  15 , the inner tubular elements  22  are replaced by short tubular nipples  44 , inserted into apertures  5  and  5   a  of headers  2  and  6  and heat transfer elements  20  respectively. Teflon washers  40  and sleeve inserts  42  perform the same function as described previously. As can be best shown by  FIG. 11 , the heat transfer fluid in area  32  can now transfer heat directly to heat transfer element  20  by direct contact with inner surface  33  of heat transfer element  20 , which can increase the heat transfer rate. Alternatively, the short tubular nipples  44  can be connected to either apertures  5  or  5   a  by other ways than described, such as by threading or gluing together to eliminate some of the seals  42  on each end of heat transfer element  20 . Furthermore, the fluid contact surface area  33  becomes greater when continuous tubular element  22  is not used if the size of opening  23  in heat transfer element  20  ( FIG. 3 ) stays the same. This can also increase the heat transfer rate. Flow control tube  26   a  would need to be enlarged to compensate for the larger area of the passageway when tubular element  22  is eliminated. 
   From the foregoing, it is now apparent that a heat transfer support surface has been disclosed, obtaining the objects and advantageous features set out hereinbefore as well as others, and that numerous modifications as the precise shapes, configurations, and details made by those having ordinary skill in the art without departing from the spirit of the invention or the scope thereof as set out by the claims that follow.