Abstract:
A conveyor oven in which a heated circulating air stream provides impingement air toward a conveyor, which is turned to flow horizontally along the conveyor toward an inlet and/or an outlet thereof. The conveyor oven includes a ductwork that provides a positive pressure airflow to form the impingement air as well as a positive pressure a second air flow that intersects with the horizontal air flow with a more positive pressure adjacent the inlet and/or outlet to redirect the horizontal airflow toward an air return plenum so as to substantially reduce the escape of heat to ambient.

Description:
RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/503,223, filed Sep. 16, 2003, the entire contents of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a conveyor oven and method that has an improved heat loss performance.  
       BACKGROUND OF THE INVENTION  
       [0003]     A conventional convection conveyor oven uses suction pressure to induce the hot air from within an oven chamber to upper and lower negatively pressurized plenums in fluid communication with hot air circulation fans. This method of air capture is only effective in capturing the air layers close to the surfaces of the return air plenums. Since the effective length of vacuum influence is short, air moving out horizontally near the middle of the conveyor opening is not captured and becomes lost heat via an inlet and/or an outlet of the oven chamber.  
         [0004]     There is a need for a conveyor oven with improved heat loss performance.  
       SUMMARY OF THE INVENTION  
       [0005]     A conveyor oven embodiment of the present invention comprises an oven chamber that includes an inlet and an outlet. A conveyor is disposed to transport food through the oven chamber. At least one blower is disposed to provide at least a first air stream to the oven chamber that traverses the oven chamber in a first path toward one of the inlet and outlet and a second air stream that redirects the first path of the first air stream so as to substantially prevent the first air stream from escaping to ambient via the at least one of the inlet and outlet.  
         [0006]     In another embodiment of the conveyor oven of the present invention, at least the first air stream is heated. The redirected path avoids a substantial loss of heat to ambient.  
         [0007]     In another embodiment of the conveyor oven of the present invention, the second air stream intersects the first air stream adjacent the at least one of the inlet and outlet.  
         [0008]     In another embodiment of the conveyor oven of the present invention, a pressure of the second air stream is more positive than a pressure of the first air stream at a point of intersection where the first path of the first air stream is redirected.  
         [0009]     In another embodiment of the conveyor oven of the present invention, the conveyor oven further comprises a heating chamber disposed adjacent the oven chamber and a ductwork in fluid communication with the at least one blower. The ductwork comprises an impingement plenum disposed to provide the first air stream toward the conveyor as columns of impingement air that turn into the first path along the conveyor.  
         [0010]     In another embodiment of the conveyor oven of the present invention, the ductwork further comprises a second plenum in fluid communication with the impingement plenum to provide the second air stream.  
         [0011]     In another embodiment of the conveyor oven of the present invention, the oven chamber comprises a tunnel oven chamber.  
         [0012]     In another embodiment of the conveyor oven of the present invention, the second air stream intersects the first air stream adjacent the at least one of the inlet and outlet.  
         [0013]     In another embodiment of the conveyor oven of the present invention, the conveyor oven further comprises a heating chamber disposed adjacent the oven chamber and a ductwork in fluid communication with the at least one blower. The ductwork comprises an impingement plenum disposed to provide the first air stream toward the conveyor as columns of impingement air that turn into the first path along the conveyor.  
         [0014]     In another embodiment of the conveyor oven of the present invention, the ductwork further comprises a second plenum in fluid communication with the impingement plenum to provide the second air stream.  
         [0015]     In another embodiment of the conveyor oven of the present invention, the ductwork comprises a plurality of impingement plenums disposed on either side of the conveyor. The second plenum is in fluid communication with one of the plurality of impingement plenums.  
         [0016]     In another embodiment of the conveyor oven of the present invention, the ductwork is shaped to provide the first air stream in the first path toward the inlet, a third air stream in the tunnel oven chamber along a third path toward the outlet, and a fourth air stream that redirects the third path of the third air stream so as to substantially reduce the third air stream from escaping to ambient via the other of the inlet and outlet.  
         [0017]     In another embodiment of the conveyor oven of the present invention, an additional blower is in fluid communication with the ductwork.  
         [0018]     In another embodiment of the conveyor oven of the present invention, the ductwork further comprises a plurality of impingement plenums disposed to provide the first and third air streams.  
         [0019]     In another embodiment of the conveyor oven of the present invention, the ductwork further comprises first and second plenums disposed in fluid communication with two of the impingement plenums to provide second and fourth air streams, respectively.  
         [0020]     In another embodiment of the conveyor oven of the present invention, the impingement plenums are disposed above and below the conveyor.  
         [0021]     In another embodiment of the conveyor oven of the present invention, the impingement plenums are disposed to provide first and second cooking regions within the tunnel oven chamber.  
         [0022]     In another embodiment of the conveyor oven of the present invention, at least the first air stream is heated. A substantial loss of heat to ambient is avoided by the redirected first path.  
         [0023]     In another embodiment of the conveyor oven of the present invention, the second air stream is also heated.  
         [0024]     In another embodiment of the conveyor oven of the present invention, the second air stream intersects the first air stream adjacent the at least one of the inlet and outlet.  
         [0025]     In another embodiment of the conveyor oven of the present invention, a pressure of the second air stream is more positive than a pressure of the first air stream at a point of intersection where the first path of the first air stream is redirected.  
         [0026]     In a method embodiment of the present invention, a first air stream and a second air stream are provided in an oven chamber of a conveyor oven The first air stream is directed in a first path that traverses the oven chamber toward at least one of an inlet and an outlet of the oven chamber. The first path of the first air stream is redirected with the second air stream so as to substantially prevent the first air stream from escaping to ambient via the at least one of the inlet and outlet.  
         [0027]     In another method embodiment of the present invention, the second air stream intersects the first air stream adjacent the at least one of the inlet and outlet.  
         [0028]     In another method embodiment of the present invention, the conveyor oven further comprises a conveyor that extends through the oven chamber via the inlet and the outlet and a ductwork that comprises an impingement plenum disposed to provide the first air stream toward the conveyor as columns of impingement air that turn into the first path.  
         [0029]     In another method embodiment of the present invention, the ductwork further comprises a second plenum in fluid communication with the impingement plenum to provide the second air stream.  
         [0030]     In another method embodiment of the present invention, the ductwork comprises a plurality of impingement plenums disposed on either side of the conveyor. The second plenum is in fluid communication with one of the plurality of impingement plenums.  
         [0031]     In another method embodiment of the present invention, at least the first air stream is heated, and wherein a substantial loss of heat to ambient is avoided by the redirected first path.  
         [0032]     In another method embodiment of the present invention, the second air stream is also heated.  
         [0033]     In another method embodiment of the present invention, the second air stream intersects the first air stream adjacent the at least one of the inlet and outlet.  
         [0034]     In another method embodiment of the present invention, a pressure of the second air stream is more positive than a pressure of the first air stream at a point of intersection where the first path of the first air stream is redirected. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]     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:  
         [0036]      FIG. 1  is a sectional view in elevation of a conveyor oven of the present invention;  
         [0037]      FIG. 2  is a sectional view taken along line  2 - 2  of  FIG. 1 ;  
         [0038]      FIG. 3  is a sectional view taken along line  3 - 3  of  FIG. 1 ; and  
         [0039]      FIG. 4  is a sectional view taken along line  4 - 4  of  FIG. 1 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0040]     Referring to  FIGS. 1-4 , a conveyor oven  10  includes a housing  12  that includes an oven chamber  22  and a heating chamber  24 . A divider  26  that is disposed in housing  12  separates oven chamber  22  from heating chamber  24 . Oven chamber  22  includes an inlet  14  at one end and an outlet  16  at the other end. A conveyor  18  is disposed within oven chamber  22  so as to extend through inlet  14  and outlet  16 .  
         [0041]     Conveyor  18  is driven by any suitable motive device and linkage to convey food through oven chamber  22  in a direction to enter via inlet  14  and exit via outlet  16 . Conveyor  22  preferably includes a perforate surface that allows an air stream to pass through. For example, conveyor  18  may suitably be of the type described in U.S. patent Publication No. US-2003-0056658-A1 dated Mar. 27, 2003, which is hereby incorporated in its entirety by reference.  
         [0042]     A heater  40 , a blower  42  and a blower  44  are disposed in heating chamber  24  to provide via a ductwork  46  a heated air stream that circulates between oven chamber  22  and heating chamber  24 . Heater  40  can be any suitable heater known to those skilled in the art for heating air streams in ovens. For example, heater  40  is shown as a gas heater in  FIGS. 3 and 4 . In alternate embodiments, heater  40  may be an electrical heater.  
         [0043]     Blowers  42  and  44  may be any suitable blower known to those skilled in the art for circulating air in an oven. For example, blower  42  is shown as a radial blower in  FIGS. 3 and 4 . In alternate embodiments, heater  42  may be an axial blower.  
         [0044]     Ductwork  46  includes divider  26 , an upper plenum  28 , an upper plenum  30 , a lower plenum  32 , a lower plenum  34 , a plenum  36  and a plenum  38 .  
         [0045]     Upper plenum  28  and lower plenum  32  are disposed in oven chamber  22  on opposite sides of conveyor  18  above and below one another. Upper plenum  28  and lower plenum  32  extend through divider  26  to be in fluid communication with blower  42 . Upper plenum  30  and lower plenum  34  are disposed in oven chamber  22  on opposite sides of conveyor  18  above and below one another. Upper plenum  30  and lower plenum  34  extend through divider  26  to be in fluid communication with blower  44 .  
         [0046]     Upper plenums  28  and  30  and lower plenums  32  and  34  each have a surface that faces conveyor  18  and that comprises a plurality of delivery openings to deliver air toward conveyor  18 . For example, upper plenum  28  is shown in  FIG. 3  to have a surface  48  with a plurality of openings  50  that face conveyor  18 . Preferably, openings  50  are shaped to provide columns  52  of impingement air. For example, openings  50  may include any of the openings described in the above mentioned U.S. patent Publication No. US-2003-0056658-A1.  
         [0047]     An upper central air return plenum  54  and a lower central air return plenum  56  are disposed between upper plenums  28  and  30  and lower plenums  32  and  34 , respectively. An upper inlet air return plenum  58  is disposed to the inlet side of upper plenum  28  and an upper outlet air return plenum  60  is disposed to the outlet side of upper plenum  30 . Upper inlet and outlet air return plenums  58  and  60  each include a surface that faces conveyor  18  and that has a port for a return flow of air. For example, upper outlet air return plenum  58  is shown in  FIG. 4  as including a surface  62  that has a port  64  with one or more openings  66  for return air flow.  
         [0048]     Blowers  42  and  44  are operable to provide an air stream that circulates between oven chamber  22  and heating chamber  24 . The circulating air flows from blower  42  under positive pressure through upper and lower plenums  28  and  32  and returns via upper inlet return plenum  58  and upper and lower central air return plenums  54  and  56 . The circulating air also flows from fan  44  under positive pressure through upper and lower plenums  30  and  34  and returns via upper outlet return plenum  60  and upper and lower central air return plenums  54  and  56 . The circulating return air is heated by heater  40  to a predetermined oven temperature. The impingement air provided by upper and lower plenums  28  and  32  merge above conveyor  18  and turn toward inlet  14  and upper and lower central return plenums  54  and  56 . The impingement air provided by upper and lower plenums  30  and  34  merge above conveyor  18  and turn toward outlet  16  and upper and lower central return plenums  54  and  56 .  
         [0049]     Ideally, all of the circulating air moving toward inlet  14  and outlet  16  would be sucked into upper return air plenums  58  and  60 , respectively. However, some of the heated air stream tries to escape via inlet  14  and outlet  16  toward the lower pressure ambient. Also, as the air streams traverse paths along conveyor  18  their pressure decreases as they approach inlet  14  or outlet  16 .  
         [0050]     In order to more efficiently capture the heated air trying to escape from inlet  14  and outlet  16 , a positively pressurized stream of oven temperature air is forced out of ports located adjacent inlet  14  and outlet  16 . These positively pressurized air streams intersect the air streams in the paths along conveyor  18  at an angle so as to redirect the airflow along conveyor  18  toward upper air return plenums  58  and  60 . Preferably the angle is about 90°.  
         [0051]     The positively pressurized stream of heated air is provided by lower plenums  36  and  38  disposed adjacent inlet  14  and outlet  16 . Lower plenums  36  and  38  are in fluid communication with lower plenums  32  and  34 , respectively. For example, lower plenums  36  may be extensions of lower plenums  32  and  34 , respectively. In one alternate embodiment, lower plenums  36  and  38  could have fluid communication with respective lower plenums  32  and  34  via connecting ports. In another alternate embodiment, lower plenums  36  and  38  could be separate from lower impingement plenums  32  and  34  could be supplied with positively pressurized air from blowers  42  and  44  or from one or more additional blowers.  
         [0052]     The pressure of the air streams provided by lower plenums  36  and  38  at the points of intersection is more positive than the pressures of the air streams traversing the paths along conveyor  18  toward inlet  14  and outlet  16 . This enhances the ability to redirect the paths toward upper return plenums  58  and  60 .  
         [0053]     Preferably, plenums  36  and  38  are substantially identical so only plenum  36  will be described in detail. Plenum  36  includes a surface  70  with a port  72  through which a portion of the positively pressurized circulating air stream passes upwardly through conveyor  18  to intersect with and redirect the airflow along conveyor  18  from the horizontal to the vertical so as to enter upper inlet return plenum  58 . This forces the hot oven air up closer to openings  66  of upper inlet air return plenum  58  where the vacuum pressure zone is able to capture the escaping hot oven air more efficiently. That is, the redirection of heat substantially reduces heat from escaping to ambient via inlet  14 . The vertical positive pressured hot air stream also serves as a pre and post bottom heat boost to the food product being conveyed over the port. This improves bottom heat transfer and thereby increases cooking speed. Similarly, plenum  38  provides a positively pressurized circulating air stream that passes upwardly through conveyor  18  to intersect with and redirect the airflow along conveyor  18  from the horizontal to a more vertical direction so as to enter upper outlet return plenum  60 .  
         [0054]     Port  72  includes at least one opening  74  that may have any suitable shape. For example, opening  74  may suitably be a slot. Alternately, port  72  may include a plurality of openings  74 .  
         [0055]     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.