Abstract:
An apparatus provides pulsed impingement jets to a sub-chamber within an impingement hood of a freezer, and includes a blower having an inlet and an outlet at an interior of the freezer; a duct having a first end in fluid communication with the outlet and a second end opening into the sub-chamber; and a flow valve disposed in the duct proximate the second end opening, the flow valve movable in repetitive open and closed positions for providing repetitive, discrete pulses of the impingement jets from the second end opening of the duct into the sub-chamber.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present embodiments relate to apparatus and methods to provide pulsed impingement jets in food freezers. 
         [0002]    A production capacity or throughput of a cryogenic food freezing tunnel is limited due to its overall heat transfer coefficient. The majority of known food freezing tunnels increase heat transfer by increasing air flow velocities over the products to be chilled or frozen. There are, however, practical and economic limitations to these known methods of increasing heat transfer. Accordingly, the food processing industry seeks efficient and cost-effective methods for increasing the overall heat transfer of a freezing process. This is because an increase in overall heat transfer allows for smaller freezer systems to be fabricated or for increased production rates through existing systems. 
         [0003]    An area of opportunity for increasing the overall heat transfer of a freezing process is with the employment of pulsed flow impingement jets. Unfortunately, while lab scale testing has proven the effectiveness of pulse flow impingement, no practical method for pulsing the jets in a full scale impingement freezing tunnel has been developed. 
       SUMMARY OF THE INVENTION 
       [0004]    There is therefore provided an apparatus for providing pulsed impingement jets to a sub-chamber within an impingement hood of a freezer for a food product, which includes a blower having an inlet and an outlet at an interior of the freezer; a duct having a first end in fluid communication with the outlet and a second end opening into the sub-chamber; and a flow valve disposed in the duct proximate the second end opening, the flow valve movable in repetitive open and closed positions for providing repetitive, discrete pulses of the impingement jets from the second end opening of the duct into the sub-chamber. 
         [0005]    There is therefore provided the apparatus above, further including a shroud mounted at the interior of the freezer for protecting the blower. 
         [0006]    The apparatus may include the blower inlet and the blower outlet being positioned external of the impingement hood. 
         [0007]    The apparatus may also include at least one nozzle opening at an interior of the freezer for providing a cryogenic substance to said interior. 
         [0008]    The apparatus may further include at least one nozzle opening at the sub-chamber. 
         [0009]    Additional features of the present embodiments are described below and set forth in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    For a more complete understanding of the present invention, reference may be had to the following description of exemplary embodiments considered in connection with the accompanying drawing Figures, of which: 
           [0011]      FIG. 1  shows a side view in cross-section of a food freezer having mounted thereto a pulsed impingement jet apparatus according to the present embodiments; and 
           [0012]      FIG. 2  shows the pulsed impingement jet apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Before explaining the inventive embodiments in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, if any, since the invention is capable of other embodiments and being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. 
         [0014]    In the following description, terms such as a horizontal, upright, vertical, above, below, beneath and the like, are to be used solely for the purpose of clarity illustrating the invention and should not be taken as words of limitation. The drawings are for the purpose of illustrating the invention and are not intended to be to scale. 
         [0015]    In order to produce effective impingement pulses for use in the food freezers, for example, a pulse must be generated as close as possible to the heat transfer surface (impingement plate of the freezer). It is also much more practical to generate pulses within enclosed volumes. As the volume of the cavity increases around the heat transfer surface, there is created a dampening effect which minimizes the degree of pulsation which can be achieved. Therefore, an enclosed restricted volume is necessary to generate an effective pulse. 
         [0016]    The embodiments described provide discrete impingement hoods for generating the pulsed impingement jets. The smaller volume of the hood is a much more suitable environment for generating pulses. The pressure inside the hood for generation of an impingement jet is 2-3 inches of water column. A centrifugal blower is used to generate the gas flow necessary for building pressure in the hood to create the impingement gas flow jets. 
         [0017]    In the present embodiments, a secondary high pressure blower is added to coact with the impingement hood. The secondary pressure blower is capable of generating high flows at high static pressures (18-20 inches of water column). Gas from the freezer tunnel feeds the secondary pressure blower and an internal duct connects a discharge of the pressure blower to feed the impingement hood. A damper-type valve is incorporated into the duct from the pressure blower. The damper has a cross-sectional shape and area which does not contact an inner surface of the duct, but instead passes in close proximity thereto and can restrict the majority of flow from the secondary pressure blower. 
         [0018]    Referring to  FIGS. 1 and 2 , a pulsed impingement jet apparatus embodiment is shown generally at  10  mounted for operation in a freezer  12  such as for example a tunnel freezer. The freezer  12  includes sidewalls  14  for forming a housing  15  having a top  16  and a bottom  18 , which also define an internal space  20  through which a conveyor belt  22  will transit. The conveyor belt  22  transports products  24  such as for example food products through the internal space for chilling and/or freezing. The internal space  20  contains a processing atmosphere  26 . 
         [0019]    An impingement hood  28  is mounted in the internal space  20 , the impingement hood having an upper opening  30  and a lower opening  32 . The impingement hood  28  defines a sub-chamber  34  in which a main blower  36  is disposed for operation. The main blower  36  is operated by a motor  38  mounted to an exterior of the housing  15  by a shaft  40  that extends through the internal space  20  to the motor. 
         [0020]    An impingement plate  42  is mounted at the lower opening  32  of the impingement hood  28  above the conveyor belt  22 , which passes below. The impingement plate  42  is provided with the plurality of impingement holes  44  which are in registration with the underlying conveyor belt  22 . 
         [0021]    A chilling substance (eg, cryogen), and such as for example nitrogen, carbon dioxide, either of which can be in liquid or gaseous state, or cold air or other cold gas, is introduced into the processing atmosphere  26  of the internal space  20  by known apparatus and methods. For example, the cryogen may be injected into the internal space  20  through nozzles  27  connected to pipes (not shown) from a remotely located bulk storage tank (not shown). The nozzles  27  can be positioned at various locations of the internal space  20  as shown, or mounted to a spray bar (not shown) extending into the internal space. Regardless of the cryogen delivery system used, such system should be able to reliably and uniformly disperse the cryogen throughout the internal chamber  20 . 
         [0022]    The main blower  36  circulates the processing atmosphere  26  as shown by the arrows  46  representing the circulatory flow. The circulatory flow  46  of the chilled processing atmosphere  26  is drawn from the internal space  20  through the upper opening  30  and into the sub-chamber  34  for distribution through the impingement holes  44  and onto the products  24  being transported on the conveyor belt  22  through the internal space. Heat transfer and the related chilling or freezing of the products  24  therefore occurs. 
         [0023]    As shown with more particularity in  FIG. 2 , the apparatus  10  includes a pressure blower  50  disposed in the internal space  20  proximate the top  16  of the housing. Another motor  52  to drive the pressure blower  50  is mounted external to the housing  15  and connected by a shaft  54  extending through the top  16  into the internal space  20  to drive the blower  50 . 
         [0024]    A shroud  56  is mounted to the top  16  at the internal space  20  to protect the pressure blower  50 ′which is disposed within the confines of the shroud as shown in  FIG. 2 . A lower or lid portion of the shroud  56  shown generally at  58  is mechanically hinged at  60  so that the lid can be deployed to an open position to provide access to clean the blower  50  and an internal surface area of the shroud, and then closed. The shroud  56  is provided with an intake opening  62  through which a flow  64  is drawn from the processing atmosphere  26  of the internal space  20  into the shroud by the pressure blower  50 , and to thereafter be exhausted through a shroud outlet  66  into a distribution pipe  68  or duct in fluid communication with the outlet. The distribution pipe  68  extends to an exhaust opening  70  in fluid communication with the sub-chamber  34  of the impingement hood  28 . 
         [0025]    Disposed proximate the exhaust opening  70  is mounted a flow valve  72  controlled by an actuator  74  connected to the valve and mounted external to the distribution pipe  68 . The flow valve  72  by way of example includes a rotatable shaft  76  connected to the actuator  74 . At least one and in another embodiment a plurality of vanes  78  are attached to the shaft  76 , each one of the vanes having a diameter sufficient to span an internal diameter of the distribution pipe  68  but not contact or be inhibited by an internal surface of the distribution pipe so that the vanes are free to rotate with the shaft  76  to which the vanes are attached. The actuator  74  is connected by wires  80  to a controller (not shown) which can be disposed at a remote location. 
         [0026]    The distribution pipe  68  includes a cleaning port  82  accessed by a cover  84  which can be mechanically hinged or releasably engaged to the distribution pipe by known connections. The cleaning port  82  permits access to an interior of the distribution pipe  68  for cleaning thereof, and to remove any frozen condensate or other material lodged within the distribution pipe. 
         [0027]    In operation and referring to  FIGS. 1-2 , the main blower  36  continuously circulates a flow of  46  of cryogen gas within the internal space  20  and sub-chamber  34 . The gas flow is at atmospheric pressure within the space  20  and is drawn into the upper opening  30  and the main blower  36 , where it is pressurized up to 2-3 inches of water column in the sub-chamber  34 . The impingement plate(s)  42  set with a 5-10% open area provide sufficient back pressure to create high pressure within the sub-chamber  34 . As a result, high velocity (eg, 20 m/s) cryogen gas jets  48  or impingement jets are created and discharged through impingement holes  44  during a steady state operation condition, wherein there is a continuous uniform jet flow through the impingement holes. 
         [0028]    When pulsed impingement jets  86  are required, the pressure blower  52  is started and lower pressure gas from the internal space  20  is drawn into the blower  50  and pressurized up to 20 inches of water column within duct  68  when valve  72  is closed. Upon opening of the valve  72 , pressure in the duct  68  is released into the internal space  34 , thereby increasing the pressure in the internal space  34  for a total of 4-6 inches of water column. During this change in pressure, impingement jet velocities are increased from 20 m/s to 40 m/s. As a result, increased turbulence is created near the surface of the product  24 . The valve  72  is only open for a short duration of from 0.5-1 second and then it is closed again, thereby decreasing pressure in the sub-chamber  34 , and reducing impingement jet velocities to 20 m/s. Pressure in the duct  68  is increased again to 20 inches of water column. The process continues repeating in this manner with valve  72  opening and dosing the vane(s)  78  at a rate of 30-60 times per minute. Continuous pulsing impingement jets result, with increased turbulence and overall convective heat transfer coefficients at the product  24 . 
         [0029]    During operation, as the system is running, the “damper” valve continuously rotates providing nearly full flow to no flow from the pressure blower into the impingement hood. The rotational speed of the “damper” results in pressure pulses from the pressure blower entering the impingement hood. Depending on the volume of gas supplied from the pressure blower and the frequency of pulse the pressure in the impingement hood could double or triple and oscillate in this fashion. The impingement jet velocities would also oscillate, thereby creating increased turbulence and higher heat transfer coefficients on the surface of the food product. 
         [0030]    The impingement jets can include nitrogen, carbon dioxide, cold air or any other cold gas suitable for use with food products. 
         [0031]    It will be understood that the embodiments described herein are merely exemplary, and that a person skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described above and defined the appended claims. It should be understood that the embodiments described above are not only in the alternative, but can be combined.