Abstract:
An apparatus for providing a liquid-gas entrained cryogen mixture onto a food product includes a first pipe through which is provided a flow of liquid cryogen; a second pipe through which is provided a flow of gaseous cryogen, the second pipe in fluid communication with the first pipe at a mixing region; and a pulsing valve disposed at an interior of the second pipe upstream of the mixing region, the pulsing valve adapted for releasing the gaseous cryogen into the liquid cryogen at select intervals of time to provide a pulsating flow of the liquid-gas entrained cryogen mixture downstream of the mixing region for contacting the food product. A related method is also provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present embodiments relate to food freezer tunnel apparatus for cryogenically chilling for example food products, and related processes therefore. 
         [0002]    Food freezing tunnels, such as for example those that use cryogenic substances to chill and/or freeze food products, are limited in their capacity by the overall heat transfer co-efficient that they can use on the products. For example, many food freezing tunnels rely upon increasing heat transfer effect by correspondingly increasing air flow velocity across the product for which the heat transfer is to be applied. There are, unfortunately, practical and economic limitations in many of these apparatus and methods and therefore, the increased heat transfer effect is not fully realized, especially with large scale industrial operations. The food processing industry would benefit from increased heat transfer effect with food freezing applications, because greater heat transfer effect results in being able to use smaller apparatus or conversely, using apparatus which can increase the production or flow through rate of products to be chilled or frozen. 
         [0003]    Some improvements have found their way into food freezing tunnels. For example spray nozzles are now used to increase the overall heat transfer effecting during the freezing process by spraying liquid nitrogen (N 2 ) through the nozzles directly onto the surface of the food product to contact same with droplets of the cryogenic substance. These small nitrogen droplets contact the warm food product and evaporate quickly, thereby removing or transferring heat immediately from the surface of the food product to chill and further freeze same. 
         [0004]    Other apparatus and systems use high pressure liquid nitrogen to provide heat transfer at the surface of the food product. However, this is an expensive process and can result in an unusually large amount of the nitrogen product which must therefore be lost to waste or alternatively additional equipment provided to recycle the nitrogen. In both instances, increased costs and a larger footprint of the food freezing tunnel is necessary, thereby making this type of application less desirable. 
       SUMMARY OF THE INVENTION 
       [0005]    There is provided herein a pulsed heat transfer effect apparatus and method for products, such as for example food products, wherein a high pressure nitrogen gas is pulsed into a liquid nitrogen flow stream, which stream thereafter is sprayed from nozzles thereby increasing turbulence on a surface of a food product to facilitate and promote increased heat transfer effect at the food product. The combination of the nitrogen gas, liquid nitrogen, and pulsing of same, results in extremely small nitrogen droplets which evaporate more quickly and therefore result in a higher evaporative surface cooling (heat transfer effect) at the surface of the food product. In addition, the pulsed spray results in increasing turbulence of the cryogenic substance on the surface of the product which accordingly promotes increased heat transfer, i.e. heat removal from the product. Carbon dioxide may be used instead of nitrogen. 
         [0006]    There is therefore provided an apparatus embodiment for providing a liquid-gas entrained cryogen mixture onto a food product which includes a first pipe through which is provided a flow of liquid cryogen; a second pipe through which is provided a flow of gaseous cryogen, the second pipe in fluid communication with the first pipe at a mixing region; and a pulsing valve disposed at an interior of the second pipe upstream of the mixing region, the pulsing valve adapted for releasing the gaseous cryogen into the liquid cryogen at select intervals of time to provide a pulsating flow of the liquid-gas entrained cryogen mixture downstream of the mixing region for contacting the food product. 
         [0007]    Another apparatus embodiment calls for the pulsing valve including an axle spanning an internal diameter of the second pipe and rotatably mounted therein; a planar member mounted to the axle and having a surface area substantially similar to a cross-sectional diameter of the second pipe; and a motor operatively connected to the axle for rotation of said axle and the planar member mounted thereto. 
         [0008]    Various valves and backflow preventers are used to control and restrict flow of the cryogen liquid and gas. 
         [0009]    There is also provided a method embodiment of providing a flow of a liquid-gas entrained cryogen mixture onto a food product which includes providing a first flow of liquid cryogen to the food product; providing a second flow of a gaseous cryogen to contact the first flow at a mixing region of the first and second flows; and repetitively interrupting the second flow upstream of the mixing region to provide a pulsating flow of the gaseous cryogen into the liquid cryogen for providing a pulsating flow of a liquid-gas entrained cryogen mixture to the food product. 
         [0010]    The liquid and gaseous cryogen may be selected from nitrogen (N 2 ) and carbon dioxide (CO 2 ). 
         [0011]    Other features of the present embodiments are described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0012]    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 FIGURE, which FIGURE shows a pulsed liquid-gas entrained cryogen flow generator apparatus to be used with for example food products. 
       
    
    
     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]    Referring to the FIGURE, an apparatus is shown generally at 10 for pulsing liquid nitrogen droplets from nozzles onto a food product or products being conveyed for providing increased heat transfer effect at the food product to chill and/or freeze same. In certain applications, carbon dioxide (CO 2 ) can be used instead of nitrogen (N 2 ). By way of example only, nitrogen (in liquid and gaseous phase) will be referred to herein when describing the present embodiments. 
         [0015]    The present embodiments provide for the mixing of gaseous nitrogen and liquid nitrogen to produce an arrangement of pulsing spray jets of the nitrogen to provide a high heat transfer effect at food products being conveyed or transported in close proximity to the spray nozzles. The gaseous nitrogen may be provided at 200 psig, while the liquid nitrogen (LIN) can be provided at 30 psig. 
         [0016]    For purposes herein, the nitrogen droplets emitted from the nozzles have a diameter of approximately 20 to 100 μm. 
         [0017]    Referring to the FIGURE, the apparatus  10  of the present embodiments and related method embodiments can be used in conjunction with or retrofitted to a food freezing tunnel such as that shown generally at  12 . The tunnel  12  has an interior space  14  or chamber for chilling and freezing, and through which product  16 , such as for example food products, are transported on a conveyor belt  18 . The conveyor belt  18  transits the space  14  in a direction represented by arrow  20 , by way of example only. The tunnel  12  is also provided with an inlet (not shown) and an outlet (not shown) in communication with the space  14  for introducing the food product  16  on the conveyor belt  18  through the space. The food freezing tunnel  12  can be disposed for operation in many different types of food processing plants and facilities. The tunnel  12  includes a housing having a sidewall  22  which defines the space  14 . At a region of the sidewall  22 , usually at an upper area of the sidewall, there is provided an aperture  24  or port therein. 
         [0018]    Referring more specifically to the apparatus  10  of the present embodiments, said apparatus includes a pipe  26  having an upper end with an opening  28  into which can be introduced by gravity or otherwise liquid nitrogen (LIN)  30 . The pipe  26  extends through the aperture  24  in the sidewall  22  of the freezing tunnel  12  and terminates in another opening  32  in the space  14 . At the opening  32  of the pipe  26 , said opening splits into a “T” for branches  34 , 36  which are in fluid communication with an internal space  38  of the pipe  26 . Each one of the branches  34 , 36  has at least one corresponding nozzle  40  or nozzle  42 , respectively. The nozzles  40 , 42  are also disposed in the space  14 , each nozzle having a respective opening  44 , 46  in close proximity to the conveyor belt  18  and food product  16  being transported thereon. 
         [0019]    The LIN pipe  26  has disposed within the internal space  38  a back flow preventer  48  and, further downstream in the pipe  26 , a control valve  50 . Accordingly, the LIN  30  introduced through the opening  28  into the pipe  26  travels through the internal space  38  where its flow rate is controlled by the control valve  50 , while the backflow preventer  48  prevents the LIN, regardless of pressure in the internal space or the chamber  14 , from being exhausted or regurgitated upstream and back through the opening  28  and into the plant or other processing facility. 
         [0020]    The LIN flow  30  being introduced into the pipe  26  flows continuously through the internal space  38  as indicated generally at  52 , until such time as the LIN flow comes in contact with gaseous nitrogen, as will be explained below. 
         [0021]    The apparatus  10  includes another pipe  60  having an opening  62  into which gaseous nitrogen  64  can be introduced into an internal space  66  of the pipe. The pipe  60  extends to have another opening  68 . The pipe  60  is constructed to join in fluid communication with the internal space  38  of the pipe  26 . The region where the opening  68  of the pipe  60  is in fluid communication with the internal space  38  of the pipe  26  is shown generally at  70 . A flow of the gaseous nitrogen is shown generally by arrows  72 . 
         [0022]    Disposed in the internal space  66  of the pipeline  60  is a modulating valve  74  and an on/off valve  76 . As is shown in the FIGURE, the modulating valve  74  is disposed upstream of the on/off valve  76  in the internal space  66 . 
         [0023]    Downstream in the internal space  66  from the on/off valve  76  and upstream of the opening  68  there is disposed a pulsing valve  78 . The pulsing valve  78  is disposed slightly upstream from the opening  68  and the region  70 , just before the gaseous nitrogen  64  is introduced into the LIN flow  52  travelling through the pipe  26 . The pulsing valve  78  includes a planar member  79 , such as for example a circular disc, mounted to an axle  81  or spindle which is connected to a motor  82  or other power source to rotate the axle. The disc has a diameter slightly less than a diameter of the internal space  66 , and a circumference slightly less than a cross-sectional circumference of the internal space  66  so that the disc can freely rotate therein. The pulsing valve  78  operates by rotating the flat circular disk in the pipe  60  at a selected speed to provide the pulse rate of gas flow  72  into the LIN flow stream  52 . That is, a higher rotational speed of the disk will result in a higher pulse rate, while a lower rotational speed of the disk will result in a lower pulse rate. 
         [0024]    The modulating valve  74  is used to control the flow of the gaseous nitrogen  64 , while the on/off valve  76  is used to shut off the flow completely or allow same to pass. 
         [0025]    The region  70  where the pipelines  26  and  60  are in fluid communication is shown as a “Y” junction for the gaseous nitrogen to be “pulsed” into the LIN flow  52 . The region  70  could alternatively be constructed as a “T” junction. 
         [0026]    The operation of the apparatus  10  will now be described. The LIN control valve  50  is opened to permit liquid nitrogen to begin flowing along the internal space  38  of the pipe  26  in a direction to the food freezing tunnel  12 . The LIN flow  52  flows into the spray manifold which consists of the branches  34 , 36  in fluid communication with the pipe  26  and thereafter through the nozzles  40 , 42 , whereupon the LIN is deposited onto the food product  16  being transported on the conveyor belt  18  through the space  14 . 
         [0027]    After the LIN flow  52  is established, a pulsed atomized flow of gaseous nitrogen is produced by actuating the pulsing valve  78 , after which the modulating valve  74  and the on/off valve  76  are also opened. High pressure gaseous nitrogen  64  at a pressure higher than the LIN flow  52  travels down the pipeline  60  and into the LIN flow  52 . The pulsing valve  78  opens and closes at a fixed or variable rate. When the pulsing valve  78  is closed, a minimal gas flow into the LIN flow  52  occurs. However, when the pulsing valve  78  is opened, the gaseous nitrogen  64  flows into and contacts the LIN flow  52  at the region  70 . The rate of rotation of pulsing valve  78  determines the frequency of liquid/gas pulsing  80  to be sent from the nozzle openings  44 ,  46  to the underlying food product  16 . The pulsing valve  78  is a butterfly valve which is constructed for this application to attain high speed, continuous rotation. An actuator or motor for the valve  78  can be speed controlled, and also stopped for the valve to be in either open or closed positions with respect to the internal space  66 . 
         [0028]    The apparatus  10  also provides for maintaining the pulsing valve  78  in an open or closed position or “unbalanced durations” in order to vary a degree of liquid or gas pulse composition to be used for the particular application. It is also possible to use the modulating valve  74  and control valve  50  to control the gas-liquid mixture ratio to occur at the region  70 . This ratio can determine the degree of atomization and the resulting nitrogen droplet size to be present in the liquid gas pulses  80  emitted from the nozzle openings  44 ,  46 . This arrangement permits the apparatus  10  to, in effect, provide a pocket of gas followed by a pocket of liquid repetitively and continuously as necessary for the liquid-gas pulses  80  to flow from the region  70  through the nozzles  40 ,  42  and the nozzle openings  44 , 46 . 
         [0029]    When liquid and gaseous nitrogen are used, the gaseous nitrogen  64  must always be at a higher pressure than the LIN  30  to prevent a backflow of the LIN into the internal space  66  of the pipe  60 . 
         [0030]    In those applications where carbon dioxide is used, both liquid and gaseous carbon dioxide must be maintained at a pressure exceeding 100 psig so that the liquid CO 2  can be delivered in the apparatus. However, the gaseous CO 2  delivered to the pipe  60  must always be at a pressure above a pressure of the liquid CO 2  delivered through the pipe  26  to similarly prevent a backflow of the liquid CO 2  from entering into the internal space  66  of the pipe  60 . 
         [0031]    The pipes  26 , 60  can be manufactured from stainless steel, copper, aluminum or any other material suitable for being exposed to fluids at a cryogenic temperature. 
         [0032]    The apparatus  10  and related method of the present embodiments increases overall heat transfer effect to cryogenic tunnel freezers and therefore, increases the overall efficiency of freezing applications. 
         [0033]    It will be understood that the embodiments described herein are merely exemplary, and that one 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 and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.