Abstract:
An apparatus for providing a liquid cryogen with pulsed flow includes a first tank  14  containing liquid cryogen; a second tank  16  containing gaseous cryogen under pressure, the second tank in fluid communication with the first tank and including an outlet; and a pair of valves including a first valve  70  disposed to alternate between interruption and continuance of the fluid communication between the first and second tanks, and a second valve  74  disposed for coaction up to 180° out-of-phase with the first valve to repetitively cycle between pressurizing and releasing pressure of the liquid cryogen for providing discrete pulses of the liquid cryogen from the outlet. 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 can be used 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 and during large scale industrial operations. 
         [0003]    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. 
         [0004]    Some improvements are known and being used in food freezing tunnels. For example, spray nozzles are now used to increase the overall heat transfer effect during the freezing process by spraying liquid nitrogen (LIN) through the nozzles directly onto the surface of the food product to contact same with droplets of that cryogenic substance. These small nitrogen droplets evaporate quickly upon contact with the food product, thereby removing or transferring heat immediately from the surface of the food product to chill and further freeze same. 
         [0005]    Other apparatus and systems use high pressure LIN to provide heat transfer at the surface of the food product. 
         [0006]    Unfortunately, these known apparatus and processes are expensive, can result in an unusually large amount of the nitrogen product being lost to waste or alternatively, require additional equipment to recycle unused nitrogen. In both instances, increased costs and a larger footprint of the food freezing tunnel are necessary, thereby making the known type of apparatus and processes less efficient and less cost-effective. 
       SUMMARY OF THE INVENTION 
       [0007]    There is therefore provided a generator apparatus embodiment for providing a pulsed flow of liquid cryogen which includes a first tank containing a first portion of liquid cryogen; a second tank containing a second portion of liquid cryogen, the second tank in fluid communication with the first tank and having an outlet; a third tank containing gaseous cryogen under pressure, the third tank in fluid communication with the first and second tanks; and a pair of valves consisting of a first valve disposed to alternate between interrupting and providing fluid communication between the second and third tanks, and a second valve constructed and arranged to coact 180° out-of-phase with the first valve and disposed to alternate between pressurizing and releasing pressure of the second portion of the liquid cryogen for providing discrete pulses of liquid cryogen from the outlet. 
         [0008]    There is also provided an apparatus embodiment for providing liquid cryogen with a pulsed flow including a first tank containing liquid cryogen; a second tank containing gaseous cryogen under pressure, the second tank in fluid communication with the first tank and including an outlet; and a pair of valves including a first valve disposed to alternate between interruption and continuance of the fluid communication between the first and second tanks, and a second valve disposed for coaction up to 180° out-of-phase with the first valve to repetitively cycle between pressurizing and releasing pressure of the liquid cryogen for providing discrete pulses of said liquid cryogen from the outlet. 
         [0009]    Another embodiment of the apparatus calls for the first and second valves to coact 180° out-of-phase with each other. 
         [0010]    There is also provided a method embodiment of providing liquid cryogen with a pulsed flow including providing a first tank containing liquid cryogen therein; providing a second tank containing gaseous cryogen therein, the second tank in fluid communication with the first tank; and repetitively pressurizing the first tank with the gaseous cryogen from the second tank and releasing the pressure for correspondingly forcing discrete pulses of the liquid cryogen to be released from the first tank. 
         [0011]    There is also provided another method embodiment of providing liquid cryogen with a pulsed flow including containing an amount of liquid cryogen; containing an amount of gaseous cryogen under pressure; providing fluid communication between the liquid cryogen and the gaseous cryogen; and repetitively interrupting and continuing the fluid communication of the pressurized gaseous cryogen to contact the liquid cryogen for generating the pulsed flow of liquid cryogen. 
         [0012]    Other features of the present apparatus and method embodiments are described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]    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 shows a pulsed liquid cryogen flow generator apparatus to be used with for example food products. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    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. 
         [0015]    Generally, a pulsed liquid cryogen flow generator apparatus of the present embodiments produces small droplets of a cryogenic substance, such as for example LIN, in combination with high pressure pulses of the LIN to provide high heat transfer rates for products, such as for example food products. The result is that an impingement heat transfer effect is created by cryogen beneath a spray nozzle for the apparatus. Additionally, if the LIN is in a saturated range while a liquid pressure wave pulse is introduced some nitrogen gas could be created in the flow stream as a result of rapid pressure change. This may occur because the saturated LIN is at its thermodynamic state of liquid nitrogen in vapor liquid equlibrium or at its boiling point whereby it exists as a pure liquid at this stage, but can either vaporize a subcool in response to changes in pressure or temperature. Accordingly, the degree or range of pressure fluctuation will have an impact on the degree of a two-phase flow passing through nozzle(s) of the apparatus, and can be used as a method of controlling the discharge of the pulsed UN from the nozzle(s). 
         [0016]    A pulsed liquid cryogen flow generator apparatus of the present embodiments is shown generally at  10 . As used herein, the apparatus  10  may also be referred to as a “generator” or a “generator apparatus”. Cryogens that can be used in the generator are, for example, LIN or CO 2  liquid, although pulsing of CO 2  would require control parameters having to be limited due to the triple point of CO 2 . 
         [0017]    For the purpose of the description herein and by way of example only, the cryogen referred to will be nitrogen, whether LIN or gaseous nitrogen. 
         [0018]    The apparatus  10  includes a plurality of tanks  12 , 14 , 16  or vessels. The tank  12  is a liquid nitrogen (LIN) bulk tank, vertically arranged by way of example only, and includes a pressure control vaporizer  18  of conventional construction and operatively associated with the tank. A bottom  20  of tank  12  is provided with an outlet  22 , such as for example a spigot, which is in fluid communication with one end of the vaporizer  18  and through which LIN  24  in the tank can be passed to phase change into gaseous nitrogen and be introduced at an opposite end of the vaporizer into a headspace  26  or ullage of the tank  12 . The pressure in the tank  12  is maintained at approximately 30 psig. Supports  28  or footings, adjustable or fixed, support the tank  12  off an underlying surface. The tank  12  may also be referred to herein as the “bulk tank” or the “main tank”. 
         [0019]    There is also provided at the bottom  20  of the tank  12  an outlet  30  in fluid communication with a pipe  32  having an opposed end in fluid communication with the tank  14  which has a smaller volume than the tank  12 . The tank  14  may be referred to as the “secondary” or “ancillary” tank. A control valve  34  is interposed in the pipe  32  for a purpose to be described hereinafter. The tank  14  receives a stream of the LIN  24  from the tank  12  via the pipe  32 , wherein a substantially constant volume of LIN  40  is maintained in the tank  14 . 
         [0020]    To accomplish this, level probes  36 , 38  are installed in the tank  14  to sense a maximum height of the LIN  40  in the tank (probe  36 ) and a minimum level of the LIN in the tank (probe  38 ), The level probes  36 , 38  transmit respective signals to a controller  39  which is connected to the control valve  34  via wiring  39  to accordingly respond to the signals transmitted by the probes to determine what additional amount of the LIN  24  must be permitted to flow through the pipe  32  into the tank  14 . Any known arrangement of probes  36 , 38 , valving  34  and controller  35  coacting to maintain a fluid level of the LIN  40  in the tank  14  can be used. The amount of the LIN  40  in the tank  14  is therefore maintained at a level not to exceed a probe capacitance at  36  or be less than a probe capacitance at  38 . 
         [0021]    A bottom  42  of the tank  14  is supported off an underlying surface with supports  44  or footings, adjustable or fixed. A headspace  46  or ullage of the tank  14  is present above the LIN  40  and into which the LIN  24  flows from the pipe  32 . That is, the headspace  46  of the tank  14  is in fluid communication with the LIN  24  in the tank  12 . The bottom  42  of the tank  14  also includes an outlet  48  in fluid communication with an exhaust  50  which functions as the injection pipe for the apparatus  10  The LIN  40  in the tank  14  flows through the injection pipe  50  for application processes and/or to nozzles  51  downstream of the tank  14  and in a manner to be described hereinafter, The injection pipe  50  also includes a control valve  52  or gate valve. 
         [0022]    The tank  16  is constructed and arranged to hold a volume of high pressure nitrogen (N 2 ) gas  54 . The tank  16  may also be referred to herein as the “pressurizing tank” or the “gas tank”, and such gas is provided from the main tank  12 . That is, gaseous nitrogen from the headspace  26  of the tank  12  is withdrawn through a pipe  56  in fluid communication with the head space and provided to the pressure tank  16 . The gas is removed from the head space  26  along the pipe  56  by a pressure pump  58  interposed in the pipe  56 . The pressure pump  58  increases the pressure of the gas from approximately 30 psig in the tank  12  up to 200 psig within the tank  16 . A gate valve  60  is also provided in the pipe  56  to control the flow of the gas from the head space  26  to the pressure pump  58 . The tank  16  includes a bottom  62  from which supports  64  or legs, adjustable or fixed, extend to support the tank  16  off an underlying surface. The bottom  62  is provided with an outlet  66  which is in fluid communication with pipe  68 . The pipe  68  functions as a gas line in fluid communication with the headspace  46  of the secondary tank  14 . A high speed valve  70  is interposed in the gas line  68  to control the flow of the gas  54  from the tank  16  to the head space  46  of the secondary tank  14 , and to also control a pressure pulsation rate of the gas as explained below. 
         [0023]    A nitrogen gas vent line  72  or pipe has one end in fluid communication with the headspace  46  of the secondary tank  14  and an opposite end in fluid communication with an outlet  73  to atmosphere or subsequent application process. Another high speed valve  74  is interposed in the vent line  72  upstream of the outlet  73 . The high speed valves  70 , 74  will operate 180 degrees out-of-phase with each other during operation of the apparatus  10 . That is, when valve  70  is open, valve  74  will be closed, and vice versa. 
         [0024]    Operation of the apparatus  10  is as follows. The secondary or ancillary tank  14  is filled with the LIN  40  to the higher level indicated by the level probe  36  or sensor. The LIN  40  in the tank  14  is obtained from the pipeline  32  which is in fluid communication with the LIN  24  in the main tank  12 . At this time in the process, pressure in the tank  14  is 30 psig, and the LIN  40  discharged from the outlet  48  and through the injection pipe  50 , and the nozzles  51  if used, is flowing into the freezing process at 30 psig to contact food products (not shown), for example. Nitrogen gas is present in the gas tank  16  up to a pressure of as much as 200 psig, for example, as provided by the pump  58 . The pump draws gaseous nitrogen from the headspace  26  through the pipe  56  to the tank  16 . 
         [0025]    Valve  70  is actuated to an open position, while valve  74  is actuated to a closed position. The corresponding pressure which results from introducing the gaseous nitrogen from the gas tank  16  through the pipe  68  to the headspace  46  in the ancillary tank  14  is thereby increased up to 200 psig by this positioning of the valves  70 , 74 . The rapid opening of the valve  70  concurrent with the valve  74  being closed permits a pulse  76  of LIN to be emitted from the outlet  48  of the tank  14 . This occurs because when the valve  70  is quickly opened a burst of pressurized nitrogen gas is introduced into the headspace  46  for pulsing a portion  76  of the LIN  40  from the outlet  48  to and through the nozzles  51  (if used). The valve  70  is then closed, and valve  74  is opened so that the pressure in the headspace  46  is again reduced. The pressure in the tank  16  is maintained at 200 psig by the pump  58  at which time the valve  70  is again opened and the valve  74  is closed to again emit the LIN pulse  76  from the tank  14 . 
         [0026]    The result is that a pressure pulse is generated in the flowing LIN for the process, such that the pressure increases from 30 psig to 200 psig for a short period of time, approximately 0.1-1.0 seconds. This process continues repetitively with valves  70 , 74  opening and closing up to 180 degrees)(180° out-of-phase with each other as the LIN flow is forced from the tank  14  and into the injection pipe  50  as pulses  76  of LIN. Another embodiment has the valves  70 , 74  opening and closing exactly (180°) out-of-phase with each other. An alternate embodiment includes having a continuous stream or flow of the LIN  40  flowing through the injection pipe  50 , even as pressure in the pipe is between 30 to 200 psig during occurrence of the pulses  76 . That is, the pulses  76  occur in the LIN  40  flowing through and out of the pipe  50 , and the nozzle  51  if being used, 
         [0027]    Eventually, the LIN  40  in the tank  14  will need to be replenished from the tank  12 . At such time, the LIN  24  will be fed through the outlet  30  into the pipe  32  and thereafter into the tank  14  either between pulses if needed, or when the level probe  38  or sensor is triggered and transmits a signal that a refill of the LIN  40  is needed for the tank  14 . At such time for replenishment, a delay in the operation process must be provided in order to implement a refill of the LIN  40  to the tank  14 . 
         [0028]    If the nature of the process of chilling the food product is such that a refill time period for the tank  14  cannot be accommodated, then a plurality of the apparatus  10  can be used so that there is never down time of the apparatus and a delay or cessation of the process. Accordingly, when a plurality of the apparatus  10  are used, at least one apparatus can be in operation, while the other apparatus is in a recharge mode. If a plurality of the apparatus  10  are used, only one additional apparatus of the plurality needs to have another one of the tanks  14 , so that one tank can be in refill mode while the other tank is in operation mode, whereby the process can continue uninterrupted for as long as necessary. 
         [0029]    As shown in the Figure, LIN pulses  76  pass through the injection pipe  50  to be provided to a freezing system and/or spray nozzle  51  used in food chilling and/or processing applications. 
         [0030]    The apparatus provides the pulses  76  of LIN without any gas entrainment in the LIN pulses, such that the LIN alone contacts the food products for heat transfer at same. If saturated LIN is fed into the tank  14 , however, nitrogen gas will be created in pulses having increased pressure if the pulses are exhausted from the tank. If subcooled LIN is fed into the tank  14 , an upper pressure limit of the pulses could be controlled so that no nitrogen gas is created during the pulsing process. 
         [0031]    CO 2  and liquid CO 2  can be used instead of the LIN and gaseous nitrogen, but other control equipment and parameters would be necessary to operate the apparatus  10  and related process with the CO 2 . 
         [0032]    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.