Abstract:
A injector nozzle for a cryogenic fluid wherein both the kinetic energy of the discharge stream, and the residual volume of cryogenic fluid contained within the nozzle is reduced, the dispensing nozzle of a generally showerhead type configuration, with discharge ports disposed at the periphery of the showerhead discharge face, and a filler member disposed internal to the showerhead assembly, to reduce the volume of the conical chamber immediately upstream of said discharge faceplate.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to cryogenic liquid delivery systems and, more particularly to a managed dosing system for injecting metered droplets of liquid nitrogen into beverage, food or other product containers as they move along high-speed production lines before being sealed. In particular, it relates to a dispensing nozzle of unique design which accurately delivers a measured dose of liquid nitrogen as a dispersed stream of reduced kinetic energy. 
         [0003]    2. Description of the Related Art 
         [0004]    With thin walled containers, especially thin walled metal cans and plastic bottles, it has been found useful to stiffen them after filling, but prior to further processing, such as labeling, shipping and handling to prevent subsequent container damage. To achieve such stiffening, a liquid cryogen such as nitrogen may be injected just prior to sealing. Injected as droplets, the liquid cryogen undergoes a phase change to a gas, increasing the pressure inside the sealed container, the increased pressure acting to stiffen the container walls. 
         [0005]    Typically, the liquid cryogen drops or droplets, once injected, will coalesce as they sit on the contents, the vaporization process taking anywhere from 5-15 seconds. Accordingly, the time between injection and container closure must be kept short. It is to be appreciated the exact time of vaporization is dependent upon the size of the injected droplet, and the temperature of the container contents. The resulting pressure within the container will similarly be a function of the size of the injected drop, the free space to be filled, and the time between droplet injection and container closure. 
         [0006]    In commercial applications, specialized liquid nitrogen delivery systems have been developed for injection of small amounts of nitrogen into containers as they pass along an assembly line. Such systems are sold by VBS Industries of Campbell, Calif. (now Cryotech, International), under the trade names LCI-300, 400, and 2000M. See also U.S. Pat. No. 6,182,715 to Alex R. Ziegler, et al, which patent is incorporated herein by reference in its entirety, as well as copending application US2005/0011580 A1. 
         [0007]    In these systems, a stream of liquid cryogen droplets is dispensed vertically into a moving container. One such type of nozzle used in the past is shown in FIG. 1, item 108 of application US2005/0011580 A1. With such an injector nozzle having a singular opening, however, it was found that the force of injection caused the droplets to substantially penetrate the surface of the container contents. These high impact forces can result in splash-back of the contents onto the dosing head, where the splashed liquid may accumulate and later interfere with the operation of the dosing head itself. 
         [0008]    Conveyer systems are run at fairly high speeds where containers pass by fixed stations at the rate of 500 units per minute or more. In fact, some processing conveyor lines run to speeds in excess of 1500 to 2000 containers per minute. At lower speeds, e.g. 500 units per minute, the liquid nitrogen feed systems of the referenced prior art perform well. However, at higher line speeds, the dispensing assemblies must operate at higher frequencies. With such high speed lines where containers pass a fill point at the rate of upwards of 1000 to 2000 units per minute, the residence time at the liquid injection station also becomes a factor, with the time allowed for fill becoming shorter than the time required for delivery of the dispensed liquid dose stream. This mismatch, in combination with high impact forces, can result in a good portion of the injected dose missing the container opening, and thus lost to the atmosphere by vaporization. As a further result, maintenance of dose accuracy and repeatability can be lost. 
         [0009]    One approach has been to employ a shower head delivery nozzle of the type depicted in  FIG. 1 , and which is more fully described hereafter, for the injection of the liquid cryogen. With reference to the figure, a shower head dispensing nozzle (i.e. injector)  100  is illustrated which includes a threaded body portion  105 , valve seat  102 , valve throat  106 , inverted conical chamber  110 , and shower head face plate  112 . Valve seat  102  is configured to receive sealing stem  104 , which stem is rapidly opened and closed to meter a measured amount of cryogen to the dispensing nozzle. A more complete description of the operation of the dosing head and sealing stem can be found in my copending application US 2005/0011580A1. Cryogen dispensed to the nozzle enters the conical chamber  110  and is discharged through a plurality of discharge openings  114  peripherally disposed in face plate  112 . 
         [0010]    By distributing the measured cryogen stream over a wide area, the kinetic energy of the injected dose is reduced [compared to size of single opening of nozzle shown in FIG. 1 of the copending application], thus reducing the amount of splashback. However, it has been found with this shower head configuration, the to-be-injected dose is not immediately discharged, with a substantial residual volume of the cryogen remaining in the nozzle chamber  110  behind face plate  112 . This retained volume tends to drain itself over a time period in the order of about one half second (or more). However, in the process of high speed container filling, during this time interval the container being dosed will have been displaced from its fill position, resulting in some of the dose, i.e. the residual drips, falling outside of the container, either onto the sides of the container, the conveyor line, or even possibly onto the next, oncoming container. This inconsistent dosing can lead to inconsistent pressures within the containers being filled. Thus there remains a need to accurately dose a cryogenic liquid into a container, while reducing and preferably eliminating cryogenic liquid splash back, and spill over onto and into an oncoming container. 
       SUMMARY OF THE INVENTION 
       [0011]    By way of this invention a unique shower head type of dispensing nozzle is provide having a generally inverted conical configuration, the dispensing nozzle including a nozzle body, and an intake passageway disposed within the nozzle body. At a first end, the said intake passageway is in fluid communication with a valve seat. At its other end, said passageway is in fluid communication with an inverted conical chamber, the chamber further defined at its base by a discharge face plate. A plurality of openings provided in said face plate are arranged around the perimeter of said plate. In addition, a filler member or post integral to the back side of the face plate is provided to reduce the residual (i.e. void) volume within the conical chamber of the nozzle. By this configuration, the dripping problem caused by the slow release of the residual cryogenic fluid existing with the prior art shower head dispenser is reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    So that the above-recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to various embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0013]      FIG. 1  is a three dimensional cross sectioned view of a traditional shower head injector nozzle of the prior art. 
           [0014]      FIG. 2  is a three dimensional cross sectioned view of an embodiment of the shower head dispensing nozzle of the present invention. 
           [0015]      FIG. 3  is a three dimensional view of the injector nozzle of  FIG. 2  rotated to display the face plate of the nozzle. 
           [0016]      FIG. 4  is a cross sectional view of a typical injection head assembly for the dispensing of cryogen, including the injector nozzle of this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The shower head injector nozzle  200  of this invention is depicted in  FIG. 2 , the injector nozzle including threaded body  202 , valve seat  206  and a shower head dispensing portion  212 . Threaded body  202  is sized so as to be received by the internal threads of the dosing head to which it is to be engaged. Valve seat  206 , positioned at one end of injector  200 , is sized to receive the sealing stem  208  of a dosing head (later to be described in connection with  FIG. 4 ). Intake passageway  210  is in fluid communication with valve seat  206  and conical chamber  220 , providing a continuous path for the flow for liquid cryogen from the cryogen source through the injector nozzle to the container to be filled. The threaded lower end of injector  200  terminates as hexagonal bolt head  204 , bolt head  204  provided to facilitate threading of the injector nozzle into the dosing head. 
         [0018]    Shower head dispensing portion  212  includes discharge face plate  214 , the face plate having inwardly and outwardly facing surfaces. The back (i.e. the inwardly facing surface) of discharge face plate  214  includes a filler member or post such as an inverted cone or plug  218  which may or may not be solid. A plurality of nozzle openings  222  are provided around the periphery of face plate  214  communicating between said inwardly and outwardly facing surfaces) to allow for the discharge of liquid cryogen from the nozzle. The shape of the openings is not critical. In one embodiment, they may be circular, as shown in  FIG. 1 . In another embodiment, the may be square as shown in  FIG. 3 . In the latter case, the square openings provide a greater open area compared to circular openings of the same diameter, the larger surface area serving to further reduce the kinetic energy of the discharged liquid cryogenic stream. 
         [0019]    The number of openings  222  is not critical. However, the combined cross sectional area of the openings provided should be at least the same, if not more than the cross-sectional area of intake passageway  210 . Further, if too many openings are provided, such that the distance between openings is reduced, a tenancy has been observed for liquid streams to recombine. Thus, it is preferred the face plate have fewer, but larger openings so as to maintain a minimum distance between openings. By way of example, for a shower head face plate  214  of a diameter of 5-6 mm, the minimum distance between nozzle openings at typical cryogenic liquid pressures of 0.5 PSI can vary from between 1 mm and 3 mm, and is optimally about 2 mm. 
         [0020]    Filler member  218  extends upwardly from face plate  214  towards intake passageway  210 . As shown in  FIG. 2 , filler member  218  may extend close to but not into passageway  210 . In various embodiments, member  218  can extend a limited distance into passageway  210 . In still further embodiments, member  218  can be a cone, a cone like frustum (as illustrated in the figure), or a post. 
         [0021]    Interior, conical chamber  220  is defined by sloping, diverging wall  216  of body  202 . An annular passageway  217  is defined between walls  216  of body  202  and the sloped wall of filler member  218 . In general, the slope of the wall of member  218  is greater than the slop of opposing wall  216 , whereby the spacing between these opposing walls increases moving longitudinally in the direction towards intake passageway  210 . At a minimum, the difference in slope of the walls is selected such that the cross sectional area of annular passageway  217  remains constant in the direction of fluid flow. 
         [0022]    In one embodiment, the slope of these opposing walls is adjusted such that the cross sectional area of passageway  217  increases in the direction of fluid flow. In other embodiment the cross sectional area of said passageway decreases, moving in the direction of fluid flow towards discharge face plate  214 . Further, the ratio of the cross sectional area of the annular passageway relative to the cross sectional area of the connecting intake passageway can vary from 0.5 to 1.5. The smaller the ratio, the greater is the kinetic energy of the flow exiting nozzle openings  222 , the larger the ratio, the lower is the kinetic energy of the exiting flow. It another embodiment, it is preferred to maintain close to laminar flow in annular passageway  217 , the above ratios consistent with near laminar flow conditions. 
         [0023]    The materials of construction for the injector nozzle are not critical, but must take into account the discharge head with which it is to be used. Most importantly, the thermal expansion properties of the shower head nozzle should be matched to that of the dispensing unit into which it will be affixed. Preferably the materials used to construct the nozzle and dispensing unit will have the same thermal coefficient of expansion. Typically, the nozzle will be formed of stainless steel to match the stainless steel used with the dispensing unit. 
         [0024]    With reference now to  FIG. 4 , shower head injector  200  is shown in combination with a typical dosing head assembly  301  sold by Cryotech International, whereby droplets of liquid nitrogen are metered from a dosing head  302 . The dosing head  302  includes a needle valve system for dispensing of the liquid nitrogen, the needle valve including a valve sealing stem  304 , with valve head  306  at its distal end, the valve head  306  sized for sealable engagement with valve seat  206  of the shower head injector  200 . Reservoir  310  defined by valve body  312  acts as a local liquid cryogen supply chamber for holding liquid cryogen, inundating the seating area of the needle valve. Liquid nitrogen is fed to reservoir  310  through source conduit  314 , extending from flexible dosing arm  332 . It is contained in chamber  310  at slightly elevated pressure, e.g. 1 PSI above atmospheric. In a passive system, the pressure is created by the hydrostatic head of a larger cryogen source reservoir (not shown) placed above and supplying conduit  314 . This liquid nitrogen supply may be pressurized, if desired. Typical pressures can range from near zero to 10 psi above atmosphere, with 6 psi being a customary upper limit. With the valve open, liquid nitrogen will flow through the metering orifice of valve seat  206 , the flow interrupted when the valve is closed. 
         [0025]    In order to precisely meter the amount of nitrogen dispensed into each container, it is important to be able to quickly open and close the dosing valve. This is achieved with a pneumatic actuator of the type shown in  FIG. 4 . Therein, and by way of illustration, valve stem  304  is secured at its proximate end to the end of a pneumatically actuated piston  316 . The piston includes a piston head  318 , a stem  320 , upper and lower chambers  322  and  324 , and ports for sequentially injecting and exhausting a gas such as nitrogen into both the upper and lower chambers to cause movement of the piston either upwardly or downwardly, in turn moving the needle valve to either the open or closed position. 
         [0026]    The actuator may be spring loaded to bias the valve to the closed position. With the valve open as shown in  FIG. 4 , the lower chamber  324  of the pneumatic piston is pressurized, the upper chamber exhausted to atmosphere via vent  331 . To lower valve head  306  and thus close the valve, upper chamber  322  is pressurized by flowing gas into that chamber, while the lower chamber is exhausted to atmosphere. 
         [0027]    To effectuate such rapid opening and closing, the piston is driven by a 4-way solenoid valve  330  which controls the flow of nitrogen gas to the chambers above and below the piston head. As shown in the  FIG. 4 , this valve is separately mounted on dosing arm  332 , some distance from the liquid nitrogen dispensing valve. In the mode illustrated, a pressurized source of nitrogen (or other inert gas) is supplied via supply line  326 , the 4-way valve  330  biased in the closed position. When opened, the gas flows through the solenoid actuated valve to one of the piston chambers, to cause either opening or closing of the needle valve. The operation of the solenoid is controlled by a controller, not shown, which can be programmed to adjust valve cycle time, and thus control dose settings. 
         [0028]    In the case of the injector nozzle of this invention, the liquid cryogen dispenses during the time that the sealing stem is raised and the needle valve is thus in the open condition. The dispensed cryogen first enters intake passageway  210 , and then into annular passageway  217  where the velocity of the stream slows before it is discharged through openings  222 . The effect of thus reducing the kinetic energy of the discharge stream is achieved. With the reduction in the volume of conical chamber  220  due to the presence of filler cone member  218 , the amount of residual cryogen remaining in the chamber after closure of the needle valve is greatly reduced, and thus the degree of latent drip of cryogen onto the sides of the container being filled, the conveyor belt and possibly onto the next container to be filled is significantly reduced. 
         [0029]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.