Patent Application
20080230634
1. Field of the Invention
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.
2. Description of the Related Art
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.
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.
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.
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.
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.
One approach has been to employ a shower head delivery nozzle of the type depicted in
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.
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.
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.
The shower head injector nozzle 200 of this invention is depicted in
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
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.
Filler member 218 extends upwardly from face plate 214 towards intake passageway 210. As shown in
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.
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.
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.
With reference now to
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
The actuator may be spring loaded to bias the valve to the closed position. With the valve open as shown in
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
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.
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.
