Abstract:
A vortex suppression device is provided which includes a plurality of spaced apart porous panels arranged generally parallel with respect to each other for placement adjacent a suction pipe inlet. The panels of the suppression device are oriented generally perpendicular to, or parallel to the suction pipe inlet. The device serves to prevent formation of a sufficiently strong vortex capable of pulling a continuous gas core into the suction piping.

Description:
CLAIM TO PRIORITY 
       [0001]    This application claims priority to U.S. provisional application No. 60/914,098 filed Apr. 26, 2007, entitled “Cartridge Type Vortex Suppression Device.” 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to a device for suppressing vortices. More specifically, the present invention is directed to a modular device for suppressing vortices associated with the outlet from a tank or inlet to suction piping. 
       BACKGROUND OF THE INVENTION 
       [0003]    While draining liquid from a tank or other similar enclosure, formation of a coriolis effect vortex or a vortex induced by the approach flow geometry is commonly encountered. The likelihood of such a vortex formation increases as the ratio of the height of the liquid above the drain compared to the diameter of the drain decreases. In other words, decreasing liquid levels and/or increasing drain sizes increase the likelihood of vortex formation. Another factor which can increase the likelihood of vortex formation is increasing drain flow rates, such as where a suction pump is connected to the drain to pull liquid from the enclosure. 
         [0004]    Typical nuclear and chemical plants have numerous tanks which are commonly drained to levels in which the free surface between a gas and liquid can approach the drain level (discharge). Commonly, the discharge from such tanks is connected to suction pumps which expedite removal of the liquid from the tank. Experiments have shown that, under certain conditions, a vortex could be formed that permits gas from the freeboard space above the surface of the liquid to be pulled into the suction flow. Such a vortex is undesirable because it can limit the rate at which the liquid can be drained from the tank and can lead to cavitation in the suction (drain) pump. Accumulation of gas in a pump can result in a significant decrease in the pumping capacity and potentially damage the pump internals. 
         [0005]    For tanks which have been designed to drain the liquid level to elevations that approach a depth where such a vortex could be formed, it is desirable to provide a device that prevents the formation of a sufficiently strong vortex capable of pulling a continuous gas core into the suction piping and pump. 
         [0006]    It is also desirable to provide a device capable of being retrofit to existing tank outlets and suction piping inlets which may have limited accessibility. 
         [0007]    It is also desirable that such a device be of reliable construction in both material and design for use in applications where harsh conditions and limited access provide for limited inspection and maintenance. 
       SUMMARY OF THE INVENTION 
       [0008]    These needs and other are met by the embodiments of the invention, which provide a device of modular construction that prevents the formation of a sufficiently strong vortex capable of pulling a continuous gas core into the suction piping and pump. The modular construction allows for the device to be retrofit to existing tanks and piping where accessibility may be limited. Few necessary parts made from durable materials provide for a highly robust design particularly applicable to use in harsh conditions with limited maintenance. Additionally, the modular construction allows for the size of the device to be varied dependent on the needs of a specific application. 
         [0009]    In accordance with an embodiment of the invention, a vortex suppression device is provided which includes a plurality of spaced apart porous panels arranged generally parallel with respect to each other adjacent a pipe inlet. The pipe inlet having an inlet opening lying generally in an inlet plane, with the panels of the suppression device oriented generally perpendicular to, or parallel to (depending on the inlet orientation) the inlet plane and secured relative to the pipe inlet by a frame structure. 
         [0010]    In accordance with another embodiment of the invention, a vortex suppression device is provided which includes a plurality of spaced apart porous panels arranged generally parallel with respect to each other adjacent a pipe inlet. The pipe inlet having an inlet opening lying generally in an inlet plane, with the panels of the suppression device oriented generally perpendicular to, or parallel to, the inlet plane. The porous panels grouped together in pairs to form modules. The spacing between adjacent modules being generally equivalent to the spacing between porous panels within a module. Each module may be formed from a single sheet of perforated material or from multiple sheets of said material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
           [0012]      FIG. 1  shows a general view of a tank system which incorporates the present invention. 
           [0013]      FIG. 2  shows an isometric view of a vortex suppression device in accordance with embodiments of the invention. 
           [0014]      FIG. 3  shows a plan view of the vortex suppression device of  FIG. 2   
           [0015]      FIG. 4  is a chart showing different types of vortices and their classification on a numerical scale. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]      FIG. 1  illustrates an example tank system  10  incorporating an embodiment of the present invention. The system  10  consists of a tank  12  having an inlet  14  and an outlet  16 . Details of the tank such as size, shape, number and positioning of inlet and outlet is shown for example purposes only and is not meant to limit the present invention. (For example, the outlet could be on the side wall of the tank.) The outlet  16  is commonly configured at or near a lower portion of the tank  12  to provide for complete or almost complete drainage of the tank if so desired through suction piping  17 . As such, the tank outlet  16  could also be referred to as a suction piping inlet. The tank  12  contains a fluid  18  shown having a height h relative to the outlet  16 . A suction pump  20 , connected to the outlet  16  via suction piping  17 , expedites removal of the fluid  18  from the tank  12 . A vortex suppression device  22  is located generally near the outlet  16 . 
         [0017]      FIGS. 2 and 3  show detailed views of a preferred embodiment of the vortex suppression device  22  situated adjacent a tank outlet  16  (suction piping inlet). Device  22  includes a plurality of spaced apart panels  24  (best shown in  FIG. 3 ), each panel  24  having a plurality of pores  26  (shown in  FIG. 2 ). The panels  24  are grouped together in pairs to form modules  28 . 
         [0018]    In the preferred embodiment shown, each module  28  is formed from a single, or multiple sheets of perforated stainless steel material bent to form corners of the module  28  with the ends of the perforated sheet being joined by a single weld joint (not shown) to close the structure. Such a design is preferred due to ease of fabrication and durability due to reduced parts and weldments. It is noted that sidewalls  29  shown in the preferred embodiment of  FIGS. 2 and 3  are a product of using a single sheet of material to form each module  28  and are not necessary for the present invention to function in suppressing vortices. An alternate embodiment using individual panels  24  held in the spatial relationship shown in the Figs. by rods  30  also has shown to successfully suppress vortex formation. 
         [0019]    Modules  28  are secured relative to each other via a structural mounting frame, such as rods  30  as shown, and positioned at a relative height with respect to the outlet  16  via the structural frame. Typically, the vortex suppression device has an overall height that is at least 1.5 times the outlet diameter. It is noted that other structural elements commonly known to one skilled in the art could be employed to secure the panels  24  and modules  28  relative to each other and the outlet  16 . As such, the use of rod  30  is shown as an exemplary mounting set-up only and not meant to limit the invention. 
         [0020]    The use of modules  28  has been found to be advantageous over using separate panels  24  as individual panels tend to be flimsy and require added reinforcement. Conversely, the structure of module  28  adds rigidity to the two associated panels  24  and allows for the two separate panels  24  to be made from a single sheet of perforated material. The modular construction of the vortex suppression device  22  allows for such a device to be readily adapted to any suction flow rate or any size suction piping by adding additional modules as required to cover the diameter of the piping. Additionally, the modular construction allows for the device to be added to existing tanks with limited access. As best seen in  FIG. 3 , the spacing between the two separate modules  28  is preferably generally the same as the spacing between the two panels  24  associated with an individual module  28 . 
         [0021]    Preferably, the vortex suppression device  22  is fabricated from stainless steel and can be used in any environment including water, borated water, fuel oil, hydrocarbons, etc. It is foreseen that the suppression device  22  could also be fabricated from other materials or combination of materials, such as, but not limited to other metals, fiberglass (mesh or structural components) or the like. 
         [0022]    When placed in a working environment, the vortex suppression device  22  is preferably centered over the tank outlet  16  (suction piping inlet) and sized such that device  22  covers the outlet  16  with a dimension that is at least twice the outlet diameter as best shown in the top view of  FIG. 3 . It is noted that the device  22  could be utilized in situations where centering over the outlet and/or sizing to cover the outlet are not possible or potentially desirable. While not producing optimum results, use of the device  22  in such a less than ideal manner could still produce favorable results versus not using the device  22 . 
         [0023]    In use, the porous grid structure of the panels  24  counter formation of large scale swirl flows by preventing their formation in the near vicinity of the entrance to the suction piping such as outlet  16 . This is accomplished by the limited cross sectional flow area in the direction of the swirl (the holes in the porous panels) while only presenting a minimal resistance in the direction of flow toward the suction piping. 
         [0024]    In a preferred embodiment, the porous panels  24  of an individual module  28  are designed to be approximately 1½ inches apart and the modules  28  are installed also approximately 1½ inches apart. With this dimension, the porous panels are involved in any surface circulation that would be the beginning of any large scale vortex. Consequently, the transverse flow resistance through the panels which have holes (for example ¼ inch in diameter) spaced sufficiently to give an open area of over 25%, is too large to enable the induced swirl flow to escalate into a full scale vortex that has the capability to develop a continuous gas core. Such a development is the manner in which large scale vortices can transmit the cover gas to the pump suction piping. 
         [0025]    The characterization for various vortices is shown in  FIG. 4 . Of the various vortex types shown, only type  6  has the capability of transmitting sufficient quantities of gas to a pump to challenge the pumping performance of the pump. By using the vortex suppression device  22  described herein, the type  6  vortices are prevented from being induced by swirl flows near the entrance to the suction piping  17 . The present design also limits the formation of vortices that are type  5  which further reduce the potential for air transport to the suction piping  17  and connected suction pump  20 . 
         [0026]    While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those detailed could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.