Abstract:
Apparatus and methods for deheading shrimp using the Venturi Effect. A shrimp-laden fluid is pumped through a conduit system and lined with one or more venturi tubes. The acceleration of the fluid through the venturis detaches the heads from the shrimp. The cross-sectional areas of the venturis each have a major axis and a shorter minor axis. The major axis is long enough to receive the majority of or all the length of a shrimp and minimize hard collisions with the entrance to the venturi that could damage the shrimp.

Description:
BACKGROUND 
       [0001]    The invention relates generally to shellfish processing and more particularly to apparatus and methods for deheading shrimp with hydrodynamic forces. 
         [0002]    Deheading shrimp by hydrodynamic force is known from U.S. Pat. No. 5,195,921, “Apparatus for Deheading and Cleansing Shrimp,” issued Mar. 23, 1993. In that patent, a shrimp-laden fluid is pumped through conduit that abruptly narrows. The abrupt decrease in the cross-section of the conduit causes the flow to accelerate through the narrow cross section according to the Venturi Effect. Hydrodynamic forces caused by the change in cross section tend to detach heads from shrimp. The cross section of the conduit in the patent is circular along its entire length. When a pipe with a four-inch diameter is used as the main conduit, the diameter of the narrow region is even smaller. Shrimp, whose outer dimensions are greater than the diameter of the narrow region, tend to bump into the narrowing conduit. The collisions with the conduit walls can damage the shrimp, especially fragile cold-water shrimp. As shown in  FIGS. 1A and 1B , cold-water shrimp  10  have a long, thin sixth segment  12  that is easy to damage. The joint  14  between the third and fourth segments is also susceptible to damage. In general, the muscle tissue in cold-water shrimp is much weaker than in the sturdier warm-water shrimp. When a cold-water shrimp  10  approaches the narrow region of the conduit side-on, as opposed to head or tail first, it bangs into the sides of the opening into the narrow region. The collisions do help remove the head, but they also can cause the shrimp to break at its weak spots. 
       SUMMARY 
       [0003]    This shortcoming in detaching heads from shrimp is addressed by apparatus embodying features of the invention. One such apparatus comprises a conduit enclosing a fluid channel and flow control means inducing a flow of shrimp-laden fluid in the conduit. The conduit has an open first end and an opposite open second end downstream of the first end along the fluid channel. An input portion of the conduit extends downstream along the fluid channel from the first end and defines the fluid channel with a first cross-sectional area. A venturi extends upstream along the fluid channel from the second end and defines a length of the fluid channel with a second cross-sectional area smaller than the first cross-sectional area. The second cross-sectional area has a major axis and a shorter minor axis. A transition portion of the conduit is disposed between the input portion and the venturi. The transition portion defines a length of the fluid channel with a cross-sectional area converging from the first cross-sectional area to the second cross-sectional area. The shrimp-laden fluid flows through the first end of the conduit, the fluid channel, and the second end. The speed of the fluid along the length of the fluid channel in the converging cross-sectional area of the transition portion increases to a speed in the venturi sufficient to detach heads from shrimp. 
         [0004]    Another version of such an apparatus comprises a conduit system defining a fluid channel and venturis disposed in the conduit system in line with the fluid channel at spaced apart positions. Flow control means induce a flow of shrimp-laden fluid in the fluid channel to convey the shrimp-laden fluid through the conduit system. The venturis cause an increase in the speed of the shrimp-laden fluid in each of the venturis sufficient to detach heads from shrimp. 
         [0005]    According to another aspect of the invention, a method for detaching the heads of shrimp comprises: (a) flowing a shrimp-laden fluid through a fluid channel in a conduit system; and (b) restricting the fluid channel in venturis at spaced apart locations along the conduit system to increase the speed of the shrimp-laden fluid in each of the venturis sufficient to detach heads from shrimp. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These aspects and features of the invention are described in more detail in the following description, appended claims, and accompanying drawings, in which: 
           [0007]      FIGS. 1A and 1B  are side and top views of a cold-water shrimp; 
           [0008]      FIG. 2  is an isometric view of a venturi tube for a deheading apparatus embodying features of the invention; 
           [0009]      FIGS. 3A-3C  are side views of a venturi tube as in  FIG. 2  with a tapered transition region with taper angles of 30°, 45°, and 60°; 
           [0010]      FIGS. 4A and 4B  are front and rear isometric views of a deheading system including venturi tubes as in  FIG. 2 ; 
           [0011]      FIG. 5  is a schematic diagram of a multi-venturi deheading system using venturis as in  FIG. 2 ; and 
           [0012]      FIG. 6  is a schematic diagram of a multi-venturi deheading system as in  FIG. 5  including an additional boost pump. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    A venturi tube, or venturi, usable in a deheading system embodying features of the invention is shown in  FIG. 2 . The venturi  16  is a restricted portion of a conduit  18  enclosing a fluid channel  19  conveying a shrimp-laden fluid along a fluid path  20 . The conduit has an open entrance end  22  and an opposite open exit end  23  downstream of the entrance end. An input portion  24  of the conduit extends downstream from the entrance end  22  and defines the fluid channel with a cross-sectional area A 1 . 
         [0014]    A transition portion  26  of the conduit extends downstream from the input portion  24  to the venturi  16 . The transition portion  26  defines a length of the fluid channel with a converging cross-sectional area formed by two pairs of converging parabolic walls: large walls  25  and small walls  27 . The venturi  16  has a cross-sectional area A 2  that is less than that of the input portion  24 . In the example of  FIG. 2 , the shape of the cross-sectional area A 2  of the venturi is rectangular, but may be other shapes, e.g., elliptical or oval, having a minor axis  28  shorter than its major axis  29 . The venturi  16  extends downstream to an open end  30 . In  FIG. 2 , the venturi&#39;s end  30  opens into a downstream transition portion  32  of the conduit defining a length of the fluid channel  19  diverging outward from the cross-sectional area A 2  of the venturi to a larger cross-sectional area of an output portion  34  of the conduit. In this example, the output portion  34  has the same cross-sectional area A 1  as the input portion  24 . Thus, the conduit  18  in  FIG. 2  is reversible. But the downstream transitional portion  32  may be eliminated and replaced with a flat plate having an opening forming an end wall of the output portion  34  at the open end  30  of the venturi  16 . 
         [0015]    As shown in  FIGS. 3A-3C , the transition portion of the conduit  18  may be gradual ( FIG. 3A  with a 30° taper of the long parabolic walls  25  relative to the direction of the fluid path  20  and a long length), sharp ( FIG. 3C  with a 60° taper of the long parabolic walls  25  and a short length), or intermediate ( FIG. 3B  with a 45° taper of the long parabolic walls  25  and an intermediate length). The sharp transition portion  26  of  FIG. 3  causes a more abrupt acceleration of the fluid through the channel than the longer tapers of  FIGS. 3A and 3B  and is more useful for sturdier shrimp. As indicated by the convergence of streamlines  36  in the transition portion  26  of the conduit, the flow accelerates to a higher speed in the venturi  16 . The converging flow tends to orient the shrimp along the streamlines by minimizing the surface area broadside to the flow. The hydrodynamic forces caused by the rapid acceleration of the flow at the venturi and by the non-uniformity of the flow just upstream of the venturi is sufficient to detach heads from the shrimp. The major axis  29  of the venturi cross-sectional area A 2  is long enough to admit a major portion of, if not all, the length of a shrimp into the venturi without severe collisions with the interior walls of the conduit that could break the shrimp between segments. For this reason, the venturi of  FIG. 2  is especially useful for deheading fragile cold-water shrimp. 
         [0016]    One version of a complete deheading system  40  is shown in  FIGS. 4A and 4B . Shrimp are conveyed out of a feed tank  42  by a conveyor belt  44  and dropped into a fluid-filled trough  46 . A food pump  48  draws shrimp-laden fluid from the trough  46  and pumps it into a conduit system  50 , which has two venturis  52 ,  53  at spaced apart locations along its length. Shrimp are deheaded in the venturis and conveyed by the fluid through the conduit system to a feed plenum  54 . The shrimp bodies and detached heads drop from the plenum onto a screen slide  56 . The fluid drains through the screen and into a tank  58  in fluid communication with the trough  46 . A perforated plate  60  between the tank and the trough prevents shrimp in the trough from entering the tank  58 . The food pump  48  is driven by a pump motor  62 . Together, the pump and the motor form flow control means that controls the flow rate and the fluid speed through the conduit system. 
         [0017]    The deheading system shown in  FIG. 5  has five venturis  64  connected in series in a conduit system  66 . A food pump  68  induces a flow through the conduit system  66 . Such a multiple-venturi system can be effective for deheading sturdy shrimp. The deheading system of  FIG. 6  adds fluid-pressure sensor  69  at sensor locations in the conduit system  66 , for example, at locations just upstream of the final four venturis  64  to measure the hydrodynamic force of the flow. The outputs  70  of the pressure sensors control valves  72  connected between a boost pump  74  and fluid lines  76  injecting fluid into the conduit system at injection locations  78  near the sensor locations, for example, to replace any leaked fluid and to maintain the fluid pressure along the length of the fluid channel. 
         [0018]    Although the invention has been described in detail with respect to a few versions, other versions are possible. For example, if large-diameter conduit, such as ten-inch—diameter pipes instead of 4-inch—diameter pipes, the cross-sectional area of the venturis could be circular or square because the diameter of the circular opening or the lengths of the sides of the square opening would be large enough to allow shrimp through without damaging collisions with the walls of the conduit. As another example, a complete system using only a single venturi may be sufficient to detach heads from the shrimp in some situations. So, as these suggestions suggest, the claims are not meant to be limited to the details of the exemplary embodiments.