Abstract:
An agitator, in particular for dispersing gases in liquids, includes a plurality of blades, with each blade being constructed to have a blade portion bent forwards in a rotation direction.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
         [0001]    This application claims the priority of German Patent Application, Serial No. 203 07 199.0, filed May 8, 2003, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates, in general, to an agitator, in particular to an agitator for dispersing gases in liquids.  
           [0003]    Agitators of a type involved here are used to disperse gas, supplied to a liquid being stirred, in smallest possible bubbles to create a large surface for a material transfer between gas and liquid.  
           [0004]    It would be desirable and advantageous to provide an improved agitator which is constructed to shorten a mixing time while still keeping a drop in power to a minimum.  
         SUMMARY OF THE INVENTION  
         [0005]    According to one aspect of the present invention, an agitator, in particular for dispersing gases in liquids, includes a plurality of blades, with each blade being constructed to have a blade portion bent forwards in a rotation direction. Suitably, the blade portion may be positioned at a trailing end of the blade, as viewed in rotation direction.  
           [0006]    According to another feature of the present invention, the blade portion may be positioned at a radially outer zone of the blade.  
           [0007]    According to another feature of the present invention, the ratio of the radial length of the blade portion to the radial length of the blade may be in a range of about 0.2 to 1.0, preferably about 0.4 to 0.6.  
           [0008]    According to another feature of the present invention, the ratio of the width of the blade portion to the width of the blade may be in a range of about 0.1 to 1.0, as viewed in circumferential direction, preferably about 0.15 to 0.4, as viewed in circumferential direction.  
           [0009]    According to another feature of the present invention, the ratio of the radius of curvature of the blade portion to the outer radius of the blade may be in a range of about 0 to 0.3, preferably about 0.01 to 0.15.  
           [0010]    According to another feature of the present invention, the blade portion may have a leading end region, as viewed in the rotation direction, with the end region being constructed to have a flat section and an end section which extends at an angle of about 0° to 45°, preferably about 10° to 30°, to the flat section and is directed away from the blade. Suitably, the end section is substantially triangular in shape. Advantageously, the end section has a radial length, and the blade portion has a radial length, wherein the ratio of the radial length of the end section to the radial length of the blade portion is about 0 to 1.0, preferably about 0.5 to 1.0. Also, the ratio of the width of the end section to the width of the blade portion may be about 0.05 to 0.75, preferably about 0.2 to 0.6.  
           [0011]    According to another feature of the present invention, the blade may extend in relation to a rotation plane at an angle in a range of about 100 to 45°, preferably in a range of about 200 to 300. Suitably, the blade portion extends in relation to the blade at an angle in a range of about 100 to 45°, preferably about 200 to 300.  
           [0012]    According to another feature of the present invention, the blade may have a leading end portion, as viewed in the rotation direction, with the end portion extending at an angle of about 0° to +/−40°, preferably about 0° to +/−15°, to the blade, and being bent to a plane of the blade portion. Suitably, the ratio of the width of the end portion to the width of the blade is about 0 to 0.5, preferably about 0.1 to 0.3.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0013]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
         [0014]    [0014]FIG. 1 is a plan view of an agitator according to the present invention; and  
         [0015]    [0015]FIG. 2 is a side view of the agitator. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]    Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.  
         [0017]    Turning now to the drawing, and in particular to FIG. 1, there is shown a plan view of an agitator according to the present invention, generally designated by reference numeral  10  and including a hub  12  for attaching the agitator  10  to an agitator shaft (not shown). Three mountings  16  are securely fixed about the outer periphery of the hub  12  at an angular distance of 120° for attachment of three blades  14 , which extend essentially radially outwardly. Of course, the blades  14  may also be directly mounted to the agitator shaft. In operation, the agitator  10  turns clockwise in a rotation direction of arrow P around an axis  18  which is defined by the agitator shaft. The mountings  16  may extend transversely to the axis  18  or may extend inclined at an acute or obtuse angle in relation to the axis  18 .  
         [0018]    It will be understood by persons skilled in the art that the illustration of three blades  14  mounted to the hub  12  is by way of example only, as two or more than three blades may, of course, be provided as well.  
         [0019]    Reference character R 2  designates an outer radius of each blade  14 , while reference character L 2  designates a total radial length of each blade  14 , and reference character B 2  designates a total width of each blade  14 .  
         [0020]    Each blade  14  has in rotation direction a trailing end region which is provided with a blade portion  20  bent forwards in rotation direction and extending radially at a radial length L 1  over part of the radial length L 2  of the blade  14 . The ratio of the radial length L 1  of the blade portion  20  to the radial length L 2  of the blade  14  is, for example, in a range of about 0.2 to 1.0, preferably in a range of about 0.4 to 0.6. The blade portion  20  has a width B 1 , whereby the ratio of the width B 1 , as viewed in circumferential direction, to the width B 2  of the blade  14  is, for example, in a range of about 0.1 to 1.0, preferably in a range of about 0.15 to 0.4.  
         [0021]    The blade portion  20  is comprised of a curved member  26  having a radius of curvature R 1  and terminating in a flat member  28  which, optionally, may also be curved in shape. The ratio of the radius of curvature R 1  to the outer radius R 2  of the blade  14  is, for example, in a range of about 0 to 0.3, preferably in a range of about 0.01 to 0.15. The blade portion  20  extends from the blade  14  in relation to the vertical rotation axis  18  upwards and then continues substantially forwards in rotation direction of the agitator  10 .  
         [0022]    The blade portion  20  of each blade  14  has in rotation direction a leading end region with an end section  22  that may be triangular in shape, as shown by way of example in FIG. 2, and extends at an angle γ to the flat member  28  of the blade portion  20 , away from the blade  14 . The angle γ may suitably range from about 0° to  450 , preferably, from about 100 to 300. The triangular end section  22  has a radial length L 3  and a width B 3  and is configured to have a tip  23 , which is directed radially outwards, as shown in FIG. 2. Of course, the tip  23  may also be directed radially inwards. The ratio of the radial length L 3  of the triangular end section  22  to the radial length L 4  of the blade portion  20  is in the range of about 0 to 1.0, preferably about 0.5 to 1.0. The ratio of the width B 3  of the end section  22  to the width B 1  of the blade portion  20  is in the range of about 0.05 to 0.75, preferably about 0.2 to 0.6.  
         [0023]    As shown in FIG. 2, the blade  14  extends in relation to the rotation plane D at an angle α in the range of about 100 to 45°, preferably, from about 200 to 300. The flat member  28  of the blade portion  20  extends in relation to the blade  14  at an angle β in the range of about 10° to 45°, preferably about 20° to 30°.  
         [0024]    Each blade  14  has in rotation direction a leading end which may be configured to have an end portion  24  which is bent at an angle δ in relation to the remainder of the blade  14  to extend in a direction of the plane of the flat member  28  of the blade portion  20 . The angle δ may hereby range from about 0° to +/−40°, preferably, from about 0° to +/−15°. The end portion  24  has a width B 4 , whereby the ratio of the width B 4  of the end portion  24  to the total width B 2  of the blade  14  ranges suitably from about 0 to 0.5, preferably about 0.1 to 0.3.  
         [0025]    The bending line between the blade  14  and the end portion  24  extends in the non-limiting example of the drawing, transversely to the outer edge of the blade  14 . Of course, the bending line between the blade  14  and the end portion  24  may, however, extend also at a different angle to the outer edge of the blade  14 . The end portion  24  has a front side, as viewed in rotation direction P, which may be rounded and/or beveled, whereby the bevel may suitably be configured in the radially outer zone of the blade  14 .  
         [0026]    The agitator  10  according to the present invention attains a much shorter mixing time, while still maintaining superior dispersion quality and experiencing little loss in power. As a consequence of the larger area of the blades  14  in relation to the area of the blade portion  20 , the radial pump effect is eccentric and has an axial component. The combination of axial and radial flow patterns results is significantly shorter mixing times in the agitator vessel. In view of the substantially box-shaped configuration of the blade portion  20 , formation of gas cushions behind the blades  14  is substantially prevented so that power losses during dispersion of gases are reduced. Moreover, compared to axial flow, the implementation of a strong radial flow results in a better heat transport. Thus, the agitator  10  according to the present invention combines the advantages of radially pumping and axially pumping agitators.  
         [0027]    While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.  
         [0028]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: