Abstract:
The present invention relates to a method, an apparatus and a rotor for homogenizing a medium. The invention may be utilized in all areas of industry where mere homogenisation of a medium or mixing of at least two flowing media is needed. A preferred application of the invention can be found in pulp and paper making industry where various chemicals have to be mixed with fiber suspensions. A characterizing feature of the invention is the symmetry of the homogenising operation in the homogenising chamber.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 11/578,444, filed Oct. 13, 2007, which is a National Stage of International Application No. PCT/CH2005/000151, filed Mar. 14, 2005, and which claims the benefit of European Patent Application No. 04405223.1, filed Apr. 13, 2004, the disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method, an apparatus and a rotor for homogenizing a medium. The invention may be utilized in all areas of industry where mere homogenization of a medium or mixing of at least two flowing media are needed. A preferred application of the invention can be found in the pulp- and paper-making industry where various chemicals have to be mixed with fiber suspensions. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the following, prior art mixing apparatus of the pulp and paper industry have been discussed as examples of known techniques of mixing a flowing medium to another. However, it should be understood that in spite of the fact that only mixers of the pulp and paper industry have been discussed, it has not been done for the purpose of limiting the scope of the present invention to these fields of industry. 
         [0004]    A widely used example of chemical mixers for pulp has been discussed in U.S. Pat. No. 5,279,709, which discloses a method of treating a fiber suspension having a consistency of 5-25% in an apparatus within a fiber suspension transfer line. The apparatus comprises a chamber having an axis in the direction of flow of the fiber suspension, a suspension inlet and a suspension outlet having an axis in alignment with the chamber axis, and a fluidizing rotor having an axis of rotation transverse to the direction of flow and being disposed within the chamber for rotation therein. The rotor comprises blades, each blade having a proximal and distal end and the blades diverging from the proximal end and extending in spaced relation from the axis of rotation along an axial length thereof. The method comprises feeding the suspension from the suspension transfer line through the inlet into the chamber, introducing chemicals into the fiber suspension upstream of the fluidizing rotor, rotating the fluidizing rotor within the chamber so as to form an open center bounded by a surface of revolution and subjecting the suspension moving toward the outlet to a shear force field sufficient to fluidize the suspension, to mix the chemicals evenly into the suspension and to render the suspension flowable, flowing the suspension through the open center of the rotor, and discharging the suspension from the chamber through the suspension outlet. 
         [0005]    The above-described mixer has found a number of imitations, of which, for example, U.S. Pat. No. 5,575,559 and U.S. Pat. No. 5,918,978 can be mentioned. 
         [0006]    All the above-discussed mixers have a few features in common. The rotor is brought into the mixing chamber in a direction perpendicular to the axis of the flow through the mixing chamber. The rotor is formed of finger-like blades, which leave the center of the rotor open. The rotor shaft and the rotor blades are arranged such that the mixing chamber with the rotor installed does not form a symmetrical mixing space, but an asymmetrical one, where the turbulence created by the rotor is not optimal. The result is that the mixing of the chemical with the fiber suspension is not even, but in some areas of the mixer the turbulence level is higher, resulting in more even mixing than in areas where the turbulence level is lower. 
         [0007]    There is yet another mixer where the transverse rotor construction has been used. The mixer has been discussed in EP-B2-0 606 250. Here the mixer for admixing a treatment agent to a pulp suspension having a consistency of 10-25% comprises a cylindrical housing with a mixing chamber defined between an inner wall of the cylindrical housing and a casing of a coaxially mounted, substantially cylindrical rotor provided with mixing members on its casing surface, an inlet in the housing for supplying pulp to the mixing chamber, an inlet in the housing for supplying treatment agent to the mixing chamber and an outlet for withdrawing mixed pulp and treatment agent, a mixing zone in the housing provided with stationary mixing members wherein a gap is defined between the mixing members of the rotor and the stationary mixing members. The mixing chamber and the mixing zone have a width corresponding to the axial length of the rotor. The stationary mixing members are arranged on a portion within an angle of 15-180 degrees of the inner wall of the housing. The pulp inlet and the treatment agent inlet extend along the entire width of the mixing chamber for adding the pulp and the treatment agent each in well-formed thin layers. The inlet for the treatment agent is connected to the mixing chamber at a circumferential position prior to the mixing zone. The outlet extends along the entire width of the mixing chamber, and a cylindrical surface is formed directly after the outlet to prevent pulp from flowing backward past the rotor. In other words, the mixer of the EP patent has a closed cylindrical rotor with solid mixing members on the rotor surface. The cylindrical rotor is positioned in a cylindrical mixing chamber. The basic idea in the EP document is to feed both pulp and the chemical as thin layers in the mixing zone between the rotor and the chamber wall and mix such there. 
         [0008]    However, based on practical experiences it has been learned that the mixing is not very efficient in the narrow slot between the rotor and the mixing chamber. Also, it has been learned that the energy consumption of this type of mixer is high compared, for instance, to the mixer discussed in U.S. Pat. No. 5,279,709 mentioned first. 
       SUMMARY OF THE INVENTION 
       [0009]    At least some of the problems of the prior art mixers, and homogenizers, by which are understood devices which subject a medium to such a turbulence that the homogeneity of the medium is improved irrespective of whether another medium is to be mixed with the first medium or whether only the homogeneity of the first medium is to be improved, are solved by means of the present invention, an essential feature of which is the circulation of the medium in both the radial and the axial directions in the mixing chamber. Preferably the circulation of the medium should be symmetrical in relation to the centerline of the mixing chamber. 
         [0010]    Another preferred but not necessarily an essential feature of the present invention is the symmetry of the mixing chamber and/or the rotor in relation to the centerline of the mixing chamber. 
         [0011]    Yet another preferred feature of the invention is that the center of the mixer rotor is at least partially closed so that both a direct flow through the rotor and collection of gas at the center of the rotor are prevented. 
         [0012]    The method, the apparatus and the rotor of the present invention will be described in more detail in the following with reference to various embodiments of the present invention and to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  illustrates a cross-section of a prior art mixer discussed in detail in U.S. Pat. No. 5,279,709, 
           [0014]      FIG. 2   a  illustrates a schematical axial cross-section of a first preferred embodiment of the present invention, 
           [0015]      FIG. 2   b  illustrates an oblique view of a rotor according to the first preferred embodiment shown in  FIG. 2   a,    
           [0016]      FIG. 3  illustrates a schematical axial cross-section of a second preferred embodiment of the present invention, 
           [0017]      FIG. 4  illustrates a schematical cross-section of a preferred embodiment of the present invention along line A-A of  FIG. 2   a,  and 
           [0018]      FIG. 5  illustrates a schematical cross-section of another preferred embodiment of the present invention in the manner shown in  FIG. 4 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]      FIG. 1  discloses a prior art mixer discussed in detail in U.S. Pat. No. 5,279,709. The mixer  10  comprises in general a substantially cylindrical or sometimes almost ball-shaped chamber  13  provided with an inlet  14  connected to an inlet pipe  11  and an outlet  15  connected to an outlet pipe  12 . The inlet  14  of the chamber  13  is provided with an inlet opening  23  (shown by a dotted circle) for chemicals through which opening, for instance, bleaching chemicals may be beforehand added into the pulp flow prior to mixing. The opening for the chemicals may, however, be located almost anywhere upstream of the mixer chamber. The outlet  15  is provided with a throttling  16 , i.e. an area having a reduced diameter with respect to both the chamber  13  and the outlet pipe  12 . A substantially radial shaft  21  protrudes through the wall of the chamber  13  and a fluidizing element  22  is attached to the other end of the shaft  21  inside the chamber  13 . Although the position of the shaft  21  shown in  FIG. 1  is substantially radial or perpendicular to the direction of flow or to the axis of the chamber  13 , shaft  21  may also deviate from that perpendicular position by up to about 30 degrees. The fluidizing element is a rotor having a plurality of substantially axially located blades. The blades are preferably formed of an elongated steel plate having a rectangular cross-section and having radially an inner and an outer edge. The blades may, however, be of any appropriate form as long as the center of the rotor is open. The blades are arranged with the inner edges located at a distance from the axis of the rotor in such a way that the center of the rotor remains open, thus allowing the fiber suspension to flow through the center of the rotor, whereby the rotor itself causes as little resistance to the flow as possible. The blades may be either straight axial or somewhat arcuate thus forming a cylinder-, ball- or barrel-shaped envelope surface during rotation thereof. Preferably, the rotor is provided with more than two blades so that always, even when the rotation of the rotor is for some reason stopped, at least one of the blades is creating turbulence in the suspension. In other words, the creation of an otherwise entirely open space between the rotating blades and through the rotor is being prevented. Nevertheless, the rotor, at the same time, permits the suspension flow to pass the blades and thus to go through the rotor. 
         [0020]    The operation of the apparatus is such that the fiber suspension flow, for instance, from a fluidizing centrifugal pump, is introduced to chamber  13  through inlet  14  and simultaneously chemicals are fed through opening  23 , either located in connection with the mixer chamber or somewhere upstream thereof, to the fiber suspension. The fluidizing element, i.e. the rotor, while rapidly rotating, causes the fiber suspension to break into small fiber flocs whereby the chemicals are mixed with the suspension. 
         [0021]      FIG. 2   a  shows a schematical cross-section of a preferred embodiment of the present invention. The homogenizer  30 , which from now on is called, for the sake of simplicity, a mixer, comprises a housing  32 , the interior thereof being called a homogenizing chamber or mixing chamber, with an inlet duct  34  having an inlet opening  340  into the homogenizing or mixing chamber and an outlet duct  36  having an outlet opening  360  from the homogenizing or mixing chamber and a rotor  38  arranged transverse to the direction of flow from the inlet opening  340  to the outlet opening  360 . The housing  32  is, in this embodiment of the invention, preferably of a substantially cylindrical shape so that the axis A R  of the rotor  38  runs at least substantially parallel to the axis A H  of the housing  32 . Yet the axis A R  of the rotor may coincide, as shown in  FIG. 2   a,  with the axis A H  of the housing, i.e. the homogenizing chamber, or the rotor could be eccentrically positioned in relation to the housing. The housing is further provided with two end caps  40  and  42 . The end cap  40  includes a substantially central opening for the shaft  44  of the rotor  38  with the necessary sealing, and possibly also with bearings for the shaft  44 . The opposite end of the housing  32  is provided with another end cap  42 , which is, in accordance with a preferred embodiment of the invention, a solid substantially round plate. However, the end cap  42  may be whichever shape is required to perform its task of closing the other end of the housing  32 . For maintenance and repair reasons at least the end cap  40  including the opening for the shaft  44  is removable, i.e. fastened by means of, for instance, bolts or screws to the housing  32 . To fulfill the requirements of the symmetry, the surfaces of the end caps  40 ,  42  facing each other are preferably alike. They may either be smooth plates, or they may be provided with turbulence elements like grooves or ridges or pins or blades as long as the elements appear substantially similar on both opposing surfaces. 
         [0022]    The substantially cylindrical wall of the housing  32  is provided with the inlet opening  340 , and the outlet opening  360 , as explained above. Both the inlet and the outlet openings are, preferably, of such a shape that they both have a center and an axis of symmetry, which lie substantially in the same plane. This plane of symmetry, so-called centerline plane CL P , runs along the centerline of the housing perpendicular to the axis A H  of the housing. The centerline plane of the openings coincides with a centerline plane of the housing, which runs at an equal distance from the end caps  40 , and  42 . However, it has to be understood that if, for instance, for manufacturing or other corresponding reasons, the line running via the centers of the inlet and the outlet openings does not exactly coincide with the centerline of the housing but is still very close thereto, or is not exactly perpendicular to the housing axis A H , but the operation of the rotor and the openings results in substantially symmetrical turbulence fields within the housing, the location of the openings should be considered as fulfilling the requirements of this invention. 
         [0023]    The rotor  38  has a shaft  44  running through the mixer housing  32  so that the end  46  of the shaft  44  is positioned at a short distance from the end cap  42 . The distance from the inner surface of the end cap to the end surface of the shaft is of the order of a few millimeters, preferably 1-5 millimeters. According to a preferred embodiment of the invention the shaft  44  extends from one end of the housing  32  to the second end of the housing. In broader terms, the gap between the shaft end surface and the end cap  42  is such that it does not change the flow behavior of the pulp within the mixing chamber to a significant degree. Thereby the allowable size of the gap depends, for instance, on the consistency of the pulp to be treated. 
         [0024]    According to another optional embodiment of the invention the end cap at the second end of the housing is provided with a member protruding axially towards the shaft such that a similar gap is left between the shaft end and the member as discussed above. The diameter and overall shape of the member correspond to that of the rotor shaft to fulfill the requirements of symmetry. The member could also be tubular such that an end part of the shaft extends inside the member whereby the shaft end part should, preferably, be provided with a smaller diameter so that the outer diameter of the tubular member corresponds to the full diameter of the shaft. 
         [0025]    As a further optional embodiment the member may extend from the second end cap at a close proximity to the first end cap whereby the rotor shaft terminates near the first end cap, whereby the rotor blades are attached to their shaft only at their first end. In this optional structure it has to be ensured that the symmetry is maintained by designing the opposite end of the rotor-housing combination such that it corresponds to the first end thereof. 
         [0026]    As a yet further option a structure can be mentioned where an opening for the shaft  44  has been arranged in the other end cap  42 , too. The opening should, at least, be provided with the necessary sealing, and possibly the end cap  42  with bearings for supporting the shaft end. 
         [0027]    Another feature of the invention is that the diameter of the shaft  44  is of significant magnitude compared to the diameter of the housing  32 . The purpose of the size, shape and location of the shaft  44  is to ensure that the center of the housing is closed whereby gas cannot collect there. This is accomplished by arranging no or very little volume of lower pressure inside the housing, in the so-called mixing or homogenization chamber where the gas could collect. 
         [0028]    The rotor  38  further has a number of blades  48  positioned at a distance from both the rotor shaft  44 , and the inner surface of the housing  32 . The blades  48  are fastened to the shaft  44  by means of distance members or arms  50 . Basically, the shape of the arms has been discussed in connection with  FIGS. 10 through 13  of U.S. Pat. No. 5,791,778, the entire contents of which are hereby incorporated as a reference herein. The arms are positioned at a substantially equal distance from the centerline plane of the rotor, the centerline of the rotor lying on the centerline plane CL P  of the housing. The centerline plane of the rotor could as well be called as a plane of symmetry of the rotor. Thus the part of the rotor within the chamber also fulfils the requirements of symmetry. 
         [0029]    The blades  48  as well as the arms  50  have several tasks. Firstly, since it is a question of a mixing or a homogenizing apparatus, it is clear that the main purpose of the apparatus is to act as an efficient turbulence generator. This has been ensured by the following measures:
       the inside of the housing is substantially symmetrical whereby the mixing or turbulence generation conditions at both ends of the housing are the same,   the blades  48  have been arranged in an optimal location between the shaft  44 , and the inner wall of the housing  32 , the exact location depending on, for instance, the medium to be treated, the consistency of the medium, the gas content of the medium, and/or the amount of gas added to the medium, the volume flow through the housing, etc.,   the circulation of the medium in the housing
           firstly, the blades  48  subject the medium to centrifugal forces pushing the medium towards the inner wall of the housing  32 . This creates a recirculation round the blades  48  as the more medium the blades  48  move to the inner wall the more medium has to move axially inwardly to clear space for the outwardly moving medium,   secondly, the blades  48  subject the medium to axial forces pushing the medium axially to the sides of the housing  32 . This has been accomplished by arranging the blades  48  to a straight inclined—such as the blades shown in  FIG. 2   b— or spiral position in relation to the axial direction. The blades  48  may extend from the proximity of the first end cap  40  to the proximity of the second end cap  42 , whereby the blades need to be bent at the centerline plane of the housing. Another alternative is to arrange separate blades on each side of the rotor. However, in such a case the blades are positioned symmetrically on both sides of the centerline plane so that the angular direction of the blades is substantially the same in relation to the centerline plane, the blades are attached to the shaft by means of arms arranged at an equal distance to the centerline plane, and both start and terminate at an equal distance to the centerline plane, and the end caps. Yet one more, in itself a natural prerequisite of the rotor of the invention, is that the number of these separate blades on both axial sides of the rotor, or the centerline plane, is the same, and that the blades are located at regular intervals on the circumference of the rotor shaft. However, when considering the symmetry requirements of the present invention, especially in view of a functioning rotor, the separate blades on each side of the centerline plane of the rotor need not be arranged as if a bent unitary blade  48  or  148  of  FIGS. 2   a,    2   b  and  3  were just cut in two parts along the centerline plane, but there may be a circumferential step between the blades on the opposite side of the centerline plane. The axial pumping effect of the blades  48  while forcing medium to the ends of the housing  32 , or mixing chamber, simultaneously creates a circulating flow as the medium already present at the ends of the housing has to move towards the centerline plane to free space for the medium pumped by the blades  48 . A preferred range for the inclination angle of the blades in relation to the centerline plane is from 20 to 60 degrees. The pumping effect of the blade is ensured by arranging the inclination such that the part of the blade closest to the centerline plane is the leading part of the blade.   due to the function of the rotor blades there is both radial and axial recirculation in the mixing chamber. The symmetrical shape of the mixing chamber and the rotor ensure that the turbulence field within the chamber is symmetrical, too.   
               
 
         [0036]    Secondly, since the device is a rotating member, the purpose of which is to homogenize or to mix a medium or media, the rotating members should not separate gas from the medium. This has been taken into account by filling the rotor center with the shaft  44  and, preferably, designing the cross-section of the rotor blades  48  and arms  50  in as optimal a manner as possible. However, also the economical factors have to be taken into account whereby the most complicated cross-sectional shapes may be out of the question due to their expensive manufacturing methods. 
         [0037]      FIG. 2   a  shows yet one more feature, which is not needed if the device is a homogenizer, but which may be needed if it is a mixer, namely the chemical inlet or inlet opening  52 . In the embodiment shown in  FIG. 2   a,  the chemical inlet opening  52  is located in the inlet duct  34  upstream of the mixer chamber. The chemical inlet may, depending mainly on the chemical, be formed of one opening, of several openings, of a perforated pipe section, or of a porous pipe section just to name a few alternatives. Again depending at least partially on the chemical, the chemical inlet may be positioned in the inlet duct, as shown in  FIG. 2   a,  or upstream thereof. Sometimes the chemical could also be introduced directly into the mixing chamber via end caps (symmetrically), via the rotor shaft, via the rotor shaft and blades, or via an opening in the housing wall either to the centerline plane of the housing or via two or more openings arranged symmetrically to the housing centerline plane. 
         [0038]      FIG. 3  illustrates schematically another preferred embodiment of the present invention. In this embodiment the mixer  130  has a substantially rotationally symmetric, for instance a barrel-shaped, housing  132  with an inlet duct  134 , an outlet duct  136 , corresponding inlet and outlet openings  1340 , and  1360 , respectively, and end caps  140 ,  142  similar to the ones discussed in connection with  FIG. 2   a.  In this embodiment the largest diameter, or largest cross-section of the mixing chamber, is at the centerline plane, i.e. at the plane of symmetry of the housing, from where the cross-section decreases towards the ends of the housing in a similar manner at both sides of the centerline plane. 
         [0039]    The rotor  138  of this embodiment has several features differing from the ones shown in the embodiment of  FIG. 2   a.  Here the rotor shaft  144  within the mixing chamber is formed of two frusto-conical parts  144 ′ and  144 ″ so that the bases of the cones lie against each other on the plane perpendicular to the axis A R  of the rotor shaft  144 , the so-called centerline plane CL P , or the plane of symmetry of the rotor, the plane also running substantially via the centers of the inlet opening  1340  and the outlet opening  1360 . Thus the diameter of the shaft  144  is reduced towards the end caps  140 , and  142 . The diameter of the rotor shaft  144  may change in whichever manner as long as it does so substantially symmetrically to the above-mentioned centerline plane. Thus the rotor shaft  144  may be, for instance, barrel-shaped, hourglass-shaped or whatever desired shape. At this stage it is worth mentioning that the non-cylindrical shaft shape may be applied to any housing shape and vice versa. The only prerequisite for both the housing and the rotor is that they are substantially symmetrical with respect to the above-defined centerline plane. 
         [0040]    The rotor  138  of this embodiment has blades  148  the outer contour of which corresponds, in accordance with a further preferred embodiment of the invention, to the shape of the inner wall of the housing  132 . The blades  148  are fastened to the shaft  144  by means of arms  150 , which are positioned, preferably, at a certain distance from both the end caps  140 ,  142 , and the centerline plane CLp. The same basic principles as discussed in connection with  FIG. 2   a  apply to the blades of this embodiment, too. In a similar manner the discussion concerning the possible introduction of the chemical applies here, too. 
         [0041]    The cross-sectional shape of the homogenizing chamber has not been discussed in more detail. It has only been mentioned that it is either cylindrical or rotationally symmetric. However, the homogenizing chamber may, in fact, be of any shape as long as it is substantially symmetric in relation to the centerline plane of the housing or, rather, of the homogenizing chamber, defined earlier. Thus the cross-section thereof may be elliptical or polygonal, just to name a couple of different forms. As to the positioning of the rotor within the homogenizing chamber, there are only two prerequisites. The first prerequisite is that the rotor axis is at least substantially parallel to the housing axis (corresponding to the axis of the homogenizing chamber), either coinciding therewith or being eccentric. The second prerequisite is that the centerline plane of the homogenizing chamber and the centerline plane of the rotor coincide. In fact the disclosure herein talks mainly about a centerline plane irrespective of the plane in question. 
         [0042]    Further, the closer structure of the chamber walls has not been discussed yet. The walls may be provided with turbulence elements like pins or bars or stationary blades or ribs, which work more or less together with the blades of the rotor. The size, shape and direction of the elements may change along the length of the chamber, however, keeping in mind that the result of the cooperation of the rotor and the elements on the chamber wall should be a turbulence field, which is symmetrical in relation to the centerline of the housing. Thus the bars or blades on the wall could, for instance, be designed or directed to aid in feeding the medium towards the end caps from the centerline plane. 
         [0043]    In a similar manner, the end caps could be provided with turbulence elements like ribs, blades or pins to increase the turbulence in the chamber. 
         [0044]    In fact, what is meant by the term “symmetric” in connection with both the rotor and the mixing chamber or the homogenizing chamber is that the shape of the rotor together with the mixing or the homogenizing chamber should be such that the turbulence field created in the chamber is as symmetrical in relation to the centerline plane of the housing as possible. Thus it is possible that the shapes of both the chamber and the rotor deviate somewhat from exactly symmetrical shapes due to, for instance, structures needed for supporting and/or sealing the shaft of the rotor within the first end cap. Also some other slight modifications in either the rotor or the chamber structure, or in both, are possible, as long as the goal, and preferably the result, is a symmetric turbulence field. 
         [0045]      FIG. 4  shows a cross-section of an apparatus in accordance with a preferred embodiment of the present invention along line A-A of  FIG. 2   a.    FIG. 4  shows the housing  32  with an inlet duct  34  and an outlet duct  36 . The inlet duct  34  has been designed such that the inlet duct opens in substantially tangential direction into the housing  32  against the direction of rotation of the rotor. The purpose of this construction is to maximize the turbulence as the speed of the medium introduced into the housing, together with the rotational velocity of the rotor acting in the opposite direction, creates a maximal velocity difference, which results in maximum turbulence. 
         [0046]    The outlet duct  36  departs the housing  32  in a, preferably, tangential direction, but contrary to the inlet duct, in the direction of rotation of the rotor. The purpose of this construction is two-fold: firstly, by streamlining the outlet duct, keeping in mind the hydrodynamic principles, the separation of gas from the medium is prevented, and secondly, the streamlined outlet duct minimizes the pressure losses in the outlet duct, as there is no need to create extra turbulence. 
         [0047]      FIG. 5  shows a cross-section of an apparatus in accordance with another preferred embodiment of the present invention. In this embodiment the only difference to the apparatus of  FIG. 4  is the location of the outlet duct  36 ′ in relation to the inlet duct  34 ′. Now the outlet duct has been positioned about 270 degrees from the inlet duct in the direction of rotation of the rotor whereas the position in  FIG. 4  was about 180 degrees. Thus the positions of the inlet duct and the outlet duct can be freely chosen, but keeping in mind that the outlet duct should be at least 180 degrees from the inlet duct in the direction of rotation of the rotor, so that the material or medium to be homogenized cannot so easily escape from the inlet duct directly to the outlet duct. 
         [0048]    It should, however, be understood that though  FIGS. 4 and 5  give an impression that the inlet duct and the outlet duct run along the centerline plane of the housing, it is just a preferred option. The inlet duct and/or the outlet duct may extend in any feasible direction from the homogenizing chamber as long as the inlet opening and the outlet opening are arranged substantially symmetrically to the centerline plane, i.e. the plane running via the centers of the openings. Thus  FIGS. 4 and 5  could as well be understood such that the apparatus in the figures has been cut along the centerlines of the ducts whereby the duct/ducts may be curved, too. 
         [0049]    Finally, it should be understood that, in the above, only a few preferred embodiments of the invention have been discussed without any intention to limit the scope of the invention to those embodiments only. Thus the scope of the invention is defined only by the appended claims.