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           FLUIDFLOW3 
           Non-Newtonian/non-settling
            liquids and Newtonian settling slurries 
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SETTLING SLURRY
            SIMULATION

          		
        

      


      FluidFlow3 Slurry will have extensive applications in
      the mining and mineral processing industries where the design
      of a pumped systems must take into account the effect of the
      solids on pipe friction and pump performance. In the screen image
      below two similar flow systems are compared, one with water only,
      the other with water containing 20% bauxite solids. The increased
      pressure drop or 'solids effect' of the bauxite is evident from
      the displayed results.


      


      
DESIGN METHOD


      
Simulating the performance of
      settling slurries, ie a "carrier fluid" conveying solid
      particles, is complicated due to the wide range of variables
      involved, viz particle size and size distribution, solids density
      and shape, percent solids, mixture velocity etc.



      The accepted approach is to determine the 'solids effect';
      the extra friction loss caused by the solids content over that
      for an equivalent flow of the carrier fluid. The carrier fluid
      may simply be water if the solids are relatively coarse with
      no fraction below about 0.4mm but solids smaller than 0.4mm can
      be held in suspension and create a 'homogeneous' carrier fluid,
      the friction characteristics of which needs to be determined.



      Typical applications will involve a water-based settling slurry.
      A number of inter-related factors then influence the excess pressure
      drop in a pipeline over the pressure loss for water alone (or
      the carrier fluid if a fine particle fraction exists). The two
      main factors are the solids characteristics and the velocity
      of flow of the mixture but pipe inclination is also important.
      For solids of size less than about 0.4mm and at higher velocities
      the particles are distributed in a homogenous manner and the
      head drop can be considered directly proportional to that of
      water.


      
At the other extreme with coarser
      particles moving only as a contact load, ie as a sliding bed
      with none in suspension, the solids effect is considerable and
      the pressure loss much greater than for water alone. This is
      referred to as fully stratified flow. In between these extremes
      are two regimes, pseudo-homogenous and heterogeneous. Pseudo-homogenous
      flow contains particles between about 0.4mm and 1.5mm and displays
      a variation of solids concentration with height across the pipe
      diameter, depending on velocity. Again the pressure drop is proportional
      to that obtained for an equal discharge of water. Heterogenous
      flow - particle size around 1.5mm to 4mm and lower velocities
      - exhibits a greater non-uniformity of solids concentration.
      The solids are supported partly by fluid suspension and partly
      by inter-particle contact. The settling velocity of the solids
      and the percent by volume in the mixture are important factors.



      A mining-type slurry may contain a wide particle size distribution
      and consequently all four regimes of flow - a homogeneous carrier
      fluid, and pseudo-homogenous, heterogenous and fully stratified
      fractions - may be present at the same time. The technique is
      to estimate the excess pressure drop separately for each of the
      four regimes and then sum them for the total.



      The design method is highly empirical. "Slurry Transport
      Using Centrifugal Pumps", by KC Wilson, GR Addie, A Sellgren
      and R Clift provides the best reference with a synthesis of the
      authors' many papers. "Introduction to Practical Fluid Flow"
      by RP King provides a useful summary of the Wilson-Addie-Sellgren-Clift
      method plus a comprehensive chapter on non-Newtonian slurries.
      "Chemical Engineering Fluid Mechanics", by Ron Darby
      provides a very useful introduction to all types of flow.



      These three references, and a considerable amount of literature
      research, provided the basis for the development of the settling
      slurry simulator. A correction routine for the performance of
      end suction centrifugal pumps is also included.


      
SOLIDS DATABASE


      
The solids database allows the
      physical properties of solids to be entered, as shown on the
      screen image below


      


      
PUMP PERFORMANCE
      CORRECTION


      
The hydraulic performance of
      an end suction centrifugal pump must be derated when pumping
      a fluid containing solids. FluidFlow3 Slurry
      allows choice of two correction methods - Fixed Reduction Ratio
      or the method according to King.



      

        

           FLUIDFLOW3 
           Non-Newtonian/non-settling
            liquids and Newtonian settling slurries 
          Previous 
           Contents 
          
        

      


      

        

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