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           FLUIDFLOW
            3 
            2-Phase (multiphase)
            gas/liquid simulation 
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      Example 1 - Air water two phase model. Constant
      quality


      
Two-phase conditions can be specified
      at a boundary for a single fluid, or we can mix gas and liquid
      streams in order to make a two phase mixture. The second method
      iis used in this example.The model flowsheet below shows two
      known flows - water at node 1 and air at node 2 -

      combining and being heated via a plate exchanger (node 6), then
      flowing to a separation vessel (node 5). The red dot on the Knock
      Out Pot (separator) represents the liquid outlet and the yellow
      dot represents the vapour outlet.


      
Calculation method - Beggs Brill.


      

      
Date was entered as follows:


      
Nodes:


      

      
Pipes:


      
    
        
  • Pipes (-1 and -2 connecting
        the known flows to the connector) 0.5 m in length 2" sch
        40 pipe.
        
  • Pipe (-6 from the connector
        to the plate exchanger) 60 m in length and an inside diameter
        of 50.8 mm
        
  • Pipe (-3 connecting the plate
        exchanger to the KO Pot) 60m in length and an inside diameter
        of 50.8 mm.
        
  • Pipe (-4 vapour outlet from
        KO Pot) 5m and 6" sch 40 pipe.Pipes (-5 and -7 liquid outlet
        from the KO Pot) 10m and 2" sch 40 pipe.
      


      
Overveiw of Results



      

        

            
          
            
This is an example of two phase
            flow with constant quality. This means that the vapor mass fraction
            is constant and there is no mass transfer between the phases.
            It does not mean that the pressure loss per unit length is constant
            or that the velocity between the two phases is constant. In the
            first pipe section after mixing (pipe -6) you can see that the
            gas superficial velocity increases from the start to the end
            of pipe -6. For 60m of pipe -6, the total pressure loss is 145997
            Pa, but the friction loss is 144529 Pa. Since the pipe is horizontal
            the difference is the acceleration loss.


            
After the exchanger the mixture
            has experienced a temperature increase of 30 °C. The total
            pressure loss in the pipe after the exchanger (-3) is 198502
            Pa (pipe -3 is identical in length and diameter to -6). This
            is because gas volume and velocity as well as other fluid properties
            have changed with the increase in temperature in the outlet pipe.
            You can get a feel for the differences by displaying the Beggs
            Brill flow pattern map.


            
If you use the Whalley criteria,
            FluidFlow3: 2-Phase selects the Friedel method and in this case
            total system pressure losses reduce by 17.5%.


            


            For this example Muller Steinberg Heck, Whalley and Beggs Brill
            are probably the most appropriate methods. You can see the total
            system pressure loss estimation can vary considerably.
          

        

      


      

        

           FLUIDFLOW 3 
            2-Phase (multiphase)
            gas/liquid simulation 
          Previous 
           Contents 
          Next
           
        

      

        

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