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


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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