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Pressure Drop



This is a continuation of the Process Intensifier - Optimization with CFD: Part 1 paper.

It is always important to know the pressure drop of items in a pipeline. These pressure drops were measured over a 78.7 inch (2 m) pipe section, which included the Process Intensifier. The shaft of the mixer was in the exact middle of the pipe section. Therefore, there were almost 4 pipe diameters upstream and downstream of the mixer for this study.

Pressures computed in ACUSOLVE are formulated using equal order interpolation with the velocity variables yielding a consistent structure, which permits and facilitates the total formulation stability and convergence proofs. Hence, along with the velocities, the pressures have the identical solution accuracy, stability and convergence characteristics, including local and global conservation, as the primary variables for velocity. ACUSOLVE admits a variety of boundary conditions, ranging from specified velocity and mass flux conditions, to being totally determined and computed by the solution. ACUSOLVE can even handle the case where the momentum and energy supplied by a pumping impeller determines the inflow / outflow of a system, including both velocity and pressure determination. A related characteristic is that the pressure boundary condition does not make any requirement of velocity specification, and that in the general case, any given surface could have flow going in both directions. In the case of the Process Intensifiers, designs may be developed that either introduce a pressure drop, or a pressure boost (see Part 2). The accuracy of ACUSOLVE permits the proper evaluation of the pressure state of the system.

1100 GPM Radial Process Intensifier Axial Process Intensifier
Lightnin
  Red = 40,000 Pa = 5.8 psig Red = 2,300 Pa = 0.3 psig
Hayward Gordon
  Red = 45,000 Pa = 6.5 psig Red = 5,500 Pa = 0.8 psig
Figure 8: Pressure drop determination in the Process Intensifiers at 1100 GPM (250 m3/hr). Click on any picture for a larger view.

The pressure drops were determined by looking at the pressure distribution plots (Figure 8) of each device. The following pictures show the local pressure distributions in a vertical plane directly through the middle of the pipe at 1100 GPM (250 m3/hr) flow. The scale is not the same for each device, but red always corresponds with the highest pressure (inlet) and blue always corresponds with the outlet pressure. Blue is in each case = 0, meaning that this shows pressure above the outlet pressure (gauge pressure). This form of representation makes it very easy to determine the pressure drop. The numbers are in Pascals. The maximum value on the scale (red) is thus the pressure drop from inlet to outlet, which is over a 78.7-inch (2 m) section. The values of all the pressure drops are in Table 4.

PSI (Pa) Radial Process Intensifiers Axial Process Intensifiers
  Lightnin LTR Hayward Gordon HGR Lightnin LTA Hayward Gordon HGA
Click on any picture for a bigger picture ltr model.jpg (58598 bytes) hgr model.jpg (51967 bytes) lta model.jpg (56180 bytes) hga model.jpg (58588 bytes)
650 GPM 2.8 (19305) 3.9 (26890) 0.15 (1034) 0.4 (2758)
1100 GPM 5.8 (39990) 6.5 (44816) 0.3 (2068) 0.8 (5516)
Table 4: Pressure drops across the Process Intensifier in PSI (Pa).

The pressure drops (Table 4) appear to be directly related to the power consumption of the impellers but are obviously a stronger function of the overall flow rate through the pipe. The pressure drops at 650 GPM (148 m3/hr) are approximately the values at 1100 GPM (250 m3/hr). The LTA at 1100 GPM (250 m3/hr) is particularly low probably because it is "flooded" by the cross flow and has little affect on disturbing the flow through the pipe. The pictures for 650 GPM (148 m3/hr) is not shown.

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