completely replaces the primary flow at shut off. Interestingly, to be
sustained, the secondary flow requires almost as much power as the
primary flow, as the input power curve in Figure 2 shows.
Second, numerical simulation processes become stable at flows below
20% of maximum because the solution is continuous and unique and,
therefore, computational fluid dynamics (CFD) codes can accurately predict
the solution. In other words; the transition from primary flow to secondary
flow happens in an orderly and continuous way such that CFD analysis can
fully capture.
CFD codes, on the other hand, cannot predict solutions for
compressible flows (0.1 < M < 0.3) in the vicinity of shut off due to
discontinuity in the solution, the pressure rise curve measured when the
flow is decreasing may be different from the pressure rise curve
measured when the flow is increasing (from 0 to 20%), this
non-uniqueness is called hysteresis. In fact, if LNG is replaced by a
compressible fluid (such as air or light hydrocarbon with very low
specific gravity, M > 0.3), then there will be a lower limit on flow, called
the surge point, below which a stable solution does not exist, and near
which CFD numerical simulations would breakdown.
Conclusion
Centrifugal pump optimisation can be achieved by utilising inducers with
avocado shaped hub contours, impellers and diffusers with circular arc
blades, and preferred functional parameters. To meet different flow and
head requirement, centrifugal pumps can be geometrically scaled and
their performance accurately predicted. Incompressibility of LNG
renders it conducive to numerical analysis over the entire flow range, as
the consumed power is utilised to sustain mean flow, secondary flow, or
both. ACD is developing proprietary software to predict performance
curves of new pump designs utilising optimum design parameters, test
database of production pumps, scaling and gulping of existing hardware,
CFD codes to calibrate and enhance software accuracy, and an
embedded warning system to alert the user when fluid/thermal/
structural parameters deviate from allowable ranges.
Vacuum Systems
Process-integrated solutions for
many types of vacuum system.
More than 80 years of ex-
perience in the development,
design, and construction of
steam ejectors and hybrid
vacuum systems.
Thousands of references in
numerous industrial sectors all
over the world
.
engineering for a better world
GEA Process Engineering
GEA Wiegand GmbH
Phone: +49 7243 705-0
Internet:
GJP4e14
Figure 4.
Contours of preferred blade tip back sweep angle
(Beta2).
