Summary
This paper presents experimental data and a preliminary analysis of the
influence of fluid viscosity on centrifugal-pump performance. Two centrifugal
pumps, a conventional radial (specific speed Nq=8 rev/min)
and a semi axial electrical submersible pump (ESP) (Nq=28
rev/min) were tested with 1-cp water and clear glycerin. Adjusting and
controlling the fluid temperature in a closed test loop, it was possible to
vary the glycerin viscosity from 67 to 1,020 cp within the range of light and
heavy crude oils.
The main purpose of these tests, in addition to appraising the influence of
viscosity on the pump’s overall performance through the measurement of the
derating factors for head, flow, and power, was to supply detailed information
on the energy-transfer processes taking place in the pump's internal
components. To accomplish this, the pressure distribution along the flow path
from the pump inlet eye to the discharge section, including detailed pressure
difference across impellers and diffusers, was measured. Thus, in addition to
measuring the flow rate, the overall pressure difference, the speed, the power
and the mean operation temperature for fluids with various viscosities within a
full range of operational conditions, detailed data on the energy-transfer
processes performed by impellers and diffusers were also taken.
Later analyses indicated that, in addition to the physical dimensions,
operational conditions, and fluid properties, the pump performance is set by
the strong flow interactions that exist between impellers and diffusers. In
other words, these succeeding internal blade rows influence each other in terms
of the head gain and the viscous dissipation effects. Thus, any generalizing
approach dealing with the influence of viscosity on the pump performance must
account for those interactions to give a proper measure of the derating factors
over an extended range of operational conditions. Unfortunately, this is not
true for the procedures available in the open literature. They lack
representation and do not deliver proper correction factors for pumps that are
not similar to those that generate the correlation database or for pumps
working under operational conditions other than at the best-efficiency point
(BEP). The data presented herein can be a launching point for a deeper analysis
aimed to tackle these limitations.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
1 August 2007
- Meeting paper published:
11 November 2007
- Revised manuscript received:
3 April 2008
- Manuscript approved:
7 May 2008
- Published online:
1 May 2009
- Version of record:
1 May 2009
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