Chemical Engineering April 2019 - 45

1.2
1.1
1
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.03
Prediction (MU2 = 1.0)
Prediction (MU2 = 0.9)
Prediction (MU2 = 0.7)
Prediction (MU2 = 0.5)
Test (MU2 = 1.0)
Test (MU2 = 0.9)
Test (MU2 = 0.7)
Test (MU2 = 0.5)
0.05
0.07
0.09
Flow coefficient
0.11
0.13
0.9
0.8
0.7
0.6
0.5
0.4
0.03
Code. International Organization for Standardization,
www.iso.org.
4. Brun, K., and Nored, M., Guideline for Field Testing
of Gas Turbine and Centrifugal Compressor Performance,
Release 2.0, GMRC 2006.
Prediction (MU2 = 1.0)
Prediction (MU2 = 0.9)
Prediction (MU2 = 0.7)
Prediction (MU2 = 0.5)
Test (MU2 = 1.0)
Test (MU2 = 0.9)
Test (MU2 = 0.7)
Test (MU2 = 0.5)
0.05
0.07
0.09
Flow coefficient
FIGURE 4. The graphs show example performance data for a centrifugal compressor [5]
When making a comparison between
current and previous field measurements,
it is important to recognize
that measurements taken at different
operating conditions cannot be directly
compared. Therefore, it is necessary
to either ensure that exactly the same
operating conditions are duplicated for
the two sets of measurements, or that
there are non-dimensional parameters
that can be used for comparing the
data from tests taken under different
operating conditions.
The six most common non-dimensional
performance parameters
used for centrifugal compressors are
the specific volume ratio, Machine
Mach and Reynolds numbers, and
the head, flow and work input coefficients.
These terms are defined in
Table 1. Test conditions that closely
match the specific volume ratio and
flow coefficient are expected to produce
similar results for the head coefficient
and work input coefficient,
with some variation due to different
Mach and Reynolds numbers. These
variations can be minimal or can be
corrected based on test standards if
the Mach and Reynolds number deviations
are within allowable limits.
Example plots showing measured
isentropic head coefficient efficiency
versus flow coefficient are provided in
Figure 4 for a single centrifugal compressor
stage that was tested at multiple
Machine Mach numbers (MU2).
The predicted curves (solid lines) compare
reasonably well with the measured
curves (dashed lines), although
the peak head and choke flow measurements
are both below predicted
values, and efficiencies near the design
flow coefficient of 0.08 exceed
predictions. The results for head coefficient
show a typical characteristic of
increasing head rise at lower flowrates,
with a zero slope at low flow (surge
point). The choke line at high flow is
shown to be a strong function of the
Machine Mach number. The normalized
efficiency results show peak efficiencies
near the design flow coefficient
regardless
of Machine Mach
number, and also highlight reduced efficiencies
and lower choke flow at high
Mach numbers.
Concluding remarks
Field-performance tests can benefit
compressors in all stages of equipment
life. For new units, performance
tests can validate product
performance, while for existing units,
performance tests can help to monitor
for maintenance practices. In addition,
performance can be used to
determine an end-of-life metric.
Centrifugal
compressor
performance
metrics are based primarily
on measured temperatures, pressures,
flows and gas compositions,
as well as an appropriately selected
equation of state. Careful selection
and placement of measurement
transducers are necessary to reduce
test uncertainty. Proper planning of
the testing is also necessary to define
operating conditions and the desired
ultimate objective of the test.
n
Edited by Scott Jenkins
References
Content in this article was taken from material presented
at the 2018 Turbomachinery and Pump Symposium.
1. ASME PTC 10-1997, Performance Test Code on
Compressors and Exhausters, American Society of
Mechanical Engineers, www.asme.org.
2. ASME PTC 19-5-2004, Flow Measurement, American
Society of Mechanical Engineers, www.asme.org.
3. ISO 5389, Turbocompressors - Performance Test
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
APRIL 2019
45
0.11
0.13
5. Allison, T.C., Moore, J.J., Rimpel, A.M., Wilkes, J.C.,
Pelton, R., Wygant, K., Manufacturing and Testing
Experience with Direct Metal Laser Sintering for
Closed Centrifugal Compressor Impellers, Proceedings
of 43rd Turbomachinery Symposium, Houston,
September 2014.
6. Smith, N.R., Clarke, C., Allison, T.C., Cave, M., and
Wilkes, J.C., The Comparison of Aerodynamic Performance
Data Acquired from Thermal Measurements
and a Torquemeter on a Compressor Impeller,
Proceedings of ASME Turbo Expo, Paper #GT201877016,
Oslo, Norway, June 2018.
7. Kurz, R. and Brun, K., On Test Uncertainties in Field
Performance Tests, Proceedings of ASME Turbo
Expo, Paper #GT2015-42035, Montreal, Canada,
June 2015.
Authors
Nathan Poerner is a senior research
engineer in the Fluid Machinery
Section at Southwest
Research Institute (6220 Culebra
Road, San Antonio, TX 78238;
Phone:
210-864-5111; Email:
nathan.poerner@swri.org; www.
swri.org). He holds B.S. and M.S.
degrees in mechanical engineering
from Texas Tech University.
His work experience has primarily been in field measurements
and troubleshooting mechanical systems,
specifically pulsation and mechanical resonance issues.
This work is supported by mechanical and fluid
simulations and modeling. Poerner is involved in numerous
research projects focused on rotating and reciprocating
machinery.
Tim Allison is the manager of the
Rotating Machinery Dynamics
Section at Southwest Research
Institute (same address as above;
Email: tim.allison@swri.org). His
research at SwRI includes finite
element analysis, modal testing,
instrumentation and performance
testing for applications including
high-pressure
turbomachinery,
centrifugal compressors, gas turbines, reciprocating
compressor valves, high-frequency piping vibration
and test rigs for rotordynamics, blade dynamics and
aerodynamic performance. He has published over 50
articles on various turbomachinery topics and is an associate
editor for the ASME Journal of Engineering for
Gas Turbines & Power. He holds a Ph.D. in mechanical
engineering from Virginia Polytechnic Institute and
State University.
Hector Delgado leads the Machinery
Services group at Southwest
Research Institute (same
address as above: Email: hector.
delgado@swri.org). Delgado received
B.S. and M.S. degrees,
both in mechanical engineering
from the University of Nuevo Leon
(Mexico) and University of Texas
at San Antonio, respectively. Delgado's
research interests are in the areas of turbomachinery
dynamics, root-cause failure analysis and
mechanical design. He has significant experience in
the study of mechanical vibration, especially related to
the applied analysis of the blade and impeller dynamics.
His experience also includes diagnosing causes
and recommending solutions for machinery reliability
improvement, as well as pipeline pulsation and vibration
control.
Isentropic head coefficient (TT)
Normalized isentropic
http://www.iso.org http://www.swri.org http://www.asme.org http://www.asme.org http://WWW.CHEMENGONLINE.COM
Chemical Engineering April 2019

Table of Contents for the Digital Edition of Chemical Engineering April 2019
