Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Measuring Water Film Thickness in a Wet Gas Compressor Diffuser—Design, Calibration, and Testing of Electromagnetic Probes

[+] Author and Article Information
Craig Nolen

Fluids and Machinery Engineering,
Southwest Research Institute,
San Antonio, TX 78238
e-mail: craig.nolen@swri.org

Melissa Poerner

Fluids and Machinery Engineering,
Southwest Research Institute,
San Antonio, TX 78238
e-mail: melissa.poerner@swri.org

Contributed by the Controls, Diagnostics and Instrumentation Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 5, 2017; final manuscript received August 18, 2017; published online December 27, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(5), 051601 (Dec 27, 2017) (9 pages) Paper No: GTP-17-1295; doi: 10.1115/1.4038151 History: Received July 05, 2017; Revised August 18, 2017

The distribution of water in the diffuser of a wet gas compressor is not well understood. Measurements of water film thickness across the diffuser surface would improve the understanding of two-phase flow phenomena in wet gas compressors. Electromagnetic probes were designed in order to measure water film thickness in the diffuser of a SwRI-designed wet gas compressor. The probes consisted of two electrode foils plated on a thin insulating substrate, allowing them to be bonded in place without drilling through the diffuser. An AC signal was passed between the electrodes, and the voltage across a resistor in series with the electrodes was recorded. As the water level covering the electrodes increased, the recorded voltage increased. A method of calibrating the probes was developed and used prior to installation in the diffuser. Testing showed the probes to be effective at detecting the presence of water in the diffuser and indicating the general water level. Improvements in probe design, calibration, and installation are needed to provide more precise water film thickness data.

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Fig. 1

Typical resistivity/capacitance-based film thickness probe design

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Fig. 2

Bondable film thickness probe concept

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Fig. 3

Bondable solder tabs

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Fig. 4

Sensor circuit diagram

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Fig. 5

Film thickness probes installed in diffuser

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Fig. 6

Calibration concept

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Fig. 7

Early calibration setup

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Fig. 8

Temperature dependence of sensor voltage

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Fig. 9

Difference between maximum and minimum sensor voltage for various input signal frequencies

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Fig. 10

Calibration of installed sensors in water bath

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Fig. 11

Labeled sensor arrangement

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Fig. 12

Installed calibration results, uncorrected

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Fig. 14

Measured film thicknesses for CV setting of 17%, before and after corrections

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Fig. 15

Representation of calibration circuit leakage

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Fig. 16

Installed calibration results, corrected

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Fig. 17

Film thickness sensor signal versus LVF at 18,000 rpm

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Fig. 18

Sensor signal versus LVF for 18,000 rpm and control valve setting of 17%

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Fig. 19

Camera images of water inside compressor at 18,000 rpm and a control valve setting of 17%

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Fig. 20

FM100 signal for three different control valve positions at 18,000 rpm

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Fig. 21

Camera image from 18,000 rpm, control valve setting of 17% and LVF of 0.91%

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Fig. 22

Leakage corrected results for varying flow rate and control valve setting for all probes



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