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

Pulsed Light-Emitting Diode Photography for Coarse Water Characterization

[+] Author and Article Information
Kris Vernon

Alstom Power Ltd.,
Rugby CV21 2NH, UK
e-mail: kristopher.vernon@power.alstom.com

David Hann

Faculty of Engineering,
University of Nottingham,
Nottingham NG7 2RD, UK

Tim Rice

Alstom Power Ltd.,
Rugby CV21 2NH, UK

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 10, 2014; final manuscript received July 11, 2014; published online August 18, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(1), 011602 (Aug 18, 2014) (8 pages) Paper No: GTP-14-1361; doi: 10.1115/1.4028096 History: Received July 10, 2014; Revised July 11, 2014

An optical photography probe employing pulsed light-emitting diode (LED) illumination has been developed for application to coarse water measurement in wet steam. High image resolution (1.38 μm/pixel) and low exposure time (100 ns) photographs capture details of microdynamic flow features with reduced motion blur. Camera and lens are held inside a 50 mm O.D. cylindrical tube, with a custom designed titanium probe head allowing purging air to clear the front optical surface of stagnant liquid. Double exposure images are analyzed using standard image processing techniques to extract the size and velocity of liquid droplets. The accuracy and repeatability of the measurement probe has been verified on air–water sprays with direct comparison to phase-Doppler anemometry (PDA) measurements, which show good agreement.

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Fig. 1

(a) Photographic probe and LED, (b) no air purge, and (c) with air purge

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Fig. 2

Effects of mismatching sensor and lens

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Fig. 3

Percentage error in droplet diameter detection as a function of droplet diameter

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Fig. 4

Response of LED to a 50 ns current pulse

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Fig. 5

Experimental test facility

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Fig. 6

Schematic layout of equipment during probe testing

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Fig. 7

Effects of spraying into vacuum on (a) spherical validation profiles, (b) velocity profiles, and (c) Sauter mean diameter profiles

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Fig. 8

(a) Liquid jet core at exit of nozzle FOV 1.2 × 1.39 mm and (b) ligament breakup and droplet formation

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Fig. 9

Double exposure droplet image FOV 872 × 715 μm

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Fig. 10

Image processing algorithm for (a) droplet sizing and (b) velocity measurement

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Fig. 11

Morphological image processing following Sobel filter

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Fig. 12

Autocorrelation for velocity measurement (anticlockwise) autocorrelation, threshold and crop, reject border, and connected region analysis

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Fig. 13

Comparative study (a) D32 at air pressure 2 bar, (b) D32 at air pressure 4 bar, (c) mean velocity at air pressure 2 bar, and (d) mean velocity at air pressure 4 bar



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