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Measuring Water Droplets to Detect Atmospheric Icing
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.ORCID iD: 0000-0002-5324-002X
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes the exploration of a method to measurethe droplet size and the concentration of atmospheric liquid water. The purpose is to find a cost effective technique to detect the conditions for icing on structures.

Icing caused by freezing atmospheric water can be a signifi- cant problem for infrastructure such as power lines, roads and air traffic. About one third of the global installed wind power capacity is located in cold climates, where icing of rotor blades is one of the major challenges.

The icing process is complex and the result depends on a combination of the aerodynamic shape of the structure or airfoil, the velocity of the air and its contained water, the temperature, the mixing of snow and water, the concentration of liquid water and the Droplet Size Distribution (DSD).

The measurement method is based on a shadowgraph imag- ing system using light emitting diode (LED) light as background illumination and digital image processing. A prototype instru- ment has been constructed. The components were selected keeping the possibility of low-cost volume production in mind. The applications of a commercial instrument based on this tech- nique are e.g. real-time in-situ icing condition measurements and assimilation and verification of data in numerical weather models.

The work presented shows that measurements of the size and concentration of water droplets using shadowgraph images can be used for the comparison and validation of Numerical Weather Prediction (NWP) models and other instruments. The accuracy of the particle size measurement is high. The accuracy of the concentration measurement has the potential to become high due to the single-particle measurement range calibraiton. The precision of the instrument depends mainly on the number of images that is used to find each measurement value. The real-time performance of the instrument is limited by the image retrieval and processing speed and depends on the  precisionrequired.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2017. , p. 72
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 134
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-31827ISBN: 978-91-88527-29-5 (print)OAI: oai:DiVA.org:miun-31827DiVA, id: diva2:1148684
Presentation
2017-11-01, O102, Holmgatan 10, Sundsvall, 10:00 (English)
Opponent
Supervisors
Note

Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 3 inskickat.

At the time of the defence the following papers were unpublished: paper 3 submitted.

Available from: 2017-10-13 Created: 2017-10-12 Last updated: 2017-10-13Bibliographically approved
List of papers
1. Liquid Water Content and Droplet Sizing Shadowgraph Measuring System for Wind Turbine Icing Detection
Open this publication in new window or tab >>Liquid Water Content and Droplet Sizing Shadowgraph Measuring System for Wind Turbine Icing Detection
2016 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 16, no 8, p. 2714-2725, article id 7384444Article in journal (Refereed) Published
Abstract [en]

This study shows that the liquid water content (LWC) and the median volume diameter (MVD) can be derived from images of water droplets using a shadowgraph imaging system with incoherent LED illumination.

Icing on structures such as a wind turbine is the result of a combination of LWC and MVD and other parameters like temperature, humidity and wind speed. Today, LWC and MVD are not commonly measured for wind turbines. Systems for measuring these properties are often expensive or impractical in terms of location or remote reading. The aim of this study is to gain knowledge about how to design a single instrument based on imaging that has the ability to measure these properties with enough precision and accuracy to detect icing conditions for wind turbines.

A method to calculate both the LWC and the MVD from the same images is described in this paper. The size of one droplet is determined by measuring the shadow created by the droplet in background illumination. The concentration is calculated by counting the measured droplets and estimating the volumes in which these droplets can be observed.

In the described study, the observation volume is shown to be dependent on the particle size and the signal to noise ratio (SNR) for each measured particle. An expected coefficient of variation of the LWC depending on the droplet size is shown to be 2.4 percent for droplets 10 µm in diameter and 1.6 percent for 25 µm droplets. This is based on an error estimation of the laboratory measurements calibrated using a micrometer dot scale.

Place, publisher, year, edition, pages
IEEE Sensors Council, 2016
Keywords
LWC, MVD, Icing, Clouds, Image processing, Machine vision, Meteorology, Optical microscopy, Wind power generation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-27321 (URN)10.1109/JSEN.2016.2518653 (DOI)000372419100061 ()2-s2.0-84962128668 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Funder
Swedish Energy Agency
Available from: 2016-03-22 Created: 2016-03-22 Last updated: 2017-10-12Bibliographically approved
2. Droplet Imaging Instrument Metrology Instrument for Icing Condition Detection
Open this publication in new window or tab >>Droplet Imaging Instrument Metrology Instrument for Icing Condition Detection
2016 (English)In: 2016 IEEE INTERNATIONAL CONFERENCE ON IMAGING SYSTEMS AND TECHNIQUES (IST), IEEE, 2016, p. 66-71, article id 7738200Conference paper, Published paper (Refereed)
Abstract [en]

An instrument for measuring water droplets is described and constructed. It is designed to measure the volume concentration and the size distribution of droplets in order to detect icing conditions in a natural fog. The instrument works by shadowgraph imaging, with a collimated blue LED as background illumination. We show how to use a reference object to obtain a calibration of the droplet size and the measurement volume. These properties are derived from a measurement of the object's shadow intensity and its edge second derivative. From the size of every measured droplet and its expected detection volume, a measure of the liquid water content (LWC) and the median volume diameter (MVD) can be estimated. The instrument can be used for continuous measurement in a remote weather-exposed location and is tested in a small environment chamber. We also describe this chamber and how we can change the LWC using an ultrasonic fog generator and a fan.

Place, publisher, year, edition, pages
IEEE, 2016
Series
IEEE International Conference on Imaging Systems and Techniques, ISSN 2471-6162
Keywords
atmospheric measurements, fog chamber, image analysis, liquid water content, machine vision
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-29765 (URN)10.1109/IST.2016.7738200 (DOI)000388735200012 ()2-s2.0-85004010273 (Scopus ID)STC (Local ID)978-1-5090-1817-8 (ISBN)STC (Archive number)STC (OAI)
Conference
IEEE International Conference on Imaging Systems and Techniques (IST) / IEEE International School on Imaging, OCT 04-06, 2016, Chania, GREECE
Available from: 2016-12-22 Created: 2016-12-22 Last updated: 2017-10-12Bibliographically approved

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