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Droplet Imaging Instrument Metrology Instrument for Icing Condition Detection
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.ORCID iD: 0000-0002-5324-002X
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
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. p. 66-71, article id 7738200
Series
IEEE International Conference on Imaging Systems and Techniques, ISSN 2471-6162
Keywords [en]
atmospheric measurements, fog chamber, image analysis, liquid water content, machine vision
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-29765DOI: 10.1109/IST.2016.7738200ISI: 000388735200012Scopus ID: 2-s2.0-85004010273Local ID: STCISBN: 978-1-5090-1817-8 (print)OAI: oai:DiVA.org:miun-29765DiVA, id: diva2:1059401
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: 2019-11-07Bibliographically approved
In thesis
1. Measuring Water Droplets to Detect Atmospheric Icing
Open this publication in new window or tab >>Measuring Water Droplets to Detect Atmospheric Icing
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:nbn:se:miun:diva-31827 (URN)978-91-88527-29-5 (ISBN)
Presentation
2017-11-01, O102, Holmgatan 10, Sundsvall, 10:00 (English)
Opponent
Supervisors
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
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: 2019-06-13Bibliographically approved
2. Development and Test of an Imaging Instrument for Measurement of Water Droplets in Icing Conditions
Open this publication in new window or tab >>Development and Test of an Imaging Instrument for Measurement of Water Droplets in Icing Conditions
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Structural icing is a persistent challenge for the production of renewable energy from wind. It is mainly caused by supercooled atmospheric droplets of water, which are very common in cold climates. In the most exposed wind parks in Sweden, more than 10 per cent of annual energy production can be lost. Some properties of liquid water are included in current \gls{nwp} models and are used as input parameters for the estimation of icing, but they are rarely measured in-situ for verification or validation.

To address this problem, a new instrument was developed. This compilation thesis is a collection of five articles describing the development, testing and verification of this instrument. Finally, icing and ice loads are measured and compared with a standard model and a model using \gls{ai} and empirical data.

The new instrument, called \gls{dii}, is based on shadowgraph imaging using \gls{led} light as background illumination and digital image processing. The components were selected with the possibility of low-cost volume production in mind. The applications of a commercial instrument based on this technique include, for example, real-time in-situ icing condition measurements and assimilation and verification of data in \gls{nwp} models. The instrument, alongside a reference instrument, was tested in two locations with different icing conditions. Shadowgraph imaging and its limitations as a measurement method for droplet size and concentration were investigated.

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 \gls{nwp} models and other instruments. The \gls{cv} for a given value of the concentration is lower than \SI{1.6}{\percent} for droplets \SI{25}{\micro\meter} in diameter, based on uncertainty in the size measurement only. The accuracy of the sampling volume can be improved by measuring the background light intensity in the position of the measured droplet.

A fog chamber was used for initial tests. However, to evaluate models of ice accumulation, in-situ measurements are necessary. These measurements should use a temporal resolution of at least one sample per minute, preferably higher. With a limited amount of data, multivariate data analysis can be used to estimate the level of ice accretion. Together with a heuristic model of erosion/ablation, the resulting figures can be used to simulate the ice load.

All of the instruments, as well as many other components used during the described field measurements, did at some point break due to the difficult weather conditions. An instrument for measurement of icing conditions needs to be designed with high environmental protection and endurance. The results in the attached papers may help and motivate further technical development of instruments that can measure atmospheric liquid water in icing conditions.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2019. p. 68
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 306
Keywords
Icing measurements, field study, shadowgraph imaging, edge detection, LWC, MVD.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-37639 (URN)978-91-88947-22-2 (ISBN)
Public defence
2019-12-05, C326, Holmgatan 10, Sundsvall, 10:00 (English)
Opponent
Supervisors
Note

Vid tidpunkten för disputationen var följande delarbete opublicerat: delarbete 5 (accepterat).

At the time of the doctoral defence the following paper was unpublished: paper 5 (accepted). 

Available from: 2019-11-07 Created: 2019-11-07 Last updated: 2019-11-07Bibliographically approved

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Rydblom, StaffanThörnberg, Benny

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