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Liquid Water Content and Droplet Sizing Shadowgraph Measuring System for Wind Turbine Icing 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: 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. Vol. 16, no 8, p. 2714-2725, article id 7384444
Keywords [en]
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: urn:nbn:se:miun:diva-27321DOI: 10.1109/JSEN.2016.2518653ISI: 000372419100061Scopus ID: 2-s2.0-84962128668Local ID: STCOAI: oai:DiVA.org:miun-27321DiVA, id: diva2:913742
Funder
Swedish Energy AgencyAvailable from: 2016-03-22 Created: 2016-03-22 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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