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Field Study of LWC and MVD Using the Droplet Imaging Instrument
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.
Swedish Meteorol & Hydrol Inst (SMHI), Sundsvall.
2019 (English)In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 68, no 2, p. 614-622Article in journal (Refereed) Published
Abstract [en]

The droplet imaging instrument (DII) is a new instrument for cost-effective in situ measurements of the size and concentration of water droplets. The droplet size distribution and the concentration of atmospheric liquid water are important for the prediction of icing on structures, such as wind turbines. To improve the predictions of icing, there is a need to explore cost-effective working solutions. Through imaging, a wide range of droplet sizes can be measured. This paper describes a study of the atmospheric liquid water content and the median volume diameter using the DII and a commercial reference instrument--the cloud droplet probe 2 from Droplet Measurement Technologies Inc. The measurement is done at a weather measurement station in mid-Sweden. For a second validation, the result is compared with predictions using a numerical weather prediction model. The size measurement of the DII is verified using polymer microspheres of four known size distributions. The study shows that the DII measurement is precise, but there is a systematic difference between the two compared instruments. It also shows that droplets larger than 50 μm in diameter are occasionally measured, which we believe is important for the prediction of icing.

Place, publisher, year, edition, pages
IEEE, 2019. Vol. 68, no 2, p. 614-622
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-34304DOI: 10.1109/TIM.2018.2843599ISI: 000454332000030OAI: oai:DiVA.org:miun-34304DiVA, id: diva2:1242543
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Note

Date of Publication: 20 June 2018

Available from: 2018-08-28 Created: 2018-08-28 Last updated: 2019-11-07Bibliographically approved
In thesis
1. 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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