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Experimental analysis of thermal mixing at reactor conditions
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.ORCID iD: 0000-0001-8743-7157
2016 (English)Licentiate thesis, monograph (Other academic)
Abstract [en]

High-cycle thermal fatigue arising from turbulent mixing of non-isothermal flows is a key issue associated with the life management and extension of nuclear power plants. The induced thermal loads and damage are not fully understood yet.

With the aim of acquiring extensive data sets for the validation of codes modeling thermal mixing at reactor conditions, thermocouples recorded temperature time series at the inner surface of a vertical annular volume where turbulent mixing occurred. There, a stream at either 333 K or 423 K flowed upwards and mixed with two streams at 549 K. Pressure was set at 72E5 Pa. The annular volume was formed between two coaxial stainless-steel tubes. Since the thermocouples could only cover limited areas of the mixing region, the inner tube to which they were soldered was lifted, lowered, and rotated around its axis, to extend the measurement region both axially and azimuthally.

Trends, which stemmed from the variation of the experimental boundary conditions over time, were subtracted from the inner-surface temperature time series collected. An estimator assessing intensity and inhomogeneity of the mixing process in the annulus was also computed. In addition, a frequency analysis of the detrended inner-surface temperature time series was performed. In the cases examined, frequencies between 0.03 Hz and 0.10 Hz were detected in the subregion where mixing inhomogeneity peaked.

The uncertainty affecting such measurements was then estimated.

Furthermore, a preliminary assessment of the radial heat flux at the inner surface was conducted.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. , 78 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2016:74
Keyword [en]
mixing estimator, empirical mode decomposition, Hilbert-Huang transform, uncertainty assessment, radial heat flux
National Category
Energy Engineering
Research subject
Energy Technology; Physics
Identifiers
URN: urn:nbn:se:kth:diva-196544ISBN: 978-91-7729-190-9OAI: oai:DiVA.org:kth-196544DiVA: diva2:1046878
Presentation
2016-12-16, FB55, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Radiation Safety Authority, 47385
Note

QC 20161116

Available from: 2016-11-16 Created: 2016-11-15 Last updated: 2016-11-16Bibliographically approved

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Bergagio, Mattia
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