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Analysis of temperature fluctuations caused by mixing of non-isothermal water streams at elevated pressure
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.ORCID iD: 0000-0001-8743-7157
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.ORCID iD: 0000-0001-5595-1952
2017 (English)In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 104, p. 979-992Article in journal (Refereed) Published
Abstract [en]

Temperatures were measured at the inner surface of an annulus between two coaxial tubes, where three water streams mixed. These temperatures were sampled at either 100 Hz or 1000 Hz. The acquisition time was set to 120 s. Two water streams at 549 K, with a Reynolds number between 3.56 × 105 and 7.11 × 105, descended in the annular gap and mixed with a water stream at 333 K or 423 K, with a Reynolds number ranging from 1.27 × 104 to 3.23 × 104. Water pressure was kept at 7.2 MPa. Inner-surface temperatures were collected at eight azimuthal and five axial positions, for each combination of boundary conditions. To better analyze these temperatures and mixing in the vicinity of the wall, scalars estimating the mixing intensity at each measurement position were computed from detrended temperature time series. Fourier and Hilbert–Huang marginal spectra were calculated for the time series giving rise to the highest values of a mixing estimator of choice. The relationship between temperature and velocity was explored by examining the results of an LES simulation using the same boundary conditions as in one of the experimental cases.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 104, p. 979-992
Keywords [en]
Mixing intensity, Spectral analysis, Thermal mixing
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-192558DOI: 10.1016/j.ijheatmasstransfer.2016.08.082ISI: 000387627400087Scopus ID: 2-s2.0-84990036834OAI: oai:DiVA.org:kth-192558DiVA, id: diva2:970708
Projects
THEMFE
Funder
Swedish Radiation Safety Authority, 47385
Note

QC 20160927

Available from: 2016-09-14 Created: 2016-09-14 Last updated: 2018-10-20Bibliographically approved
In thesis
1. Experimental and analytical study of thermal mixing at reactor conditions
Open this publication in new window or tab >>Experimental and analytical study of thermal mixing at reactor conditions
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High-cycle thermal fatigue due to turbulent mixing of streams at distinct temperatures is an interdisciplinary issue affecting safety and life extension of existing reactors together with the design of new reactors. It is challenging to model damage and thermal loads arising from the above mixing.

In order to collect vast data sets for the validation of codes modeling turbulent thermal mixing under reactor conditions, temperatures were sampled at the inner surface of the vertical annular volume between two concentric 316LN stainless steel tubes. This annulus simplifies that between control-rod guide tube and stem in Swedish boiling water reactors (BWRs) Oskarshamn 3 and Forsmark 3. In 2008, several stems there were reported as broken or cracked from thermal fatigue. Cold water entered the annulus at 333 K, at axial level z = 0.15 m. It moved upward and mixed with hot water, which entered the annulus at 549 K, at z = 0.80 m. Pressure read 7.2 MPa. Hot and cold inlet temperatures and pressure match BWR conditions. The thermocouples attached to the inner tube could only acquire inner-surface temperatures at six locations, so the inner tube was translated and rotated about the z-axis to expand the measurement zone.

Mixing inhomogeneity was estimated from such measurements. In the cases examined, the inner-surface temperatures from areas with the highest mixing inhomogeneity show dominant frequencies lower than ten times the inverse of the experiment time.

The uncertainty of this temperature measurement appears to be equal to 1.58 K.

A large eddy simulation (LES) of mixing in the above annulus was conducted. Experimental boundary conditions were applied. The conjugate heat transfer between water and tubes was modeled. The wall-adapting local eddy viscosity (WALE) subgrid model was adopted. A finite element analysis (FEA) of the inner tube was performed using LES pressure and temperature as loads. Cumulative fatigue usage factors (CUFs) were estimated from FEA stress histories. To this end, the rainflow cycle-counting technique was applied. CUFs are highest between z = 0.65 m and z = 0.67 m. Cracking is predicted to initiate after 97 h. LES and experimental inner-surface temperatures agree reasonably well in relation to mean values, ranges, mixing inhomogeneity, and critical oscillation modes in areas sensitive to fatigue. LES inner-surface temperatures from areas with the highest CUFs show dominant frequencies lower than ten times the inverse of the simulation time.

A robust, effective iterative algorithm for reconstructing the transient temperature field in the inner tube from redundant boundary data was implemented and verified. Temperature-dependent properties were included. Initial conditions and over-specified boundary data in the inverse problem were perturbed with Gaussian noise to check the robustness of the solving method to noise.

Abstract [sv]

Termisk högcykelutmattning på grund av turbulent blandning av flöden av olika temperaturer är en tvärvetenskaplig fråga som har bäring på säkerhet, underhåll och livstidsförlängning av kärnkraftverk i drift tillsammans med utvecklingen av nya reaktorer. Det är utmanande att modellera delskador och termiska belastningar som härrör från denna blandning.

För att samla stora datamängder för validering av koder modellerande turbulent termisk blandning vid reaktordriftförhållanden, mättes temperaturer vid den inre ytan av den vertikala annulära (ringformade) kanalen mellan två koncentriska rör i 316LN rostfritt stål. Denna annulära kanal representerar den verkliga geometrin mellan styrstavsledrör och styrstavsförlängare i svenska kokvattenreaktorer (BWR) Oskarshamn 3 och Forsmark 3. Vid dessa reaktorer uppvisade ett antal styrstavsförlängare sprickbildning till följd av termisk utmattning under år 2008. I den annulära kanalen strömmade kallare vattenflöden vid 333 K, vid axiell nivå z = 0.15 m. Flödena rörde sig uppåt och blandades med varmare vattenflöden, vilka strömmade i den annulära kanalen vid 549 K, vid z = 0.80 m. Trycket sattes till 7.2 MPa. 333 K, 549 K och 7.2 MPa överensstämmer med BWR-förhållanden. Termoelement fastlödda vid det inre röret kunde endast mäta innerytans temperatur på sex platser. För att kunna mäta temperaturen i hela blandningsområdet kunde röret roteras från 0° till 360° och förflyttas vertikalt över en sträcka av 387 mm.

Blandningsinhomogenitet uppskattades från sådana mätningar. I de undersökta fallen visar innerytans temperatur från områden där blandningen är som minst homogen dominerande frekvenser som är lägre än tio gånger inversen till experimenttiden.

Osäkerheten i dessa temperaturmätningar visar sig vara 1.58 K.

En storvirvelsimulering (LES) av blandning i den annulära kanalen utfördes. Experimentella randvillkor applicerades. Den konjugerade värmeöverföringen mellan vatten och rör modellerades. De små virvlarna (oupplösta skalor) approximerades med hjälp av en turbulensmodell kallad WALE, som ger rätt asymptotiskt beteende för turbulent viskositet nära väggen. En finitelementanalys (FEA) av det inre röret utfördes med LES-tryck och temperatur som belastningar. Totala delskador uppskattades från FEA-spänning/tid kurvor. För detta ändamål applicerades regndroppsmetoden. De totala delskadorna når sina högsta värden mellan z = 0.65 m och z = 0.67 m. Sprickinitiering förväntas inträffa efter 97 timmar. Innerytans CFD-temperatur är i en rimlig överensstämmelse med experimentella data med avseende på medelvärde, omfång, blandningsinhomogenitet och kritiska svängande modalfunktioner som utgör temperaturtidsserier i områden som är utsatta för utmattning. Innerytans CFD-temperatur från områden med högsta totala delskador visar dominerande frekvenser som är lägre än tio gånger inversen till simuleringstiden.

En robust, effektiv, iterativ algoritm för att beräkna det transienta temperaturfältet i det inre röret utifrån överflödiga randdata implementerades och verifierades. Temperaturberoende egenskaper inkluderades. Initiala förhållanden och överflödiga randdata i det inversa problemet stördes av gaussiskt brus för att undersöka lösningsmetodens robusthet mot brus.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 113
Series
TRITA-SCI-FOU ; 2018:45
Keywords
High-cycle thermal fatigue, Hilbert-Huang transform, large eddy, WALE, rainflow, inverse heat conduction, adjoint conjugate gradient
National Category
Energy Engineering
Research subject
Energy Technology; Physics
Identifiers
urn:nbn:se:kth:diva-236530 (URN)978-91-7873-001-8 (ISBN)
Public defence
2018-12-06, FB53, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Radiation Safety Authority, 47385
Note

QC 20181022

Available from: 2018-10-22 Created: 2018-10-20 Last updated: 2018-11-13Bibliographically approved

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