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A model for inertial drop deposition suitable to predict obstacle effect
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
Paul Scherrer Institute. (Lab of Reactor Physics and System Behaviour)
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.ORCID iD: 0000-0001-5595-1952
2013 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 260, 121-133 p.Article in journal (Refereed) Published
Abstract [en]

The drop deposition increase due to flow obstruction is usually quantified solely by empirical coefficients. In this work we propose a new way to calculate the drop deposition with the capability to predict the obstacle effect. The model is based on the drop volume fraction, slip ratio and turbulence quantities of the continuous phase obtained from the two-fluid calculations. Additional relations are needed to calculate the fluctuating velocities of the drop phase. These relations are based on the fluid integral time scales. A number of relations are tested, which include the effect of drop inertia and drift parameter. The new model is tested in a number of flow combinations, including air-water and helium-water of 1.5 bar and steam-water at 70 bar pressure, for low and high drop concentration. The high concentration flow shows that further studies are needed to include drop size increase due to coalescence and reduction of velocity fluctuation due to drop collisions. The new model is tested for pipe flow containing an obstacle of steam-water flows of 5, 10 and 15 bar pressure. The new model shows the capability to qualify the obstacle effect. Further improvements are needed to increase the quantitative capability.

Place, publisher, year, edition, pages
2013. Vol. 260, 121-133 p.
Keyword [en]
inertial drops, deposition, Eulerian, annular two-phase flow, obstacle
National Category
Energy Engineering
URN: urn:nbn:se:kth:diva-106799DOI: 10.1016/j.nucengdes.2013.03.010ISI: 000319645800011ScopusID: 2-s2.0-84876116417OAI: diva2:574085

QC 20140617

Available from: 2012-12-06 Created: 2012-12-04 Last updated: 2014-06-17Bibliographically approved
In thesis
1. On drops and turbulence in nuclear fuel assemblies of Boiling Water Reactors
Open this publication in new window or tab >>On drops and turbulence in nuclear fuel assemblies of Boiling Water Reactors
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The study aims to develop the understanding of the mechanistic-type approach to quantify drop deposition in nuclear fuel assemblies of Boiling Water Reactors. This includes the effect of spacers. Spacers have a complex geometry to serve their purposes, but optimization of them alone can improve the thermal limit parameters in nuclear fuel assemblies. Thus, a mechanistic model might prove useful to increase the safety of the reactor as well as economic competitiveness of the nuclear power plant.

In this thesis, measurement techniques, such as mobile pressure rod and Laser Doppler Velocimetry are developed and tested to provide local data of the flow around spacers. It is shown experimentally that the effect of spacer on the flow differs depending on the placement of the subchannel in the rod bundle. Partly, because the spacer part differs, but also due to a global velocity profile development. Very few studies in the literature indicate this effect. It is shown that single subchannel models using Computational Fluid Dynamics (CFD) can predict the average velocity increase downstream of the spacer; however, they are not capable of calculating the spacer effect on turbulence parameters. The single subchannel CFD model has limited capability to predict the pressure development inside the spacer part, mainly because cross-flows are not taken into consideration.

The deposition of drops in annular two-phase flow is still a scientific challenge. Only empirical correlations are used nowadays to quantify this process. Empirical coefficients are needed for each spacer type to calculate the deposition increase due to obstacle. The discussion about the deposition starts with the phenomenological description. The important input parameter, namely drop size, is carefully analysed, and a new correlation is proposed to calculate the mean drop diameter. The correlation is constructed on a larger experimental data base. Lagrangian Particle Tracking model is tested in its capability to calculate deposition. Additionally, a Eulerian-type model is developed and tested. Turbulent parameters of drops are tightly related to the turbulence of the gas phase and the inertia of the drops. Several approaches are discussed about how to calculate the root-mean-square fluctuating velocities of drops. Both, Lagrangian Particle Tracking and the Eulerian-type of models show good capability in calculating the obstacle effect on deposition, providing improvements are made in prediction of drop size. The effect of increased drop concentration plays a large role and it must be taken into consideration if good quantitative approaches are envisaged.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xi, 45 p.
Trita-FYS, ISSN 0280-316X ; 2012:85
National Category
Energy Engineering
urn:nbn:se:kth:diva-107115 (URN)978-91-7501-572-9 (ISBN)
Public defence
2012-12-14, FD5, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:30 (English)
EU, European Research Council

QC 20121207

Available from: 2012-12-07 Created: 2012-12-06 Last updated: 2012-12-07Bibliographically approved

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