| 1. |
- Anghel, Ionut, 1971-, et al.
(author)
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Experimental investigation of post-dryout heat transfer in annuli with flow obstacles
- 2012
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In: Nuclear Engineering and Design. - : Elsevier. - 0029-5493 .- 1872-759X. ; 246, s. 82-90
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Journal article (peer-reviewed)abstract
- An experimental study on post-dryout heat transfer was conducted in the High-pressure WAter Test (HWAT) loop at the Royal Institute of Technology in Stockholm, Sweden. The objective of the experiments was to investigate the influence of flow obstacles on the post-dryout heat transfer. The investigated operational conditions include mass flux equal to 500 kg/m2 s, inlet sub-cooling 10 K and system pressure 5 and 7 MPa. The experiments were performed in annuli in which the central rod was supported with five pin spacers. Two additional types of flow obstacles were placed in the exit part of the test section: a cylinder supported on the central rod only and a typical BWR grid spacer cell. The measurements indicate that flow obstacles improve heat transfer in the boiling channel. It has been observed that the dryout power is higher when additional obstacles are present. In addition the wall temperature in post-dryout heat transfer regime is reduced due to increased turbulence and drop deposition. The present data can be used for validation of computational models of post-dryout heat transfer in channels with flow obstacles.
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| 2. |
- Anghel, Ionut Gheorghe, et al.
(author)
-
Experimental investigation of post-dryout heat transfer in annuli with flow obstacles
- 2010
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In: International Conferecne Nulclear Energy for New Europa 2010.
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Conference paper (pop. science, debate, etc.)abstract
- An experimental study on post-dryout heat transfer was conducted in the High-pressure WAter Test (HWAT) loop at the Royal Institute of Technology in Stockholm, Sweden. The objective of the experiments was to investigate the influence of flow obstacles on the post-dryout heat transfer. The investigated operational conditions include mass flux equal to 500 kg/(m2s), inlet sub-cooling 10 K and system pressure 5 and 7 MPa. The experiments were performed in annuli in which the central rod was supported with five pin spacers. Two additional types of flow obstacles were placed in the exit part of the test section: a cylinder supported on the central rod only and a typical BWR grid spacer cell. The measurements indicate that flow obstacles improve heat transfer in the boiling channel. It has been observed that the dryout power is higher when additional obstacles are present. In addition the wall temperature in post-dryout heat transfer regime is reduced due to increased turbulence and drop deposition. The present data can be used for validation of computational models of postdryout heat transfer in channels with flow obstacles.
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| 3. |
- Anghel, Ionut Gheorghe, et al.
(author)
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Experimental Investigation of the Influence of Flow Obstacles on Post-Dryout Heat Transfer in an Annulus
- 2009
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In: ICONE 17. - NEW YORK : AMER SOC MECHANICAL ENGINEERS. - 9780791843536 ; , s. 277-286
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Conference paper (peer-reviewed)abstract
- This paper describes the experimental setup, instrumentation and procedures which have been developed in the thermal-hydraulic laboratory at the Royal Institute of Technology (KTH), Stockholm, Sweden, to perform new post-dryout heat transfer investigations in an annulus with flow obstacles. Previous investigations performed in the same laboratory indicated that flow obstacles had a considerable influence on the post-CHF heat transfer. The measured heat transfer enhancement was significantly under-predicted by existing models. However, the net effect of obstacles could not be deduced from the measurements, since reference - obstacle-free measurements- had not been performed. In addition, the number of thermocouples that could be installed inside the heated rod was limited to 8. These deficiencies have been removed in the current approach. Firstly, the present design of the test section allows for measurements both with and without flow obstacles. In this way the net effect of the obstacles will be captured. Secondly, a newly developed technique allowed the installation of 40 thermocouples inside of the heated rod. An additional 40 thermocouples have been installed on the external wall of the heated tube. Therefore, a significant improvement of the accuracy of measurements can be expected. The present arrangement of instrumentation is suitable to perform measurements of heat transfer under both steady-state and transient conditions.
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| 4. |
- Anghel, Ionut Gheorghe, et al.
(author)
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Study of post dryout heat transfer in annulus with flow obstacles
- 2010
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In: Proceedings of the 14th International Heat Transfer Conference (IHTC14).
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Conference paper (peer-reviewed)abstract
- The purpose of this paper is to present the experimental setup, experimental method and results of the recent post-dryout heat transfer investigations in an annulus with pin spacers. The experiments were performed in the thermal-hydraulic laboratory at the Royal Institute of Technology (KTH), Stockholm, Sweden. The experimental facility has an annular test section which consists of two double-heated concentric tubes manufactured of Inconel 600. Five levels of pin spacers were installed along the test section to keep the rod and the tube equidistant during experiments. The experimental matrix includes measurements of wall temperature distributions for single phase and twophase flows, for both convective boiling and postdryout heat transfer regimes. The influence of variations in mass flux (500-1500) kg/(m2s) and inlet subcooling 10 and 40 K at system pressure of 7 Mpa were investigated. The experimental results indicate that post dryout heat transfer is influenced by the pin spacers. In particular it has been observed that the dry patch appearing in the test section can be quenched downstream of the pins-spacer. The current results provide additional experimental database which can be used for validation of post-dryout heat transfer models including the flow obstacle effects.
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| 5. |
- Anglart, Henryk, et al.
(author)
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EXPERIMENTAL INVESTIGATION OF STATIONARY AND TRANSIENT POST-DRYOUT HEAT TRANSFER IN 22.1X10 MM ANNULUS WITH SPACERS
- 2005
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In: Proceedings of the Eleventh International Topical Meeting on Nuclear Reactor Thermal-Hydraulics.
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Conference paper (peer-reviewed)abstract
- Experimental investigation of the post-dryout heat transfer in annulus test section has been performed in the high-pressure two-phase loop at the Royal Institute of Technology (KTH). The test section has an annular geometry with 10 mm rod outer diameter and 22.1 mm tube inner diameter. Seven spacers are located along the test section to keep the rod and the tube equidistant along the test section. Both the tube and the rod are manufactured of Inconel 600 to withstand high temperatures. Several thermocouples have been installed on the tube and the rod surface to measure the local temperature.The measurements have been performed for a wide range of the inlet mass flow rate, keeping the inlet subcooling equal to 10 K and the pressure to 70 bars. Uniform axial power distributions have been applied on the rod and tube walls, however, several different ratios between the heat fluxes on the two surfaces have been applied. Both steady-state and transient measurements have been performed in which axial distribution of wall temperatures have been registered.The experiments indicate a very strong influence of spacers on post-dryout heat transfer. In particular, for several cases with relatively low local quality the dryout spot is limited to a direct proximity of spacers, stretching from approximately 10 cm upstream of the spacer to 5 cm downstream of the spacer. Only for relatively high powers the dryout patch could cover the whole distance between two neighboring spacers.
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| 6. |
- Anglart, Henryk, et al.
(author)
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Measurement of Wall Temperature Fluctuations during Thermal Mixing of Non-isothermal Water Streams
- 2015
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In: Proceedings of the 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16). - : American Nuclear Society.
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Conference paper (peer-reviewed)abstract
- This paper is dealing with measurement of temperature fluctuations during mixing of two water streams in an annular test section at BWR operational conditions. The experiments are simulating conditions existing in a guide tube of BWR control rods, where relatively cold water at about 333 K is mixing with hot water at ~550 K. It is shown that the mixing is causing high amplitude temperature fluctuations in the solid walls of the control rod extender. Using new movable multi-sensors it became possible to obtain a large experimental database, containing wall temperature measurements at 8 azimuthal and 5 axial positions, with 13 thermocouples at each position. In total 520 temperature readings were performed, each lasting about 2 minutes and recording transient temperature with frequency of at least 100 samples per second and with estimated non-calibrated uncertainty less than 3.9 K. The present experimental results can be used to analyze the governing phenomena during thermal mixing and also to validate CFD conjugate heat transfer models of thermal mixing applied to actual reactor geometries.
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| 7. |
- Bergagio, Mattia, et al.
(author)
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Instrumentation for Temperature and Heat Flux Measurement on a Solid Surface under BWR Operating Conditions
- 2015
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In: Proceedings of the 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16). - : American Nuclear Society. - 9781510811843 ; , s. 5962-5975
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Conference paper (peer-reviewed)abstract
- A new experimental facility has been developed at KTH Royal Institute of Technology to measure temperature and heat flux propagations in solid walls due to mixing of non-isothermal water streams in their vicinity. The main purpose of the measurements has been to obtain a high-precision experimental database suitable for validation of Computational Fluid Dynamics (CFD) codes. Consequently, a set of experiments have been performed in a test section simulating the annular region in the BWR control-rod guide tubes. Since preliminary CFD results implied that 0.1-1 Hz temperature oscillations were to be expected, this experimental research intends to assess the magnitude of temperature fluctuations within the abovementioned frequency range. To this end, water and wall temperatures have been measured in the innermost part of the test-section annulus, with a variety of boundary conditions. As thermocouples would otherwise be available at few axial and azimuthal coordinates only, the tube they are installed on has been lifted, lowered and rotated by a software-controlled motor to record temperature fluctuations in the whole mixing region. At each measurement point, data have been collected over a time long enough to detect the existence of the aforesaid fluctuations. Moreover, an uncertainty analysis has been carried out concerning water temperatures. Thermocouples meant to monitor these temperatures have been modelled with a finite-element method for this very purpose. The wall heat flux has also been estimated using experimental data, thanks to a corrected finite-difference Crank-Nicolson scheme.
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| 8. |
- Persson, Per, et al.
(author)
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Experimental investigation of post-dryout heat transfer in an annulus with spacers
- 2004
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In: Proceedings of the 42th European Two-Phase Flow Group Meeting. ; , s. 1-6
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Conference paper (other academic/artistic)abstract
- Experimental investigation of the post-dryout heat transfer in annulus test section has been performed in the high-pressure two-phase loop at the Royal Institute of Technology (KTH), Nuclear Reactor Technology division. The test section has an annular geometry with 10 mm rod outer diameter and 22.1 mm tube inner diameter. Seven spacers are located along the test section to keep the rod and the tube equidistant along the test section. Both the tube and the rod are manufactured of Inconel 600 to withstand high temperatures. The experiments indicate a very strong influence of spacers on post-dryout heat transfer. In particular, for several cases with relatively low local quality the dryout spot was limited to a direct proximity (upstream) of spacers. Only for relatively high powers the dryout patch could cover the whole distance between two neighboring spacers. For low mass flow rates dryout and post-dryout occurred near the test section outlet. With increasing mass flow rates the location of the dryout spot moved upstream of the upper-most spacer, for the cases when dryout occurred on the outer tube. The present experimental data give a new insight into the mechanism of dryout occurrence in annuli with spacers as well as indicate a strong ability of spacers to quench dryout spots and enhance the heat-transfer coefficient in the post-dryout heat transfer regime.
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