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  • 1.
    Anghel, Ionut
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Experimental and theoretical study of post-dryout heat transfer in annuli with flow obstacle2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    An experimental study on post dryout heat transfer regime in annuli with flow obstacles wasconducted in the High-pressure Water Test (HWAT) loop at the Royal Institute of Technologyin Stockholm, Sweden. An annulus with flow obstacles, consisting of two concentric heatedpipes (12.7x24.3) mm, with total heated length equal to 3650 mm was employed as a testsection. The experimental investigations were performed in a wide range of the operationalconditions: mass flux (500-1750) kg/(m2s), inlet subcooling (10-40) K and system pressure(5-7) MPa. The wall superheat was measured at 88 different axial positions. A significanteffect of the flow obstacles on the wall temperature has been observed. A new correlation toevaluate the wall superheat in the post-dryout developing region and downstream of the flowobstacles was suggested. The new approach is taking into account in a combined manner theonset of the dryout point and the flow obstacle location. The coefficients and constants of thecorrelation have been optimized based on 1211 points obtained experimentally. Thecorrelation is applicable starting with the point of the onset of the dryout towards fullydeveloped post-dryout heat transfer regime and shows a correct asymptotical trend. Toaccount for the flow obstacle effect on the critical quality, an expression similar to theLevitan-Lanstman dryout correlation is suggested. The newly developed methodology can beused to predict the wall temperature in the post-dryout heat transfer regime over a wide rangeof mass fluxes and pressures typical for boiling water reactors.

  • 2.
    Anghel, Ionut
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Experimental Study of Post Dryout Heat Transfer in Double Heated Annulus with Flow Obstacles2013Conference paper (Refereed)
  • 3.
    Anghel, Ionut
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Experimental Study of Post-Dryout Heat Transfer in Annuli with Various Flow Obstacles2011In: Transactions of the American Nuclear Society, 2011Conference paper (Refereed)
    Abstract [en]

    The influence of flow obstacles on post-dryout heat transfer at typical BWR operational conditions has been investigated in bilaterally heated annuli. The objective of the study is two-fold: (a) capture the net effect of various obstacles by comparing the experimental results obtained in the “obstacle-free” test section with the results obtained in a test section with obstacle; (b) obtain a high spatial resolution of wall temperature measurements to allow for a precise determination of the dry-patch location in the heated channel. Present study provides an extensive experimental database with more than 22000 heat transfer coefficient values in pre-, trans- and post-dryout regimes in a wide range of operational conditions: pressure equal to 5 and 7 MPa, water mass flux from 500 to 1750 kg/m2.s, inlet subcooling equal to 10 and 40 K. The heated wall temperature has been measured with 88 thermocouples located along 3.65 m long annulus with diameters 12.7x24.3 mm.

  • 4.
    Anghel, Ionut
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Experimental Study of the Onset of Dryout and Post Dryout Heat Transfer in a Bilaterally Heated Annulus with Flow Obstacles2011Conference paper (Other academic)
    Abstract [en]

    New experimental studies of the onset of dryout and post-dryout heat transfer have been performed in the High-pressure Water Test (HWAT) loop at the Nuclear Reactor Engineering division, KTH, Stockholm, Sweden. The experiments have been performed in a bilaterally heated annulus with dimensions 12.7x24.3x3650 mm and with various flow obstacles placed in the exit part of the channel. The objective of the study has been to obtain a new data set of high accuracy which can be used for validation of detailed computational models for prediction of the influence of flow obstacles on the occurrence of dryout and on the post-dryout heat transfer. To meet the objective, in total 88 K-type thermocouples have been installed in the test section, providing both lateral and axial distribution of the heated wall temperature. Several thermocouples have been placed within and in a direct vicinity of selected flow obstacles to obtain a high spatial resolution of the measured temperature field. A thorough analysis of the experimental uncertainties indicates that the accuracy of temperature measurements is better than +/-2 K.

    The measurements have been performed at conditions relevant to nuclear reactor safety applications: system pressure in a range from 5 to 9 MPa, mass flux from 500 to 1500 kg/(m2.s) and inlet sub-cooling from 10 to 40 K. The heat flux applied in the test section was limited to not allow the wall temperature to exceed 900 K.

    The experimental results indicate that flow obstacles can either remove a dry-patch completely, or reduce the wall temperature downstream of their location. It has been noted that this effect depends on operational conditions and also on the geometry and axial location of the obstacle. In general, stronger influence has been noted for high mass flow rates and for obstacles with a larger projected cross-section area.

  • 5.
    Anghel, Ionut
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    MEASUREMENT OF POST DRYOUT HEAT TRANSFER COEFFICIENT IN A DOUBLE HEATEAD ANNULUS WITH FLOW OBSTACLES2011In: Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, 2011Conference paper (Refereed)
    Abstract [en]

    An experimental study on post dryout heat transfer regime in annuli with flow obstacles was conducted in the High-pressure Water Test (HWAT) loop at the Royal Institute of Technology in Stockholm, Sweden. The experimental investigations were performed in a wide range of the operational conditions: mass flux (500-750) kg/(m2s), inlet subcooling (10-40) K and system pressure (5-7) MPa. The wall superheat was measured at 88 different axial and azimuthal positions (40 on the inner tube and 48 on the outer tube). The results show an enhancement of heat transfer downstream of flow obstacles. The biggest influence has been observed in case of pin spacers. This result is consistent with blockage area of various obstacles, which was the highest in case of pin spacers

  • 6.
    Anghel, Ionut
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    On post-dryout heat transfer in channels with flow obstacles2014In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 270, p. 351-358Article in journal (Refereed)
    Abstract [en]

    This paper describes a new approach to predict post-dryout heat transfer in channels with flow obstacles. Using experimental data obtained in annular test sections at prototypical BWR conditions, the existing Saha correlation for post-dryout heat transfer has been modified to account for the presence of obstacles. The obstacle effect is taken into account in the following way: (a) the critical quality downstream of an obstacle is found; (b) an exponential function of equilibrium quality is applied to describe the decrease of heat transfer coefficient in the developing post-dryout region; (c) an additional heat transfer enhancement term is applied downstream of the obstacle. The new approach is applied to annular test sections with various flow obstacles and a significant improvement of accuracy of wall temperature prediction, as compared to reference methods, is shown.

  • 7.
    Anghel, Ionut
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Validation of the TRACE code against post-dryout experiments in tubes and annuli2006In: Proceedings of the 14th International Conference on Nuclear Engineering, 2006Conference paper (Refereed)
    Abstract [en]

    The present paper presents results of the TRACE code assessment against post dryout experimental data obtained in tubes and annuli. The investigations have been focused on the experiments carried out at 70 bar pressure, 10 K inlet subcooling and the mass flux variation between 500-2000 kg/(m2s). Various axial power distributions (uniform, inlet peaked, middle peaked, and outlet peaked) have been used in the tube geometry. Uniform power distributions, with various ratios between the inner and the outer power have been used in the annulus geometry. The validation results indicated that the discrepancies between measured and calculated data are in a range of ± 20%. In addition a sensitivity study has been performed in which the influence of several parameters (including cell size and boundary conditions) on computational results have been investigated.

  • 8.
    Anghel, Ionut
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Wall Temperature Prediction in Annular Geometry during Post-Dryout Heat Transfer2014In: Journal of Power Technologies, ISSN 2083-4187, E-ISSN 2083-4195, Vol. 94, p. 1-7Article in journal (Refereed)
    Abstract [en]

    In this paper a new approach to predict wall temperature during post-dryout heat transfer in annuli with flow obstacles is presented. The proposed approach takes into account the obstacle specifics and location in the channel to determine the onset of post-dryout patch. The wall temperature in the dry patch area is predicted from a correlation that is taking into account the developing post-dryout heat transfer regime. The method is applied to post-dryout conditions in annulus with pin-spacers and a significant improvement of prediction accuracy in comparison to other reference methods is demonstrated.

  • 9.
    Anghel, Ionut
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Hedberg, Stellan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Experimental investigation of post-dryout heat transfer in annuli with flow obstacles2012In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 246, p. 82-90Article in journal (Refereed)
    Abstract [en]

    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.

  • 10.
    Anghel, Ionut Gheorghe
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Experimental Study of Post-Dryout Heat Transferin Annuli with Flow Obstacles2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    An experimental study on post dryout heat transfer regime in annuli with flow obstacles was conducted in the High-pressure Water Test (HWAT) loop at the Royal Institute of Technology in Stockholm, Sweden. An annulus consisting of two concentric heated pipes (12.7x24.3) mm, with total heated length equal to 3650 mm was employed as a test section. Three kinds of flow obstacles were used: pin-spacers, cylindrical obstacles and grid obstacles. The experiments performed in the test section with pin-spacers only were considered as the reference case. In two consecutive sets of runs, additional obstacles were placed inside the flow channel while keeping the pin spacers in the same positions. In that way the net effect of obstacles on heat transfer was measured. The experimental investigations were performed in a wide range of the operational conditions: mass flux (500-1750) kg/(m2s), inlet subcooling (10-40) K and system pressure (5-7) MPa. The wall superheat was measured at 88 different axial positions (40 on the inner tube and 48 on the outer tube) for the conditions mentioned above. A local heat transfer coefficient was calculated based on the measured annulus wall temperatures and the saturated fluid (water) properties. The results show an enhancement of the heat transfer coefficient downstream of flow obstacles. The most significant influence has been observed in case of pin spacers. This result is consistent with blockage area of various obstacles, which was the highest in case of pin spacers. The data obtained in more than 200 runs were compared with two pre-dryout and post-dryout correlations. The correlations show a slight over-prediction of the heat transfer coefficient in both pre-dryout and post-dryout regions. The thesis contains a detailed description of experimental procedures as well as an analysis of the results of measurements.

     

  • 11.
    Anghel, Ionut Gheorghe
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Experimental investigatons of heat transfer at dry patch location in annular two-phase flow2011In: Proceedings of ICONE19. 19th International Conference on Nuclear Engineering, 2011Conference paper (Refereed)
    Abstract [en]

    New experiments have been performed to investigate heat transfer to water/steam two-phase mixture flowing in annular test section at trans-dryout conditions. The measurements have been carried out in the High-pressure Water Test (HWAT) loop at the Royal Institute of Technology, Stockholm, Sweden. The primary objective of the experimental investigations has been to study heat transfer at conditions typical for Boiling Water Reactors (BWR), when heat transfer regime changes from convective boiling to post-dryout heat transfer. The experiments indicate a significant enhancement of heat transfer just upstream of dryout patch. It has been observed that the measured heat transfer coefficient is in good agreement with the Chen correlation for quality less than 30%, however, increasing discrepancy is noted for near-critical quality.

     

  • 12.
    Anghel, Ionut Gheorghe
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Post-dryout heat transfer to high-pressure water flowing upward in vertical channels with various flow obstacles2012In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 55, no 25-26, p. 8020-8031Article in journal (Refereed)
    Abstract [en]

    Post-dryout heat transfer to high pressure water was investigated experimentally in vertical tubes and annuli containing various flow obstacles. The operational conditions during the experiments were as follows: mass flux from 500 to 1750 kg/m(2) s. pressure from 5 to 9 MPa, inlet subcooling from 10 to 40K and heat flux up to 1.5 MW/m(2). Five different test sections were used in experiments: three annular test sections with inner diameter 12.7 mm and outer diameter 24.3 mm, containing cylindrical and grid flow obstacles in the upper part, and two tubular test sections with inner diameter 24.3 mm with and without pin flow obstacles. The heated length in all test sections was 3650 mm. The wall temperature was measured with 88 thermocouples located along the inner rod and the outer tube surfaces. Due to the presence of flow obstacles, only developing post-dryout heat transfer was observed. Selected post-dryout heat transfer correlations were compared to the experimental data. It has been concluded that all tested correlations predict significantly higher wall temperatures than those obtained in the present experiment. A simple correction function to the Saha model has been suggested which significantly improves the agreement between the correlation and the present data.

  • 13.
    Anghel, Ionut Gheorghe
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Hedberg, Stellan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Experimental investigation of post-dryout heat transfer in annuli with flow obstacles2010In: International Conferecne Nulclear Energy for New Europa 2010, 2010Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    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.

     

  • 14.
    Anghel, Ionut Gheorghe
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Hedberg, Stellan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Study of post dryout heat transfer in annulus with flow obstacles2010In: Proceedings of the 14th International Heat Transfer Conference (IHTC14), 2010Conference paper (Refereed)
    Abstract [en]

    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.

  • 15.
    Anghel, Ionut Gheorghe
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Hedberg, Stellan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Rydström, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Experimental Investigation of the Influence of Flow Obstacles on Post-Dryout Heat Transfer in an Annulus2009In: ICONE 17: PROCEEDINGS OF THE 17TH INTERNATIONAL CONFERENCE ON NUCLEAR ENGINEERING, VOL 3, NEW YORK: AMER SOC MECHANICAL ENGINEERS , 2009, p. 277-286Conference paper (Refereed)
    Abstract [en]

    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.

  • 16.
    Anglart, Henryk
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Anghel, Ionut
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    On post-dryout heat transfer in channels with flow obstacles2014In: International Congress on Advances in Nuclear Power Plants, ICAPP 2014, 2014, Vol. 2, p. 1518-1523Conference paper (Refereed)
    Abstract [en]

    In this paper a new approach to predict wall temperature during post-dryout heat transfer in channels with flow obstacles is presented. The proposed approach takes into account the obstacle specifics and location in the channel to determine the post-dryout patch onset. The wall temperature in the dry patch area is predicted from Anghel and Anglart correlation to account for developing post-dryout conditions. The method is applied to post-dryout conditions in annulus with pin-spacers and a significant improvement of prediction accuracy in comparison to other reference methods is demonstrated.

1 - 16 of 16
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