| 1. |
- Adamsson, Carl, et al.
(författare)
-
A reinterpretation of measurements in developing annular two-phase flow
- 2011
-
Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 241:11, s. 4562-4567
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of developing films in adiabatic high pressure steam-water flow in annular geometry have been reanalyzed and compared to a linearized film-flow model. The development rate of the outer film could be determined with good accuracy in four cases. In one case it was also possible to conclude that the inner film develops faster than the outer one. When compared to the linearized model, these observations show that the deposition rate has to be almost independent of the drop concentration at the investigated conditions. Furthermore, any significant deposition by direct impaction of drops can be excluded as it would couple the development of the two films. These conclusions are quite general and do not depend on the use of any particular correlation for the deposition or entrainment rates. Finally, a rough estimate of the deposition rate was possible, confirming that deposition rates are considerably lower at high pressure steam-water flows than in air-water flows.
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| 2. |
- Adamsson, Carl, et al.
(författare)
-
An investigation of cross-section geometry effects on the deposition rate in annular two-phase flows with a Lagrangian model
- 2007
-
Ingår i: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12. - 9780894480584 - 0894480588
-
Konferensbidrag (refereegranskat)abstract
- The motion of liquid drops in annular two-phase flow in pipes, annuli and subchannels has been investigated with a model based on Lagrangian particle tracking. The results confirm that large drops may deposit by direct impaction. It is also demonstrated that the deposition rate does not differ significantly between pipes and subchannels except for very large drops, which deposit slower in subchannels. Furthermore the Saffman lift force is shown to have a large impact on the results but it is questionable of the standard formulation is applicable to the drops considered here. Finally it is concluded that accurate modeling of high pressure steam-water flows requires a model for drop-drop collisions.
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| 3. |
- Adamsson, Carl, 1976-
(författare)
-
Dryout and Power Distribution Effects in Boiling Water Reactors
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Film flow measurements at several axial positions in round pipes with variousaxial power distributions are presented for conditions corresponding to normaloperation of a BWR. It is confirmed that the film flow rate approaches zero atthe onset of dryout. Selected phenomenological models of annular two-phaseflow are shown to reasonably reproduce the measurements. It is concluded thatmodels are in better agreement with measurements if terms corresponding topossible boiling induced entrainment are excluded. A method to perform film flow analysis in subchannels as a post-processto a standard two-field subchannel code is suggested. It is shown that thisapproach may yield accurate prediction of dryout power in rod bundles to alow computational cost and that the influence of the power distribution is wellpredicted by the model.
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| 4. |
- Adamsson, Carl, et al.
(författare)
-
Dryout predictions in bwr fuel assemblies with spacers
- 2004
-
Ingår i: Proceedings of the Sixth International Conference on Nuclear Thermal-Hydraulics, Operation and Safety.
-
Konferensbidrag (refereegranskat)abstract
- A new spacer model has been implemented into the subchannel code Mona-3 and validated against dryout experiments in various rod bundles with different number of spacers and different spacer designs. The spacer-induced deposition enhancement is captured by proper modeling of the turbulence intensity downstream of a spacer.The Mona-3 code with the new spacer model captures spacer effects in a correct manner. Both the effect of the number of spacers and the effect of the spacer design are predicted correctly. In particular, the critical power difference between 24-rod bundles with 6 and with 7 spacers is measured to be larger than the difference between 25-rod bundles with 6 and with 7 spacers. This experimental finding is well captured with the Mona-3 code with the present spacer model.
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| 5. |
- Adamsson, Carl, et al.
(författare)
-
Eperimental Investigation of the Liquid Film for Annular Flow in a Tube with Various Axial Power Distributions
- 2005
-
Ingår i: NURETH 11, Avignon, France, October 2–6, 2005.
-
Konferensbidrag (refereegranskat)abstract
- This paper was published when the measurements with non-uniform powerdistribution were still ongoing. Therefore only the measurements with uniformand top-peaked power profiles were included. The paper compares the measured data with deposition and entrainmentmodels by Hewitt & Govan (1990) and Okawa et al. (2003). These models are also discussed in Sections 4.2.1 and 4.2.2. The issue of a correct boundarycondition at the onset of annular flow was avoided by starting the integrationof the film flow model from the most upstream measurement point. In this way the net mass exchange rate (deposition less entrainment) could be studied without any initial bias from the boundary condition.The entrainment correlation proposed by Okawa et al. (2003) included a heat flux dependent term to account for boiling entrainment (Section 4.2.2). Paper 2 concludes that the model agrees better with measurements if this term is omitted. The result suggests that boiling entrainment may not be an important effect at the investigated conditions.
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| 6. |
- Adamsson, Carl, et al.
(författare)
-
Film flow measurements for high-pressure diabatic annular flow in tubes with various axial power distributions
- 2006
-
Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 236:23, s. 2485-2493
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of film flow rates in diabatic annular flow in tubes with various axial power distributions were carried out in the high-pressure two-phase flow loop at the Royal Institute of Technology (KTH), Sweden. The measurements were performed at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m(2)s. Four different axial power distributions were used and the film mass flow was measured at 7 axial locations for each set of boundary conditions. The results show that the outlet peaked distribution gives less film than the inlet peaked one. This result is consistent with well known trends from measurements of dryout power. The measurements also show that the film flow at the onset of dryout is very small at investigated conditions in agreement with earlier studies. Finally it is shown that the present data is well predicted by two selected phenomenological models of annular flow.
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| 7. |
- Adamsson, Carl, et al.
(författare)
-
Influence of Axial Power Distribution on Dryout : Film-Flow Models and Experiments
- 2010
-
Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 240:6, s. 1495-1505
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of axial power distributions on dryout occurrence in nuclear fuel assemblies has been studied extensively for several decades. Even though it is well known that axial power shapes which may significantly vary in nuclear reactors during their operation significantly change the dryout power level, this particular influence is rather difficult to capture with current correlations. In this paper it is shown that this influence can be captured using a phenomenological liquid film model coupled to a standard sub-channel code. The model has been applied to various geometries, including a round pipe, as well as 5 x 5 and 8 x 8 fuel rod assemblies, and highly accurate predictions have been obtained.
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| 8. |
- Adamsson, Carl, 1976-
(författare)
-
Measurements of Film Flow Rate in Heated Tubes with Various Axial Power Distributions
- 2006
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Measurements of film mass flow rate for annular, diabatic steam-water flow in tubes are presented. The measurements were carried out with four axial power distributions and at several axial positions at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m2s. The results show that the influence of the axial power distribution on the dryout power corresponds to a consistent tendency in the film flow rate and that the film tends to zero when dryout is approached. Furthermore it is demonstrated that two selected phenomenological models of annular flow well predict the present data. A model for additional entrainment due to boiling is shown to degrade the predictions.
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| 9. |
- Adamsson, Carl, et al.
(författare)
-
Measurements of the Liquid Film Flow Rate in High Pressure Annular Flow with Various Axial Power Distributions
- 2005
-
Ingår i: HEAT 2005, Gdansk, Poland, June 26–30, 2005.
-
Konferensbidrag (refereegranskat)abstract
- This paper presents film flow measurement technique and the results with uniform power distribution. Based on these measurements it is possible to estimate the critical film thickness. The measured film thickness was plotted versus steam quality and slightlyextrapolated up to the measured critical steam quality. The conclusions werein line with Hewitt et al. (1965), i.e. that the critical film thickness is insignificantly small. This does not contradict e.g. Ueda & Isayama (1981) since the conditions were not the same, but for the flow conditions and heat fluxes that are typical for BWR operation it was concluded that the critical film thickness is, for practical purposes, zero.
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| 10. |
- Anghel, Ionut, 1971-
(författare)
-
Experimental and theoretical study of post-dryout heat transfer in annuli with flow obstacle
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 11. |
- Anghel, Ionut, 1971-, et al.
(författare)
-
Experimental investigation of post-dryout heat transfer in annuli with flow obstacles
- 2012
-
Ingår i: Nuclear Engineering and Design. - : Elsevier. - 0029-5493 .- 1872-759X. ; 246, s. 82-90
-
Tidskriftsartikel (refereegranskat)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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| 12. |
- Anghel, Ionut, et al.
(författare)
-
Experimental Study of Post-Dryout Heat Transfer in Annuli with Various Flow Obstacles
- 2011
-
Ingår i: Transactions of the American Nuclear Society.
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 13. |
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| 14. |
- Anghel, Ionut, et al.
(författare)
-
Experimental Study of the Onset of Dryout and Post Dryout Heat Transfer in a Bilaterally Heated Annulus with Flow Obstacles
- 2011
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 15. |
- Anghel, Ionut Gheorghe, et al.
(författare)
-
Experimental investigation of post-dryout heat transfer in annuli with flow obstacles
- 2010
-
Ingår i: International Conferecne Nulclear Energy for New Europa 2010.
-
Konferensbidrag (populärvet., debatt m.m.)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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| 16. |
- Anghel, Ionut Gheorghe, et al.
(författare)
-
Experimental Investigation of the Influence of Flow Obstacles on Post-Dryout Heat Transfer in an Annulus
- 2009
-
Ingår i: ICONE 17. - NEW YORK : AMER SOC MECHANICAL ENGINEERS. - 9780791843536 ; , s. 277-286
-
Konferensbidrag (refereegranskat)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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| 17. |
- Anghel, Ionut Gheorghe, et al.
(författare)
-
Experimental investigatons of heat transfer at dry patch location in annular two-phase flow
- 2011
-
Ingår i: Proceedings of ICONE19. 19th International Conference on Nuclear Engineering.
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 18. |
- Anghel, Ionut Gheorghe
(författare)
-
Experimental Study of Post-Dryout Heat Transferin Annuli with Flow Obstacles
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 19. |
- Anghel, Ionut Gheorghe, et al.
(författare)
-
Post-dryout heat transfer to high-pressure water flowing upward in vertical channels with various flow obstacles
- 2012
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 55:25-26, s. 8020-8031
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 20. |
- Anghel, Ionut Gheorghe, et al.
(författare)
-
Study of post dryout heat transfer in annulus with flow obstacles
- 2010
-
Ingår i: Proceedings of the 14th International Heat Transfer Conference (IHTC14).
-
Konferensbidrag (refereegranskat)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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| 21. |
- Anghel, Ionut, et al.
(författare)
-
MEASUREMENT OF POST DRYOUT HEAT TRANSFER COEFFICIENT IN A DOUBLE HEATEAD ANNULUS WITH FLOW OBSTACLES
- 2011
-
Ingår i: Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics.
-
Konferensbidrag (refereegranskat)abstract
- 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
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| 22. |
- Anghel, Ionut, et al.
(författare)
-
On post-dryout heat transfer in channels with flow obstacles
- 2014
-
Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 270, s. 351-358
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 23. |
- Anghel, Ionut, et al.
(författare)
-
Validation of the TRACE code against post-dryout experiments in tubes and annuli
- 2006
-
Ingår i: Proceedings of the 14th International Conference on Nuclear Engineering.
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 24. |
- Anghel, Ionut, et al.
(författare)
-
Wall Temperature Prediction in Annular Geometry during Post-Dryout Heat Transfer
- 2014
-
Ingår i: Journal of Power Technologies. - 2083-4187 .- 2083-4195. ; 94, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 25. |
- Anglart, Henryk
(författare)
-
An Overview of Nuclear Power Economics
- 2010
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The development of nuclear industry is influenced by the following four major factors: plant safety, non-proliferation of nuclear materials, economics and sustainability. Recently, the safety records of nuclear power plants are excellent and it can be believed that this factor will not limit the development in the nuclear field in the future. The same can be said about the non-proliferation, even though care must be taken to limit the number of countries that will try to develop all facilities that are needed for fuel cycle operations. It is believed that the future development of nuclear power will be – to a large extend – governed by over-all economics of this type of electricity generation. This paper gives an overview of the major aspects of an economic analysis of a nuclear power plant. The method of calculation of the levelised cost of electricity is described. Selected data found in literature indicate that nuclear electricity production will be economically favorable when CO2 emission charge is taken into account for the coal and gas electricity production. Additional improvement of nuclear economy will be obtained by the shortening of the construction period, and in general, by reduction of the capital cost during the construction of a plant.
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| 26. |
- Anglart, Henryk
(författare)
-
Analysis of Laminar Mixed Convection Heat Transfer to Supercritical Water Flowing in a Vertical Duct
- 2009
-
Ingår i: Proceedings of the 13th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics.
-
Konferensbidrag (refereegranskat)abstract
- In this paper analytical solutions have been obtained for the case of laminar supercritical water flow between two infinite walls at two slightly different temperatures. The existence of the fully-developed flow condition is postulated and thus the problem is reduced to solutions of a set of non-linear ordinary differential equations representing the conservation of mass, energy and momentum. The equations are numerically solved using the Matlab code, and employing water property functions based on the IAPWS-IF97 library. The Matlab program has been verified against known analytical solutions for the laminar duct flow of fluids with constant properties and an excellent agreement has been obtained. The solutions of conservation equations give an expression for the over-all heat transfer coefficient in mixed convection. The analysis indicates that the heat transfer coefficient is a very strong function of local properties and flow conditions. The predicted Nusselt number and the convection coefficient are in a reasonably good agreement with existing correlations once the fluid temperature is far from the pseudo-critical value. However, the existing correlations deviate from the predicted values when the fluid is at the pseudo-critical temperature.
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| 27. |
- Anglart, Henryk, et al.
(författare)
-
Analysis of Post-Dryout Heat Transfer in Heated Channels with Spacers
- 2006
-
Ingår i: Proceedings of the 13th International Heat Transfer Conference.
-
Konferensbidrag (refereegranskat)abstract
- Post-dryout heat transfer plays an important role in safe and economical operations of Light Water Reactors (LWR). This type of heat transfer is avoided under normal operational conditions of nuclear reactors; however, it may occur in emergency situations. To estimate the risk of clad damages due to increase of temperature associated with the occurrence of post-dryout, it is necessary to properly model heat transfer conditions in such situations. Present paper contains results of measurements performed in a high-pressure thermal hydraulic loop at the Reactor Technology Division, Royal Institute of Technology, Stockholm, Sweden. Post-dryout heat transfer was investigated in an annular test section with inner and outer diameters equal to 10 and 21.1 mm, respectively, and heated length equal to 3650 mm. Seven spacers with typical BWR design were located along the test section to keep the heated rod at the centre of the heated tube. Surface temperatures of both inner and outer wall were measured by several thermocouples installed at various locations along the test section. Distributions of wall temperatures were measured for mass flux in a range from 500 to 2000 kg m-2 s-1, inlet subcooling 10 and 40 K, wall heat flux from 480 to 1380 kW m-2 and pressure 7 MPa. The experiments revealed that spacers have a very strong influence on post-dryout heat transfer and very effectively reduce the heated wall temperatures just downstream of their locations. Only for very high powers the dryout patches could cover the whole distance between two neighbouring spacers. Under moderate powers such dryout patches were limited to a close distance to the downstream spacer, where the influence of the upstream spacer already vanished. The influence of various parameters on heat transfer downstream of spacer was investigated. It was concluded that heat transfer enhancement due to spacers is largely under-predicted for flows with relatively low quality. For such flows the effect of droplets impinging heated walls is significant and must properly be taken into account. Clearly, more work is needed to improve the over-all predictability of post-dryout heat transfer in heated channels with spacers.
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| 28. |
- Anglart, Henryk
(författare)
-
Analysis Of The Onset Of Dryout Conditions In Diabatic Annular Two-Phase Flows
- 2012
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Ingår i: Proceedings Of The 20th International Conference On Nuclear Engineering And The ASME 2012 Power Conference - 2012, Vol 3. - 9780791844977 ; , s. 627-630
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Konferensbidrag (refereegranskat)abstract
- An analysis is presented that predicts the conditions which allow for a formation of a stable dry patch in diabatic annular two phase flows. The analysis employs a force balance formulated for the leading edge of the liquid film In addition to stagnation, thermo-capillary and vapor thrust forces, the analysis includes effects of the pressure gradient and the interfacial shear stress. It is shown that the equilibrium conditions of a dry patch are dominated by the stagnation force, the surface tension force, the capillary force and the skin drag force. For high heat flux conditions only the first three forces are important.
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| 29. |
- Anglart, Henryk
(författare)
-
Application Of The Convolution Theorem To Predict Heated Wall Temperature Subject To Various Axial Power Distributions
- 2012
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Ingår i: Proceedings Of The 20th International Conference On Nuclear Engineering And The ASME 2012 Power Conference - 2012, Vol 4. - 9780791844984 ; , s. 575-579
-
Konferensbidrag (refereegranskat)abstract
- One of the important parameters that affect the thermal-hydraulic performance of nuclear fuel assemblies is the spatial - that is the lateral and the axial distribution of power. Since this parameter may have a significant influence on thermal margins of nuclear reactors, it is necessary to take it into account in various models and/or correlations. One practical difficulty in doing so is the fact that the spatial power distribution is a function of space variables, which makes it very inconvenient to implement into single-parameter correlations. In addition, there is still lack of a simple theoretical model that captures the effect of spatial power distributions on the thermal-hydraulic performance of nuclear fuel assemblies. In this paper, an accurate and fast running convolution method is presented to predict the influence of axial power distribution on wall temperature distributions. The method has been verified against CFD predictions of the wall temperature in a heated pipe and an excellent agreement between the two approaches is demonstrated. The method is applicable only for constant fluid properties and for a fully developed flow regime.
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| 30. |
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| 31. |
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| 32. |
- Anglart, Henryk
(författare)
-
Attractive Nuclear Energy
- 2011
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Ingår i: Energetyka. - : Wydawnictwo NOT -SIGMA. - 0013-7294. ; 5, s. 267-271
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 33. |
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| 34. |
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| 35. |
- Anglart, Henryk, et al.
(författare)
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CFD modeling of boiling annular-mist flow for dryout investigations
- 2011
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Ingår i: Multiphase Science and Technology. - : Begell House. - 0276-1459 .- 1943-6181. ; 23, s. 223-251
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents applications of computational fluid dynamics (CFD) to modeling of two-phase annular-mist flows with evaporating liquid films. This type of two-phase flow exists in boiling channels prior to the onset of dryout. Annular-mist flows have a very complex structure since they contain liquid and vapor, both as the continuous and the dispersed phase. Due to this feature, both the Eulerian-Eulerian as well as the Eulerian-Lagrangian approaches are often used to model such flows. The two approaches, with pertinent conservation equations and closure relationships, are reviewed in this paper.
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| 36. |
- Anglart, Henryk, 1954-
(författare)
-
CFD modelling of annular two-phase flow and heat transfer
- 2017
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Ingår i: 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2017. - : Association for Computing Machinery, Inc.
-
Konferensbidrag (refereegranskat)abstract
- This paper describes the governing phenomena and current approaches in their modeling for annular two-phase flow and heat transfer. The complexity of the flow, including liquid film, disturbance waves, turbulent gas core, droplet deposition and entrainment, are discussed. Computational Fluid Dynamics (CFD) approach to model the phenomena is presented.
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| 37. |
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| 38. |
- Anglart, Henryk
(författare)
-
CFD Prediction of Heat Transfer Deterioration to Supercritical Water
- 2010
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Ingår i: ASME Transactions. ; , s. 641-642
-
Konferensbidrag (refereegranskat)abstract
- Supercritical water will serve as a coolant in the Generation-IV Supercritical Water-Cooled Reactor (SCWR). The important advantage of supercritical water as a coolant is the lack of the phase-change phenomenon. As a result one of the most limiting factors applicable to the current Light Water Reactors (LWR) – namely the occurrence of the Critical Heat Flux (CHF) – is no longer existent. Considering the high heat capacity, supercritical water is indeed an excellent choice for a coolant. However, even though CHF is no longer an issue, heat transfer to supercritical water suffers from a sudden Heat Transfer Deterioration (HTD) phenomenon. HTD manifests itself with a sudden reduction of the local heat transfer coefficient and local increase of the heater wall temperature. Even though the phenomenon has been intensively investigated in the past 50 years, there is a lack of a robust and accurate criterion for the onset of HTD. Recently, Palko and Anglart (2007) demonstrated that the onset of HTD can be captured with a computational model based on the Reynolds Averaged Navier Stokes (RANS) equations and using the Shear-Stress Transport (SST) turbulence model implemented in the CFX code (Menter, 1993). The calculations revealed that there are two principal mechanisms of the onset of HTD: (a) reduction of the turbulence intensity close to the wall due to the buoyancy effects, (b) creation of a thin layer of supercritical water with low thermal conductivity (corresponding to the “vapor” phase of the supercritical fluid). The former mechanism occurs for relatively low mass fluxes, whereas the latter occurs when the mass flux of coolant is pretty high. The present paper presents further numerical investigation of the HTD phenomenon, and in particular, a derivation of the criterion for the onset of HTD based on numerical simulations.
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| 39. |
- Anglart, Henryk
(författare)
-
Current Development Trends in Nuclearenergy Engineering
- 2010
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Ingår i: Archives of Energetics. - 0066-684X. ; XL:1-2, s. 3-17
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Tidskriftsartikel (refereegranskat)abstract
- The recent focus on the global warming caused by greenhouse gases has drawn attention to thenuclear energy as a reliable, carbon-dioxide free source of electricity. The current optimistic view onthe nuclear energy can be compared to the situation that took place in sixties and early seventies ofthe past century, when the potential of the nuclear energy seemed to be almost unlimited. However,today’s enthusiasm, frequently referred to as the nuclear renaissance, is different. The nuclearcommunity learned its lessons, such as resulting from the two major accidents in Three Mile Islandand in Chernobyl, but also resulting from the competition with other energy sources and – last butnot least – due to the increasing public awareness of nuclear safety issues. Thus, the current trends ofdevelopment in nuclear energy engineering have different priorities than in the past. Currentlydesigned and constructed nuclear power plants will have so-called generation III+ reactors. Suchreactors are designed with focus on safety and efficiency aspects. Future generation IV reactors arecurrently under development and subject of intensive world-wide research. These reactors will notonly be safe and efficient, but also resistant to proliferation and will support the sustainabledevelopment in the nuclear energy field.
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| 40. |
- Anglart, Henryk
(författare)
-
Dry Patch Formation in Diabatic Annular Two-Phase Flows
- 2014
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Ingår i: Journal of Power Technologies. - 2083-4187 .- 2083-4195. ; 94, s. 85-95
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Tidskriftsartikel (refereegranskat)abstract
- Conditions for the formation of a stable dry patch in vertical annular two-phase flows in heated channels are investigated. An analytical model of the force balance for the leading edge of the liquid film is developed. In addition to surface tension, evaporation thrust and capillary forces, the model includes the effect of turbulence, the pressure gradient and the interfacial shear stress. Numerical evaluations are performed to validate the model and to indicate the importance of various factors on the dry patch stability and on the resulting minimum wetting rate of the liquid film. The analyses indicate that good agreement with measurements is obtained in case of stagnant patch formed on liquid film flowing down a vertical surface. It is shown that for low and moderate mass flow rate of the gas phase in vertical co-current annular flow, the force balance is dominated by the stagnation and the shear stress forces. With growing mass flow rate of the gas phase, the pressure gradient and the interfacial shear stress are increasingly important. As a result, in accordance with measurements, the predicted minimum flow rate of the liquid film at which the patch is re-wetted decreases.
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| 41. |
- Anglart, Henryk, 1954-, et al.
(författare)
-
Experimental and numerical investigations of wall temperature fluctuations due to thermal mixing in an annulus
- 2016
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Konferensbidrag (refereegranskat)abstract
- Wall temperature fluctuations during thermal mixing of water in an annular test section have been measured and numerically predicted. The characteristics of the temperature fluctuations, such as their amplitudes and frequencies, are closely related to a premature structural failure due to the thermal fatigue. The goal of the present work has been to obtain experimental data on the convective heat transfer in presence of thermal mixing and use the data for validation of computational codes. During the experiments, two water streams at significantly different temperatures and at pressure 7.2 MPa are mixing in an annular test section, causing significant fluctuations of temperatures in walls surrounding the mixing zone. In parallel to experiments, the analyses of water mixing and of the resulting wall temperature fluctuations have been carried out using the Large Eddy Simulations (LES) with conjugate heat transfer approach. A similar behavior of temperature fluctuations has been observed in experiments and calculations. In particular, it has been both calculated and measured that the wall temperature spectrum varies at different locations in the test section and the dominant frequencies of fluctuations for the case presented in the paper are in the range of 0.1 to 0.2 Hz.
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| 42. |
- Anglart, Henryk, et al.
(författare)
-
Experimental investigation of post-dryout heat transfer in annulus with spacers
- 2007
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322 .- 1879-3533. ; 33:8, s. 809-821
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Tidskriftsartikel (refereegranskat)abstract
- Experimental investigations of post-dryout heat transfer in 10 x 22.1 annulus test section with space. rs were carried out in the high-pressure two-phase flow loop at the Royal Institute of Technology (KTH). The test section was manufactured of Inconel 600 to withstand high temperatures. Several thermocouples were installed on tube and rod surfaces to measure the local wall temperature. Measurements were performed for mass flow rate in range from 500 to 2000 kg m(-2) s(-1), with inlet subcooling equal to 10 and 40 K, heat flux in a range from 480 to 1380 kW m(-2) and for the system pressure of 7 MPa. Uniform axial power distributions were applied on rod and tube walls. Using different distributions of heat flux between walls, post-dryout was achieved either on the inner or on the outer wall. The experimental results indicate a very strong influence of spacers on post-dryout heat transfer. For low mass flow rates the wall superheat was significantly reduced downstream of spacers, even though the whole distance between spacers was still under post-dryout conditions when heat flux was high enough. At high mass flow rates and under investigated range of heat flux the dryout patches were effectively quenched downstream of spacers.
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| 43. |
- Anglart, Henryk, et al.
(författare)
-
EXPERIMENTAL INVESTIGATION OF STATIONARY AND TRANSIENT POST-DRYOUT HEAT TRANSFER IN 22.1X10 MM ANNULUS WITH SPACERS
- 2005
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Ingår i: Proceedings of the Eleventh International Topical Meeting on Nuclear Reactor Thermal-Hydraulics.
-
Konferensbidrag (refereegranskat)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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| 44. |
- Anglart, Henryk, et al.
(författare)
-
Fluid mechanics of Taylor bubbles and slug flows in vertical channels
- 2002
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Ingår i: Nuclear science and engineering. - 0029-5639 .- 1943-748X. ; 140:2, s. 165-171
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Tidskriftsartikel (refereegranskat)abstract
- Fluid mechanics of Taylor bubbles and slug flows is investigated in vertical, circular channels using detailed, three-dimensional computational fluid dynamics simulations. The Volume of Fluid model with the interface-sharpening algorithm, implemented in the commercial CFX4 code, is used to predict the shape and velocity of Taylor bubbles moving along a vertical channel. Several cases are investigated, including both a single Taylor bubble and a train of bubbles rising in water. It is shown that the potential flow solution underpredicts the water film thickness around Taylor bubbles. Furthermore, the computer simulations that are performed reveal the importance of properly modeling the three-dimensional nature of phenomena governing the motion of Taylor bubbles. Based on the present results, a new formula for the evaluation of bubble shape is derived. Both the shape of Taylor bubbles and the bubble rise velocity predicted by the proposed model agree well with experimental observations. Furthermore, the present model shows good promise in predicting the coalescence of Taylor bubbles.
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| 45. |
- Anglart, Henryk
(författare)
-
Heat Transfer Deterioration in Application to HPLWR-Mechanisms Identification and Ranking Table
- 2009
-
Ingår i: Proceedings of the 4th International Symposium on Supercritical Water-Cooled Reactors.
-
Konferensbidrag (refereegranskat)abstract
- One of the major objectives of HPLWR Phase 2 project is to assess the feasibility ofthe super-critical water-cooled and moderated reactor. To this end it is necessary toevaluate the thermal performance and the distribution of temperature in the reactorcore under target operation conditions (25 MPa pressure and 280÷500 °C temperature).The critical scientific issue in this subject is to evaluate the efficiency of heattransfer in the reactor core and in particular, to determine the conditions of the occurrenceof the Heat Transfer Deterioration (HTD) phenomenon. The objective of this paperis to investigate and rank the key parameters that are governing the onset of HTDin general and in the HPLWR in particular. The paper describes the major heat transferdeterioration mechanisms and criteria, and contains evaluation of the importance ofparticular mechanisms on the onset of HTD. The major mechanisms are listed in a tableand ranked according to their estimated relative importance. It is concluded thateven though HTD has been investigated by many researchers and the world-wide experimentaldatabase counts tens of thousands of experimental points; still prediction ofthe onset of HTD is difficult and is subject to essential uncertainties. As a result, thereare many expressions for the onset of HTD available; however, they give very oftennon-consistent predictions. Thus more work is needed to develop a reliable HTD criterionthat can be used in nuclear applications. Operational conditions and complex geometryof HPLWR introduce additional uncertainties into the prediction of the onset ofHTD. Limited experiments in rod bundles and in parallel channels indicate a significantdeparture of the HTD conditions as compared to the experiments in single channels.Such factors as the bundle effect and the flow oscillation effect (in case of parallelchannels) have been noted and discussed.
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| 46. |
- Anglart, Henryk, 1954-
(författare)
-
Initial entrained fraction at onset of annular flow
- 2019
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Ingår i: 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 20192019. ; , s. 1023-1034
-
Konferensbidrag (refereegranskat)abstract
- One of the frequently employed current models to predict the occurrence of dryout in boiling annular flows is using conservation equations to determine the liquid film mass flux. The accuracy of predictions of dryout depends to a large extend on the initial conditions, which are employed in the model. In this paper it is shown that the accuracy of predictions can be significantly improved if the initial entrained fraction of liquid is correlated to the flow conditions at the onset of annular flow. Using experimental data for liquid film flow rates in pipes with variable power distributions, a new closure relationship for the initial entrained fraction of liquid at the onset of annular flow is proposed.
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| 47. |
- Anglart, Henryk, et al.
(författare)
-
International students workshop on innovative light water reactors
- 2008
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Ingår i: ATW. Internationale Zeitschrift für Kernenergie. - 1431-5254. ; 53:6, s. 380-386
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear reactor design is still one of the most fascinating subjects of mechanical engineering. Thirty students from 10 worldwide nations demonstrated this impressively in a recent workshop on supercritical water cooled reactors of the 4(th) generation, held from March 31 to April 3, 2008, in Karlsruhe, Germany, hosted by the Karlsruhe Institute of Technology. Bachelor and master students as well as young scientists working on their doctorate presented their own particular contribution to design and analyses of innovative reactor components, including its safety systems and other plant design. Their presentations were accompanied by lectures of leading scientists working in the European project of the "High Performance Light Water Reactor" which is sponsored by the if European Commission as part of its 6(th) Framework Programme. The workshop is an initiative of the Generation IV International Forum.
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| 48. |
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| 49. |
- Anglart, Henryk, et al.
(författare)
-
Measurement of Wall Temperature Fluctuations during Thermal Mixing of Non-isothermal Water Streams
- 2015
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Ingår i: Proceedings of the 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16). - : American Nuclear Society.
-
Konferensbidrag (refereegranskat)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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| 50. |
- Anglart, Henryk, 1954-, et al.
(författare)
-
Mechanistic modelling of dryout and post-dryout heat transfer
- 2018
-
Ingår i: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 161, s. 352-360
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a new mechanistic model for the diabatic annular two-phase flow is presented and applied to prediction of dryout and post-dryout heat transfer in various channels. The model employs a computational fluid dynamics code - OpenFOAM (R) - to solve the governing equations of two-phase mixture flowing in a heated channel. Additional closure laws have been implemented to calculate the location of the dryout and to predict wall temperature in the post-dryout region. Calculated results have been compared with experimental data obtained in pipes and good agreement between predictions and measurements has been achieved. The presented model is applicable to complex geometries and thus can be used for prediction of post-dryout heat transfer in a wide variety of energy conversion systems.
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