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  • 1
    Language: English
    In: Nuclear Engineering and Design
    Description: ► Turbulent mixing of fluid in a T-junction is investigated being relevant for thermal fatigue. ► Special case of extremely low side flows (leakage flows) are studied. ► High spatial and time resolution results are obtained using wire mesh sensors. ► Entrainment into side branch occurs at very low side flows, which disappears above a critical side flow rate. ► Entrainment causes significant low-frequency oscillations in the side branch potentially dangerous to induce thermal fatigue. The mixing of coolant streams of different temperatures in pipe junctions leads to temperature fluctuations that may cause thermal fatigue in the pipe wall. Numerous T-junction experiments are known from literature, which were performed to study the nature of thermal loads in the pipe walls occurring during the mixing of hot and cold liquid. It is common to all known experiments that the experimental boundary conditions are set to reflect cases, in which the flow velocities in both main and side branches of the T-junctions are of the same order of magnitude. In the present experiments, carried out using wire-mesh sensors, it was observed that very low flow velocities in the side branch compared to the main pipe may lead to conditions potentially severe for thermal fatigue due to the low frequency of the temperature fluctuations occurring. The T-junction presented here consists of a perpendicular connection of two pipes of 50 mm inner diameter. The straight and the side branches are supplied with water of different electrical conductivities, to enable performing generic, isothermal tests on turbulent mixing with the idea to model the temperature fluctuations in thermal mixing processes. A pair of wire-mesh sensors, each with a grid of 16 × 16 measuring points, are used to record conductivity distributions in the downstream of the T-junction as well as directly at the junction in both branches. At very low flow rates in the side branch, a characteristic entrainment of liquid from the main branch into the side branch was found. Typically the entrainment flow in the side branch results in relatively high fluctuations at the low-frequency range. While the sensor in the main flow shows fluctuations with a power spectrum similar in character to mixing experiments with comparable flow velocities in both branches of the T-junction. The phenomenon of entrainment of water from the main branch into the side branch against the main flow direction vanishes at a certain critical velocity in the side branch.
    Keywords: Engineering
    ISSN: 0029-5493
    E-ISSN: 1872-759X
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  • 2
    Language: English
    In: The Science of the Total Environment, April 15, 2014, Vol.478, p.226(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2014.01.069 Byline: Andrea E. Ulrich, Ewald Schnug, Horst-Michael Prasser, Emmanuel Frossard Abstract: This study seeks to identify and specify the components that make up the prospects of U recovery from phosphate rock. A systems approach is taken. The assessment includes i) reviewing past recovery experience and lessons learned; ii) identifying factors that determine recovery; and iii) establishing a contemporary evaluation of U endowments in phosphate rock reserves, as well as the available and recoverable amounts from phosphate rock and phosphoric acid production. We find that in the past, recovery did not fulfill its potential and that the breakup of the Soviet Union worsened then-favorable recovery market conditions in the 1990s. We find that an estimated 5.7milliontU may be recoverable from phosphate rock reserves. In 2010, the recoverable tU from phosphate rock and phosphoric acid production may have been 15,000tU and 11,000tU, respectively. This could have filled the world U supply-demand gap for nuclear energy production. The results suggest that the U.S., Morocco, Tunisia, and Russia would be particularly well-suited to recover U, taking infrastructural considerations into account. We demonstrate future research needs, as well as sustainability orientations. We conclude that in order to promote investment and production, it seems necessary to establish long-term contracts at guaranteed prices, ensuring profitability for phosphoric acid producers. Article History: Received 10 November 2013; Revised 16 January 2014; Accepted 19 January 2014
    Keywords: Phosphate Minerals -- Analysis ; Endowments -- Analysis ; Uranium -- Analysis ; Phosphates -- Analysis ; Phosphoric Acid -- Analysis
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Science of the Total Environment, 15 April 2014, Vol.478, pp.226-234
    Description: This study seeks to identify and specify the components that make up the prospects of U recovery from phosphate rock. A systems approach is taken. The assessment includes i) reviewing past recovery experience and lessons learned; ii) identifying factors that determine recovery; and iii) establishing a contemporary evaluation of U endowments in phosphate rock reserves, as well as the available and recoverable amounts from phosphate rock and phosphoric acid production. We find that in the past, recovery did not fulfill its potential and that the breakup of the Soviet Union worsened then-favorable recovery market conditions in the 1990s. We find that an estimated 5.7 million tU may be recoverable from phosphate rock reserves. In 2010, the recoverable tU from phosphate rock and phosphoric acid production may have been 15,000 tU and 11,000 tU, respectively. This could have filled the world U supply-demand gap for nuclear energy production. The results suggest that the U.S., Morocco, Tunisia, and Russia would be particularly well-suited to recover U, taking infrastructural considerations into account. We demonstrate future research needs, as well as sustainability orientations. We conclude that in order to promote investment and production, it seems necessary to establish long-term contracts at guaranteed prices, ensuring profitability for phosphoric acid producers.
    Keywords: Uranium ; Phosphorus ; Energy Security ; Environmental Pollution ; Food Security ; Resources Conservation ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 4
    Language: English
    In: Chemical Engineering Science, Jan 27, 2015, Vol.122, p.321(15)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ces.2014.09.037 Byline: Hassan Badreddine, Yohei Sato, Bojan Niceno, Horst-Michael Prasser Abstract: A new method has been developed for the numerical simulation of finite size dispersed bubbly flows. Finite size bubbles are bigger than the numerical grid cell size, meaning that Lagrangian particle tracking (LPT) cannot be used, but they are yet too small to be accurately resolved by interface tracking (IT) methods. The need for such an approach arises mostly if large eddy simulation (LES) paradigm is used to resolve turbulence since it requires fine grids, and bubbles could easily cover several grid cells. The proposed method inherits features of IT and LPT, and features two-way coupling. The governing equations for the continuous phase are solved on Eulerian static grid. Bubbles are assumed to have a spherical shape, and a color function is used to monitor bubbles' position and to update the physical properties in every grid cell same way as one does in IT. However, the color function is not updated by solving an advection equation, but is rather re-initialized at every time step by the new bubbles' position calculated by solving Newton's second law of motion for each bubble. A new method to calculate the undisturbed liquid velocity required to model the hydrodynamic forces is also proposed in this paper. Two methods are proposed to impose the two-way coupling (i.e. bubbles feedback on the fluid). The first approach considers the bubbles as spherical rigid particles, and bubbles' velocities are imposed to the computational cells that lie inside the bubbles. In the second approach, a correction force is added inside each bubble to model the filtered scales due to usage of coarse grid resolution per bubble. The method is validated against terminal velocity of an air bubble rising in stagnant water to test the buoyancy and drag forces and its lateral motion in linear shear flow to check the lift force. The results are compared with simulations done with IT Constrained Interpolation Profile (CIP) method to verify the accuracy of the two-way coupling. Author Affiliation: (a) Laboratory for Thermal Hydraulics, Nuclear Energy and Safety Research Department, Paul Scherrer Institute, Villigen PSI 5232, Switzerland (b) Laboratory of Nuclear Energy Systems, Department of Mechanical and Process Engineering, ETH Zurich, Switzerland Article History: Received 3 June 2014; Revised 8 September 2014; Accepted 23 September 2014
    Keywords: Advection (Earth Sciences) -- Analysis ; Advection (Earth Sciences) -- Models ; Newton'S Laws Of Motion -- Analysis ; Newton'S Laws Of Motion -- Models ; Nuclear Energy -- Analysis ; Nuclear Energy -- Models ; Turbulence (Fluid Dynamics) -- Analysis ; Turbulence (Fluid Dynamics) -- Models
    ISSN: 0009-2509
    Source: Cengage Learning, Inc.
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  • 5
    Language: English
    In: Chemical Engineering Science, 27 January 2015, Vol.122, pp.321-335
    Description: A new method has been developed for the numerical simulation of finite size dispersed bubbly flows. Finite size bubbles are bigger than the numerical grid cell size, meaning that Lagrangian particle tracking (LPT) cannot be used, but they are yet too small to be accurately resolved by interface tracking (IT) methods. The need for such an approach arises mostly if large eddy simulation (LES) paradigm is used to resolve turbulence since it requires fine grids, and bubbles could easily cover several grid cells. The proposed method inherits features of IT and LPT, and features two-way coupling. The governing equations for the continuous phase are solved on Eulerian static grid. Bubbles are assumed to have a spherical shape, and a color function is used to monitor bubbles’ position and to update the physical properties in every grid cell same way as one does in IT. However, the color function is not updated by solving an advection equation, but is rather re-initialized at every time step by the new bubbles’ position calculated by solving Newton’s second law of motion for each bubble. A new method to calculate the undisturbed liquid velocity required to model the hydrodynamic forces is also proposed in this paper. Two methods are proposed to impose the two-way coupling ( bubbles feedback on the fluid). The first approach considers the bubbles as spherical rigid particles, and bubbles’ velocities are imposed to the computational cells that lie inside the bubbles. In the second approach, a correction force is added inside each bubble to model the filtered scales due to usage of coarse grid resolution per bubble. The method is validated against terminal velocity of an air bubble rising in stagnant water to test the buoyancy and drag forces and its lateral motion in linear shear flow to check the lift force. The results are compared with simulations done with IT Constrained Interpolation Profile (CIP) method to verify the accuracy of the two-way coupling.
    Keywords: Bubbly Flows ; Lagrangian Particle Tracking ; Semi-Resolved Simulations ; Interface Tracking ; Two-Way Coupling ; Engineering
    ISSN: 0009-2509
    E-ISSN: 1873-4405
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  • 6
    Language: English
    In: Chemical Engineering Science, 16 March 2018, Vol.178, pp.61-69
    Description: This work reports on the development and application of a new approach, corrective interface tracking, to simulate finite size bubbles. Finite-size bubbles, which are by definition bigger than the grid cell size but not well resolved, are not capable of being modeled with any standard two-phase flow approaches, such as interface tracking (IT), Euler-Euler (EE), or Lagrangian particle tracking (LPT). This poses a problem when simulating bubbly flows with different bubble sizes on the same computational grid. The Finite-size Lagrangian particle tracking (FSL) approach (Badreddine et al., 2015), aimed at simulating finite-size bubbly flows by inheriting features of IT and LPT approaches, simulated a single bubble with good accuracy. However, deficiencies with the FSL approach led to a newly developed approach based on interface tracking with the addition of a correcting force. The correcting force, derived from modeling the hydrodynamic forces on a bubble, attempts to correct for errors introduced when a coarse grid is used and the flow and pressure fields around the bubble are under-resolved. Therefore, as a finer grid is used the correcting force decreases. The corrective interface tracking approach is validated against a single bubble rising in stagnant and linear flow, and then results are compared to FSL and to finely resolved IT simulations.
    Keywords: Bubbly Flows ; Interface Tracking ; Lagrangian Particle Tracking ; Finite-Size Bubbles ; Two-Way Coupling ; Engineering
    ISSN: 0009-2509
    E-ISSN: 1873-4405
    Source: ScienceDirect Journals (Elsevier)
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  • 7
    Language: English
    In: Nuclear Engineering and Design, July, 2013, Vol.260, p.188(16)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.nucengdes.2013.03.026 Byline: Robert Zboray, Horst-Michael Prasser Abstract: acents Annular flows w/wo functional spacers are investigated by cold-neutron imaging. acents Performance of liquid film thickness measurement under different imaging modalities is evaluated and optimized. acents MC simulations of the cold neutron imaging are performed to help quantifying the measurement accuracy. acents Spectral, scatter corrections and minimizing the blur are necessary to avoid bias in film thickness estimate. acents Empty channel referencing offers in general the highest accuracy and quality. Author Affiliation: (a) Laboratory for Thermal-Hydraulics, Nuclear Energy and Safety Research Department, Paul Scherrer Institute, Switzerland (b) ETH Zurich, Department of Mechanical and Process Engineering, Sonneggstrasse 3, 8092 Zurich, Switzerland Article History: Received 8 August 2012; Revised 8 March 2013; Accepted 13 March 2013
    ISSN: 0029-5493
    Source: Cengage Learning, Inc.
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  • 8
    Language: English
    In: Solar Energy, Sept, 2013, Vol.95, p.181(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2013.06.009 Byline: Ralph Eismann, Horst-Michael Prasser Abstract: acents The efficiency of non-ideal absorbers was calculated by two-dimensional simulations. acents From the results, a new correlation for the fin efficiency was derived. acents The new correlation is easy to use for engineering purposes. acents The correlation allows for more accurate efficiency/cost optimization. acents One of the major uncertainties of analytical models is eliminated. Article History: Received 15 February 2013; Revised 5 June 2013; Accepted 10 June 2013 Article Note: (miscellaneous) Communicated by: Associate Editor Brian Norton
    Keywords: Solar Collectors -- Analysis ; Solar Collectors -- Models
    ISSN: 0038-092X
    Source: Cengage Learning, Inc.
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  • 9
    Language: English
    In: Nuclear Engineering and Design, Sept, 2013, Vol.262, p.589(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.nucengdes.2013.06.005 Byline: Robert Zboray, Horst-Michael Prasser Abstract: acents Annular flows with and without functional spacer in a tight lattice fuel bundle geometry are investigated. acents Cold-neutron imaging of adiabatic flows is performed. acents Liquid film thickness distributions are determined with high accuracy and resolution. acents The influence of the spacer on the film thickness and liquid hold up is analyzed in details. Author Affiliation: (a) Laboratory for Thermal-Hydraulics, Nuclear Energy and Safety Research Department, Paul Scherrer Institute, Switzerland (b) ETH Zurich, Department of Mechanical and Process Engineering, Sonneggstrasse 3, 8092 Zurich, Switzerland Article History: Received 5 April 2013; Revised 29 May 2013; Accepted 12 June 2013
    ISSN: 0029-5493
    Source: Cengage Learning, Inc.
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  • 10
    Language: English
    In: Nuclear Engineering and Design, August, 2011, Vol.241(8), p.3201(15)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.nucengdes.2011.06.029 Byline: Robert Zboray (a), John Kickhofel (b), Manuel Damsohn (b), Horst-Michael Prasser (a)(b) Abstract: a* Annular flows w/wo functional spacers are investigated by cold neutron imaging. a* Liquid film thickness distribution on fuel pins and on spacer vanes is measured. a* The influence of the spacers on the liquid film distributions has been quantified. a* The cross-sectional averaged liquid hold-up significantly affected by the spacers. a* The sapers affect the fraction of the entrained liquid hold up in the gas core. Author Affiliation: (a) Laboratory for Thermal-hydraulics, Nuclear Energy and Safety Research Department, Paul Scherrer Institute, Switzerland (b) ETH Zurich, Department of Mechanical and Process Engineering, Sonneggstrasse 3, 8092 Zurich, Switzerland Article History: Received 13 March 2011; Revised 20 June 2011; Accepted 23 June 2011
    Keywords: Nuclear Energy ; Nuclear Reactors
    ISSN: 0029-5493
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