The Experts below are selected from a list of 57 Experts worldwide ranked by ideXlab platform
Ihsan Dagtekin - One of the best experts on this subject based on the ideXlab platform.
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entropy generation through Hexagonal cross sectional Duct for constant wall temperature in laminar flow
International Journal of Energy Research, 2004Co-Authors: Ahmet Z şahin, Ihsan DagtekinAbstract:Second law analysis of heat transfer in laminar flow for Hexagonal cross-section Duct was analysed analytically. Geometrical effect of Hexagonal Duct was considered. The variation of total entropy generation was studied along the Duct length. As a working fluid water and unused engine oil were used to compare the effect of fluid in the Duct. Results were compared with circular cross-section Duct. It is found that the non-dimensional entropy generation in a Hexagonal cross-section Duct can be as high as a factor of four than that for a circular Duct. Further, the unused engine oil gives up to about ten times lower non-dimensional entropy generation values than that of water but needs about ten times more pumping power to heat transfer ratio. Copyright © 2004 John Wiley & Sons, Ltd.
Yassin A Hassan - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of turbulent wake flows in a helically wrapped rod bundle in presence of localized blockages
Physics of Fluids, 2020Co-Authors: Thien Nguyen, Rodolfo Vaghetto, Yassin A HassanAbstract:In nuclear sodium fast reactors, bundles of rods are tightly packed into a triangular lattice, enclosed in a Hexagonal Duct, and each pin is spirally wrapped with a thin wire. Flow blockages can potentially impact the local flow characteristics and heat transfer mechanisms in the bundle due to its small subchannel size. The effects of the blockage on the flow structures and heat transfer mechanisms are important aspects that require an accurate investigation. In this study, the flow-field characteristics in the vicinity of a blockage located in the exterior subchannel of rod bundles with helically wrapped wires were experimentally investigated. The velocity fields in the exterior subchannel were acquired by applying matched-index-of-refraction and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of Re1 = 4000 and Re2 = 17 000, i.e., equivalent to Rew1 = 19 600 and Rew2 = 83 200, respectively, based on the blockage width. The results from the TR-PIV measurements revealed an arch-shaped vortex with a large flow recirculation and a pair of counter-rotating vortices in the wake region downstream of the blockage, which is commonly observed in the wake flow of bluff bodies. The relative lateral distance and angle between the two vortices decreased when the Reynolds numbers increased. Profiles of maximum turbulence intensity along the shear layers illustrated the transition process including the growth, peak, and decay along the flow direction. From the spectral analysis of the turbulent velocities extracted at points along the shear layer, the Strouhal numbers (St) representing the vortex shedding frequency were found to be St = 0.25 and St = 0.56 for the left and right shear layers, respectively. Characteristics of shear layers generated by the blockage in the exterior subchannel were investigated via the two-point cross correlation of fluctuating velocities. The spatiotemporal cross correlations of turbulent velocities, computed at points in the region where the left shear layer exhibited rolling effects and vortex breakdowns, were considerably wider and longer. The convection velocity Uc was estimated to be ∼0.82Um to 0.93Um. Proper orthogonal decomposition (POD) analysis was applied to the instantaneous velocity fields to extract the statistically dominant flow structures. It was found that POD modes 2–3 and 4–5 formed the pair modes when the corresponding POD temporal coefficients depicted sinusoidal shapes and exhibited nearly circular orbits in the phase space. Spectral analysis of the POD temporal coefficients confirmed the vortex shedding frequencies detected in the analysis of turbulent velocities.
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ptv piv measurements of turbulent flows in interior subchannels of a 61 pin wire wrapped Hexagonal fuel bundle
International Journal of Heat and Fluid Flow, 2018Co-Authors: Nolan Goth, Philip Jones, Thien Nguyen, Rodolfo Vaghetto, Yassin A Hassan, Nathaniel Salpeter, Elia MerzariAbstract:Abstract This study summarizes the experimental effort to characterize the flow fields of various interior subchannels in a 61-pin wire-wrapped Hexagonal fuel bundle prototypical for a sodium fast reactor. The objective was to generate high spatiotemporal velocity field data for computational fluid dynamics turbulence model validation. The experimental facility employed the matched-index-of-refraction and modern laser-based optical measurement techniques. It is the largest transparent Hexagonal test fuel assembly. Measurements were performed in two planes parallel to the axial flow, Interior-1 and Center-2. The Interior-1 location captured fluid interactions in four narrower subchannels formed by the exterior row of pins near the Hexagonal Duct wall. The Center-2 location captured fluid interactions in two wider subchannels spanning from the center pin out to the Hexagonal Duct wall. All measurements have been performed at a Reynolds number of 19,000. Results include discussion about statistical convergence of the dataset, along with flow statistics such as ensemble-averaged velocity, root-mean-square fluctuating velocity, Reynolds stress, and integral length scales.
Thien Nguyen - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of turbulent wake flows in a helically wrapped rod bundle in presence of localized blockages
Physics of Fluids, 2020Co-Authors: Thien Nguyen, Rodolfo Vaghetto, Yassin A HassanAbstract:In nuclear sodium fast reactors, bundles of rods are tightly packed into a triangular lattice, enclosed in a Hexagonal Duct, and each pin is spirally wrapped with a thin wire. Flow blockages can potentially impact the local flow characteristics and heat transfer mechanisms in the bundle due to its small subchannel size. The effects of the blockage on the flow structures and heat transfer mechanisms are important aspects that require an accurate investigation. In this study, the flow-field characteristics in the vicinity of a blockage located in the exterior subchannel of rod bundles with helically wrapped wires were experimentally investigated. The velocity fields in the exterior subchannel were acquired by applying matched-index-of-refraction and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of Re1 = 4000 and Re2 = 17 000, i.e., equivalent to Rew1 = 19 600 and Rew2 = 83 200, respectively, based on the blockage width. The results from the TR-PIV measurements revealed an arch-shaped vortex with a large flow recirculation and a pair of counter-rotating vortices in the wake region downstream of the blockage, which is commonly observed in the wake flow of bluff bodies. The relative lateral distance and angle between the two vortices decreased when the Reynolds numbers increased. Profiles of maximum turbulence intensity along the shear layers illustrated the transition process including the growth, peak, and decay along the flow direction. From the spectral analysis of the turbulent velocities extracted at points along the shear layer, the Strouhal numbers (St) representing the vortex shedding frequency were found to be St = 0.25 and St = 0.56 for the left and right shear layers, respectively. Characteristics of shear layers generated by the blockage in the exterior subchannel were investigated via the two-point cross correlation of fluctuating velocities. The spatiotemporal cross correlations of turbulent velocities, computed at points in the region where the left shear layer exhibited rolling effects and vortex breakdowns, were considerably wider and longer. The convection velocity Uc was estimated to be ∼0.82Um to 0.93Um. Proper orthogonal decomposition (POD) analysis was applied to the instantaneous velocity fields to extract the statistically dominant flow structures. It was found that POD modes 2–3 and 4–5 formed the pair modes when the corresponding POD temporal coefficients depicted sinusoidal shapes and exhibited nearly circular orbits in the phase space. Spectral analysis of the POD temporal coefficients confirmed the vortex shedding frequencies detected in the analysis of turbulent velocities.
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ptv piv measurements of turbulent flows in interior subchannels of a 61 pin wire wrapped Hexagonal fuel bundle
International Journal of Heat and Fluid Flow, 2018Co-Authors: Nolan Goth, Philip Jones, Thien Nguyen, Rodolfo Vaghetto, Yassin A Hassan, Nathaniel Salpeter, Elia MerzariAbstract:Abstract This study summarizes the experimental effort to characterize the flow fields of various interior subchannels in a 61-pin wire-wrapped Hexagonal fuel bundle prototypical for a sodium fast reactor. The objective was to generate high spatiotemporal velocity field data for computational fluid dynamics turbulence model validation. The experimental facility employed the matched-index-of-refraction and modern laser-based optical measurement techniques. It is the largest transparent Hexagonal test fuel assembly. Measurements were performed in two planes parallel to the axial flow, Interior-1 and Center-2. The Interior-1 location captured fluid interactions in four narrower subchannels formed by the exterior row of pins near the Hexagonal Duct wall. The Center-2 location captured fluid interactions in two wider subchannels spanning from the center pin out to the Hexagonal Duct wall. All measurements have been performed at a Reynolds number of 19,000. Results include discussion about statistical convergence of the dataset, along with flow statistics such as ensemble-averaged velocity, root-mean-square fluctuating velocity, Reynolds stress, and integral length scales.
Rodolfo Vaghetto - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of turbulent wake flows in a helically wrapped rod bundle in presence of localized blockages
Physics of Fluids, 2020Co-Authors: Thien Nguyen, Rodolfo Vaghetto, Yassin A HassanAbstract:In nuclear sodium fast reactors, bundles of rods are tightly packed into a triangular lattice, enclosed in a Hexagonal Duct, and each pin is spirally wrapped with a thin wire. Flow blockages can potentially impact the local flow characteristics and heat transfer mechanisms in the bundle due to its small subchannel size. The effects of the blockage on the flow structures and heat transfer mechanisms are important aspects that require an accurate investigation. In this study, the flow-field characteristics in the vicinity of a blockage located in the exterior subchannel of rod bundles with helically wrapped wires were experimentally investigated. The velocity fields in the exterior subchannel were acquired by applying matched-index-of-refraction and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of Re1 = 4000 and Re2 = 17 000, i.e., equivalent to Rew1 = 19 600 and Rew2 = 83 200, respectively, based on the blockage width. The results from the TR-PIV measurements revealed an arch-shaped vortex with a large flow recirculation and a pair of counter-rotating vortices in the wake region downstream of the blockage, which is commonly observed in the wake flow of bluff bodies. The relative lateral distance and angle between the two vortices decreased when the Reynolds numbers increased. Profiles of maximum turbulence intensity along the shear layers illustrated the transition process including the growth, peak, and decay along the flow direction. From the spectral analysis of the turbulent velocities extracted at points along the shear layer, the Strouhal numbers (St) representing the vortex shedding frequency were found to be St = 0.25 and St = 0.56 for the left and right shear layers, respectively. Characteristics of shear layers generated by the blockage in the exterior subchannel were investigated via the two-point cross correlation of fluctuating velocities. The spatiotemporal cross correlations of turbulent velocities, computed at points in the region where the left shear layer exhibited rolling effects and vortex breakdowns, were considerably wider and longer. The convection velocity Uc was estimated to be ∼0.82Um to 0.93Um. Proper orthogonal decomposition (POD) analysis was applied to the instantaneous velocity fields to extract the statistically dominant flow structures. It was found that POD modes 2–3 and 4–5 formed the pair modes when the corresponding POD temporal coefficients depicted sinusoidal shapes and exhibited nearly circular orbits in the phase space. Spectral analysis of the POD temporal coefficients confirmed the vortex shedding frequencies detected in the analysis of turbulent velocities.
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ptv piv measurements of turbulent flows in interior subchannels of a 61 pin wire wrapped Hexagonal fuel bundle
International Journal of Heat and Fluid Flow, 2018Co-Authors: Nolan Goth, Philip Jones, Thien Nguyen, Rodolfo Vaghetto, Yassin A Hassan, Nathaniel Salpeter, Elia MerzariAbstract:Abstract This study summarizes the experimental effort to characterize the flow fields of various interior subchannels in a 61-pin wire-wrapped Hexagonal fuel bundle prototypical for a sodium fast reactor. The objective was to generate high spatiotemporal velocity field data for computational fluid dynamics turbulence model validation. The experimental facility employed the matched-index-of-refraction and modern laser-based optical measurement techniques. It is the largest transparent Hexagonal test fuel assembly. Measurements were performed in two planes parallel to the axial flow, Interior-1 and Center-2. The Interior-1 location captured fluid interactions in four narrower subchannels formed by the exterior row of pins near the Hexagonal Duct wall. The Center-2 location captured fluid interactions in two wider subchannels spanning from the center pin out to the Hexagonal Duct wall. All measurements have been performed at a Reynolds number of 19,000. Results include discussion about statistical convergence of the dataset, along with flow statistics such as ensemble-averaged velocity, root-mean-square fluctuating velocity, Reynolds stress, and integral length scales.
Arthur E. Bergles - One of the best experts on this subject based on the ideXlab platform.
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performance evaluation of Ducts with non circular shapes laminar fully developed flow and constant wall temperature
International Journal of Thermal Sciences, 2014Co-Authors: Valentin M Petkov, Ventsislav D Zimparov, Arthur E. BerglesAbstract:Abstract Extended performance evaluation criteria (ExPEC) have been used to assess the performance characteristics of single-phase fully developed laminar flow through bundle of Ducts with non-circular shape – rectangular, isosceles triangular, elliptical, trapezoidal and Hexagonal. The bundle of circular tubes has been used as a reference heat transfer unit. Constant wall temperature has been selected as the thermal boundary condition. The performance characteristics of the bundles with non-circular Ducts have been evaluated and compared to those of the reference unit for different objectives and constraints imposed. As a common constraint, the hydraulic diameter of the Duct has been specified. The results clearly show that the rectangular, trapezoidal or Hexagonal Duct configuration can compete, in some cases, with the circular tube configuration. The choice of the tube shape and geometrical details depends on the constraints imposed and the objectives pursued. The results obtained from the present study revealed that they differed from those obtained with a common constraint of specified cross sectional area.