• Proceedings of the KSME Conference
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• 2001.06e
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• pp.482-487
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• 2001

A CFD study was conducted to evaluate the nuclear fuel assembly coolant mixing that is promoted by the flow-mixing vanes on the grid spacer. Four mixing vanes (split vane, swirl vane, twisted vane, hybrid vane) were chosen in this study. A single subchannel of one grid span is modeled using the flow symmetry. The three mixing vanes other than swirl vane generate a large crossflow between the subchannels and a skewed elliptic swirling flow in the subchannel near the grid spacer. The swirl vane induces a circular swirling flow in the subchannel and a negligible crossflow. The split vane and the twisted vane were predicted to result in relatively larger pressure drop across the grid spacer. Since the average turbulent kinetic energy in the subchannel rapidly decreases to a fully developed level downstream of the spacer, turbulent mixing caused by the mixing vanes appears to be not as effective as swirling flow mixing in the subchannel. In summary, the CFD analysis represented the overall characteristics of coolant mixing well in a nuclear fuel assembly with the flow mixing vanes on the grid spacer. The CFD study is therefore quite useful for the development of an advanced flow-mixing vane.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.331-336
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• 1996

The effects of a mixing vane on air-water mixed flow have been experimentally studied in this work, to investigate the basic mechanisms that the mixing vane affects critical heat flux (CHF). Experiment was performed for various flow rates focusing on bubbly flow and annular flow patterns. Acrylic tube (1.7m long, 11 mm I.D.) and the split vane type mixing vane were used, and ring-type conductance probes were used to measure the liquid film thickness in annular flow. Experimental results show that, (a) bubbly-to slug flow transition and churn-to-annular flow transition occur respectively near the mixing vane compared to the tests without mixing vane, (b) in bubbly flow region, the mixing vane breaks the bubbles into smaller ones and forwards bubbles to the center region of the tube by the centrifugal force, (c) the liquid film thickness in annular flow is decreased near the mixing vane for mass fluxes.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1819-1824
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• 2004

The common method to improve heat transfer in Nuclear fuel rod bundle is install a mixing vane in space grid. The previous split mixing vane is guides cooling water to swirl flow in sub-channel of fuel assembly. But, this swirl flow decade rapidly after mixing vane and the effect of enhancing the heat transfer vanish behind this short region. The large scale secondary vortex flow was generated by rearranging the inclined angle direction of mixing vanes to the coordinated directions. This LSVF mixing vanes generate the most strong secondary flow vortices which maintain about 35 $D_H$ after the spacer grid and the streamwise vorticity in subchannel with LSVF mixing vane sustain two times more than that in subchannel with split mixing vane. The turbulent kinetic energy and the Reynolds stresses generated by the mixing vanes have nearly same scales but maintain twice more than previous type.

• Nuclear Engineering and Technology
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• v.33 no.3
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• pp.327-338
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• 2001

A computational fluid dynamics (CFD) analysis was performed to propose the optimum design of flow mixing vane on the space grid in a PWR fuel assembly. The flow mixing vanes considered in this study for optimum design are swirl-vane and twisted-vane. A single subchannel of one grid span was modeled using flow symmetry to minimize the computational effort. The CFD predictions are in good agreement with the experimental results for the split- vane, which shows the applicability of the CFD method. The mixing effect by swirling flow and crossflow, and the pressure drop were estimated and compared for the various vane angles. The optimum vane angle is proposed to be 40。 and 35。 from the direction of axial flow for the swirl-vane and the twisted-vane, respectively.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2396-2401
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• 2007

Freon CHF experiments are carried out to investigate the CHF enhancements by mixing vane shapes of spacer grids in nuclear fuel assembly. The experiments were performed for a wide range mass flux, 50$\sim}$3000 kg/$m^2s$. Three kinds of spacer grids in 5${\times}$5 rod bundles are tested: no mixing vane grids, hybrid mixing vane grids, and split mixing vane grids. The CHF performances are compared along with the data belong to the PWR operating conditions based on a water equivalence through a fluid-to-fluid modeling method. The average of the data in this range is 16.4% for 37 data of hybrid vane grid and 12.5% for 24 data of split vane. In the lower mass flux, however, the split vane grid shows slightly higher performance than the hybrid vane grid.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.311-318
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• 2003

The present work evaluates the effects of mixing vane shape on the flow structure and heat transfer downstream of mixing vane in a subchannel of fuel assembly. by obtaining velocity and pressure fields. turbulent intensity. flow-mixing factors. heat transfer coefficient and friction factor using three-dimensional RANS analysis. Four different shapes of mixing vane. which were designed by the authors were tested to evaluate the performances in enhancing the heat transfer. Standard k-$\varepsilon$ model is used as a turbulence closure model. and. periodic and symmetry conditions are set as boundary conditions. The flow blockage ratio is kept constant. but the twist angle of mixing vane is changed. The results with three turbulence models were compared with experimental data.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.408-413
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• 2003

Naphthalene sublimation technique is used to investigate the average and local heat transfer from the circular rod, and to determine the average and local heat transfer from the circular rod with and without square wing type mixing vane in axial flow. The experiments are performed for a circular rod and flat plate with and without mixing vane in wind tunnel. In comparison with flat plate and circular rod in axial flow, averaged Nusselts number is increased 2 times as the increase of Reynolds number with mixing vane. Longitudinal vortex induced by square wing type has the stronger vortex strength, so square wing type vortex generator shows an effect further in downstream.

• The KSFM Journal of Fluid Machinery
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• v.10 no.4
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• pp.9-14
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• 2007

The purpose of present work is to analyze the convective heat transfer downstream of mixing vane in subchannel of nuclear reactor with three-dimensional Navier-Stokes equations. SST model is selected as a turbulence closure by comparing the performances of two different turbulent closures. Three different shapes of mixing vane are tested. And, thermal-hydraulic performances of these vanes are discussed. The results show that twist of the vane improves the heat transfer performance far downstream of the vane.

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.79-87
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• 2002

The present work analyzed the effect of mixing vane shape on the flow structure and heat transfer downstream of mixing vane in a subchannel of fuel assembly, by obtaining velocity and pressure fields, turbulent intensity, flow-mixing factors, heat transfer coefficient and friction factor using three-dimensional RANS analysis. NJl5, NJ25, NJ35, NJ45, which were designed by the authors, were tested to evaluate the performances in enhancing the heat transfer. Standard $\kappa-\epsilon$ model is used as a turbulence closure model, and, periodic and symmetry conditions are set as boundary conditions. The flow blockage ratio is kept constant, but the twist angle of mixing vane is changed. The results with three turbulence models( $\kappa-\epsilon$, $\kappa-\omega$, RSM) were compared with experimental data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.1 s.244
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• pp.24-31
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• 2006

Mixing vanes have been installed in the space grid of nuclear fuel rod bundle to improve turbulent heat transfer. Split mixing vanes induce the vortex flow in the cooling water to swirl in sub-channel of fuel assembly. But, The swirling flow decays rapidly so that the heat transfer enhancing effect limited to short length after the mixing vane. In thi present study, the large scale vortex flow(LSVF) is generated by rearranging the mixing vanes to the coordinated directions. This LSVF mixing vanes generate the most strong secondary flow vortices which maintain about 35 $D_H$ after the spacer grid. The streamwise vorticity generated by LSVF sustain two times more than that split mixing vane. Heat transfer in the rod bundle occurs greatly at the same direction to cross flow, and maximum temperature at the surface of bundle drops about 1.5K