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Research Papers

Computational Fluid Dynamics Investigation of Supercritical Water Flow and Heat Transfer in a Rod Bundle With Grid Spacers

[+] Author and Article Information
Malwina Gradecka

Warsaw University of Technology,
Nowowiejska 21/25, Warsaw 00-665, Poland
e-mail: mgradec@itc.pw.edu.pl

Roman Thiele

Royal Institute of Technology, KTH,
Roslagstullsbacken 21, Stockholm 106 91, Sweden
e-mail: romant@kth.se

Henryk Anglart

Royal Institute of Technology, KTH,
Roslagstullsbacken 21, Stockholm 106 91, Sweden
e-mail: romant@kth.se, henryk@kth.se

1Corresponding author.

Manuscript received May 17, 2015; final manuscript received January 7, 2016; published online June 17, 2016. Assoc. Editor: Thomas Schulenberg.

ASME J of Nuclear Rad Sci 2(3), 031015 (Jun 17, 2016) (9 pages) Paper No: NERS-15-1087; doi: 10.1115/1.4032635 History: Received May 17, 2015; Accepted January 21, 2016

This paper presents a steady-state computational fluid dynamics approach to supercritical water flow and heat transfer in a rod bundle with grid spacers. The current model was developed using the ANSYS Workbench 15.0 software (CFX solver) and was first applied to supercritical water flow and heat transfer in circular tubes. The predicted wall temperature was in good agreement with the measured data. Next, a similar approach was used to investigate three-dimensional (3D) vertical upward flow of water at supercritical pressure of about 25 MPa in a rod bundle with grid spacers. This work aimed at understanding thermo- and hydrodynamic behavior of fluid flow in a complex geometry at specified boundary conditions. The modeled geometry consisted of a 1.5-m heated section in the rod bundle, a 0.2-m nonheated inlet section, and five grid spacers. The computational mesh was prepared using two cell types. The sections of the rods with spacers were meshed using tetrahedral cells due to the complex geometry of the spacer, whereas sections without spacers were meshed with hexahedral cells resulting in a total of 28 million cells. Three different sets of experimental conditions were investigated in this study: a nonheated case and two heated cases. The nonheated case, A1, is calculated to extract the pressure drop across the rod bundle. For cases B1 and B2, a heat flux is applied on the surface of the rods causing a rise in fluid temperature along the bundle. While the temperature of the fluid increases along with the flow, heat deterioration effects can be present near the heated surface. Outputs from both B cases are temperatures at preselected locations on the rods surfaces.

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References

Figures

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Fig. 1

Comparison of experimental work in pipe geometries and CFX computations with k−ω−SST model. Left: Calculations carried out by Jaromin [7] for experiments by Ackerman [8] (p=31.03  MPa, G=1220  kg/m2/s, hin=1621  kJ/kg, q′′=472.5  kW/m2, d=9.4  mm). Right: Comparison between ANSYS CFX and experiments by Ornatskij et al. [9] (p=25.5  MPa, G=1500  kg/m2/s, hin=662  kJ/kg, q′′=1810  kW/m2, d=3  mm).

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Fig. 2

Geometry of the rod bundle and the spacer details: (a) full 7-rod bundle domain, (b) nonsimplified geometry of the bundle, (c) spacer design. Spacer locations from heated inlet: 0, 300, 700, 900, and 1300 mm.

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Fig. 3

Computational mesh in the XZ plane

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Fig. 4

Pressure variation along the bundle, where the spacers are located at 0, 300, 700, 900, and 1300 mm from the inlet of the heated section.

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Fig. 5

YZ plane at x=1.1431  m: (a) velocity contour and (b) temperature contour.

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Fig. 6

Temperature at the rods surface: (a) the hottest point at D rod and (b) hot spot at rod A at the fifth spacer.

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Fig. 7

YZ plane at x=1.1431  m: (a) velocity contour and (b) temperature contour.

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Fig. 8

ZX plane at y=0.0004  m, view of 5th spacer closest to the outlet: (a) velocity contour and (b) temperature contour on the ZX plane and the temperature directly at the wall of rod A.

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Fig. 9

DHT visible at water section near outlet: (a) hot spot location and (b) detailed view of DHT.

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Fig. 10

Maximum rod surface temperature as a function of height for case B2. Temperatures are the maximum temperature at any rod in the cross sections at height x. The spacers are located at 0, 300, 700, 900, and 1300 mm from the inlet of the heated section.

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Fig. 11

Comparison of the CFD results for Case B1 with experimental data from Misawa et al. [1]

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Fig. 12

Comparison of the CFD results for Case B2 with experimental data from Misawa et al. [1]

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Fig. 13

HTC calculated in CFX and via correlations for case B1

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Fig. 14

HTC calculated in CFX and via correlations for case B2

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