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Flows in Complex Systems

Computational Fluid Dynamic Studies of Vortex Amplifier Design for the Nuclear Industry—II. Transient Conditions

[+] Author and Article Information
J. Francis

John Tyndall Institute for Nuclear Research, UCLan | Nuclear, School of Computing, Engineering and Physical Sciences,  University of Central Lancashire, Preston PR1 2HE, UKjfrancis1@uclan.ac.uk

M. J. Birch

John Tyndall Institute for Nuclear Research, UCLan | Nuclear, School of Computing, Engineering and Physical Sciences,  University of Central Lancashire, Preston PR1 2HE, UKmjbirch@uclan.ac.uk

D. Parker

John Tyndall Institute for Nuclear Research, UCLan | Nuclear, School of Computing, Engineering and Physical Sciences,  University of Central Lancashire, Preston, UK; Telereal Trillium, 140 London Wall, London EC2Y 5DN, UKdarren.parker@telerealtrillium.com

J. Fluids Eng 134(2), 021103 (Mar 19, 2012) (12 pages) doi:10.1115/1.4005950 History: Received March 07, 2011; Revised January 16, 2012; Published March 16, 2012; Online March 19, 2012

In this paper computational fluid dynamics (CFD) techniques have been used to investigate the effect of changes to the geometry of a vortex amplifier (VXA) in the context of glovebox operations in the nuclear industry. These investigations were required because of anomalous behavior identified when, for operational reasons, a long-established VXA design was reduced in scale. The study simulates the transient aspects of two effects: back-flow into the glovebox through the VXA supply ports, and the precessing vortex core in the amplifier outlet. A temporal convergence error study indicates that there is little to be gained from reducing the time step duration below 0.1 ms. Based upon this criterion, the results of the simulation show that the percentage imbalance in the domain was well below the required figure of 1%, and imbalances for momentum in all three axes were all below measurable values. Furthermore, there was no conclusive evidence of periodicity in the flow perturbations at the glovebox boundary, although good evidence of periodicity in the device itself and in the outlet pipe was seen. Under all conditions the modified geometry performed better than the control geometry with regard to aggregate reversed supply flow. The control geometry exhibited aggregate nonaxisymmetric supply port back-flow for almost all of the simulated period, unlike the alternative geometry for which the flow through the supply ports was positive, although still nonaxisymmetric, for most of the period. The simulations show how transient flow structures in the supply ports can cause flow to be reversed in individual ports, whereas aggregate flow through the device remains positive. Similar to the supply ports, flow through the outlet of the VXA under high swirl conditions is also nonaxisymmetric. A time-dependent reverse flow region was observed in both the outlet and the diffuser. It is possible that small vortices in the outlet, coupled with the larger vortex in the chamber, are responsible for the oscillations, which cause the shift in the axis of the precessing vortex core (and ultimately in the variations of mass flow in the individual supply ports). Field trials show that the modified geometry reduces the back-flow of oxygen into the glovebox by as much as 78%. At purge rates of 0.65 m3 /h the modified geometry was found to be less effective, the rate of leakage from the VXA increasing by 16–20%. Despite this reduced performance, leakage from the modified geometry was still 63% less than the control geometry.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 4

Transient variation of supply port mass flow rate for geometries 7.0 and 2.2

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Figure 5

Transient supply port mass flow rate (Ws ) through the supply ports for geometry 7.0 (Pc  = −373 Pa: z = −5 mm)

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Figure 6

Velocity vectors, geometry 7.0, SP1 (Pc  = −373 Pa: z = −5 mm): (a) 0.352 s; (b) 0.362 s; (c) 0.372 s; (d) 0.382 s; (e) 0.392 s; (f) 0.402 s

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Figure 7

Transient supply port mass flow rate (Ws ) through the supply ports for geometry 2.2 (Pc  = −371.5 Pa: z = −5 mm)

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Figure 8

Velocity vectors, geometry 2.2, SP1 (Pc  = −373 Pa: z = −5mm): (a) 0.351 s; (b) 0.365 s; (c) 0.379 s; (d) 0.393 s; (e) 0.408 s; (f) 0.422 s

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Figure 9

Velocity vectors, geometry 2.2, SP4 (Pc  = −373 Pa: z = −5mm): (a) 0.351 s; (b) 0.365 s; (c) 0.379 s; (d) 0.393 s; (e) 0.408 s; (f) 0.422 s

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Figure 10

Geometry 2.2, w and P vortex iso-volumes: (a) 0.350 s (b) 0.365 s (c) 0.379 s (d) 0.393 s (e) 0.408 s (f) 0.442 s

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Figure 1

Simple diagram of VXA geometry, showing the proposed modifications in blue (The ordering of supply ports SP1–4 around the chamber is shown in the left-hand panel.)

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Figure 2

Error in outlet port mass flow rate (Wo ) for a given physical time step, for each geometry

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Figure 3

Transient variation of control and output port mass flow rates for geometries 7.0 and 2.2

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