Case study: Vortex amplifier assemblies for glovebox applications containing radiological hazard

Journal of Fluids Engineering

Birch

Parker

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 m 3 =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.

“…[4]. The recent prototype tests demonstrating an improved performance as a result of reduced reverse flow are included therein.…”

Section: Industrial Testsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Journal of Fluids Engineering

Birch

Parker

2012

“…Since the late 1990s, a scaled-down version known as the 'miniature vortex amplifier' has become the device of choice, owing to its space and ergonomic advantages. 5 This device is sometimes referred to as the 'mini-vortex amplifier', 'mini-VXA' or 'mini-VA'. Practical operation of the mini-VA led to disappointing inert gas usage on inerted gloveboxes, with oxygen from the control ports passing back up the supply channels into the gloveboxes.…”

Section: Vortex Amplifier Operationmentioning

confidence: 99%

“…As a result of laboratory tests 5 and visualisation studies, 4,12 it is known that under some operating conditions, flow in the radial supply ports of a scaled mini-VA is complex. If operated with excess momentum from the tangential control ports, the jet issuing therefrom hits the end of the opposing radial supply wall (which for a scaled mini-VA is closer to the control port than was the case with previous VA designs).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Numerical simulation of observed flow phenomena in the supply and control ports and associated feed channels of a mini-vortex amplifier

Proceedings of the Institution of Mechanical Engineers, Part C:

Parker²

2015

Self Cite

The trajectory and reach of jets issuing from tangential control ports at the periphery of a vortex amplifier's swirl chamber depend largely on design geometry, size and pressures applied. Excessive control port pressure causes these jets to extend too far across the face of the radial supply ports, to impact on the opposing supply port wall whereupon, they bifurcate to create back diffusion of control port flow along the supply port channels. Flow through vortex amplifier geometry is simulated using a baseline Reynolds stress turbulence model with Computational Fluid Dynamics (CFX) automatic wall treatment. Anisotropic stress and vortex stretching in the swirl chamber and outlet have not prevented convergence (based on normalised vortex amplifier residuals). Known flow structures are reproduced. This paper is focussed on simulation close to pressures needed for bifurcation. Just before the point on an operating characteristic at which bifurcated tangential flow appears, the recirculation zone crossing most of the radial supply stretches to intermittently cut off the radial flow. The steady state results indicate asymmetry between the four ports, as smoke visualisation tests also imply. The transient results are sufficient to demonstrate time-dependent structures and suggest periodicity of flow structures. The model can be used to inform design and operability studies. Moreover, a curious near-wall structure of spinning flow not previously reported has been predicted close to the axis and hugging the swirl chamber wall opposite the outlet, at radii within the forced part of the Rankine vortex.

Control Port Influence on Swirl, Operating, and Flow Characteristics of a Mini-Vortex Amplifier on Glove Box Service

Journal of Fluids Engineering

Parker²,

Whitty

et al. 2014

Vortex amplifiers (VA) use fluidic phenomena to modify flow through a containment breach, when used to protect glove box workers from exposure to the contents. The influence of control port geometry on swirl, operating characteristics, global flow, and momentum characteristics is studied experimentally. Shape and size of the control flow channels and the pressure applied at the tangential ports are critical in determining the trajectory of the jet issuing from the tangential ports and deflection of radial flow and vortex strength. Dominance of control-to-exit area ratio is confirmed. A clear improvement in performance is noted for a practical geometry derived from shaped passages of the device. Flow and momentum characteristics provide additional design data. The relationship of swirl number to output flow is demonstrated. Global flow and momentum characteristics provide insight into design and operation that is useful when avoiding back diffusion.