Abstract
Co-axial tubes have been used to produce a co-flowing confined jet similar to that found in an Extracorporeal Membrane Oxygenation return cannula flow configuration. Particle Image Velocimetry was used to investigate the flow rate ratio between jet and co-flow as well as changes in flow characteristics due to cannula position. The flow was found to be dominated by three main structures: lateral flow entrainment, shear layer induced vortices and backflow along the wall. An increase in cannula flow rate amplified entrainment and recirculation, resulting in a decrease in length required to reach a fully developed flow. Changing cannula position relative the outer cylinder induced a significant reduction in recirculation zone as well as vortex formation on the side to which the cannula was tilted towards, whereas on the other side, the recirculating flow region was enhanced. Proper Orthogonal Decomposition demonstrated that the dominating structure found in the flow is the backflow, composing of several structures having different oscillation frequencies. The significance of the observed and measured flow structures is in enhancing mixing.
Highlights
In several medical applications, e.g. extracorporeal membrane oxygenation (ECMO), a life-saving therapy in the critically ill with cardio-respiratory failure, blood needs to be drained and returned to the patient’s circulation requiring accesses via cannulae
In ECMO, the configuration of the return cannula in the vessel is similar to a confined round jet surrounded by a co-flow
Velocity measurements have been carried out using Particle Image Velocimetry (PIV) on a confined co-flowing jet in a narrow mixer, corresponding to return cannula flows in ECMO
Summary
E.g. extracorporeal membrane oxygenation (ECMO), a life-saving therapy in the critically ill with cardio-respiratory failure, blood needs to be drained and returned to the patient’s circulation requiring accesses via cannulae. In ECMO, the configuration of the return cannula in the vessel is similar to a confined round jet surrounded by a co-flow. In most cases, confined jets for mixing applications have been investigated, focusing on mean velocity and turbulence characteristics. Kandakure et al [9] used computational fluid dynamics (CFD) to study the effect of the enclosure size, i.e. confinement, over a wide range (6 ≤ D/d ≤ 50). They observed an increase in turbulent dissipation as well as a reduction in turbulent viscosity, entrainment rates and jet spreading angle with decreasing enclosure size. The jet decayed faster when the surrounding enclosure size became smaller
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