EMC3-EIRENE simulations of neon impurity seeding effects on heat flux distribution on CFETR

The numerical modelling of the heat flux distribution with neon impurity seeding on CFETR has been performed by the three-dimensional (3D) edge transport code EMC3-EIRENE. The maximum heat flux on divertor targets is about 18 MW m-2 without impurity seeding under the input power of 200 MW entering into the scrape-off layer. In order to mitigate the heat loads below 10 MW m-2, neon impurity seeded at different poloidal positions has been investigated to understand the properties of impurity concentration and heat load distributions for a single toroidal injection location. The majority of the studied neon injections gives rise to a toroidally asymmetric profile of heat load deposition on the in- or out-board divertor targets. The heat loads cannot be reduced below 10 MW m-2 along the whole torus for a single toroidal injection location. In order to achieve the heat load mitigation (<10 MW m-2) along the entire torus, modelling of sole and simultaneous multi-toroidal neon injections near the in- and out-board strike points has been stimulated, which indicates that the simultaneous multi-toroidal neon injections show a better heat flux mitigation on both in- and out-board divertor targets. The maximum heat flux can be reduced below 7 MWm-2 on divertor targets for the studied scenarios of the simultaneous multi-toroidal neon injections.

Human In Silico Trials for Parametric Computational Fluid Dynamics Investigation of Cerebrospinal Fluid Drug Delivery: Impact of Injection Location, Injection Protocol, and Physiology

BackgroundIntrathecal drug delivery has a significant role in pain management and CNS disease therapeutics. A fluid-physics based tool to assist clinicians in choosing specific drug doses to the spine or brain may help improve treatment schedules. MethodsThis study applied computational fluid dynamics (CFD) and in vitro model verification to assess intrathecal drug delivery in an anatomically realistic model of the human CSF system. Key parameters analyzed included the role of a) injection location including lumbar puncture (LP), cisterna magna (CM) and intracerebroventricular (ICV), b) LP injection rate, injection volume, and flush volume, c) physiologic factors including cardiac-induced and deep respiration-induced CSF stroke volume increase. Simulations were conducted for 3-hours post-injection and used to quantify spatial-temporal tracer concentration, regional area under the curve (AUC), time to maximum concentration (T max ), and maximum concentration (C max ), for each case. ResultsCM and ICV increased AUC to brain regions by ~2 logs compared to all other simulations. A 3X increase in bolus volume and addition of a 5 mL flush both increased intracranial AUC to the brain up to 2X compared to a baseline 5 mL LP injection. In contrast, a 5X increase in bolus rate (25 mL/min) did not improve tracer exposure to the brain. An increase in cardiac and respiratory CSF movement improved tracer spread to the brain, basal cistern, and cerebellum up to ~2 logs compared to the baseline LP injection. ConclusionThe computational modeling approach provides ability to conduct in silico trials representative of CSF injection protocols. Taken together, the findings indicate a strong potential for delivery protocols to be optimized to reach a target region(s) of the spine and/or brain with a needed therapeutic dose. Parametric modification of bolus rate/volume and flush volume was found to have impact on tracer distribution; albeit to a smaller degree than injection location, with CM and ICV injections resulting in greater therapeutic dose to brain regions compared to LP. CSF stroke volume and frequency both played an important role and may potentially have a greater impact than the modest changes in LP injection protocols analyzed such as bolus rate, volume, and flush.

Aspiration Before Tissue Filler – An Exercise in Futility and Unsafe Practice

Background Aesthetic physicians rely upon certain anecdotal beliefs regarding the safe practice of filler injections. These include a presumed safety advantage of bolus injection after a negative aspiration. Objectives The article aims to review and summarize the published literature on inadvertent intravascular injection of hyaluronic acid and to investigate whether the technique of aspiration confers any safety to the practitioner and the patient. Methods Pertinent literature was analyzed and our understanding of the safety of negative and positive aspiration outlined. Results The available studies demonstrate that aspiration cannot be relied upon and should not be used as a safety measure. It is safer to adopt injection techniques that will avoid injecting an intravascular volume with embolic potential than use an unreliable test to permit a risky injection. Conclusions To prevent intravascular injection, understanding “injection anatomy” and injection plane and techniques such as slow, low-pressure injection are important safety measures. Assurance of safety when delivering a bolus after negative aspiration, does not appear to be borne out by the available literature. If there is any doubt about the sensitivity or reliability of a negative aspiration, then there is no role for its use. Achieving a positive aspiration would just defer the risk to the next injection location where a negative aspiration would then be relied upon.

Influence of Shunt Injection on Predicted Rotordynamic Coefficients of a Labyrinth Seal Using Transient CFD

Shunt injection is one of the methods used to improve rotordynamic stability of centrifugal compressors. It involves eliminating swirl by injecting fluid in an intermediate cavity of a seal. The fluid injection is usually directed from the discharge volute or diffuser section of the compressor. In this paper, shunt injection is modeled for a center seal in a back-to-back compressor arrangement. The test case is from an actual machine which was shown to be unstable during a factory loaded mechanical test (as per API standard 617) without shunt injection and stable with shunt injection. The center seal is a tooth-on-rotor type of labyrinth seal. Impeller back-face cavity passages at the entrance and exit of the seal are also modeled. To investigate the influence on shunt injection, models with and without shunt injection geometry are considered. Steady state Computational Fluid Dynamics (CFD) is used to study the influence on steady state characteristics such as leakage rate and swirl ratio. The CFD analysis shows a significant swirl reduction with shunt injection at the injection location. The estimated swirl ratio is 0.55 at the injection location without shunt injection and approximately 0 with shunt injection. Frequency dependent seal rotordynamic coefficients are evaluated using transient CFD. Both translational and moment coefficients are evaluated for the seal and impeller passages. For the case without shunt injection, CFD results show negative (destabilizing) effective damping from the seal at the rotor first damped natural frequency. Shunt injection case shows a positive (stabilizing) estimated effective damping at the frequency of interest. The CFD results are shown to be consistent with the factory test case observations.

Comparison of Pathogens Dispersion in an Aircraft Cabin Using Gas Injection Source Versus a Coughing Manikin

The dispersion characteristics of airborne pathogens were investigated in a Boeing 767 mockup cabin containing 11 rows with 7 seats per row, using two tracer gas source methods: continuous injection at low velocity and a coughing manikin. Both the injection source and the coughing manikin were located on the same seat in the sixth row. The injection source utilized CO2 gas at an injection rate of 5.0 liters per minute mixed with helium at a rate of 3.07 liters per minute to neutralize buoyancy. The manikin coughed approximately once every 75 seconds, with a volume of 4.2 liters of CO2 per cough. To ensure sufficient data were collected at each sampling location, each coughing manikin test was run for 6 coughs and each injection source test for 30 minutes of continuous injection. In both test methods, the tracer gas concentration was measured using CO2 gas analyzers at seated passenger breathing height of 1.2 m and radially up to 3.35 m away from the gas injection location, representing approximately four rows of a standard B767 aircraft. The collected data obtained from each tracer method was then normalized to provide a suitable comparison basis that is independent of tracer gas introduction flowrate. The results showed that both tracer source methods gave similar dispersion trends in diagonal and lateral directions away from the injection location. However, the tracer gas concentration was higher along the longitudinal direction in the coughing manikin tests due to the cough momentum. The results of this work will help researchers analyze different experimental and numerical approaches used to determine contaminant dispersion in various environments and will provide a better understanding of the associated transport phenomena.