A low current intensity study of a cutting plasma torch is presented. The operating gas is oxygen discharging in an air environment. A two-dimensional turbulent plasma model is developed with the commercial code Fluent 4.5. An experimental and a theoretical study are presented. Two configurations were used: one where the arc is transferred to a rotating anode 19 mm away and the other in a real cutting configuration (distance nozzle exit-workpiece around a few millimetres). In the first configuration, spectroscopic measurements are made and compared with the model. The supersonic plasma behaviour is shown with a Mach number of 1.5 at the nozzle exit. The turbulent effect on the mass fraction field is presented. It concerns the effects of turbulence on the presence of oxygen near the plate, and by a comparison of theoretical and experimental temperatures we conclude that the arc presents turbulent behaviour. In the second configuration, a power balance of the cutting process is presented above and in the thickness of the plate. The model shows that the most important contribution to the fusion process is due to convection, conduction and radiation terms.
Pressure-flow relationships measured in human plastinated specimen of both nasal cavities and maxillary sinuses were compared to those obtained by numerical airflow simulations in a numerical three-dimensional reconstruction issued from CT scans of the plastinated specimen. For experiments, flow rates up to 1,500 ml/s were tested using three different gases: HeO(2), Air, and SF(6). Numerical inspiratory airflow simulations were performed for flow rates up to 353 ml/s in both the nostrils using a finite-volume-based method under steady-state conditions with CFD software using a laminar model. The good agreement between measured and numerically computed total pressure drops observed up to a flow rate of 250 ml/s is an important step to validate the ability of CFD software to describe flow in a physiologically realistic binasal model. The major total pressure drop was localized in the nasal valve region. Airflow was found to be predominant in the inferior median part of nasal cavities. Two main vortices were observed downstream from the nasal valve and toward the olfactory region. In the future, CFD software will be a useful tool for the clinician by providing a better understanding of the complexity of three-dimensional breathing flow in the nasal cavities allowing more appropriate management of the patient's symptoms.
Computational fluid dynamics (CFD) and magnetic resonance (MR) gas velocimetry were concurrently performed to study airflow in the same model of human proximal airways. Realistic in vivo-based human airway geometry was segmented from thoracic computed tomography. The three-dimensional numerical description of the airways was used for both generation of a physical airway model using rapid prototyping and mesh generation for CFD simulations. Steady laminar inspiratory experiments (Reynolds number Re = 770) were performed and velocity maps down to the fourth airway generation were extracted from a new velocity mapping technique based on MR velocimetry using hyperpolarized (3)He gas. Full two-dimensional maps of the velocity vector were measured within a few seconds. Numerical simulations were carried out with the experimental flow conditions, and the two sets of data were compared between the two modalities. Flow distributions agreed within 3%. Main and secondary flow velocity intensities were similar, as were velocity convective patterns. This work demonstrates that experimental and numerical gas velocity data can be obtained and compared in the same complex airway geometry. Experiments validated the simulation platform that integrates patient-specific airway reconstruction process from in vivo thoracic scans and velocity field calculation with CFD, hence allowing the results of this numerical tool to be used with confidence in potential clinical applications for lung characterization. Finally, this combined numerical and experimental approach of flow assessment in realistic in vivo-based human airway geometries confirmed the strong dependence of airway flow patterns on local and global geometrical factors, which could contribute to gas mixing.
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