Rôle of contrast media viscosity in altering vessel wall shear stress and relation to the risk of contrast extravasations

Iodinated contrast media (CM) are the most commonly used injectables in radiology today. A range of different media are commercially available, combining various physical and chemical characteristics (ionic state, osmolality, viscosity) and thus exhibiting distinct in vivo behaviour and safety profiles. In this paper, numerical simulations of blood flow with contrast media were conducted to investigate the effects of contrast viscosity on generated vessel wall shear stress and vessel wall pressure to elucidate any possible relation to extravasations. Five different types of contrast for Iodine fluxes ranging at 1.5–2.2 gI/s were modelled through 18 G and 20 G cannulae placed in an ideal vein at two different orientation angles. Results demonstrate that the least viscous contrast media generate the least maximum wall shear stress as well as the lowest total pressure for the same flow rate. This supports the empirical clinical observations and hypothesis that more viscous contrast media are responsible for a higher percentage of contrast extravasations. In addition, results support the clinical hypothesis that a catheter tip directed obliquely to the vein wall always produces the highest maximum wall shear stress and total pressure due to impingement of the contrast jet on the vessel wall

Assessment of Cavitation Models for Compressible Flows Inside a Nozzle

This study assessed two cavitation models for compressible cavitating flows within a single hole nozzle. The models evaluated were SS (Schnerr and Sauer) and ZGB (Zwart-Gerber-Belamri) using realizable k-epsilon turbulent model, which was found to be the most appropriate model to use for this flow. The liquid compressibility was modeled using the Tait equation, and the vapor compressibility was modeled using the ideal gas law. Compressible flow simulation results showed that the SS model failed to capture the flow physics with a weak agreement with experimental data, while the ZGB model predicted the flow much better. Modeling vapor compressibility improved the distribution of the cavitating vapor across the nozzle with an increase in vapor volume compared to that of the incompressible assumption, particularly in the core region which resulted in a much better quantitative and qualitative agreement with the experimental data. The results also showed the prediction of a normal shockwave downstream of the cavitation region where the local flow transforms from supersonic to subsonic because of an increase in the local pressure

Flow characteristics and turbulence analysis of a large-scale pressure-atomized spray

International audienceA typical water round-nozzle jet for agricultural applications is presented in this study. The dispersion of a liquid for irrigation or pesticides spraying is a key subject to reduce both water consumption and air pollution. A simplified study case is constructed to tackle both scenarios, where a round dn = 1.2mm nozzle of a length Ln = 50dn is considered. The water injection bulk velocity is equal to Uj = 35m/s, aligned with gravity, placing the liquid jet in a turbulent atomization regime. Experimental and numerical approaches are considered. LDV and DTV optical techniques are used to gather statistical information from both the liquid and the gas phases of the spray. The experimental campaign is carried out from x/dn = 0 to 800. Concerning the LDV, small (∼ 1µm) olive-oil tracers are used to capture the gas phase, where a distinction between the liquid droplets and tracers is achieved by a specific setup of the laser power source and the burst Doppler setting (BP-Filter and SNR). On the dispersed zone, DTV measurements are carried out to determine velocities and sizes of droplets. Special attention to the depth-of-field (DOF) estimation is taken in order to obtain a less biased droplet's size-velocity correlation. Finally, an optical probe (OP) was also used to determine the liquid volume fraction í µí±Œ ̅ , liquid mass fraction í µí±Œ ̃ , and mixture density í µí¼Œ̅ , which are important features for such flows. These are key quantities for the determination of the mixture mean velocities and Reynolds stresses, and evaluation of the terms in their balance equations. Combining OP, LDV and DTV data allows to determine quantities such as the mixture mean density, í µí¼Œ̅ = í µí±Œ ̅ í µí¼Œ í µí°¿ + (1 − í µí±Œ ̅)í µí¼Œ í µí°º , mixture mean velocity along the i direction, í µí±¢ ̃ í µí±– = í µí±Œ ̃ í µí±¢ ̃ í µí±–,í µí°¿ + (1 − í µí±Œ ̃)í µí±¢ ̃ í µí±–,í µí°º , or mean slip velocity, í µí±¢ ̅ í µí±–,í µí±† = í µí±¢ ̅ í µí±–,í µí°¿ − í µí±¢ ̅ í µí±–,í µí°º = í µí±¢ í µí±– ′′ í µí±Œ ′′ ̃ í µí±Œ ̃ (1−í µí±Œ ̃) , where the notation '' denotes fluctuations with respect to the Favre averaged mean values. Similar relations hold for the Reynolds stresses. For such a flow, three dimensionless quantities can be constructed as a function of the forces that intervene in the atomization process. First, the nozzle Reynolds number, í µí±í µí±’ = í µí±ˆ í µí±— í µí±‘ í µí±› í µí¼ˆ í µí°¿ , allows to identify if the liquid flow inside the injector is turbulent. Then, the liquid Weber number, í µí±Ší µí±’ í µí°¿ = í µí¼Œ í µí°¿ í µí±ˆ í µí±—í µí±‘ í µí±› 2 í µí¼Ž , and the gas Weber number, í µí±Ší µí±’ í µí°º = í µí¼Œ í µí°º í µí±ˆ í µí±—í µí±‘ í µí±› 2 í µí¼Ž , which weights the importance of surface tension once the flow is in contact with the surrounding air. Finally, the Ohnesorge number, í µí±‚ ℎ = í µí¼Œ í µí°¿ í µí¼ˆ í µí°¿ √í µí¼Œ í µí°¿ í µí¼Ží µí±‘ í µí±› , characterizes the form of the liquid packets or droplets in the atomization process. Choosing Re = 41833 and Ln/dn = 50 makes the internal flow fully turbulent and ensures that the boundary layer inside the nozzle is fully developed for any upstream conditions. With WeL = 20158, WeG = 24.3 and Oh = 0.0034, the liquid phase turbulent kinetic energy should be the main responsible of the liquid-jet primary break-up, these flow conditions lying within the second wind-induced atomization regime

Effects of Drilling Fluid Rheological Properties on Drill Cuttings Transport

During well drilling process, drill cuttings were produced. Drill fluid (or mud) has been used to remove the drill cuttings that are produced in the well by transporting it to the surface. The removal of drill cuttings is important in ensuring a smooth drilling process. In order for the drilling fluid to transport the drill cuttings effectively, the rheological properties of the drilling fluid such as viscosity, suspension, yield stress and velocity must be taken into consideration. Biopolymers such as xanthan gum and scleroglucan have been widely used as additives to improve the rheological properties of the cutting fluid. This project is about studying the Effects of Drilling Fluid Rheological Properties on Drill Cuttings Transport. The project consists of rheological data gathering of the drilling fluids, performing numerical simulations of the drilling fluids, and study of the relationship between the drill cuttings accumulation and the drilling fluid rheology in achieving optimum drill cuttings management. This report will describe in detail the background study of the project, the problem statement that leads to the objectives of this project, the objectives, the scope of studies during this project, literature review, methodology or steps taken to complete this project, results, discussions and recommendation

Multiphase CFD Simulation of Solid Propellant Combustion in a Small Gun Chamber

The interior ballistics simulations in 9 mm small gun chamber were conducted by implementing the process into the mixture multiphase model of Fluent V6.3 platform. The pressure of the combustion chamber, the velocity, and the travel of the projectile were investigated. The performance of the process, namely, the maximum pressure, the muzzle velocity, and the duration of the process was assessed. The calculation method is validated by the comparison of the numerical simulations results in the small gun with practical tests, and with lumped-parameter model results. In the current numerical study, both the characteristics and the performance of the interior ballistic process were reasonably predicted compared with the practical tests results. The impact of the weight charge on the interior ballistic performances was investigated. It has been found that the maximum pressure and the muzzle velocity increase with the increase of the charge weight