Boris V. Balakin

Computational fluid dynamic evaluation of the side-to-side anastomosis for arteriovenous fistula

OBJECTIVE The goal of this research was to compare side-to-side (STS) and end-to-side (ETS) anastomoses in a computer model of the arteriovenous fistula with computational fluid dynamic analysis. METHODS A matrix of 17 computer arteriovenous fistula models (SolidWorks, Dassault Systèmes, France) of artery-vein pairs (3-mm-diameter artery + 3-mm-diameter vein and 4-mm-diameter artery +6-mm-diameter vein elliptical anastomoses) in STS, 45° ETS, and 90° ETS configurations with cross-sectional areas (CSAs) of 3.5 to 18.8 mm(2) were evaluated with computational fluid dynamic software (STAR-CCM+; CD-adapco, Melville, NY) in simulations at defined flow rates from 600 to 1200 mL/min and mean arterial pressures of 50 to 140 mm Hg. Models and configurations were evaluated for pressure drop across the anastomosis, arterial inflow, venous outflow, arterial outflow, velocity vector, and wall shear stress (WSS) profile. RESULTS Pressure drop across the anastomosis was inversely proportional to anastomotic CSA and to venous outflow and was proportional to arterial inflow. Pressure drop was greater in 3 + 3 models than in 4 + 6 STS models; 90° ETS configurations had the lowest pressure drops and were nearly identical, whereas 45° ETS configurations had the highest pressure drops. Venous outflow in the 4 + 6 model in STS configurations, evaluated at 100 mm Hg arterial inflow pressure, was 390, 592, 610, and 886 mL/min in anastomotic CSAs of 3.5, 5.3, 7.1, and 18.8 mm(2), respectively, and was similar in 90° ETS (609 and 908 mL/min) and lower in 45° ETS (534 and 562 mL/min) configurations at CSAs of 5.3 and 18.8 mm(2). The mean increase in venous outflow was 69 mL/min (range, -59 to 134) between 3 + 3 and 4 + 6 models at 100 mm Hg arterial inflow. The most uniform WSS profile occurs in STS anastomoses followed by 45° ETS and then 90° ETS anastomoses. CONCLUSIONS The STS and 90° ETS anastomoses have high venous outflow and a tendency toward reversed arterial outflow. The 45° ETS anastomosis has reduced venous outflow but resists reversed arterial outflow. The STS anastomosis has more uniform WSS characteristics compared with the 45° and 90° ETS anastomoses.

Eulerian-Eulerian CFD Model for the Sedimentation of Spherical Particles in Suspension with High Particle Concentrations

Abstract A computational study of the process of sedimentation of spherical particles in suspensions with high particle concentrations has been performed with the two-fluid Eulerian approach. The solid stress induction in the dispersed phase was modelled through modification of the suspension viscosity. Convectional flow patterns were found and studied during the simulations. The presence of these patterns, which are also observed experimentally, makes the sedimentation process dependent on the rheological behaviour of the suspension. The results of the simulation were validated with experimental results. The present paper shows that Eulerian-Eulerian simulations can account for some of the detailed processes taking place in a settling suspension of particles.

Combined CFD/Population Balance Model for Gas Hydrate Particle Size Prediction in Turbulent Pipeline Flow

A combined computational fluid dynamics/population balance model (CFD‐PBM) is developed for gas hydrate particle size prediction in turbulent pipeline flow. The model is based on a one‐moment population balance technique, which is coupled with flow field parameters computed using commercial CFD software. The model is calibrated with a five‐moment, off‐line population balance model and validated with experimental data produced in a low‐pressure multiphase flow loop.

Eulerian‐Eulerian Simulation of Sedimentation of Uniformly‐sized, non‐Brownian Spheres in Viscous Fluids

A Eulerian‐Eulerian 3‐dimensional CFD‐model has been built in order to study the sedimentation process of uniformly‐sized, non‐Brownian spheres in a viscous fluid. It is shown that proper agreement with experimental data for high particle loadings strongly depends on using a correct drag force relation. Convection currents in the carrier phase were observed during simulation. They were found to present a hydraulic resistance to the solids settling. The particle interactions were implemented through a solids stress tensor dependent on the viscosity of the carrier phase and the solids local volume fraction. The completed model was validated by comparison with experimental data.

Non-invasive studies of multiphase flow in process equipment. Positron emission particle tracking technique.

Positron emission particle tracking (PEPT) is a novel experimental technique for non-invasive inspection of industrial fluid/particle flows. The method is based on the dynamic positioning of a positron-emitting, flowing object (particle) performed through the sensing of annihilation events and subsequent numerical treatment to determine the particle position. The present paper shows an integrated overview of PEPT studies which were carried out using a new PET scanner in the Bergen University Hospital to study multiphase flows in different geometric configurations.

Numerical study of gas-liquid flow morphology in a vertical flowmeter nozzle

Industrial multiphase flow measurement systems often contain meters based on Venturi principle. Those instruments deal with the differential pressure measurements whose accurate interpretation is possible when the flow morphology is known a-priori. The present paper reports the results of CFD-modelling of a gas-liquid flow through a vertical nozzle accompanied by a blind-T flow conditioner. The model is used for evaluation of the flow morphology in case the volume fractions of both phases are comparable. The model demonstrates high non-uniformities of the flow field after the blind-T, which indicates that this type of flow conditioners may lead to inaccurate results.Industrial multiphase flow measurement systems often contain meters based on Venturi principle. Those instruments deal with the differential pressure measurements whose accurate interpretation is possible when the flow morphology is known a-priori. The present paper reports the results of CFD-modelling of a gas-liquid flow through a vertical nozzle accompanied by a blind-T flow conditioner. The model is used for evaluation of the flow morphology in case the volume fractions of both phases are comparable. The model demonstrates high non-uniformities of the flow field after the blind-T, which indicates that this type of flow conditioners may lead to inaccurate results.

Numerical and experimental analysis of particle dispersion in dust explosions

Dust explosions take place when small particles of flammable material such as grain, wood, plastic, coal and metal are dispersed in air and ignited. An important research tool that is used for describing dust explosion characteristics is the Hartmann apparatus, where dust is dispersed by a pressure wave. This makes it possible to find e.g. the minimum ignition energy. Nevertheless, there is a question whether the formed dust cloud is uniformly dispersed and how the solid particles behave as they flow. In addition to the scientific curiosity there is also a practical application, namely at what point in time the explosive mixture should be ignited in order to obtain the most representative results. The objective of this research was to run computational fluid dynamic (CFD) simulations, using the commercial software Star CCM+, with the purpose to numerically investigate the dispersion of a single particle in a modified Hartmann tube. Numerical models affecting the particle-wall and the particle-gas interact...

Aerodynamic evaluation of the empty nose syndrome by means of computational fluid dynamics

Abstract The potential outcome of a surgical enlargement of internal nasal channels may be a complication of nasal breathing termed the Empty Nose Syndrome (ENS). ENS pathophysiology is not entirely understood because the expansion of air pathways would in theory ease inhalation. The present contribution is aimed at defining the biophysical markers responsible for ENS. Our study, conducted in silico, compares nasal aerodynamics in pre- and post-operative geometries acquired by means of computer tomography from the same individual. In this article, we elucidate and analyse the deviation of airflow patterns and nasal microclimate from the healthy benchmarks. The analysis reveals 53% reduction in flow resistance, radical re-distribution of nasal airflow, as well as dryer and colder nasal microclimate for the post-operative case.

Numerical Prediction of the Cooling of Burnt Cable for the Prevention of Re-Ignition

Fires in the cable structures are a serious danger for the offshore facilities. Inflammations of the cables are mostly caused by cable overheating as a result of power loads in the net or by the shortcut circuits. Fire extinguishing comes, in the first place, to neutralization of the external flame on its surface. However, even when the external flame is prevented, the re-ignition of the cable’s insulation may happen in case its metal core has not been sufficiently cooled down to a safe temperature level. It is therefore important to clarify the dynamics of the core cooling under the influence of the flow of extinguishing agents in order to manage the temporal characteristics of the entire process. The current paper reports a numerical model of a hot cable cooling under the influence of external flow. The model resolves the temperature fields as in the cable as in the surrounding media in connection with the flow profiles of the cooling agent. Several cooling scenarios are considered for the problem: natural convection of the cooling gas around the cable, and forced heat utilization due to an induced gas-water flow directed towards the cable. The model is validated with the use of experimental data presenting a suitable agreement with empirics.Copyright

CFD modeling of PEPT results of particle motion trajectories in a pipe over an obstacle

This paper aims to study the flow of a solid particle over a deposit in transport and processing equipment. Tracking particles and fluid elements moving through single- and multi-phase systems is very useful for studying numerous flow processes and identifying anomalies happening in the processes. Using Positron emission tomography (PET) and positron emission particle tracking (PEPT), that are relatively new techniques, it has become possible to visualize the movement of single particles in process equipment. The results from PEPT are here compared with particle-coupled Large Eddy Simulation numerical results. In the initial stages of the numerical modelling, results were validated using the PEPT experimental data in terms of its ability to correctly predict the flow and deposition of particles in a fluid flowing at a moderately low Reynolds number.