Flow redirection endoluminal device (FRED) for treatment of intracranial aneurysms: A systematic review

Introduction The Flow Redirection Endoluminal Device (FRED; MicroVention) is a dual-layered flow diverter used for the treatment of intracranial aneurysms. The objective of this systematic review was to compile device-related safety and effectiveness data. Methods The literature from January 1, 2013 to April 30, 2021 was searched for studies describing use of the FRED for intracranial aneurysm treatment irrespective of aneurysm location and morphology. The review included anterior and posterior circulation ruptured and unruptured saccular, fusiform or dissection, and blister aneurysms. MeSH terms related to “flow re-direction endoluminal device” and “FRED for aneurysms” were used. Data related to indication, complications, and rates of aneurysm occlusion were retrieved and analyzed. Results Twenty-two studies with 1729 intracranial aneurysms were included in this review. Overall reported morbidity was 3.9% (range 0–20%). Overall procedure-related mortality was 1.4% (range 0–6%). Complication rates fell into 5 categories: technical (3.6%), ischemic (3.8%), thrombotic or stenotic (6%), hemorrhagic (1.5%), and non-neurological (0.8%). The aneurysm occlusion rate between 0 and 3 months (reported in 11 studies) was 47.8%. The occlusion rate between 4 and 6 months (reported in 14 studies) was 73.8%. Occlusion rates continued to increase to 75.1% at 7–12 months (reported in 10 studies) and 86.6% for follow-up beyond 1 year (reported in 10 studies). Conclusion This review indicated that the FRED is a safe and effective for the treatment of intracranial aneurysms. Future studies should directly compare the FRED with other flow diverters for a better understanding of comparative safety and effectiveness among the different devices.

Prediction of Pressure Drops in Liquid-Liquid Two-Phase Flow Across Circular Channels

Mechanistic models are necessary for understanding and predicting the behavior of liquid-liquid flow for multiple pipe dimensions, mixture properties, and flow patterns. In this paper, a mechanistic model is proposed to calculate pressure drop across circular channels for liquid-liquid two-phase flow. The developed model considers several key aspects of liquid-liquid flow, such as mixed and wavy liquid-liquid interfaces and dispersion within each liquid’s layers. Unique identifiers, such as height, turbulence, and dispersion, are calculated for each phase, using an augmented separated flow model and nonlinear optimization. Comparison of the proposed model with experimental data, comprising of multiple inclination angles and flow patterns, shows accurate predictions for a variety of liquid-liquid flow patterns, including double- and triple-layered flow.

CONSTRUCTION OF A MODEL FOR OBTAINING PRESS OIL IN OIL-COMPRESSION UNITS TAKING INTO ACCOUNT THE HYDRODYNAMICS OF THE LAYERED FLOW OF THE MATERIAL OF NON-NEWTONIAN RHEOLOGY

Решением уравнения Навье–Стокса в задачах Куэтта–Пуазейля были определены границы, в рамках которых описан процесс отжима прессового масла с помощью геометрических и скоростных параметров витков шнека. Вычисления производились для материала с высокой вязкостью, имеющего характеристики эффективной вязкости неньютоновской реологии. С использованием балансовых соотношений потоков удалось спрогнозировать работу маслоотжимных агрегатов в режиме форпрессования и экспеллера. В результате выведена модель отжима растительных масел на основе гидродинамики слоистого течения масличного материала в маслоотжимных агрегатах с учетом распределения потока и гидростатического давления в каналах витков шнека. Использование модели двумерного слоистого течения на основе решения задачи Куэтта–Пуазейля базируется на уравнении Навье–Стокса для установившегося режима. Результаты моделирования основаны на технологических параметрах мезги, поступающей на прессование, начальной масличности подсолнечной мезги и начальном расходе, равном 380 кг/ч, который определяется согласно пропускной способности как аналитическое решение этой задачи. Верхняя граница применимости модели слоистого течения масличного материала определяется соотношением геометрии витка шнека с минимальной пропускной способностью 154 кг/ч и содержанием масла в этом материале в диапазоне от 0 до 0,5 кг на 1 кг масличного материала. Нижняя граница применимости этой модели определяется идеализированным случаем экструдирования мезги по каналам шнека при отсутствии отжима. Зависимости изменения давления от расхода мезги, получаемые на основе слоистой модели, позволяют надежно интерполировать распределение давления по виткам шнека в процессе отжима масличного материала. На практике достигнута остаточная масличность жмыха 10% при производительности 200 кг/ч, что дает хорошее совпадение с полученными расчетными значениями. By solving the Navier–Stokes equation in the Couette–Poiseuille problems, the boundaries were determined, within which the process of pressing oil is described using the geometric and speed parameters of the auger turns. The calculations were performed for a high viscosity material having non-Newtonian rheology effective viscosity characteristics. Using the balance flow ratios, it was possible to predict the operation of the oil-pumping units in the pre-pressing and expeller mode. As a result, a model of vegetable oil extraction is derived based on the hydrodynamics of the layered flow of oilseed material in oil-pressing units, taking into account the flow distribution and hydrostatic pressure in the channels of the auger turns. The use of a two-dimensional layered flow model based on the solution of the Couette–Poiseuille problem is based on the Navier–Stokes equation for the steady-state regime. The simulation results are based on the technological parameters of the pulp entering the pressing – the initial oil content of the sunflower pulp and the initial flow rate of 380 kg/h, which is determined according to the throughput as an analytical solution to this problem. The upper limit of the applicability of the model of layered flow of oil-bearing material is determined by the ratio of the geometry of the auger turn with a minimum throughput of 154 kg/h and the oil content in this material in the range from 0 to 0,5 kgper 1 kgof oil-bearing material. The lower limit of the applicability of this model is determined by the idealized case of extrusion of pulp through the auger channels in the absence of pressing. The dependences of the pressure change on the pulp flow rate, obtained on the basis of the layered model, allow us to reliably interpolate the pressure distribution along the auger turns during the pressing of oilseed material. The residual oil content of the oilcake is about 10% at a capacity of 200 kg/h, which gives a good match with the calculated values.

ANALYSIS AND MODELING OF THE KINETICS OF THE EXTRACTION OF VEGETABLE OILS ON THE TURNS OF OIL-PRESSING UNITS

Используемые в промышленности форпрессы для предварительного съема масла и экспеллеры для окончательного отжима различаются геометрией витков шнекового вала. В настоящее время наметилась тенденция к объединению этих аппаратов в единый маслоотжимной агрегат на основе геометрии наборов витков форпресса и экспеллера или двух совращающихся шнековых валов, позволяющих значительно увеличить продолжительность процесса за счет увеличения длины шнековых каналов. Предложено аналитическое решение математической модели распределения потока и гидростатического давления масличного материала в процессе отжима растительного масла непрерывным способом в канале витка шнекового пресса. Показана возможность математического моделирования этого процесса на основе двумерной модели слоистого течения неньютоновской жидкости с учетом геометрии витков шнекового вала и скорости его вращения, позволяющая рассмотреть этот процесс для современных маслоотжимных агрегатов на основе геометрии наборов витков форпресса и экспеллера или двух совращающихся шнековых валов. Получена оценка пропускной способности канала с учетом сопротивлений выходного устройства, а также аналитическое решение распределения потока и гидростатического давления масличного материала в процессе отжима растительного масла. Used in the industry the pre-oil extraction pre-presses and the expellers for the final spin differ in the geometry of the screw shaft turns. Currently, there is a tendency to combine these devices into a single oil-pumping unit based on the geometry of the sets of turns of the forpress and expeller or two rotating screw shafts, which can significantly increase the duration of the process by increasing the length of the screw channels. An analytical solution is proposed for a mathematical model of the distribution of flow and hydrostatic pressure of oil-bearing material in the process of pressing vegetable oil in a continuous way in the channel of the screw press. The possibility of mathematical modeling of this on the basis of a two-dimensional model of a layered flow of a non-newtonian fluid, taking into account the geometry of the turns of the screw shaft and the speed of its rotation, is shown, which makes it possible to consider this process from a single point of view of using modern oil-extracting units, both on the basis of the geometry of sets of turns of the forpress and expeller, and two screw shafts. As a result of the conducted studies, an estimate of the channel capacity was obtained, taking into account the resistances of the output device, as well as an analytical solution for the distribution of the flow of oilseed material and the hydrostatic pressure of the oilseed material during the extraction of vegetable oil.

Polymer Solutions and Their Mathematical Models

Mathematical models for the motion of weak solutions of polymers have been studied over the past 50 years. The initial model (Voitkunskii, Amfilokhiev, and Pavlovskii, 1970) contains two key parameters - relaxation viscosity and shear stress relaxation time. In the limiting case, when the last parameter is small, the Pavlovskii model (1971) arises. Its equations are close to second-grade fluid equations (Rivlin and Eriksen, 1955). The paper contains an overview of the works on all three models and new results related to the Pavlovskii model. The solution to the problem of the un-steady layered flow of an aqueous polymer solution in a layer with a free boundary, the boundary condition on which includes the time derivative of the desired function is constructed. We derive the equations that describe the motion of a polymer solution in a laminar boundary layer near a rectilinear plate. The parameter included in equations characterizes the ratio of the thickness of the Prandtl boundary layer to the thickness of the relaxation boundary layer. We study the influence of this parameter on the motion picture by the example of a stationary flow near a critical point.

Exact solutions for n-layer concentric flow of PTT fluids through a cylindrical pipe

Flows of multiple layers of fluids are encountered in many industrial and manufacturing processes. This paper investigates the concentric n-layer flow for Phan–Thien–Tanner (PTT) fluids through a cylindrical pipe. Finitely many immiscible non-Newtonian fluids are considered to be flowing concentrically in a tube. The flow is modelled using the exponential PTT fluid model and exact solutions for velocity fields and volume flow rates are computed. It has been shown that the corresponding results for linear PTT fluid model as well as Newtonian fluids can be deduced from the obtained expressions, and that they match with the present literature. It has also been observed that for such layered flow, the non-Newtonian parameters significantly affect the flow of fluids in adjacent layers. The effects of involved parameters on the velocity profiles are also shown graphically. We show that a unique velocity maximum exists along the axis of the pipe. Moreover, it is observed with the help of an example that layer thickness can be adjusted to obtain maximal flow rate with a given pressure gradient.

Lattice-Boltzmann Simulation and Experimental Validation of a Microfluidic T-Junction for Slug Flow Generation

We investigate the interaction of two immiscible fluids in a head-on device geometry, where both fluids are streaming opposite to each other. The simulations are based on the two-dimensional (2D) lattice Boltzmann method (LBM) using the Rothman and Keller (RK) model. We validate the LBM code with several benchmarks such as the bubble test, static contact angle, and layered flow. For the first time, we simulate a head-on device by forcing periodicity and a volume force to induce the flow. From low to high flow rates, three main flow patterns are observed in the head-on device, which are dripping-squeezing, jetting-shearing, and threading. In the squeezing regime, the flow is steady and the droplets are equal. The jetting-shearing flow is not as stable as dripping-squeezing. Moreover, the formation of droplets is shifted downstream into the main channel. The last flow form is threading, in which the immiscible fluids flow parallel downstream to the outlet. In contrast to other studies, we select larger microfluidic channels with 1-mm channel width to achieve relatively high volumetric fluxes as used in chemical synthesis reactors. Consequently, the capillary number of the flow regimes is smaller than 10−5. In conclusion, the simulation compares well to experimental data.

MODEL OF THE KINETICS OF EXTRACTION DURING THE EXTRUSION OF OILSEED MATERIALS

Описана динамика выделения растительного масла из пористого материала в процессе его ламинарного слоистого течения, вызванного движущимися с заданной постоянной скоростью стенками канала шнека и неподвижной крышкой. Получена адекватная модель кинетики отжима в зеерной камере пресса, позволяющая прогнозировать работу витков маслоотжимных агрегатов по пропускной способности каналов, образованных витками шнека и выпускного устройства. Установлено, что динамика отжима масла из масличного материала определяется уменьшением потока материала по длине винтовой линии. Практически линейный характер изменения давления в зеерной камере показывает отсутствие гидравлических потерь в процессе отжима. The dynamics of the release of vegetable oil from a porous material during its laminar layered flow caused by moving at a given constant speed the walls of the screw channel and the fixed cover is described. An adequate model of the spin kinetics in the zeer chamber of the press, which allows to predict the work of the turns of the oil extraction units by the capacity of the channels formed by the turns of the screw and the exhaust device, is made. It is established that the dynamics of oil extraction from the oil material is determined by a decrease in the flow of the material along the length of the helix. The almost linear nature of the pressure change in the zeer chamber shows the absence of hydraulic losses during the extraction.

Conditions at interfaces of layered flow with intense bed load transport

Intense bed load transport in open channel flow is typically associated with a layered structure of the flow, in which individual layers exhibit different mechanisms of support and friction of transported sediment grains. In the lowermost layer adjacent to the channel bed, the grains slide over each other and maintain virtually permanent contact. In the uppermost layer below the water surface, typically no grains are transported. In the central layer, the grains collide with each other producing typical distributions of granular concentration and velocity across the collisional layer. Mathematical models describing the layered flow with intense bed load (as models based on kinetic theory of granular flows) consider flow conditions at interfaces of the individual layers in their flow predictions. Usually, experimental verification of interfacial predictions is lacking. We exploit results of our new experiments with plastic cylindrical sediment to identify a variation of the conditions at the interfaces (local interfacial granular concentrations and velocities) with varying flow discharge, depth and slope in a laboratory tilting flume. The experimental results include local granular concentration using an improved laser stripe method. The experiments are compared with predictions using our kinetic-theory based transport model with the aim to evaluate a match for experimentally-determined and model-predicted interfacial parameters.