Dynamic Flow Effects Research Articles

Characterizing the Role of Biologically Relevant Fluid Dynamics on Silver Nanoparticle Dependent Oxidative Stress in Adherent and Suspension In Vitro Models.

Silver nanoparticles (AgNPs) are being employed in numerous consumer goods and applications; however, they are renowned for inducing negative cellular consequences including toxicity, oxidative stress, and an inflammatory response. Nanotoxicological outcomes are dependent on numerous factors, including physicochemical, biological, and environmental influences. Currently, NP safety evaluations are carried out in both cell-based in vitro and animal in vivo models, with poor correlation between these mechanisms. These discrepancies highlight the need for enhanced exposure environments, which retain the advantages of in vitro models but incorporate critical in vivo influences, such as fluid dynamics. This study characterized the effects of dynamic flow on AgNP behavior, cellular interactions, and oxidative stress within both adherent alveolar (A549) and suspension monocyte (U937) models. This study determined that the presence of physiologically relevant flow resulted in substantial modifications to AgNP cellular interactions and subsequent oxidative stress, as assessed via reactive oxygen species (ROS), glutathione levels, p53, NFκB, and secretion of pro-inflammatory cytokines. Within the adherent model, dynamic flow reduced AgNP deposition and oxidative stress markers by roughly 20%. However, due to increased frequency of contact, the suspension U937 cells were associated with higher NP interactions and intracellular stress under fluid flow exposure conditions. For example, the increased AgNP association resulted in a 50% increase in intracellular ROS and p53 levels. This work highlights the potential of modified in vitro systems to improve analysis of AgNP dosimetry and safety evaluations, including oxidative stress assessments.

Study of effect of heat transfer in an air storage vessel on performance of a pumped hydro compressed air energy storage system

Pumped Hydro Compressed Air (PHCA) energy storage is a new technology which offers high energy storage performance. In this paper, the effect of dynamic flow and heat transfer in a cylindrical air storage vessel on the performance of a PHCA system is investigated using multiphase Volume of Fluid (VOF) and turbulence k−ε models. The numerical simulation is validated using experimental data available in the literature. The influence of governing parameters including the pre-set pressure, storage pressure, charging and discharging flow rates on heat transfer and performance of the PHCA system is investigated. The results show that heat transfer between air and water in the storage vessel has a large effect on compression and expansion processes. The polytropic index during the compression/expansion process ranges between 1.05 and 1.3 under the studied conditions. It increases with increasing pre-set initial pressure, lowering of the storage pressure, or with increasing charging/discharging flow rates. Consequently, the required work input increases and the generated work output decreases. Further analyses show that as the charging/discharging flow rate increases, the compression/expansion efficiency decreases with reducing heat transfer between air and water. The results also show that the stored energy level in an actual process lies in between those of isothermal and isentropic processes.

Gas transmission pipeline failure probability estimation and defect repairs activities based on in-line inspection data

Degradation of an underground pipeline during its service life leads to reduction of the pipe wall thickness. Periodic in-line inspections are performed by onshore pipelines operators to detect corrosion anomalies and size their depth and width. In the paper, a simple analytical method of burst pressure calculation for a straight pipeline repaired with a composite sleeve was investigated. Repair activities after an in-line inspection of a gas transmission pipeline were considered in this research to assess the pressure of a pipe with a flaw reinforced with a different number of layers of a fiber-based polymer sleeve. Det Norske Veritas criteria and formulation of a limit state function were applied to determine the burst pressure and corresponding failure probability of a pipeline with a large number of single and non-interacting part-wall defects. The Monte Carlo method was selected for estimation of pipeline failure probability and cumulative failure probability due to the external corrosion considering fluid pressure fluctuations in dynamic flow effects with respect to statistical distribution of input parameters were examined in this research. The proposed novel 3-step approach was validated on the real data collected from an onshore high pressure gas pipeline DN 700, MOP 5.5 MPa provided by two magnetic flux leakage inspections repeated at an interval of twelve years. A probabilistic methodology was applied to evaluate the part-wall external corrosion defects and their deterministic linear growth with time and repair activities on gas transmission pipelines were analyzed. The results of this study shall help maintenance engineers solve the problems of an optimal strategy in reliability-based high pressure gas pipelines management.

Dynamic degradation of porous magnesium under a simulated environment of human cancellous bone

This study shows the effect of dynamic flow on the degradation behaviour and mechanical integrity of porous magnesium. A test rig that mimics the environment surrounding a cancellous bone was developed and a dynamic immersion test was performed to assess the degradation rate of the material for bone scaffold application. Three different percentages of porous magnesium (30%, 41%, and 55%) were immersed in simulated body fluid. The results show that mass loss and mechanical integrity of the specimens deteriorated linearly with an increase in porosity and degradation time, correlating to a drop of 41% and 89%, respectively, within 3days.

NUMERICAL SIMULATION OF PRESSURE-INDUCED CELL PRINTING

Nowadays, because of great biomedical applications of state-of-the art prototyping (bio-printing), many studies have been conducted in this field with focus on three-dimensional prototyping. There are several mechanisms for bio-printing of live cells such as piezoelectric and thermal and pneumatic inkjeting systems. Cell viability should be preserved during the bio-printing process. Lots of researches have been carried out to investigate and compare cell viability through different prototyping mechanisms. In order to quantify percentage of the cells that are killed during the proto-typing process, applied stresses on the cell and consequently its deformation should be calculated. A maximum strain energy density that the cell can tolerate is reported in the range of 25 Kj ⋅ m-3 to 100 Kj ⋅ m-3. This can be considered as a criteria to find the percentage of the damaged cells during the bio-printing processes. In this study, the bio-printing of the cell has been modeled and the cell viability have been investigated. Firstly, it is shown that in modeling of the bio-printing process, the effects of dynamic flow on calculating the applied stress on the cell is not negligible and must be considered. In the next step, the percentage of damaged endothelial cell aggregate under 80 kPa applied pressure (64 MPa/m) and 200 micron nozzle diameter is reported. Based on findings of this study, the percentage of endothelial cells viability under mentioned condition is reported 76%. The proposed method of this study can be utilized to examine the cell viability and performance of each prototyping systems.

On the magnetic reconnection of resistive tearing mode with the dynamic flow effects

Magnetic reconnection usually occurs in turbulent environments, which may not only provide anomalous resistivity to enhance reconnection rates but also significantly modify the reconnection process through direct nonlinear interaction with magnetic islands. This study presents numerical simulations investigating the effects of an imposed dynamic flow on magnetic reconnection, based on a two-dimensional reduced resistive MHD model. Results show that while the linear stability properties of the resistive tearing mode are moderately affected by the dynamic flow, nonlinear evolution is significantly modified by radial parity, amplitude, and frequency of the dynamic flow. After the slowly evolving nonlinear Rutherford stage, the reconnection process is found to progress in two phases by including the dynamic flow. A Sweet-Parker like current sheet is formed in the first phase. Afterwards, plasmoid instability is triggered in the second phase, where multiple plasmoids are continuously generated and ejected along the current sheet, leading to an impulsive bursty reconnection. The reconnection rate is considerably enhanced in the range of low resistivity as compared to without flow. We found that plasmoid instability onset and evolution are strongly influenced by the frequency and radial parity of the dynamic flows. The scaling of effective reconnection rates with the flow is found to be independent of resistivity.

Quantifying impacts on the measurement uncertainty in flow calibration arising from dynamic flow effects

Traceability of the measurement units in fluid flow metering, as the state-of-the-art approach, is practiced as a so-called element-by-element method which relies upon the idealistic assumption that the measurement process in a flow calibration facility can be run under exact steady-state conditions, that is, absolutely no fluctuations of the flow quantities are assumed to occur during the flow measurement process. Practical experiences, combined with a model-based analytical view of the measurement process in a flow standard, have revealed that dynamic impacts on the measurement uncertainty due to flowrate fluctuations have to be taken into account, in addition to the steady-state traceability chain.

Numerical simulation of pressure pulsations in Francis turbines

In the last decades, hydraulic turbines have experienced the increase of their power density and the extension of their operating range, leading the fluid and mechanical dynamic effects to become significantly more pronounced. The understanding of the transient fluid flow and of the associated unsteady effects is essential for the reduction of the pressure pulsation level and improvement of the machine dynamic behaviour. In this study, the instationary fluid flow through the complete turbine was numerically calculated for an existing Francis machine with high specific speed. The hybrid turbulence models DES (detached eddy simulation) and SAS (scale adaptive simulation) allowed the accurate simulation of complex dynamic flow effects, such as the rotor-stator-interaction and the draft tube instabilities. Different operating conditions, as full load, part load, higher part load and deep part load, were successfully simulated and showed very tight agreement with the experimental results from the model tests. The transient pressure field history, obtained from the CFD (computational fluid dynamics) simulation and stored for each time step, was used as input for the full instationary FEA (finite element analysis) of turbine components. The assessment of the machine dynamic motion also offered the possibility to contribute to the understanding of the pressure pulsation effects and to further increase the turbine stability. This research project was developed at the Institute of Fluid Mechanics of the TU München.

First step in optimizing LNG storages for offshore terminals

The development of new LNG offshore facilities addresses new technical challenges that need to be deeply investigated to overcome the new constraints raised from the offshore operability. One of the key issues concerns the management of LNG storages. As future offshore LNG projects could be implemented in areas with harsh environmental conditions, the motions of the floating structure combined to the design and operating parameters should widely affect the behavior of the LNG inside partially filled tanks. Therefore, the knowledge available from onshore LNG storages has to be completed taking into account the offshore environment. The first concern deals with the production of Boil-Off Gas (BOG) during LNG’s unloading and storage operations under offshore conditions, where specific offshore parameters would contribute in increasing the production of BOG. For that purpose, a new optimized LNG storage process based on an increased operating pressure ( P = 500 mbarg) in the TRITON FSRU’s tanks has been investigated during LNG’s unloading and storage operations with LNG emission. It mainly showed that by operating at 500 mbarg, the production of BOG is nearly 4 times reduced during unloading operations compared to LNG carrier standard operating pressure (100 mbarg) and nearly suppressed during the storage phase. The second concern deals with managing the rollover risk under offshore conditions. In this context, GDF SUEZ performed a pioneer qualitative assessment to highlight the impact of the liquid motion on the rollover mechanisms in the TRITON FSRU’s tanks. The liquid motion completely modifies the mixing mechanisms in LNG stratified layers. The mixing is no longer governed by the molecular diffusion induced by the thermal effects but by the dynamic flow effects induced by the fluid wave movement into the layers. Moreover, this assessment showed that the time needed for a stratification to evolve up to a complete mix is severely reduced compared to the onshore LNG storage while the assessment of the induced BOG peak depends as usual on the energy stored in the stratification when being mixed and could be of the same order of magnitude as for onshore rollover.

Non-Newtonian and flow pulsatility effects in simulation models of a stented intracranial aneurysm

Three models of different stent designs implanted in a cerebral aneurysm, originating from the Virtual Intracranial Stenting Challenge '07, are meshed and the flow characteristics simulated using commercial computational fluid dynamics (CFD) software in order to investigate the effects of non-Newtonian viscosity and pulsatile flow. Conventional mass inflow and wall shear stress (WSS) output are used as a means of comparing the CFD simulations. In addition, a WSS distribution is presented, which clearly discriminates in favour of the stent design identified by other groups. It is concluded that non-Newtonian and pulsatile effects are important to include in order to avoid underestimating wss, to understand dynamic flow effects, and to discriminate more effectively between stent designs.

Effect of Dynamic Flow on the Structure of Inhibition Layer in Hot-dip Galvanizing

The effect of dynamic flow or forced convection were investigated and compared on the formation of inhibition layer, galvanizing and galvannealing reactions through the hot-dip galvanizing simulator with the oscillation of specimen in zinc bath, continuous galvanizing pilot plant with zinc pumping system through the snout and continuous galvanizing operation with Dynamic Galvanizing system. The interfacial Al pick-up was not consistent between the results of simulator, pilot plant and line operation, but the morphology of inhibition layer became compact and refined by the forced convection. The growth of Fe-Zn intermetallics at the interface was inhibited by the forced convection, whereas the galvannealing rate would be a little promoted.

Evaluation of a Three-Stage Biological Aerated Filter System Combined Recirculation/Dynamic Flow in Treating Low Carbon-to-Nitrogen Ratio Wastewater

Abstract In this study, a three-stage biological aerated filter (BAF) system was proposed to enhance nitrogen removal in the treatment of low carbon-to-nitrogen ratio (C/N ratio) municipal wastewater. Laboratory experiments were conducted at three different recirculation ratios of 1, 2, and 3. Effects of dynamic flow were also evaluated in this study. Results of the long-term operation of the three-stage BAF system in dynamic flow showed nitrogen removal was affected by the both recirculation ratio and C/N ratio in dynamic flow. Dynamic flow enabled the nitrogen removal efficiency of the system to be higher than that of nondynamic flow system in treating low C/N ratio wastewater due to the more efficient use of organic substrates. Overall NH4-N removal performance was stable with a removal efficiency of 99% on average during the operational period due to the unique system configuration where independent nitrification occurred. It was concluded that the three-stage BAF system proposed in this study provide...

Steady and Unsteady Radial Forces for a Centrifugal Pump With Impeller to Tongue Gap Variation

Experimental and numerical studies are presented on the steady and unsteady radial forces produced in a single volute vaneless centrifugal pump. Experimentally, the unsteady pressure distributions were obtained using fast response pressure transducers. These measurements were compared with equivalent numerical results from a URANS calculation, using the commercial code FLUENT. Two impellers with different outlet diameters were tested for the same volute, with radial gaps between the blade and tongue of 10.0% and 15.8% of the impeller radius, for the bigger and smaller impeller diameters, respectively. Very often, pump manufacturers apply the similarity laws to this situation, but the measured specific speeds in this case were found to be slightly different. The steady radial forces for the two impellers were calculated from both the measured average pressure field and the model over a wide range of flow rates in order to fully characterize the pump behavior. Again, a deviation from the expected values applying the similarity laws was found. The data from the pressure fluctuation measurements were processed to obtain the dynamic forces at the blade passing frequency, also over a wide range of flow rates. Afterwards, these results were used to check the predictions from the numerical simulations. For some flow rates, the bigger diameter produced higher radial forces, but this was not to be a general rule for all the operating points. This paper describes the work carried out and summarizes the experimental and the numerical results, for both radial gaps. The steady and unsteady forces at the blade passing frequency were calculated by radial integration of the pressure distributions on the shroud side of the pump volute. For the unsteady forces, the numerical model allowed a separate analysis of the terms due to the pressure pulsations and terms related to the momentum exchange in the impeller. In this way, the whole operating range of the pump was studied and analyzed to account for the static and dynamic flow effects. The unsteady forces are very important when designing the pump shaft as they can produce a fatigue collapse if they are not kept under a proper working value.

Bioreactor-based bone tissue engineering: the influence of dynamic flow on osteoblast phenotypic expression and matrix mineralization.

An important issue in tissue engineering concerns the possibility of limited tissue ingrowth in tissue-engineered constructs because of insufficient nutrient transport. We report a dynamic flow culture system using high-aspect-ratio vessel rotating bioreactors and 3D scaffolds for culturing rat calvarial osteoblast cells. 3D scaffolds were designed by mixing lighter-than-water (density, <1g/ml) and heavier-than-water (density, >1g/ml) microspheres of 85:15 poly(lactide-co-glycolide). We quantified the rate of 3D flow through the scaffolds by using a particle-tracking system, and the results suggest that motion trajectories and, therefore, the flow velocity around and through scaffolds in rotating bioreactors can be manipulated by varying the ratio of heavier-than-water to lighter-than-water microspheres. When rat primary calvarial cells were cultured on the scaffolds in bioreactors for 7 days, the 3D dynamic flow environment affected bone cell distribution and enhanced cell phenotypic expression and mineralized matrix synthesis within tissue-engineered constructs compared with static conditions. These studies provide a foundation for exploring the effects of dynamic flow on osteoblast function and provide important insight into the design and optimization of 3D scaffolds suitable in bioreactors for in vitro tissue engineering of bone.

Flow-induced twist-compression in a twisted nematic cell.

An optical convergent-beam guided-wave technique is used to explore in detail the dynamic flow effects in a twisted nematic cell. During switch-on it is found that the dynamic flow compresses the director twist to regions close to the cell walls. For high fields this twist compression takes the cell far beyond the Mauguin limit and it no longer effectively guides the polarization of the light through the cell. This results in a very fast switch to a transient dark state.

Advances in Tightly Coupled Reservoir/ Wellbore/Surface-Network Simulation

Summary One of the most perplexing and difficult challenges in the industry is deciding how to develop a new oil or gas field. It is necessary to estimate recoverable reserves, design the most efficient exploitation strategy, decide where and when to drill wells and install surface facilities, and predict the rate of production. This requires a clear understanding of energy distribution and fluid movements throughout the entire system, under any given operational scenario or market-demand situation. Even after a reservoir-development plan is selected, there are many possible facility designs, each with different investment and operating costs. An important, but not always considered, fact is that each facility scheme could result in different future production rates owing to various types, sizes, and configurations of fluid-flow facilities. Selecting the best design for the asset requires the most accurate production forecasts possible over the forecast life cycle. No other single technology has the ability to provide this insight, as well as tightly coupled reservoir and facility simulation, because it combines all pertinent geological and engineering data into a single, comprehensive, dynamic model of the entire oilfield flow system. An integrated oilfield simulation system accounts for all dynamic flow effects and provides a test environment for quickly and accurately comparing alternative designs. This paper provides a brief background of this technology and gives a review of a major development project where it is currently being applied. Finally, we describe some recent significant advances in the technology that make it more stable, accurate, and rigorous.

The representation of dynamic flow effects in a Lagrangian puff dispersion model

A technique for incorporating buoyancy-driven dynamics in a Lagrangian puff model is described. The dynamic effects are non-linear and therefore proper treatment requires interaction integrals for overlapping puffs. Conservation laws for the volume integral of momentum and buoyancy over an individual puff are based on the fundamental equations of motion. A simplified representation of the field of motion associated with the buoyancy-driven dynamics is then used to move and distort the puffs. The effects associated with dense gas `slumping' on the ground are represented by lateral divergence of the velocity field, with a magnitude based on conservation of the moment of vorticity. The model predictions are compared with a number of experimental results on buoyant plume rise and dense gas dispersion.

Peroxyoxalate chemiluminescence detection in capillary electrophoresis

The feasibility of employing peroxyoxalate chemiluminescence (PO-CL) detection in capillary electrophoresis (CE) was demonstrated using a two- step approach for the CE separation and dynamic elution (elution under pressure) of the analytes. In this approach, potential problems associated with incompatibilities between mixed aqueous-organic solvent and clectrically driven separation systems were avoided by switching off the CE power supply at an appropriate time and connecting the CE capilliary to a syringe pump to effect dynamic elution. The effect of dynamic flow- rate and PO-CL reagent concentration on the CL signal intensity and/or peak width were examined for the measurements of three dansylated amino acids. The average limit of detection for these analytes using this PO-CL method is about 1.2 fmol ( ca. 85 nM) which is approximately 35-fold lower than UV absorption methods.