Variable Fluid Flow Research Articles

Optimal design and its mixing process analysis of a novel rotor for claw vacuum pumps

Due to the particular structure of a pair of intermeshing claw rotors, the working process of claw vacuum pump includes an inevitable mixing process, which increases power consumption and reduces pump efficiency. In order to reduce the negative effects of the mixing process on pump performance, this paper presented a novel eccentric involute claw rotor (EICR) based on the performance analysis of the mixing process of the conventional claw rotor. A geometric model of the proposed EICR was established, and effects of geometric parameters on pump performance were discussed. The working characteristics of the EICR were analyzed and compared with the conventional claw rotor. The internal flow fields of the claw vacuum pump with the EICR were illustrated through numerical simulations, and the fluid flow variation of gas pressure inside a working chamber was analyzed. Results show that the EICR reduces carryover volume by 17.97% compared with the conventional claw rotor; meanwhile, multiple working chambers proceeding over-compression and expansion process of the conventional claw rotor are changed into one working chamber of the EICR during the mixing process. Therefore, the EICR dramatically improves the pump performance, and effectively alleviates the adverse effects of the mixing process.

Impacts of Mineralogy on Petrophysical Properties

Because of their extreme heterogeneity at multiple scales, carbonate rocks present a great challenge for studying and managing oil reservoirs. Depositional processes and diagenetic alterations of carbonates may have produced very complex pore structures and, consequently, variable fluid storage and flow properties of hydrocarbon reservoirs. To understand the impact of mineralogy on the pore system, we analyzed four carbonate rock samples (coquinas) from the Morro do Chaves Formation in Brazil. For this study, we used thin sections and XRD for their mineralogical characterization, together with routine core analysis, NMR, MICP and microCT for the petrophysical characterizations. The samples revealed very similar porosity values but considerably different permeabilities. Samples with a relatively high quartz content (terrigenous material) generally had lower permeabilities, mostly caused by more mineral fragmentation. Samples with little or no quartz in turn exhibited high permeabilities due to less fragmentation and more diagenetic actions (e.g., dissolution of shells). Results confirm that carbonate minerals are very susceptible to diagenesis, leading to modifications in their pore body and pore throat sizes, and creating pores classified as moldic and vug pores, or even clogging them. For one of the samples, we acquired detailed pore skeleton information based on microCT images to obtain a more complete understanding of its structural characteristics.

Piezo Capsule: Ultrasonic Way of Wireless Pressure Measurement

Heart failure (HF) rates elevate worldwide with the aging population. Miniaturized and wireless implants with real‐time data transfer capability can alleviate the surgical complexities of cardiac pressure monitoring. Despite recent developments of mm‐size implants with complex circuitries and self‐powering units, a simple, passive, and effective implant design for the real‐time pressure reading is missing. Here, the piezo capsule, a simple, cost‐effective, and miniaturized passive ultrasound pressure sensing system, is introduced. The capsule design consists of a 1 mm‐cube‐sized lead zirconate titanate (PZT) transducer and a T‐shaped mechanical pin. The impedance changes of an interrogating ultrasound probe, which is ultrasonically coupled to the receiver implant, correlate to the electrical/mechanical loading of the piezo capsule. The ultrasonic sensing properties of the proposed device are characterized across a hard‐solid medium (e.g., plexiglass) and soft tissue‐like media (e.g., polydimethylsiloxane (PDMS) and chicken breast tissue) and verified the impedance changes using finite element simulations. Last, dynamic wireless pressure readings of an artificial vessel for varying fluid flow pulse‐frequency and volumetric rate are demonstrated. The sensitivity of 0.375 Ω kPa−1is achieved as the pressure changed from 14 to 86 kPa and pulse frequency from 0 to 100 bpm with a fixed flow rate of 8 mL min−1.

A 3D printed photoreactor for investigating variable reaction geometry, wavelength, and fluid flow.

Research in the field of photochemistry, including photocatalysis and photoelectrocatalysis, has been revitalized due to the potential that photochemical reactions show in the sustainable production of chemicals. Therefore, there is a need for flexible photoreactor equipment that allows for the evaluation of the geometry, light wavelength, and intensity of the vessel, along with the fluid flow in various photochemical reactions. Light emitting diodes (LEDs) have narrow emission spectra and can be either pulsed or run continuously; being flexible, they can be arranged to fit the dimensions of various types of the reactor vessel, depending on the application. This study presents a 3D printed photoreactor with the ability to adjust distances easily and switch between high-power LED light sources. The reactor design utilizes customized printed circuit boards to mount varying numbers and types of LEDs, which enables multiple wavelengths to be used simultaneously. These LED modules, comprised of heat sinks and cooling fans, fulfill the higher heat dissipation requirements of high-power LEDs. The flexibility of the reactor design is useful for optimizing the reaction geometry, flow conditions, wavelength, and intensity of photochemical reactions on a small scale. The estimates for incident light intensity under five possible reactor configurations using ferrioxalate actinometry are reported so that comparisons with other photoreactors can be made. The performance of the photoreactor for differing vessel sizes and distances, in both the flow and batch modes, is given for a photochemical reaction on 2-benzyloxyphenol-a model substance for lignin and applicable in the production of biobased chemicals.

Emergent evolutionary forces in spatial models of luminal growth and their application to the human gut microbiota

The genetic composition of the gut microbiota is constantly reshaped by ecological and evolutionary forces. These strain-level dynamics are challenging to understand because they depend on complex spatial growth processes that take place within a host. Here we introduce a population genetic framework to predict how stochastic evolutionary forces emerge from simple models of microbial growth in spatially extended environments like the intestinal lumen. Our framework shows how fluid flow and longitudinal variation in growth rate combine to shape the frequencies of genetic variants in simulated fecal samples, yielding analytical expressions for the effective generation times, selection coefficients, and rates of genetic drift. We find that over longer timescales, the emergent evolutionary dynamics can often be captured by well-mixed models that lack explicit spatial structure, even when there is substantial spatial variation in species-level composition. By applying these results to the human colon, we find that continuous fluid flow and simple forms of wall growth alone are unlikely to create sufficient bottlenecks to allow large fluctuations in mutant frequencies within a host. We also find that the effective generation times may be significantly shorter than expected from traditional average growth rate estimates. Our results provide a starting point for quantifying genetic turnover in spatially extended settings like the gut microbiota and may be relevant for other microbial ecosystems where unidirectional fluid flow plays an important role.

Fluid Flow Induces Differential Detachment of Live and Dead Bacterial Cells from Nanostructured Surfaces.

Nanotopographic surfaces are proven to be successful in killing bacterial cells upon contact. This non-chemical bactericidal property has paved an alternative way of fighting bacterial colonization and associated problems, especially the issue of bacteria evolving resistance against antibiotic and antiseptic agents. Recent advancements in nanotopographic bactericidal surfaces have made them suitable for many applications in medical and industrial sectors. The bactericidal effect of nanotopographic surfaces is classically studied under static conditions, but the actual potential applications do have fluid flow in them. In this study, we have studied how fluid flow can affect the adherence of bacterial cells on nanotopographic surfaces. Gram-positive and Gram-negative bacterial species were tested under varying fluid flow rates for their retention and viability after flow exposure. The total number of adherent cells for both species was reduced in the presence of flow, but there was no flowrate dependency. There was a significant reduction in the number of live cells remaining on nanotopographic surfaces with an increasing flowrate for both species. Conversely, we observed a flowrate-independent increase in the number of adherent dead cells. Our results indicated that the presence of flow differentially affected the adherent live and dead bacterial cells on nanotopographic surfaces. This could be because dead bacterial cells were physically pierced by the nano-features, whereas live cells adhered via physiochemical interactions with the surface. Therefore, fluid shear was insufficient to overcome adhesion forces between the surface and dead cells. Furthermore, hydrodynamic forces due to the flow can cause more planktonic and detached live cells to collide with nano-features on the surface, causing more cells to lyse. These results show that nanotopographic surfaces do not have self-cleaning ability as opposed to natural bactericidal nanotopographic surfaces, and nanotopographic surfaces tend to perform better under flow conditions. These findings are highly useful for developing and optimizing nanotopographic surfaces for medical and industrial applications.

Numerical Investigation on the Effect of Geometric Shape and Outlet Angle of a Bladeless Fan for Flow Optimization using CFD Techniques

A three dimensional numerical study has been carried out to investigate the effect of various geometric shapes and slit angle on performance of the bladeless fan for various aerodynamic profiles. Aerofoils considered for the present study are E169, E473 and E479 which are then reformed into a typical bladeless fan arrangement. The numerical model of bladeless fan encompassing the outer domain is discretized tetrahedrally through finite volume approach using ANSYS ICEMCFD 20.0 and the necessary boundary conditions are specified in the ANSYS Fluent 20.0 pre-processor. The three dimensional fluid flow variations through and across the aerofoil have been simulated by solving the appropriate governing equations namely continuity and Reynolds Averaged Navier-Stokes equations (RANS). The turbulence induced in the fluid is modelled using SST k-ωmode of closure. Numerically predicted results of lift, drag and streamwise velocity decay along the jet centreline of a cylindrical channel are compared with literature and a very close agreement exists between the two. Upon validation, geometric shapes - circular and square cross section with aspect ratios of 1, 1,5 and 2 and slit angles of 20, 40, 60 and 80 degree for all the above three aerofoil configurations are analysed numerically for various inlet Reynolds number. Pressure, velocity contours and stream line across the bladeless fan are presented and discussed. From the study it is observed that Eppler 473 aerofoil profile with slit thickness of 1 mm and slit angle of 80° provided the maximum discharge ratio of 34.17 for an inlet mass flow rate of 80 LPS.

An investigation of variable viscosity Carreau fluid and mixed convective stagnation point flow

An investigation of variable viscosity Carreau fluid and mixed convective stagnation point flow

Fluid simulations provide more comprehensive view of cellular-level dynamics in bone

Turning attention to the pericellular matrix surrounding osteocytes, and the irregular features of the lacuna-canalicular networks that connect them, better mimics varying fluid flow found in vivo.

Extracellular Fluid Flow Induces Shallow Quiescence Through Physical and Biochemical Cues.

The balance between cell quiescence and proliferation is fundamental to tissue physiology and homeostasis. Recent studies have shown that quiescence is not a passive and homogeneous state but actively maintained and heterogeneous. These cellular characteristics associated with quiescence were observed primarily in cultured cells under a static medium. However, cells in vivo face different microenvironmental conditions, particularly, under interstitial fluid flows distributed through extracellular matrices. Interstitial fluid flow exerts shear stress on cells and matrix strain, and results in continuous replacement of extracellular factors. In this study, we analyzed individual cells under varying fluid flow rates in microfluidic devices. We found quiescence characteristics previously identified under conventional static medium, including serum signal-dependant quiescence entry and exit and time-dependant quiescence deepening, are also present under continuous fluid flow. Furthermore, increasing the flow rate drives cells to shallower quiescence and become more likely to reenter the cell cycle upon growth stimulation. This effect is due to flow-induced physical and biochemical cues. Specifically, increasing shear stress or extracellular factor replacement individually, without altering other parameters, results in shallow quiescence. We show our experimental results can be quantitatively explained by a mathematical model connecting extracellular fluid flow to an Rb-E2f bistable switch that regulates the quiescence-to-proliferation transition. Our findings uncover a previously unappreciated mechanism that likely underlies the heterogeneous responses of quiescent cells for tissue repair and regeneration in different physiological tissue microenvironments.

A Distal, High-grade Irish-type Orebody: Petrographic, Sulfur Isotope, and Sulfide Chemistry of the Island Pod Zn-Pb Orebody, Lisheen, Ireland

AbstractIrish-type Zn-Pb deposits are important global sources of zinc, but despite a fundamental understanding of ore genesis within the Irish orefield, a detailed understanding of fluid migration and chemical evolution pathways related to sulfide and carbonate precipitation is lacking. We present the first petrographic, paragenetically constrained sulfur isotope and mineral chemistry study of mineralization at the Island Pod orebody, Lisheen deposit. The Island Pod orebody comprises high-grade mineralization that is less deformed than elsewhere in the Irish orefield. Consequently, studies of the Island Pod orebody and its mineralization provide information on the evolving nature of hydrothermal fluids involved in ore deposition.The Island Pod orebody consists almost exclusively of pyrite, sphalerite, and galena, with several stages of calcite and dolomite precipitation. Pre-ore, diagenetic pyrite is commonly overgrown by early main ore-stage pyrite, with both phases frequently replaced by main ore-stage sphalerite. In many cases, early main ore-stage pyrite is texturally zoned and exhibits chemical zoning patterns, reflecting that episodic influxes of hydrothermal fluids contained variable concentrations of As, Co, Ni, and Tl. The main ore stage was dominated by the formation of sphalerite and galena from mineralizing fluids that were depleted in these trace elements (e.g., As, Co, Tl) compared to the early main ore stage. Sulfur isotope analysis reveals four distinctive but slightly overlapping isotopic groupings, corresponding to different mineral and paragenetic stages: (1) δ34S values range from –47.7 to –30.7‰, associated with diagenetic pyrite; (2) δ34S values range from –34.3 to –14.7‰, related to early main ore-stage pyrite; (3) δ34S values range from –15.5 to +1.7‰, corresponding to main ore-stage sphalerite; and (4) δ34S values range from –11.1 to +17.4‰, associated with galena. Large variations in S isotope composition are common at intragrain and at other small spatial scales. The textures, paragenetic sequence, and ranges in δ34S values are consistent with hydrothermal sulfide deposition where the fluids containing bacteriogenic sulfide mixed with metal-bearing fluids. Replacement and remobilization from other Lisheen orebodies may have contributed to some of the higher sulfur isotope ratios observed in the Island Pod orebody.The excellent preservation of sulfide textures in the Island Pod orebody observed during this study demonstrates that it is an ideal location to study hydrothermal fluid evolution, including episodic fluid flow, mixing, precipitation, and compositional variations during the early main ore stage. In other Irish Zn-Pb orebodies, these early-ore textures are often obscured due to more complex dissolution and replacement processes, making interpretation of the early hydrothermal activity challenging. Consequently, the petrographic, mineral chemistry, and sulfur isotope studies of the Island Pod orebody presented here contribute to an enhanced understanding of ore-forming processes in similar deposits, where mineralization is often associated with more complex deformation or repeated pulses of hydrothermal activity.

A unified modelling and simulation for coupled anomalous transport in porous media and its finite element implementation

This paper presents an unified mathematical and computational framework for mechanics-coupled “anomalous” transport phenomena in porous media. The anomalous diffusion is mainly due to variable fluid flow rates caused by spatially and temporally varying permeability. This type of behaviour is described by a fractional pore pressure diffusion equation. The diffusion transient phenomena is significantly affected by the order of the fractional operators. In order to solve 3D consolidation problems of large scale structures, the fractional pore pressure diffusion equation is implemented in a finite element framework adopting the discretised formulation of fractional derivatives given by Grunwald–Letnikov (GL). Here the fractional pore pressure diffusion equation is implemented in the commercial software Abaqus through an open-source UMATHT subroutine. The similarity between pore pressure, heat and hydrogen transport is also discussed in order to show that it is possible to use the coupled thermal-stress analysis to solve fractional consolidation problems.

Gunshot wound to the lumber spine – Autopsy based case report

Since their origin from China, firearms have gained popularity because of easy techniques and effectiveness. This has made them a popular choice of homicide and suicide. Here we present a case where the death is by shooting from a pistol from a point blank range. Bullet takes a crazy course once entered inside the body due to the variation in fluid flow, densities of various organs and air filled cavities. It becomes all the more difficult if there is surgical manipulation. Radiographs were done to have an idea about the place of lodgment of bullet in body. The advent of various radiographic methods like computer tomography and radiography have made the job of autopsy surgeon a little bit easier.

Live record of vortex-shaped flow by microgravity solidification

A unique type of vortex-shaped microstructure reflecting the flow pattern during the microgravity solidification formed in Al70Ag20Ge10 alloy droplets using drop tube technique. A 2D axisymmetric model coupling heat transfer, fluid flow with phase change was established to simulate the fluid flow variation of alloy droplets during microgravity solidification. The Stokes motion was suppressed and the Marangoni motion was prominent in driving the vortex-shaped flow. The melt flow affected the phase selection, consequently the Ag2Al phase nucleated primarily instead of (Al) phase under near-equilibrium solidification, and the flow pattern was preserved during the rapid growth of the metastable Ag2Al dendrites. The Marangoni effect was weakened with the decrease of droplet size, and anomalous (Al) + Ag2Al and intergranular (Al) + (Ge) eutectics formed owing to the enhanced nucleation and growth competition among phases. In comparison, Al70Ag20Ge10 alloy was solidified under gravity condition by DSC and vacuum arc melting methods respectively. No vortex-shaped microstructure formed in DSC sample ascribed to the suppressed natural convection at small cooling rate. During arc melting, the electromagnetic force and enhanced natural convection caused strong turbulent flow, the metastable Ag2Al dendrites rapidly formed with increased vortex density.

Variable fluid flow regimes alter human brain microvascular endothelial cell-cell junctions and cytoskeletal structure.

The human brain microvasculature is constantly exposed to variable fluid flow regimes and their influence on the endothelium depends in part on the synchronous cooperative behavior between cell-cell junctions and the cytoskeleton. In this study, we exposed human cerebral microvascular endothelial cells to a low laminar flow (1 dyne⋅cm-2 ), high laminar flow (10 dyne⋅cm-2 ), low oscillatory flow (±1 dyne⋅cm-2 ), or high oscillatory flow (±10 dyne⋅cm-2 ) for 24 hr. After this time, endothelial cell-cell junction and cytoskeletal structural response was characterized through observation of zonula occludens-1 (ZO-1), claudin-5, junctional adhesion molecule-A (JAM-A), vascular endothelial cadherin (VE-Cad), and F-actin. In addition, we also characterized cell morphology through measurement of cell area and cell eccentricity. Our results revealed the greatest change in junctional structure reorganization for ZO-1 and JAM-A to be observed under low laminar flow conditions while claudin-5 exhibited the greatest change in structural reorganization under both low and high laminar flow conditions. However, VE-Cad displayed the greatest structural response under a high laminar flow, reflecting the unique responses each cell-cell junction protein had to each fluid flow regime. In addition, cell area and cell eccentricity displayed most significant changes under the high laminar flow and low oscillatory flow, respectively. We believe this study will be useful to the field of cell mechanics and mechanobiology.

MODELING AND SIMULATION OF A HORIZONTAL THREE-PHASE SEPARATOR: INFLUENCE OF PHYSICOCHEMICAL PROPERTIES OF OIL

Fluids produced from oil reservoirs typically contain oil, natural gas, water, sediments, in varying amounts, and contaminating gases. Considering that economic interest usually targets mostly oil and gas, primary processing is used to separate water/oil/gas, in addition to treating these phases. Therefore, the well stream should be processed as soon as possible after reaching the surface. Separator vessels are among the main equipment used at surface production facilities, being responsible for the separation of the produced phases. This work focuses on studying the fluid dynamic behavior in a horizontal three-phase separator. To accomplish this goal, we used the computer fluid dynamics software ANSYS CFX. First, we performed a detailed analysis of a “Standard Case” to understand in detail the entire separation process within the vessel. The results show the three phases through the simulation time, analyses of the separation efficiency, different fluids flow lines, pressure gradient inside the vessel, and effect of the diverter baffle. It also considers a variation of fluid flow at the inlet of the separator. These analyses include pictures of all cases studied. Afterwards, some parameters of the standard case were altered to evaluate its influence on fluid dynamics behavior and the functioning of the separator vessel. At last, we analyzed the influences of oil density and viscosity on the separation. The oil quality affects the primary separation directly, as the oil density and viscosity increase, for example, increases the drag between the fluids and decreases the rate of sedimentation, which stickles the separation process difficult. Two out of the three cases generated satisfactory results. The simulation with the heaviest oil presented the worse results.

Simulation of Copper Electrodeposition in Millimeter Size Through-Silicon Vias

Computational predictions of copper deposition in millimeter size through-silicon vias (mm-TSV) are presented based on localized breakdown of a co-adsorbed polyether-chloride suppressor layer. The model builds upon previous work on localized Cu deposition in microscale TSV and through-holes by incorporating 3D fluid flow calculations to more effectively evaluate chemical transport of cupric ion and additives, both of which are critical to adlayer formation and disruption within the via. Simulations using potentiostatic and potentiodynamic waveforms are compared to previously reported filling experiments. Alternatively, the utility of galvanostatic control and variations in fluid flow are explored computationally. For appropriate applied potential(s) or current, deposition is localized to the via bottom, with subsequent growth proceeding in a bottom-up fashion. Selection of inappropriate current or potential waveforms, or forced convection conditions that supply insufficient cupric ion to the bottom of the via, results in prediction of voids. Simulations of deposition in via arrays (4 × 1) predict non-uniform growth across the arrays, with the passivation of individual vias associated with minor variations in convective flow and/or numerical perturbations in the simulation, that reflects the critical nature of the bifurcation process.

MODELING AND SIMULATION OF A HORIZONTAL THREE-PHASE SEPARATOR: INFLUENCE OF INLET FLOW

The fluids produced and transported to the surface by the production manifolds do not have the necessary conditions to be economically viable. Produced fluids consist of at least three fluid phases (oil, water, and gas), besides impurities and contaminants. Therefore, the well stream should be processed as soon as possible after bringing it to the surface. Separator vessels are among the main equipment used at surface production facilities, being responsible for the separation of the produced phases. This work focuses in studying the fluid dynamic behavior in a horizontal three-phase separator. For this, we used the computational fluid dynamics software ANSYS CFX. First, a detailed analysis of a “Standard Case” was performed to better understand the entire separation process within the vessel. The results showed the three phases through simulation time, an analysis of the separation efficiency, an analysis of the different fluids flow lines, an analysis of the pressure gradient inside the vessel, and an analysis of the effect of the diverter baffle, as well as, a variation of fluid flow at the inlet of the separator.

A study on effects of slug flow on dynamic response and fatigue damage of risers

A slug flow (a series of liquid slug separated by a gas pocket) is a flow pattern that often occurs in a multiphase oil and gas riser system. Dynamic and structural responses of a riser can be increased by time varying forces of the slug flow. In this paper, a methodology has been developed for the evaluation of the effects of slug flow on the dynamic and structural responses of different types of risers. A global dynamic analysis is carried out to calculate the dynamic responses of a riser induced by the slug flow and environmental loads. Idealized regular slug flow are considered as a time dependent variation of internal fluid flow according to results of multiphase flow simulations. Local stress and fatigue damage of risers are estimated using an in-house program, which considered the hysteresis effects of a flexible riser. The verifications of the numerical model and slug modeling method are carried out prior to the parametric study. Parametric studies are performed in order to quantitatively identify the design conditions that are most affected by the slug flow. The riser system connected to a moored vessel in deep-water is considered for the parametric study. Different riser materials, riser configurations, production stages (flow rates) and environmental conditions are considered. Study results demonstrate that the dynamic effects due to slug flow are significant for a flexible lazy wave riser, middle production stage and mild sea states. While the maximum value of dynamic loads is slightly changed even with considerable slug flow, range of fluctuation (standard deviation) of bending curvature is substantially increased under mild sea states with high probability of occurrence. This means that a main impact of the slug flow is the increased fatigue damage of a riser structure. The fatigue damage with and without slug flow has been estimated in order to investigate the fatigue contribution of the slug flow.

Inferring rheology and geometry of subsurface structures by adjoint-based inversion of principal stress directions

SUMMARY Imaging subsurface structures, such as salt domes, magma reservoirs or subducting plates, is a major challenge in geophysics. Seismic imaging methods are, so far, the most precise methods to open a window into the Earth. However, the methods may not yield the exact depth or size of the imaged feature and may become distorted by phenomena such as seismic anisotropy, fluid flow, or compositional variations. A useful complementary method is therefore to simulate the mechanical behaviour of rocks on large timescales, and compare model predictions with observations. Recent studies have used the (non-linear) Stokes equations and geometries from seismic studies in combination with an adjoint-based approach to invert for rheological parameters that are consistent with surface observations such as GPS velocities. Nevertheless, it would be useful to use other surface observations, such as principal stress directions, as constraints as well. Here, we derive the adjoint formulation for the case that principal stress directions are used as observables with respect to rheological parameters. Both an algebraic and a discretized derivation of the adjoint equations are described. This thus enables the usage of two data fields - surface velocities and stress directions - as a misfit for the inversion. We test the performance of the inversion for principal stress directions on simplified 3-D test cases. Finally, we demonstrate how the adjoint approach can be used to compute 3-D geodynamic sensitivity kernels, which highlight the areas in the model domain that have the largest impact on the misfit value of a particular point. This provides a simple, yet powerful, way to visualize which parts of the model domain are of key importance if changing rheological constants.