Fluid Flow Conditions Research Articles

Stability analysis of unsaturated slopes under elevated temperatures

Several natural and man-made phenomena (e.g., droughts, wildfires, shallow geothermal technologies) can subject unsaturated slopes to elevated temperatures. However, the impact of temperature on the stability of unsaturated slopes is not well understood. This study aims to examine the stability of unsaturated intact slopes under elevated temperatures. An analytical framework is developed to calculate the factor of safety (FOS) of unsaturated slopes under steady fluid flow conditions at various temperatures. The theoretical basis of the framework is built upon the concept that, within the temperatures range investigated, the influence of temperature on the soil's shear strength is primarily attributed to thermal induced changes in apparent cohesion stemming from matric suction. Temperature dependency of apparent cohesion is quantified by employing temperature-dependent soil-water retention curve (SWRC) and effective stress models, which are then integrated into an infinite slope stability analysis of unsaturated soils under steady flow. A saturation-dependent thermal conductivity is used to obtain the temperature profile versus depth. The formulations are used to determine FOS for intact slopes with different hypothetical soils including sand, silt, and clay at surface temperatures of 25, 40, and 55 °C under different steady flow rates. Results show that the effective stress, shear strength, and FOS increase by increasing temperature from 25 °C to 55 °C. Results reveal that the effect of temperature on the stability of clayey and silty slopes can be considerable. The proposed models are validated against two sets of laboratory-measured data from the literature. The presented model provides a simple and effective method for site-specific and regional-scale stability analyses of unsaturated slopes under different thermal and seepage conditions.

Analytical Method for Fluid-Solid Coupling Vibration Analysis of Hydraulic Pipeline System with Hinged Ends

The vibrations in hydraulic pipeline systems inevitably involve the interaction between the two-phase media of a solid and fluid. The fluid flowing in the pipeline generates pressure on the pipeline wall and thus causes vibration and deformation in the pipeline, which in turn changes the fluid flow condition, thereby cyclically affecting the deformation and motion of the solid and fluid and making the pipeline system vulnerable to vibration damage. Therefore, it is of great theoretical and practical value to investigate the vibration behavior and characteristics of hydraulic pipeline systems. In this study, the fluid flow-induced vibrations in a pipeline system are investigated based on Housner’s differential vibration equation of fluid pipelines. Through the application of relevant mathematical theories and methods, the derivation of the inherent characteristics and dynamic behavior of a hydraulic pipeline system with two hinged ends is simplified, and the corresponding equations for the natural frequencies and dynamic response of the system are obtained. The analytical method for analyzing the vibration behavior and characteristics of the system is presented, and the analytical results of the vibration analysis of the system are obtained through computer simulation, providing a theoretical and technical basis for the safe and reliable operation of the hydraulic pipeline system.

Finite element study of stem cells under fluid flow for mechanoregulation toward osteochondral cells

Investigating the effects of mechanical stimuli on stem cells under in vitro and in vivo conditions is a very important issue to reach better control on cellular responses like growth, proliferation, and differentiation. In this regard, studying the effects of scaffold geometry, steady, and transient fluid flow, as well as influence of different locations of the cells lodged on the scaffold on effective mechanical stimulations of the stem cells are of the main goals of this study. For this purpose, collagen-based scaffolds and implicit surfaces of the pore architecture was used. In this study, computational fluid dynamics and fluid-structure interaction method was used for the computational simulation. The results showed that the scaffold microstructure and the pore architecture had an essential effect on accessibility of the fluid to different portions of the scaffold. This leads to the optimization of shear stress and hydrodynamic pressure in different surfaces of the scaffold for better transportation of oxygen and growth factors as well as for optimized mechanoregulative responses of cell–scaffold interactions. Furthermore, the results indicated that the HP scaffold provides more optimizer surfaces to culture stem cells rather than Gyroid and IWP scaffolds. The results of exerting oscillatory fluid flow into the HP scaffold showed that the whole surface of the HP scaffold expose to the shear stress between 0.1 and 40 mPa and hydrodynamics factors on the scaffold was uniform. The results of this study could be used as an aid for experimentalists to choose optimist fluid flow conditions and suitable situation for cell culture.

Validation of droplet-generation performance of a newly developed microfluidic device with a three-dimensional structure

We fabricated a microfluidic device with a three-dimensional (3D) structure and verified its droplet-generation performance for the stable production of droplets of around 10 μm in size. We compared the performance of the 3D device with that of conventional simple T-junction and cross-junction structures. The continuous phase sheared the dispersed phase into droplets from eight directions in the 3D device, compared with only one direction in the T-junction device and two in the cross-junction device. Droplets were produced efficiently over a wide range of fluid properties and flow conditions with the 3D device, unlike with the two conventional planar devices. Fluidic experiments were conducted using mineral oil with a surfactant as the continuous phase, deionized (DI) water as the dispersed phase, and DI water with glycerin to change the viscosity of the dispersed phase. The minimum droplet length was 47.2 μm in the T-junction device, 39.0 μm in the cross-junction device, and 22.4 μm in the 3D device when using a water and glycerin mixture with a viscosity of 9.0 mPa·s. Compared with the conventional devices, smaller droplets were produced using our 3D device, indicating that it has excellent droplet-generation performance.

Determination of Intrinsic Drug Dissolution and Solute Effective Transport Rate during Laminar Fluid Flow at Different Velocities.

The objective of this study was to determine the intrinsic drug dissolution rate (IDR) and the solute effective transport rate of some drugs, using a single particle dissolution technique, satisfying qualified dissolution conditions. The IDR of three poorly water-soluble compounds was measured in milli-Q water using four different fluid velocities. The enveloped surface area of the particles was calculated from the projected area and the perimeter of the particle observed in the microscope. Furthermore, computational fluid dynamics (CFD) simulations were used to theoretically investigate the flow conditions and dissolution rate, comparing box shaped particles and spherical particles with similar dimensions and surface area as the particles used the experiments. In this study, the IDR measurement of the single particles was determined within 5–60 min using particles with an initial projected area diameter () between 37.5–104.6 µm. The micropipette-assisted microscopy technique showed a good reproducibility between individual measurements, and the CFD simulations indicated a laminar flow around the particles at all flow velocities, even though there were evident differences in local particle dissolution rates. In conclusion, the IDR and solute effective transport rate were determined under well-defined fluid flow conditions. This type of approach can be used as a complementary approach to traditional dissolution studies to gain in-depth insights into the dissolution process of drug particles.

Operation improvement of sequencing FED-batch wastewater treatment

AbstractSequencing batch reactor systems in wastewater treatment is widely applied activated sludge technology. The system performance is not only dependent on the raw sewage quality and biochemical processes, but the flow pattern within the reactor has a significant impact on the treatment itself. The varying stages of the operation require different fluid flow conditions; biological stage shall be appropriately mixed, whereas low velocity zones favor the phase separation. The aim of this study was to improve sequencing batch reactor operation in order to optimize the treatment efficiency. Numerical fluid dynamic simulations were performed to determine the substrate and biomass homogeneity inside the reactor at the biological phase and the rate of the decantation was estimated at the sedimentation phase. The settling model was calibrated by field measurements. The results revealed that the hydraulic efficiency of the reactor was 87% and the achievable settled solid content was 0.9%.

Numerical Simulation of Hydraulic Turbine During Transient Operation Using OpenFOAM

Power generation from intermittent renewable energy resources (e.g. wind, solar) requires regulation of the electric grid. Although most hydraulic turbines are designed to work in their best efficiency points, nowadays they are being used more often under varying operating conditions to stabilize the electric grid. Unstable and varying conditions of fluid flow in hydraulic turbines during transient operation cause significant pressure fluctuations and load variations that could negatively affect the turbine lifetime. Therefore, the development of high-fidelity numerical tools for hydraulic turbine flow during transient operation, i.e. changing from one condition to another or during start-up and shut-down, is of great importance for the lifetime prediction of the machines.In the present work, we are investigating the capabilities of the OpenFOAM open-source CFD tool to predict such phenomena. The transient operation of hydraulic turbines most of the time involves changing the guide vane angles while the runner is rotating, which must thus also be allowed by the employed numerical techniques. The high-head Francis-99 turbine is used as a test case, due to the availability of the geometry and rich experimental data. The turbulence resolving computations are performed using the SAS turbulence model. The numerical results are validated against the experimental data and compared with each other in terms of accuracy and usability. The results are also used for describing the flow behaviors during the shutdown.

THM response of a borehole in naturally fractured media

The response of a circular borehole to a constant fluid flow rate and a temperature step-change in a coupled hydraulic-thermal-mechanical system is formulated and quantified. A new coupled formulation is developed, based on a dual-porosity model to simulate a naturally fractured stratum under non-isothermal and two-phase fluid flow conditions. The semi-analytical closed-form solutions for pore pressure, temperature and stresses including rotational displacement effects are developed by coupling an averaged conductive heat transfer process and extended single-phase Darcy fluid flow in both fracture and matrix systems. Deformations and stress changes can be induced on the bulk skeleton during a temperature change, potentially leading to shear and tensile mechanical yield. Effective stresses on the borehole wall corresponding to either fracture or shear yield initiation are calculated and explained. In a fractured medium, tensile and shear yield may initiate along the natural fractures thus take place earlier than in a continuum, displaced from the immediate borehole wall. A negative pore pressure near the wellbore may be induced during cold fluid injection when the thermally induced back flow volumes may surpass those from the injected fluid. Thus, unexpected higher effective compressive stresses may be induced on the wellbore wall, leading to yield or formation damage for the injection well. This semi-analytical development permits rapid assessment of potential fracturing initiation and shear yield to be analyzed for various cases such as injection and production in a geothermal extraction system, fluid waste disposal including CO2 sequestration, and oil and gas related EOR processes such as an initiation stage of hydraulic fracturing.

Coupled CFD–DEM numerical modelling of perforation damage and sand production in weak sandstone formation

A coupled microscopic simulation method was implemented to investigate the bond breakage behaviour during perforation and sand production in a weak cemented sandstone. A new contact bond model was implemented in the open-source program CFDEM to simulate a large cylindrical sample of one hundred thousand numerical particles using a high-performance computer (HPC) system. The coupled simulation of the particle–fluid phases and the information exchange between them required intensive computational power and highly efficient parallelization algorithms, yet it provided the detailed information on the distribution of bond and bond breakage, new contact formation, particle migration and the associated change in the internal porosity across the sample. The perforation process was found to create a damage zone that contained a compacted core of unbonded particles. The compacted core expanded quickly under fluid flow condition and released its particles to migrate towards the perforation tunnel. Small particles were produced first from the perforation damage zone, while fewer particles of larger sizes were produced later in an overall transient sand production phenomenon.

Experiments and mechanistic modeling of viscosity effect on a multistage ESP performance under viscous fluid flow

Assembled in series with multistage, Electrical Submersible Pumps (ESP) are widely used in offshore petroleum production due to the high production rate and efficiency. The hydraulic performance of ESPs is subjected to the fluid viscosity. High oil viscosity leads to the degradation of ESP boosting pressure compared to the catalog curves under water flow. In this paper, the influence of fluid viscosity on the performance of a 14-stage radial-type ESP under varying operational conditions, e.g. rotational speeds 1800–3500 r/min, viscosities 25–520 cP, was investigated. Numerical simulations were conducted on the same ESP model using a commercial Computational Fluid Dynamics (CFD) software. The simulated average pump head is comparable to the corresponding experimental data under different viscosities and rotational speeds with less than ±20% prediction error. A mechanistic model accounting for the viscosity effect on ESP boosting pressure is proposed based on the Euler head in a centrifugal pump. A conceptual best-match flowrate QBM is introduced, at which the impeller outlet flow direction matches the designed flow direction. The recirculation losses caused by the mismatch of velocity triangles and other head losses resulted from the flow direction change, friction loss and leakage flow etc., are included in the model. The comparison of model predicted pump head versus experimental measurements under viscous fluid flow conditions demonstrates good agreement. The overall prediction error is less than ±10%.

On the role of the powder stream on the heat and fluid flow conditions during Directed Energy Deposition of maraging steel—Multiphysics modeling and experimental validation

The Directed Energy Deposition (DED) process of metals, has a broad range of applications in several industrial sectors. Surface modification, component repairing, production of functionally graded materials and more importantly, manufacturing of complex geometries are major DED’s applications. In this work, a multi-physics numerical model of the DED process of maraging steel is developed to study the influence of the powder stream specifications on the melt pool’s thermal and fluid dynamics conditions. The model is developed based on the Finite Volume Method (FVM) framework using the commercial software package Flow-3D. Different physical phenomena e.g. solidification, evaporation, the Marangoni effect and the recoil pressure are included in the model. As a new feature, the powder particles’ dynamics are modeled using a Lagrangian framework and their impact on the melt pool conditions is taken into account as well. In-situ and ex-situ experiments are carried out using a thermal camera and optical microscopy. The predicted track morphology is in good agreement with the experimental measurements. Besides, the predicted melt pool evolution follows the same trend as observed with the online thermal camera. Furthermore, a parametric study is carried out to investigate the effect of the powder particles incoming velocity on the track morphology. It is shown that the height-to-width ratio of tracks increases while using higher powder velocities. Moreover, it is shown that by tripling the powder particles velocity, the height-to-width ratio increases by 104% and the wettability of the track decreases by 24%.

Analysis of convection heat transfer on multiscale rough superhydrophobic and liquid infused surfaces

Multiscale rough superhydrophobic or slippery liquid infused porous surfaces have gained much interest in recent years for their improved transport phenomena properties. While there have been several studies on drag reduction and condensation on non-wetting surfaces, convection heat transfer that is important in many thermal and thermochemical applications has not been addressed systematically. This article utilizes a fractal description of rough surface topographies to develop analytical models for the Nusselt number and the thermal hydraulic factor for fluid flow and heat transfer inside a cylinder with non-wetting surfaces. For air-infused superhydrophobic surfaces, the model considers the dynamic stability of the air/fluid interface in the asperities. Using the analytical formulations and the stability criteria, systematic studies are presented on the effects of the fractal surface parameters, cylinder radius and Reynolds number on the convective heat transfer characteristics, from which surface texture design maps are developed for maximizing the convection heat transfer. It is shown that multiscale non-wetting surfaces are most effective in the range of lower Reynolds number and small cylinder radius for achieving the best convective heat transfer and thermal hydraulic performance. Applying the models to actual non-wetting surface topographies fabricated using electrodeposition and chemical etching, it is shown that contrary to prevailing notion, superhydrophobicity, characterized by the highest contact angles, does not always lead to the maximum convective heat transfer performance, and that under certain fluid flow conditions, hydrophobic surfaces may offer a greater thermal performance.

Static and dynamic evaluation of a novel solution path on asphaltene deposition and drag reduction in flowlines: An experimental study

Asphaltene, as a destructive fraction of crude oil, reduces productivity by deposition in wells, pipelines and porous media and causes additional pressure drop on the fluid flow. The AUT-Force 110 multifunctional additive has been developed for the first time by the team of researchers of this paper, which has been identified as an inhibitor, dispersant and solvent for asphaltene sediment and its effectiveness has previously been proven. In this study, first, two crude oil sample from southwestern fields of Iran were selected. The selection criteria were differences in asphaltene molecular structure. The structure and molecular geometry of asphaltene have been determined using elemental analysis, Fourier-transform infrared spectroscopy (FTIR) and Carbon-13 (C13) nuclear magnetic resonance test. Then asphaltene was coated onto metal powder surface (crude oil pipeline simulator) by means of a unique process. The steel coated with asphaltene was then washed with AUT-Force 110 to determine its effectiveness in separating the asphaltene adsorbed onto the metal surface. SEM images clearly showed that the multifunctional additive, regardless of asphaltene type, was able to change the mechanism of asphaltene adsorption at the metal surface from multilayer to single layer. In addition, Energy-dispersive X-ray spectroscopy (EDX) demonstrated that in the presence of AUT-Force 110, iron (as the main constituent of metal powder) would increase by more than 12% in acidic asphaltene and more than 4% in basic asphaltene. AUT-Force 110 can also remove acidic and basic groups of asphaltene from metal powder surface by altering the electrostatic properties of the surface. The results of the spectroscopy showed that in addition to polar compounds, the multifunctional additive also reduces the amount of aliphatic and paraffinic functional groups at the surface of metal powder. In addition to static conditions, the efficiency of AUT-Force 110 in fluid flow condition was also investigated. For this purpose, two separate laboratory setups were designed and implemented. In the first setup, the surface charge of asphaltene flocs was determined in the presence of an electric field and the results of the zeta potential measurement test were verified. Asphaltene was often observed around the positive electrode (cathode), indicating that the predominant charge of asphaltene samples is negative. However, the higher the number of nitrogenous agents in asphaltene, the lower the amount of asphaltene accumulated around the cathode. In the second setup, a pipeline with accessories was designed to investigate the performance of the AUT-Force 110 as a drag force reducer in the pipeline. The reduction of drag force by AUT-Force 110 occurs with increasing fluid flow rate in the pipe. An increase in the flow rate is equivalent to growth in fluid flow turbulence, which could ultimately provide a better environment for drag reducer to function more efficiently.

A Review on Augmentation in Thermal Performance of Solar Air Heater

Low thermal efficiency is the remarkable drawback of solar air heaters. They have remarkable importance for low temperature applications. In a solar air heater due to formation of laminar sublayer between absorber plate and the flowing air convection coefficient of heat transfer is small. The laminar sublayer form on the absorber plate can be braked by applying the rib roughness of distinct shape and sizes due to which turbulence in the flowing air increases tremendously due to which friction factor increases between absorber plate and flowing air, resulting in increment in the convection coefficient of heat transfer and pressure drop. Design considerations of solar air heater, rib roughness geometries, fluid flow conditions and their effect on the turbulence, absorber plate temperature, convection coefficient of heat transfer and other thermo-hydraulic augmentation parameters have been minutely discussed. In this review, ongoing research and development on thermo-physical properties of solar air heater and effect of distinct roughness’s over absorber plate on heat transfer augmentation is summarized and to provide viewpoint for future research and development.

Toward the Next Generation of Passive Micromixers: A Novel 3-D Design Approach.

Passive micromixers are miniaturized instruments that are used to mix fluids in microfluidic systems. In microchannels, combination of laminar flows and small diffusion constants of mixing liquids produce a difficult mixing environment. In particular, in very low Reynolds number flows, e.g., Re < 10, diffusive mixing cannot be promoted unless a large interfacial area is formed between the fluids to be mixed. Therefore, the mixing distance increases substantially due to a slow diffusion process that governs fluid mixing. In this article, a novel 3-D passive micromixer design is developed to improve fluid mixing over a short distance. Computational Fluid Dynamics (CFD) simulations are used to investigate the performance of the micromixer numerically. The circular-shaped fluid overlapping (CSFO) micromixer design proposed is examined in several fluid flow, diffusivity, and injection conditions. The outcomes show that the CSFO geometry develops a large interfacial area between the fluid bodies. Thus, fluid mixing is accelerated in vertical and/or horizontal directions depending on the injection type applied. For the smallest molecular diffusion constant tested, the CSFO micromixer design provides more than 90% mixing efficiency in a distance between 260 and 470 µm. The maximum pressure drop in the micromixer is found to be less than 1.4 kPa in the highest flow conditioned examined.

Numerical investigation of the thermal performance of a radiant ceiling cooling panel with segmented concave surfaces

Radiant cooling/heating (RCH) panel systems have recently received increasing attention because of their energy-efficient operation and improved comfort performance. Therefore, this study proposes a novel RCH panel with segmented concave surfaces. The new panel has the same surface area as a conventional flat surface panel. A series of laboratory tests were conducted to investigate the heat transfer characteristics inside a chamber equipped with the new panel. Moreover, a three-dimensional finite volume simulation was developed to investigate the heat transfer, fluid flow, and thermal comfort conditions inside a single room equipped with the proposed panel, and the results were compared with those of a conventional flat surface panel under the same operating conditions and cooling load. First, the curvature cord length ratio to curvature radius (L/R) was optimized in the range of 0 (flat) to 2. In all cases, the surface area was the same, but the coverage area ratio varied. In addition, the impact of different coverage area ratios from 55% to 81% and the influence of adding void spaces of 29 mm and 11 mm between adjacent curved segments were analyzed. The results showed that the simulation achieved good agreement with the experimental results with an accuracy of 98.9%. The coverage area ratio played an essential role in decreasing the indoor air temperature by 2 °C and reducing the floor temperature by 1.6 °C. When the L/R ratio changed from 0 to 1.5 at a coverage ratio of 81%, the average air temperature decreased by 1 °C. Moreover, increasing the L/R ratio from 0 to 2 with void spaces of 2.9 mm and 11 mm reduced the radiation heat transfer coefficient, hr, by 31%, while the convection heat transfer coefficient, hc, at the panel upper surface increased by 174%. Changing only the panel surface shape from flat to concave and segmented enhanced the thermal performance and thermal comfort inside the indoor environment.

Pore-scale compositional modeling of gas-condensate flow: Effects of interfacial tension and flow velocity on relative permeability

Liquid dropout and retention in gas-condensate reservoirs, specially in the near wellbore region, obstruct gas flowing paths and impact negatively the produced fluid volume and composition. Yet, condensate banking forecasting is commonly inaccurate, as experiments seldom reproduce reservoir extreme conditions and complex fluid composition, while most pore-scale models oversimplify the physics of phase transitions between gas and condensate. To address this gap, a fully implicit isothermal compositional pore-network model for gas and condensate flow is presented. The proposed pore-networks consist of 3D structures of pores connected by constricted circular capillaries. Hydraulic conductances are calculated for the capillaries, which can exhibit single-phase flow or two-phase annular flow, according to local gas and liquid saturations, or be blocked by a liquid bridge, when capillary forces overcome viscous forces. A PT-flash based on the Peng-Robinson EoS is performed at control volumes defined for the pores at each time step, updating the phases properties. Flow analyses were carried based on coreflooding experiments reported in the literature, with matching fluid composition and flow conditions, and approximated pore-space geometry. Predicted and measured relative permeability curves showed good quantitative agreement, for two values of interfacial tension and three values of gas flow velocity.

Immersed boundary simulations of fluid shear-induced deformation of a cantilever beam

A biofilm is a colony of microorganisms that adheres and grows on a surface typically in contact with a stagnant or flowing fluid environment. The hydrodynamic interaction between the fluid and the film structure plays a key role in the various phases of the biofilm life-cycle — formation, growth, detachment, and reestablishment. The fluid-flow conditions determine the shear stresses exerted upon the film structure causing it to deform up to a critical point, beyond which the biofilm is uprooted from the surface into a planktonic state in the flowing fluid. To develop a fundamental understanding of the effects of the fluid-flow parameters on the mechanics of the biofilm, this work considered an ideal 2D model scenario of ‘a rectangular cantilever beam immersed in a channel filled with viscous, incompressible fluid, where one end of the beam is fixed to the channel wall, bending in response to a shear flow.’ The Immersed boundary (IB) method was employed to simulate numerically the fluid–structure interaction. The effect of physical parameters of the problem — stiffness and height of the cantilever and flow velocity, along with the numerical parameters on the equilibrium structure of the elastic beam was investigated and the simulation results were qualitatively compared with respect to linear beam theory. A careful analysis of the “corner effects” — irregularities in beam shape near the free and fixed ends, has been presented. It was shown that this issue can be effectively eliminated by smoothing out the corners with a “fillet” or rounded shape. Finally, the IB formulation was extended to include porosity in the beam to investigate the effect of the resultant porous flow on the beam deflection.

Transient Free Convection and Heat Transfer in a Partitioned Attic-Shaped Space under Diurnal Thermal Forcing

One primordial consideration in residential ventilation standards is the comfort of provided to people living in those habitations. This is highly dependent on the thermal and fluid flow conditions, the space geometry and so ... | Find, read and cite all the research you need on Tech Science Press

Nestacionarno strujanje fluida u paralelnom cevovodu izrađenom od različitih materijala

Transient fluid flow and the occurrence of water hammer in their specifics include the conditions of the environment in which the flow takes place. The variety of pipeline construction material (steel, polyethylene or other material) defines the conditions for the development of water hammer. The construction of parallel hydraulically connected pipelines from different materials and mutual influence in the conditions of transient fluid flow conditions of operation is the subject of research in this paper. The research was performed numerically on long (line) pipelines. The AFT-Impulse software package was used, which had already been tested with comparative experimentally measured values. The analysis model considers pipelines made of steel and polyethylene material in parallel hydraulic connection. The results of the simulation conditions are given through comparative diagrams, where the interactive influence is clearly and unambiguously revealed. The conditions of exploitation and interactive influence are given in the commentary and conclusion of this paper.