Dynamics Method Research Articles

Computational fluid dynamics analysis of the fluid environment of 3D printed gradient structure in interfacial tissue engineering

Mass transport properties within three-dimensional (3D) scaffold are essential for tissue regeneration, such as various fluid environmental cues influence mesenchymal stem cells differentiation. Recently, 3D printing has been emerging as a new technology for scaffold fabrication by controlling the scaffold pore geometry to affect cell growth environment. In this study, the flow field within scaffolds in a perfusion system was investigated with uniform structures, single gradient structures and complex gradient structures using computational fluid dynamics (CFD) method. The CFD results from those uniform structures indicate the fluid velocity and fluid shear stress within the scaffold structure increased as the filament diameter increasing, pore width decreasing, pore shape decreased from 90° to 15°, and layer configuration changing from lattice to stagger structure. By assembling those uniform structure as single gradient structures, it is noted that the fluid dynamic characterisation within the scaffold remains the same as the corresponding uniform structures. A complex gradient structure was designed to mimic natural osteochondral tissue by assembly the uniform structures of filament diameter, pore width, pore shape and layer configuration. The results show that the fluid velocity and fluid shear stress within the complex gradient structure distribute gradually increasing and their maximum magnitude were from 1.15 to 3.20 mm/s, and from 12 to 39 mPa, respectively. CFD technique allows the prediction of velocity and fluid shear stress within the designed 3D gradient scaffolds, which would be beneficial for the tissue scaffold development for interfacial tissue engineering in the future.

Fracture behavior of composite piezoelectric intelligent structures formed by pasting MFC based on serial multi-scale method

The composite piezoelectric intelligent structures formed by combining piezoelectric materials with composite materials can achieve state perception and deformation control of the structure. Based on the molecular dynamics method, the continuum finite element method and the cohesive force model, the serial multi-scale research on the bonded composite piezoelectric intelligent structure was carried out from the micro, meso and macro scales. Molecular models of adhesive, macro fiber composite (MFC) surface and composite surface were established. The effects of temperature and pressure on the surface interaction energy of adhesive/MFC and adhesive/composite materials were analyzed. The traction-separation (T-S) relationship of cohesive region was obtained by virtual stretching method. Combined with the microscopic observation of the mesoscopic adhesive layer, the representative volume element (RVE) model of the mesoscopic adhesive layer considering the bubble defect was established, and the cohesive relationship curve of the adhesive layer was obtained. A double cantilever beam (DCB) macro finite element model was established to simulate the crack propagation behavior of the adhesive layer, and compared with the experimental results.

Molecular dynamics simulations into rolling scraping of nickel-copper bilayer film

In order to investigate the nanoscale friction mechanism and deformation behavior of nickel-copper bilayer film under rolling scraping, the effects of different factors during friction process such as the translation velocity, rotation velocity, radius of abrasive grain, contact depth, texture direction and crystallographic orientation are analyzed through molecular dynamics methods in terms of contact force, atomic lattice structure, internal substrate dislocation, kinetic energy and temperature. Results show that the contact force increases with the increase of the translation velocity or the decrease of the rotation velocity. Abrasive grains in a purely rolling state cause the most serious damage to the substrate. The contact force increases with the increase of contact depth or the decrease of abrasive grain radius. The crystallographic orientation has a significant effect on rolling scraping process and there is a crystallographic orientation with the minimum contact force. The degrees of substrate dislocation and the numbers of lattice reconstruction atoms under different factors and levels vary widely.

Effect of veno-arterial extracorporeal membrane oxygenation lower-extremity cannulation on intra-arterial flow characteristics, oxygen content, and thrombosis risk

PurposeThis study aimed to investigate the effects of lower-extremity cannulation on the intra-arterial hemodynamic environment, oxygen content, blood damage, and thrombosis risk under different levels of veno-arterial (V-A) ECMO support. MethodsComputational fluid dynamics methods were used to investigate the effects of different levels of ECMO support (ECMO flow ratios supplying oxygen-rich blood 100–40 %). Flow rates and oxygen content in each arterial branch were used to determine organ perfusion. A new thrombosis model considering platelet activation and deposition was proposed to determine the platelet activation and thrombosis risk at different levels of ECMO support. A red blood cell damage model was used to explore the risk of hemolysis. ResultsOur study found that partial recovery of cardiac function improved the intra-arterial hemodynamic environment, with reduced impingement of the intra-arterial flow field by high-velocity blood flow from the cannula, a flow rate per unit time into each arterial branch closer to physiological levels, and improved perfusion in the lower extremities. Partial recovery of cardiac function helps reduce intra-arterial high shear stress and residence time, thereby reducing blood damage. The overall level of hemolysis and platelet activation in the aorta decreased with the gradual recovery of cardiac contraction function. The areas at high risk of thrombosis under V-A ECMO femoral cannulation support were the aortic root and the area distal to the cannula, which moved to the descending aorta when cardiac function recovered to 40–60 %. However, with the recovery of cardiac contraction function, hypoxic blood pumped by the heart is insufficient in supplying oxygen to the front of the aortic arch, which may result in upper extremity hypoxia. ConclusionWe developed a thrombosis risk prediction model applicable to ECMO cannulation and validated the model accuracy using clinical data. Partial recovery of cardiac function contributed to an improvement in the aortic hemodynamic environment and a reduction in the risk of blood damage; however, there is a potential risk of insufficient perfusion of oxygen-rich blood to organs.

Reifying dynamical algebra: Maximal ideals in countable rings, constructively

The existence of a maximal ideal in a general nontrivial commutative ring is tied together with the axiom of choice. Following Berardi, Valentini and thus Krivine but using the relative interpretation of negation (that is, as “implies 0 = 1”) we show, in constructive set theory with minimal logic, how for countable rings one can do without any kind of choice and without the usual decidability assumption that the ring is strongly discrete (membership in finitely generated ideals is decidable). By a functional recursive definition we obtain a maximal ideal in the sense that the quotient ring is a residue field (every noninvertible element is zero), and with strong discreteness even a geometric field (every element is either invertible or else zero). Krull’s lemma for the related notion of prime ideal follows by passing to rings of fractions. By employing a construction variant of set-theoretic forcing due to Joyal and Tierney, we expand our treatment to arbitrary rings and establish a connection with dynamical algebra: We recover the dynamical approach to maximal ideals as a parametrized version of the celebrated double negation translation. This connection allows us to give formal a priori criteria elucidating the scope of the dynamical method. Along the way we do a case study for proofs in algebra with minimal logic, and generalize the construction to arbitrary inconsistency predicates. A partial Agda formalization is available at an accompanying repository.11 See https://github.com/iblech/constructive-maximal-ideals/. This text is a revised and extended version of the conference paper (In Revolutions and Revelations in Computability. 18th Conference on Computability in Europe (2022) Springer). The conference paper only briefly sketched the connection with dynamical algebra; did not compare this connection with other flavors of set-theoretic forcing; and sticked to the case of commutative algebra only, passing on the generalization to inconsistency predicates and well-orders.

Prediction of morphology of CL-20/TFAZ cocrystal crystals in binary solvents based on modified attachment energy model

Crystal morphology of CL-20/TFAZ cocrystal in vacuum was predicted using the attachment energy (AE) model. Additionally, the modified attachment energy (MAE) model and molecular dynamics (MD) method were utilized to predict the crystal morphology of CL-20/TFAZ cocrystal in four different binary solvents, namely, isopropyl alcohol (IPA)/acetone (AC), IPA/dimethyl sulfoxide (DMSO), IPA/ethyl acetate (EA), and IPA/water (H2O). The radial distribution function (RDF) between the solvent and crystal surface and the mean square displacement (MSD) of the solvent were calculated. The findings showed that the morphology of CL-20/TFAZ cocrystal in vacuum was an irregular polyhedron with eleven important growth surfaces: (001), (1−10), (110), (100), (011), (0−11), (10−1), (020), (0−20), (11−1), and (1−1−1), with the (001) surface having the highest area ratio of 31.693 %. The crystalline morphology in IPA/AC, IPA/DMSO, and IPA/EA solvents was block-shaped, while it was rod-shaped in IPA/H2O. Comparing the RDF values of the four solvents, IPA/H2O exhibited the largest g(r) value and could more easily adsorb onto the crystal surface of CL-20/TFAZ cocrystal. Interestingly, IPA/H2O solvent had the smallest MSD value, suggesting the slowest diffusion rate, while IPA/AC solvent exhibited the fastest diffusion rate. Overall, IPA/EA solvents were more suitable for the formation of CL-20/TFAZ cocrystal.

Rapid pedestrian‐level wind field prediction for early‐stage design using Pareto‐optimized convolutional neural networks

AbstractTraditional computational fluid dynamics (CFD) methods used for wind field prediction can be time‐consuming, limiting architectural creativity in the early‐stage design process. Deep learning models have the potential to significantly speed up wind field prediction. This work introduces a convolutional neural network (CNN) approach based on the U‐Net architecture, to rapidly predict wind in simplified urban environments, representative of early‐stage design. The process of generating a wind field prediction at pedestrian level is reformulated from a 3D CFD simulation into a 2D image‐to‐image translation task, using the projected building heights as input. Testing on standard consumer hardware shows that our model can efficiently predict wind velocities in urban settings in less than 1 ms. Further tests on different configurations of the model, combined with a Pareto front analysis, helped identify the trade‐off between accuracy and computational efficiency. The fastest configuration is close to seven times faster, while having a relative loss, which is 1.8 times higher than the most accurate configuration. This CNN‐based approach provides a fast and efficient method for pedestrian wind comfort (PWC) analysis, potentially aiding in more efficient urban design processes.

Design and validation of a sampling module for a cyclonic wet-wall bioaerosol sampler using a computational fluid dynamics model

Pollen in the atmosphere is one of the common bioaerosol materials that can be harmful to human health. To collect and predict the pollen in the atmosphere, a sampling module of a cyclone wet-wall bioaerosol sampler was designed using the computational fluid dynamics (CFD) method and response surface method (RSM). The parabolic shape was chosen for the sampling module based on the axial and tangential velocities of flow in the module. Then, the main diameter of the sampling module was determined. The significance analysis of the main parameters of the sampling module on the capture rate was conducted using the Plackett-Burman (PB) design method. In descending order, the items are inlet width > outlet diameter > inlet height > base diameter > cone height > cylinder height > outlet pipe insertion depth. The test center point of Box-Behnken design (BBD) for the four significant parameters, namely inlet width, outlet diameter, inlet height, and cone height, were determined using the steepest climb test. Then, the optimal parameters of the sampling module were obtained using RSM and the optimal parameters were an inlet height of 15.4 mm, an inlet width of 5.4 mm, an outlet diameter of 14.7 mm, and a base diameter of 13.3 mm. Finally, the simulated capture rate of the sampling module was validated by the experimental results. The capture rate of the optimal sampling module for 2.5 μm PSL particles was 82.93 ± 4.25%. The results of this study can provide a practical method for designing the sampling module using the CFD model and RSM. Additionally, it can provide a high collection rate sampling module for pollen and bioaerosol in the environment.

Numerical Investigations on the Effects of Dome Cooling Air Flow on Combustion Characteristics and Emission Behavior in a Can-Type Gas Turbine Combustor

To meet the requirements of achieving higher efficiency and lower NOx pollution, the flame temperature in gas turbine combustors increases continually; thus, the effusion-cooling technology has been used to ensure the combustor liner remains within the allowed temperature, by which the combustion characteristics and emission behavior are possibly influenced. In order to investigate the effects of dome cooling air flow on combustion characteristics and NOx emissions, three-dimensional combustion simulations for a swirl-stabilized can-type gas turbine combustor are carried out in this work by using the computational fluid dynamics (CFD) method. Through adjusting the ratio of the dome cooling air flow and the dilution cooling air flow, the characteristics of flow field, temperature distribution and NOx emissions under each work condition are analyzed. At different ratios of the dome-cooling air flow to the total air flow, the flow velocity field in the region near the center of the combustion chamber is not changed much, while the velocity field near the chamber wall shows a more significant difference. The temperature in the outer recirculation zone within the combustion chamber is effectively reduced as the dome cooling air flow increases. By analyzing the distribution characteristics of the concentration of OH*, it is demonstrated that the dome cooling air flow does not have a direct effect on the reaction of combustion. It is also found that as the ratio of the dome cooling air flow to the total air flow increases from 0 to 0.15, the value of the NOx emissions drops from 28.4 to 26.3 ppmv, about a 7.4% decrease. The distribution of the NOx generation rate in the combustion chamber does not vary significantly with the increasing dome cooling air flow. Furthermore, by calculating the residence time in different stages, when the the ratio of the dome cooling air flow to the total air flow varies from 0 to 0.15, the residence time in the pilot stage decreases obviously, from 42 ms to 18 ms. This means that reduction in residence time is the main factor in the decrease of NOx emissions when the dome cooling air flow increases.

Towards optimal use of the explicit [formula omitted]-Bathe time integration method for linear and nonlinear dynamics

In an earlier publication, we proposed a new explicit time integration scheme, the β1/β2-Bathe method, which is simple in its formulation and showed remarkable accuracy in the solution of problems [1]. A particular strength of the method is that it can directly be used as a first-order or second-order scheme by a change of the values of β1 and β2. While good results are obtained with reasonable values of β1 and β2, for excellent accuracy better values of the parameters need to be chosen. We propose in this paper values of β1 and β2 for the first-order scheme, best used in wave propagation analyses, and separate values for the second-order scheme, best used in analyses of structural vibrations. In each case, one set of values of (β1,β2) is given and to possibly improve the results only one of the parameters needs to be changed, that is, β1 for wave propagations and β2 for structural vibrations, making the scheme a one-parameter method. Another strength of the procedure is that physical damping can directly be included in the solution, the effect of which on the stability and accuracy of the solutions we analyze in the paper. The use of the solution scheme in nonlinear analysis is, as we show in the paper, a simple extension from linear analysis. Finally, we give various solutions using the explicit β1/β2-Bathe method in linear and nonlinear analyses to illustrate the performance of the method with the given recommendations for its use.

Effect of aircraft landing angle on hydrodynamics characteristics during wave landing

In order to study the effect of different courses on the landing performance of aircraft when landing in waves, a Computational Fluid Dynamics (CFD) method is developed to investigate the landing performance of the NACA TN 2929 A aircraft model. The solution of fluid flow is based on the Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) k−ω turbulence model, and the numerical scheme employed is the Finite Volume Method (FVM). The fifth-order Stokes wave is generated by using the velocity inlet wave-making method. In the work, the slamming load, pitch change and motion response of the aircraft landing at different wave positions are analyzed. The landing characteristics of aircraft landing parallel to the wave, perpendicular to the wave and at the yaw angle are studied. It is found that the landing characteristics of the aircraft at the 1/2 π phase are better than those at other ones, with the maximum load at the π phase. When the aircraft lands parallel to the wave, yaw displacement generated at 1/2 π phase and 3/2 π phase is equal in magnitude and opposite in direction in the initial short time. These results are important for reducing slamming loads and improving the airworthiness of the aircraft structure when landing on a wave surface.

Dynamic wire-pull rubber diaphragm for rapid formation and spatio-temporal investigation of multi-shape free-standing liquid films

Quantitative manufacturing and characterization of thin films are relevant in different scientific and industrial fields. Especially, for the studies of fluid dynamics, the experimental verification of theoretical models creates the need of a free-standing liquid film formation. Driven by the lack of fast and accurate liquid film forming technology, we present a novel device able to fabricate thin free-standing liquid films, which is based on a dynamic and adjustable diaphragm, the opening of which allows for the rapid formation of a self-supported liquid film confined in a wire-pull rubber band. The quantitative thickness mapping of the film formation and its time-resolved evolution are performed by digital holography in real-time. This builds up a strategy that allows for the accurate liquid film formation with controllable size and volume. As the results, multi-shape and multi-material thin films under controllable and stable conditions are successfully formed, including free-standing water, soapy water and glycerol films. A label-free spatio-temporal analysis method for flow dynamics is proposed: The full-field time series of film thickness is reassembled in a new coordinate system composed of radius, time, and thickness. Such spatio-temporal analysis reveals details of leveling and drainage processes. To the best of our knowledge, this is the first full-field quantitative thickness analysis of multi-shape and multi-material thin films. The proposed Dynamic Wire-pull Rubber Diaphragm (DWRD) together with the digital holography add-on offer characterization abilities with an unprecedented level of details allowing for a deeper understanding of the underlying thin film dynamics that can be useful in several different scientific and technological fields as biotechnology, life science, and nanotechnology.

Molecular simulation of competitive adsorption of CO2/N2/O2 gas in bituminous coal

The main cause of coal spontaneous combustion is the oxidation and temperature rise of coal. Injecting composite inert gas for fire prevention and extinguishing is one of the important methods to prevent coal spontaneous combustion. A large number of studies have macroscopically investigated the fire prevention and extinguishing effects of CO2/N2 and their synergistic actions. However, there is currently a lack of research at the molecular level on the competitive adsorption mechanism between mixed inert gases (CO2, N2) and O2 molecules in coal. Therefore, this study conducted adsorption experiments using Qian Yingzi(QYZ) bituminous coal and compared them with the simulation data of the Wiser coal model to verify the reliability of the Wiser model. Subsequently, employing grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods, the competitive adsorption behavior of different proportions of binary mixed component gases (CO2/O2, CO2/N2, O2/N2) at a temperature of 303.15 K was investigated from five perspectives: adsorption capacity, adsorption selectivity coefficient, potential energy distribution, competitive adsorption heat, and interaction energy. The results indicate that among the competitive component gases, CO2 exhibits the strongest adsorption effect on the entire system, which is closely correlated with the distribution range of adsorption energy sites. The adsorption heat and adsorption amount of CO2 consistently exhibit a negative correlation, whereas the relationship between the adsorption heat of N2 and O2 and the adsorption amount shows a positive correlation. Their adsorption capacities depend on the pressure and the proportion of the two gases. Based on the isothermal adsorption curve of CO2/N2, it is recommended that the gas pressure during actual inert gas injection be less than 2.5 MPa. Under this pressure, the competitive adsorption effect is no longer significant, providing a certain theoretical basis for high-pressure injection. Moreover, the preliminary determination of the optimal injection ratio range is from 4:6–3:7. Furthermore, a systematic logical framework for selecting underground inert gas composition is proposed, and an underground mobile inert gas infusion process is adopted. The actual gas composition for infusion is determined based on cost factors in practical engineering. The research results can provide guidance for the selection of gas injection parameters for mixed inert gas fire prevention and extinguishing in goaf.

Effects of wind-wave-current-earthquake interaction on the wave height and hydrodynamic pressure based on CFD method

Wind-wave-current interaction is a phenomenon which is present in many practical engineering situations and vertical earthquakes may have significant influence on the hydrodynamic pressure of seawater in regions of active seismicity. This study is devoted to probe the wave height and hydrodynamic pressure of seawater caused by the joint wind, wave, current and earthquake action based on computational fluid dynamics (CFD) method, where a homogeneous multiphase model based on the noncompressible Reynolds Averaged Navier-Stokes (RANS) equation and the k-ε turbulence model implemented in ANSYS-Fluent code was used. First, a two-dimensional (2D) numerical flume excited by wind, wave, current and earthquake loadings was established through the secondary development of a user-defined function (UDF). Subsequent, effects of wind-wave interaction and wind-wave-current interaction on the wave height and hydrodynamic pressure of seawater were investigated. Finally, effects of wave-earthquake interaction and wave-current-earthquake interaction on the wave height and hydrodynamic pressure of seawater were investigated. The nonlinearity of seawater under joint wind, wave, current and earthquake action was also studied.

Molecular dynamics study of the rheology of benzene-based nanofluids with metal particles

The purpose of this paper is to study the rheology of the nanofluids with ordinary spherical particles. The rheology of benzene and benzene-based nanofluids with copper and aluminium particles of 3 and 6 nm diameter been studied by the nonequilibrium molecular dynamics method. The maximum volume concentration of the nanoparticles was 6.11 %. It has been shown that all fluids considered, including benzene and benzene-based nanofluids, exhibit Newtonian behavior at low shear rates. However, with increasing shear rate, both benzene and nanofluids become pseudoplastic. The mechanisms of the rheology change of simple liquid and nanofluids have studied. This change in their rheology is a threshold phenomenon, in which the critical shear rate depends on the concentration, size, and material of the nanoparticles. The critical shear rate increases with increasing particle size and decreases with increasing particle concentration. Correlations describing the critical shear rates at which the rheology of nanofluids changes are obtained. It is shown that the rheology change is due to a change in the structure of both the base fluid and the nanofluid. In all cases, the change in rheology results from the weakening of the short-range order in these fluids. As the shear rate increases, the difference between viscosity of the base fluid and all studied nanofluids decreases monotonically.

CFD investigation of flow hydrodynamics and optimization in an industrial‐scale annular lance with swirl flow

AbstractSwirling flow has been applied in various fields due to its ability to enhance mass, heat, and momentum transfer performance. However, the generation of swirling flow occurs at the price of augmenting the pressure drop, and enhancing the friction and shear intensity of the jet with respect to the reactor wall. In the present work, the impact of geometrical configurations of the swirler on the hydrodynamics of the fluid in an industrial‐scale annular lance is investigated via the computational fluid dynamics method, with the discussion of the friction coefficient of the lance walls. It shows that the axial flow injected from the central lance is transformed into a weak swirl flow upon the introduction of swirl flow generated in the casing pipe. Within the mixing region, the interaction between axial and swirl flows results in elevated turbulent kinetic energy. Notably, under varying geometrical configuration conditions, the pressure drop between the inlet of the central pipe and the outlet is maximized. Additionally, the highest friction factor appears at a height of 1.35 m along the middle shell, with a value of 96.67.

Mechanism and deformation behavior of elliptical vibration-assisted cutting of FeNiCrCoAl high entropy alloy

The mechanical response of FeNiCrCoAl high entropy alloy (HEA) under conventional cutting and ultrasonic elliptical vibration-assisted cutting (UEVAC) was investigated using molecular dynamics (MD) methods. The effects of vibration period, axial amplitude, and normal amplitude on the material removal mechanism were studied. The results show that the average cutting temperature of the workpiece under UEVAC is significantly higher than that under conventional cutting. The high-temperature distribution area under UEVAC presents an intermittent distribution pattern, which not only facilitates the cutting process but also plays a positive role in the protection of the tool. Furthermore, as the vibration period shortens, both the average principal stress experienced by the workpiece and the triaxial cutting force decrease, while the height and quantity of chip atoms significantly increase. When the vibration period is shortened to 5 ns, the number of chip atoms is about twice that of conventional cutting, which is equivalent to doubling the removal efficiency of the material. Although an increase in axial amplitude causes an increase in the average temperature of the workpiece, it also results in larger negative principal stress. When the axial amplitude A increases to 20 Å, the peak value of the negative principal stress generated inside the base material exceeds 8000 GPa, and the triaxial cutting force tends to increase, without a significant increase in the number of chip atoms. With the increase in normal amplitude B, the average cutting temperature of the matrix also increases. But there is no significant change in the direction and magnitude of the principal stress, and the triaxial cutting force continuously increases. This study provides a theoretical basis for achieving high surface quality of HEAs.

Study on trapping behaviour of SiO2-containing droplets on the solid surface

The dynamic behaviour of droplets impacting solid surfaces exists in nature, production, and life. In this paper, for the first time, the molecular dynamics method is used to simulate capturing the behaviour of nanodroplets containing SiO2 on solid surfaces. The dynamic behaviour of nanodroplets impacting solid surfaces is analysed when the initial falling velocity v0 of the droplet is 0.3–1.5 nm·ps−1 and for different particle size ds, mass fraction φs of SiO2, and solid surfaces with various wettability. The contact angles of droplets containing SiO2 nanoparticles on the solid surface were measured, and the simulated values closely matched experimental results. The results show that the droplets on the smooth solid surface are completely captured after impact when v0 = 0.3–1.1 nm·ps−1. When v0 = 1.2–1.5 nm·ps−1, the droplet is fragmented, and the fragmentation ratio ns increases with the mass fraction φs. The droplet fragments when v0 = 1.4–1.5 nm·ps−1 on the rough solid surface when the ratio of the side length of the square column to the droplet diameter is 0.07, while the pure water droplet directly bounces and does not fragment. There is a linear relationship between the minimum height of the centre of mass and the mass fraction in the process of droplet impact. The maximum droplet’s spreading factor value in the spreading stage βmax increases with mass fraction φs and v0. When the spreading factor of droplets increases to βc ≈ 3.02, the droplet fragments. The droplet spreading presents the Wenzel state on the rough solid surface. Moreover, the pinning effect affects the droplet falling into the square column gap surface, hindering droplet spreading. Therefore, the rough surface has better catching ability for the droplet than the smooth surface, while the speed range that can be caught is larger. These results provide a theoretical basis for related engineering applications.

Mechanisms of CO2-rich industrial waste gas enhanced shale oil recovery in kerogen slit based on adsorption behavior, gas flooding and surfactant synergy study

Enhanced oil recovery (EOR) by injection of CO2-rich industrial waste gas has been proposed as an energy-efficient and environmentally friendly method for shale oil reservoirs, in which the waste gas can be utilized and sequestered to reduce greenhouse gas emissions. In this work, the adsorption behaviors of shale oil and waste gas components in kerogen slits and the effects of gas flooding on EOR were investigated using molecular dynamics (MD) method, which can provide technical guide for shale oil development. In terms of the adsorption behaviors, an intensity decrease of oil adsorption is observed in kerogen slits after the injection of the waste gas components. Desorption of shale oil during injection of SO2 and CO2 is more pronounced in shallow reservoirs, whereas it is more evident for NO and N2 in deep reservoirs. The desorption efficiency can be 10.91 % for pure CO2 injection and 9.09 % for NO injection at a depth of 1000 m, and the relative stability ratios of CO2 and NO sequestration are 77.09 % and 76.06 %, respectively. For gas flooding, the existence of pressure difference provides favorable conditions for gas molecules to pass through the oil zone, and waste gas can be more effective than pure CO2 as driving gas. For the waste gas injection, the percentage of CO2 retained in the kerogen nanopores is much higher than that of pure CO2 injection, suggesting that more CO2 molecules can enter into kerogen matrix to take part in the displacement process. Furthermore, the effect of surfactants on oil desorption and displacement was also investigated and the interaction energy of the surfactant/oil/gas system was calculated and analyzed, finding that addition of the oil-soluble surfactants can be beneficial to shale oil displacement. This work can provide a comprehensive evaluation of the feasibility of CO2-rich industrial waste gas application for EOR, which is of great significance in the effective production of shale oil and the sequestration of waste gas in shale reservoirs.

Study on the safety of a magnetic strainer at the deaerator outlet under two-phase and large-scale flow fields

Iron oxide corrosion exists in the deaerator, which causes serious damage to the water supply system. To absorb iron oxide impurities for the feed water quality, a magnetic strainer device has been designed at the deaerator outlet. In order to ensure the safe and stable operation of the deaerator, the computational fluid dynamics (CFD) method was used in this work to analyze the impact of complex outlet conditions on the gas-liquid two-phase flow field, pressure field, and structural safety within a deaerator. After the strainer is installed, turbulent kinetic energy (TKE) and turbulence intensity (TI) are not monotonically changing throughout strainer region and depend on the local flow state and geometry. TI relies more on turbulence disturbance and geometry. The overall flow near the strainer is accelerated, and the dimensionless velocity in the shear layer on both sides of the strainer center bracket increases by a maximum of 153.44%. Stable vortices and complex secondary vortices are formed near the strainer. The overall eddy is more fragmented, and eddy dissipation is prone to occur in the outlet region. However, this does not cause additional large turbulence losses. The impact of the strainer on the static pressure loss of the entire deaerator is very limited, and the reduction in static pressure difference does not exceed 0.04%. Finally, suggestions are made for the structural improvement and maintenance of the strainer based on the simulation results, which provide a reference for further safe and stable application of the deaerator magnetic strainer.