Critical Diameter Research Articles

Database of Ternary Amorphous Alloys Based on Machine Learning

Abstract The unique long-range disordered atomic arrangement inherent in amorphous materials endows them with a range of superior properties, rendering them highly promising for applications in catalysis, medicine, and battery technology, among other fields. Since not all materials can be synthesized into an amorphous structure, the composition design of amorphous materials holds significant importance. Machine learning offers a valuable alternative to traditional “trial-and-error” methods by predicting properties through experimental data, thus providing efficient guidance in material design. In this study, we develop a machine learning workflow to predict the critical casting diameter, glass transition temperature, and Young’s modulus for 45 ternary reported amorphous alloy systems. The predicted results have been organized into a database, enabling direct retrieval of predicted values based on compositional information. Furthermore, the applications of high glass forming ability region screening for specified system, multi-property target system screening and high glass forming ability region search through iteration are also demonstrated. By utilizing machine learning predictions, researchers can effectively narrow the experimental scope and expedite the exploration of compositions.

Experimental study on droplet dynamics behavior and combustion characteristics of high performance green propellant in electrical ignition mode

High performance green propellant represented by ammonium dinitramide-based liquid propellant and its new ignition method are the research hotspots of space propulsion in the 21st century. Exploring the complex multi-scale physical properties of multi-component ammonium dinitramide-based liquid propellant droplets in the electrical ignition mode has wide application significance for spray, propulsion system design and combustion control. The droplet dynamics behavior and combustion characteristics of propellant droplets at different ignition voltages were studied experimentally. The droplet dynamics behavior during the evaporation process, including violent volume oscillation, approximate steady-state expansion, contraction, secondary expansion, puffing and micro-explosion, have been determined by the generation, growth, and discharge of vapor bubbles. In the initial evaporation process, the heterogeneous nucleation is dominant. As the droplet is continuously heated, homogenization nucleation gradually dominates. The main physical and chemical mechanisms of bubble evolution driven by temperature involve methanol boiling, water overheating, ammonium dinitramide decomposition and combustion reaction between vapor molecules. Increasing the ignition voltage increases the droplet dynamics behavior and the combustion, but promotes the combustion instability. Increasing the ignition voltage increases the ignition delay time, puffing delay time, droplet lifetime, maximum temperature of droplet, and reduces the ignition critical diameter. It is proposed that the method of suppressing the droplet breakup dynamics at decomposition area and enhancing the droplet breakup dynamics at the combustion area are conducive to the combustion control of the thruster in electrical ignition mode. This research provides novel insight into the study of the electrical ignition mechanism of liquid fuels.

Investigation on precipitate behavior and mechanical properties of Al-Zn-Mg-Cu alloys with various Zn/Mg ratios

The effect of Zn/Mg ratio on the microstructure and properties of Al-Zn-Mg-Cu alloys under single-step and double-step aging processes were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), as well as hardness, room temperature tensile, and fracture toughness testing. During single-step aging, as the Zn/Mg ratio increases, the aging response of the alloys accelerates. However, the peak hardness and strength gradually decreased while the average size of precipitates increased. During double-step aging, as the secondary aging time increases, the strength and hardness of the alloys gradually decrease. Additionally, the higher the Zn/Mg ratio, the faster the strength and hardness decline. Under the T74 temper, the alloy with higher Zn/Mg ratios exhibits lower hardness and strength but better fracture toughness and larger precipitate sizes. A simple method was proposed to statistically determine the critical diameter size of GPII zone and η′ phase, which was approximately 4.47 nm. A strength model was developed to predict the yield strength of alloys, considering factors such as solid solution strengthening, grain boundary strengthening, and precipitation strengthening. The model demonstrates good predictive accuracy for both peak-aged and T74 temper alloys, providing valuable guidance for alloy design and microstructure regulation.

Assessing the impact of packaging materials on anoxic biotrickling filtration of siloxanes in biogas: Effectiveness of activated carbon in removal performance

Siloxanes (VMS) represent a class of organosilicon compounds known for their adverse effects on both the environment and human health. Their presence in biogas significantly hinders its economic valorisation, highlighting the need for effective treatment methods. This study investigates the performance of three different packing materials in the anoxic biofiltration of VMS (L2, L3, D4 and D5). The materials evaluated included plastic rings (BTF-1), polyurethane foam (BTF-2) and plastic rings combined with activated carbon (80:20) (BTF-3). Among them, BTF-3 exhibited superior performance, achieving maximum VMS removal efficiencies (REs) of 90%, including the complete elimination of L3 and D4, and ∼80% removal of D5, attributed to the presence of activated carbon. However, the abatement of L2 was inferior to that of other VMS (<80%), which was attributed to the activated carbon's affinity for larger molecular weights and critical diameters. In contrast, BTF-1 and BTF-2 supported maximum VMS removals of 40%. Notably, neither increasing the trickling liquid velocity from 2 to 4.5 m h⁻1 nor adding Fe-carbon nanoparticles to the solution had any impact on the BTFs' performance. Following the successful results observed in BTF-3, gas residence time was reduced from 60 to 42 min, consequently leading to an increase in the EC from 366 to 509 mg m−3 h−1 (corresponding to an RE = 87%). Despite the different performance of the BTFs, comparable bacterial communities were identified, dominated by the genera Thermomonas, Corynebacterium, Aquimonas, Thauera and Parvibaculum. The results obtained in this study highlighted the potential of activated carbon as packing material for enhancing abatement performance during biotrickling filtration and identified new bacterial genera with potential for VMS degradation.

Effect of the Dispersion Medium on NMR Relaxation Properties of Superparamagnetic Iron Oxide Nanoparticles between 0.24 mT and 14.1 T.

Due to weak exchange interactions, magnetite particles at a critical diameter of about 20 nm are considered monodomain. At this size, they exhibit a phenomenological magnetic property called superparamagnetism, making them useful as magnetic resonance imaging contrast agents, or MRI CAs. However, questions persist regarding the impact of using different physiological solvents and varying the environment in which these particles are dispersed on their performance, determined by their relaxivity. A colloidal suspension of superparamagnetic iron oxide nanoparticles (SPIONs) electrostatically stabilized by citrate ligand was synthesized using a fast, reliable, and reproducible developed microwave approach, ensuring high stability over time at pH 7. We studied the effects of three physiological media on these MRI CAs. Ultrapure water was used for the synthesis, while phosphate-buffered saline and physiological liquid were used to disperse the nanoparticles, as these media contain essential electrolytes for the functioning of the human body. The SPIONs underwent systematic characterizations to determine their physicochemical and magnetic properties. This study reports the longitudinal relaxivities of SPIONs at medically relevant magnetic field strengths. Field dependence of their relaxivity (efficacy) was evaluated using a nuclear magnetic resonance dispersion (NMRD) profile measured over a wide range of proton resonance frequencies between 5 kHz and 600 MHz. The Roch et al. model (Roch, A.; et al. J. Chem. Phys., 1999, 110, 5403-5411) was used to analyze the NMRD profile and evaluate the impact of SPIONs on water proton relaxation in the different redispersion media. It was observed in this study that the dynamics of water protons are not influenced by the redispersion media of these citrate-coated SPIONs. However, the presence of salt ions notably reduces their relaxivities by lowering the saturation magnetization of SPIONs.

Active Fréedericksz Transition in Active Nematic Droplets

Active nematic liquid crystals have the remarkable ability to spontaneously deform and flow in the absence of any external driving force. While living materials with orientational order, such as the mitotic spindle, can self-assemble in quiescent active phases, reconstituted active systems often display chaotic, periodic, or circulating flows under confinement. Quiescent active nematics are, therefore, quite rare, despite the prediction from active hydrodynamic theory that confinement between two parallel plates can suppress flows. This spontaneous flow transition—named the active Fréedericksz transition by analogy with the conventional Fréedericksz transition in passive nematic liquid crystals under a magnetic field—has been a cornerstone of the field of active matter. Here, we report experimental evidence that confinement in spherical droplets can stabilize the otherwise chaotic dynamics of a 3D extensile active nematics, giving rise to a quiescent—yet still out-of-equilibrium—nematic liquid crystal. The active nematics spontaneously flow when confined in larger droplets. The composite nature of our model system composed of extensile bundles of microtubules and molecular motors dispersed in a passive colloidal liquid crystal allows us to demonstrate how the interplay of activity, nematic elasticity, and confinement impacts the spontaneous flow transition. The critical diameter increases when motor concentration decreases or nematic elasticity increases. Experiments and simulations also demonstrate that the critical confinement depends on the confining geometry, with the critical diameter in droplets being larger than the critical width in channels. Biochemical assays reveal that neither confinement nor nematic elasticity impacts the energy-consumption rate, confirming that the quiescent active phase is the stable out-of-equilibrium phase predicted theoretically. Further experiments in dense arrays of monodisperse droplets show that fluctuations in the droplet composition can smooth the flow transition close to the critical diameter. In conclusion, our work provides experimental validation of the active Fréedericksz transition in 3D active nematics, with potential applications in human health, ecology, and soft robotics. Published by the American Physical Society 2024

Effects of ultrasound on bubble dynamic behavior of flow boiling in microchannel

Bubble dynamics is paramount in comprehending the heat transfer mechanisms of flow boiling in the microchannel within ultrasonic field, which is regarded as a promising method to confront challenges of thermal management posed by microelectronic devices. Nevertheless, the impact of ultrasound on bubble behaviors and its underlying mechanisms remain largely unexplored. This study first delves into the effect of ultrasonic parameters on bubble dynamic behaviors and associated mechanisms, subsequently further analyzing the forces acting on bubbles through the constructed force model. The findings suggest that although growth force serves as the significant resistance, the primary Bjerknes force dominates the rapid detachment of bubbles. The secondary Bjerknes force results in the bubble only sliding along the bottom wall rather than lifting off. Furthermore, the elevated ultrasonic pressure amplitude resulting from augmenting ultrasonic power induces a substantial increase in the critical detachment diameter and growth rate by 55.49% and 59.42%, respectively. The enhanced primary Bjerknes force, attributed to the rise in ultrasonic frequency, leads to a 71.42% increase in sliding velocity and a 46.45% reduction in growth time. The positive impacts arising from ultrasonic power and frequency are anticipated to notably enhance the thermal performance of microchannels. Besides, surface tension acts as the resistance and diminishes slightly with an augmentation of the boiling number, resulting in a moderate variation in sliding velocity and growth time.

Process analytical technology based quality assurance of API concentration and fiber diameter of electrospun amorphous solid dispersions

In this study, a novel quality assurance system was developed utilizing Process analytical technology (PAT) tools and artificial intelligence (AI). Our goal was to monitor the critical quality attributes (CQAs) like drug concentration, morphology and fiber diameter of electrospun amorphous solid dispersion (ASD) formulations with fast at-line techniques. Doxycycline-hyclate (DOX), a tetracycline-type antibiotic was used as a model drug with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) as the matrix excipient. The water-based formulations were electrospun with high-speed electrospinning (HSES). Raman and NIR sensors and machine vision-based color measurement techniques were employed to accurately determine the drug concentration. Given that morphology can influence the solubility of the drug, a convolutional neural network (CNN)-based AI model was developed to examine this property and detect manufacturing defects. Additionally, the diameter of electrospun fibrous samples was measured using camera images and a trained AI model, enabling rapid analysis of fiber diameter with results similar to that of scanning electron microscopy (SEM). These methods and models demonstrate potential in-line analytical tools, offering rapid, cheap and non-destructive analysis of ASD formulations.

Study on flow regime characteristics in 3×3 rod bundle channels based on wire mesh sensor

Abstract The characteristics and evolution of two-phase flow are of critical importance to the safety of pressurized water reactors. Based on the double-layer wire mesh sensors in this paper, the air-water two-phase flow experiment of the 3×3 rod bundle channels is carried out at room temperature and pressure. The results show that the critical bubble diameter range for the reversal of lateral lift direction is 4 to 5.8 mm. In addition, the time-averaged void fraction for bubbly flow reveals a wall peak distribution at lower superficial gas velocities and shifts to a core peak as these velocities increase. For cap flow, the cross-distribution of cap bubbles within adjacent subchannels triggers large-scale mixing of the liquid phase between adjacent subchannels. For slug flow, large-sized bubbles develop along the axis and cross subchannel gaps to aggregate into slug-shaped bubbles, with a more pronounced distribution of the central peak of void fraction. The drift-flux models are evaluated against the experimental data, and the Ozaki model demonstrates higher precision in estimating void fraction, exhibiting a deviation of 9.8% on average.

Multimodal 3D quantification of particle stimulated nucleation in industrially manufactured aluminium AA5182 sheet

Particle stimulated nucleation is a dominant recrystallisation mechanism observed in many industrially relevant aluminium alloys during thermomechanical processing. In this work, we quantify particle stimulated nucleation in 3D in an aluminium AA5182 alloy sheet cold-rolled to 75 % thickness reduction. Second phase particles and nuclei are mapped in the same sample volume by conventional laboratory absorption X-ray tomography and synchrotron X-ray Laue micro-diffraction. The large second phase particles are classified as Fe- and Mg-rich phases. It is found that84 % of the nuclei are particle stimulated and 40 % of the particles stimulate nucleation. The critical particle diameter is found to be 4μm. Deviatoric elastic strains are derived from micro-diffraction data and it is found that elastic strains are present in the recrystallised nuclei. The effects of the different particle types, particle clustering, particle size and aspect ratio as well as strain inheritance are discussed. This work provides a full 3D quantification of particle stimulated nucleation behaviour in AA5182 alloy sheet deformed to high strain.

Calculation Modeling of Adsorbed and Bulk-Phase Oil Resources Based on Molecular Dynamics Simulations

Summary Nanopores prevalent in shale reservoirs significantly impact shale oil occurrence characteristics due to the strong intermolecular forces between crude oil molecules and the pore walls. Unlike bulk-phase oil, which is more readily recoverable with current technologies, the behavior of oil within these small-scale environments presents unique challenges. This study utilizes molecular dynamics simulations (MDSs) to investigate the characteristics of shale oil in slit nanopores, with the goal of refining a model that estimates the quantities of both bulk and adsorbed oil in shale reservoirs. We constructed models for three types of nanopores—organic graphene, illite, and quartz—using n-hexane (n-C6H14) as a proxy for shale oil. Our analysis reveals that mineral composition significantly influences fluid adsorption capacity, ranked as graphene &amp;gt; illite &amp;gt; quartz. Unlike prior research, we found that the critical flow pore diameter, which dictates the transition from adsorbed to free-flowing oil, cannot be simplistically equated to the combined thickness of adsorption layers. Specifically, in graphene pores with a diameter of 3.8 nm, the fluid mass density at the pore center still exhibits adsorption layer characteristics, forming up to nine layers. Building on these insights, we revised the shale reservoir resource estimation model to account for adsorption variances across different pore types. Our findings highlight the significant role of adsorbed oil in nanopores within shale reservoirs. Data from the Gulong shale oil block in the Daqing oil field indicate that adsorbed oil constitutes 37.15% of geological reserves, while bulk-phase oil accounts for the remaining 62.85%. This research provides essential data for accurately calculating shale oil reserves in nanopores, which are crucial for the effective exploitation of shale oil reservoirs.

Critical diameter for a single-tank molten salt storage – Parametric study on structural tank design

Molten salt thermal energy storage (TES) is a cost-effective option for grid-connected storage in both concentrating solar power (CSP) plants and retrofitted thermal power plants in a multimegawatt scale. Current systems use two tanks (hot and cold), but future systems may use a single tank with a transient temperature profile (hot in the top and cold in the bottom) to reduce costs and space. However, the structural and mechanical design of large-scale molten salt single-tank storages at 560 °C has not been fully explored, and the impact of increasing the operating temperature to 620 °C is still uncertain. The challenge presented by a single tank is the existence of a temperature profile that results in a varying thermal expansion of the tank shell along its height. In the case of larger tanks, this discrepancy can reach a magnitude of centimeters, which in turn gives rise to bending moments. To the best of our knowledge, this study addresses the issue of bending stresses in large-sized high-temperature tanks with thermal stratification for the first time. The modelling approach is applied to single-tank CSP TES systems as a case study to evaluate the constraints imposed by tank size and wall thickness.With the help of experimentally validated numerical methods, it is revealed that a low thermocline thickness can be a limiting factor for large tank diameters. It is shown that the temperature has a major influence on maximum possible tank size: if the operating temperature is raised from 560 °C to 620 °C, the permitted tank diameter is significantly reduced when using the same tank wall material. A possible approach is to use a more heat resistant steel for 620 °C. Results of the parametric study show that designing a single tank below a critical diameter only requires a moderate increase of the wall thickness compared to the two-tank system with constant temperature profiles. Based on this parametric study a formula for the critical tank diameter is developed and presented in this work. The paper concludes with recommendations on how increased wall stresses can be addressed by an appropriate design.

Streamline-directed tunable deterministic lateral displacement chip: A numerical approach to efficient particle separation

In conventional Deterministic Lateral Displacement (DLD), the migration behavior of a particle of specific size is determined by the critical diameter (Dc), which is predefined by the device's geometry. In contrast to the typical approach that alters the angle between the pillar array and fluid streamlines by modifying the geometrical parameters, this study introduces a novel perspective that focuses on changing the direction of the streamlines. The proposed technique offers a tunable DLD chip featuring a straightforward design that allows for easy fabrication. This chip features one completely horizontal pillar array with two bypass channels on the top and bottom of the DLD chamber. The width of these bypass channels changes linearly from their inlet to their outlet. Two design configurations are suggested for this chip, characterized by either parallel or unparallel slopes of the bypass channels. This chip is capable of generating a wide range of Dc values by manipulating two distinct control parameters. The first control parameter involves adjusting the flow rates in the two bypass channels. The second control parameter entails controlling the slopes of these bypass channels. Both of these parameters influence the direction of particle-carrying streamlines resulting in a change in the path-line of the particles. By changing the angle of streamlines with pillar array, the Dc can be tuned. Prior to determining the Dc for each case, an initial estimation was made using a Python script that utilized the streamline coordinates. Subsequently, through FEM modeling of the particle trajectories, precise Dc values were ascertained and compared with the estimated values, revealing minimal disparities. By adjusting the flow rate and slope of the bypass channels, maximum Dc ranges of 4–10 μm and 8–13 μm can be achieved, respectively. This innovative chip enables the attainment of Dc values spanning from 0.5 to 14 μm.

Study on the influence of early frost attack on the performance of cement mortar

The loss of strength and durability caused by early frost attack is the macro performance of internal microstructure deterioration. Understanding the influence mechanism of early frost attack at the micro level is necessary to avoid or minimize the early frost attack to macro performance. In this study, the influence of early frost attack on the strength, water sorptivity, chloride permeability, and microstructure of cement mortar was investigated. The fresh mortars were pre-cured for 10, 12, 14, and 16 h and then frozen at −10 °C for 7 days to simulate an early frost attack. After freezing, the standard curing (20 °C) was carried out until the testing. It is found that after standard curing of 28 days, the strength of early-frozen mortar can reach more than 95 % of the 28-day strength of unfrozen mortar. Interestingly, the sorptivity coefficient and total charge passed of early-frozen mortar are much higher than the level of unfrozen mortar, and the loss of resistance to water penetration and chloride ion penetration exceeds 20 %, indicating that early frost attack causes more severe damage to the durability than to the strength of mortar. Mercury intrusion porosimetry (MIP) results show that early frost attack can increase the pore volume of >50 nm and coarsen the pores within 10–50 nm. Correspondingly, key pore parameters (critical pore diameter, threshold pore diameter, and tortuosity) that affect the durability of mortar are also negatively affected. Energy dispersive spectroscopy (EDS) analysis also shows that after suffering early frost attack, the interfacial transition zone (ITZ) thickness of mortar is increased from 4 to 10 μm to 8–13 μm, and the probability of high Ca/Si ratios (4–10) in the ITZ is also increased. Finally, it is concluded that the coupling effect of pore structure coarsening and ITZ degradation leads to more severe durability loss.

The design and fabrication of thermoplastic microfluidic chips with integrated micropillars for particle separation

Microfluidic technology utilizing the deterministic lateral displacement (DLD) method holds significant promise for efficiently separating micro-particles and biological cells. Despite the notable high throughput advantages associated with DLD chips, their widespread application is impeded by the substantial manufacturing costs of tens of thousands of micropillars. This study aims to explore the feasibility of employing the injection molding method for the mass production of DLD microfluidic chips. A multistage DLD chip with varied critical diameters was designed to isolate white blood cells from the human whole blood. The separation effectiveness was verified with the polydimethylsiloxane chip fabricated by standard soft lithography. Subsequently, nickel mold inserts were electroformed to fabricate thermoplastic DLD chips via the injection molding. The replication quality of micropillars under different molding parameters was studied. The capability of injection-molded chips to effectively achieve particle separation was validated. Results showed that thermoplastic chips with good replication quality were obtained, providing a scale-up production strategy for fabricating polymer-based microfluidic chips for disposable separation applications.

The failure and re-initiation of quasi-detonations in stoichiometric acetylene-oxygen mixtures diluted by nitrogen

In this study, the failure and re-initiation of quasi-detonations are investigated systematically in stoichiometric acetylene-oxygen mixtures diluted by nitrogen, and the nitrogen dilution range of 10–45 % is considered. Photodiodes are introduced to obtain the average velocity by recording the detonation time-of-arrival. The smoked foil technique is performed to register the detonation cellular structures, and a high-speed schlieren system is used to observe the propagation processes. Three propagation modes are defined based on nine repeated experiments, i.e., Go, No-go and Critical regimes. For the “go” regime, the exiting detonation all successfully evolves into a spherical detonation in nine repetitions of the experiments. For the “no-go” case, the detonation all fails upon exit and becomes a deflagration. The case between the Go and No-go is called as the critical mode. Near the limits, the critical pressure of successful evolution into a spherical detonation is obtained, and the data indicates that the critical pressure is approximately independent of the wall roughness. But the critical pressure can increase obviously by introducing the nitrogen dilution. The cell sizes for quasi-detonations are measured, and the ratio of the critical tube diameter (dc) to the cell size (λ) is considered to quantify the critical criterion of detonation re-initiation. Note that the previous criterion of dc/λ ≥ 13 about normal detonation re-initiation cannot be applied to the quasi-detonation, and the re-initiation condition for quasi-detonations can be nearly quantified as dc/λ ≥ 8. The results are consistent with those obtained in our previous study (Xuxu Sun et al., Combustion and Flame, 112280). Corresponding to the normal detonation in a smooth tube, the critical value of dc/λ is always lower for quasi-detonations, which indicates a favorable effect on the detonation transmission is verified.

Influence of magnesite/limestone addition on the hydration characteristics of ternary slag cement systems

To explore the potential of magnesite adopted as supplementary cementitious material (SCM) in cement industry, the authors of this paper investigated the hydration characteristics of ternary slag cement mixtures containing magnesite or limestone. All cement pastes were formulated with a water-to-binder ratio of 0.4, and a total of 50 % substitution level was applied across the blends, with varying slag and magnesite/limestone contents. Experimental results confirmed that adding limestone to slag cement can promote the hydration of cement clinker through the nucleation effect, while not for magnesite addition. As the substitution ratio of magnesite increased, there was a notable increase in both the critical pore diameter and cumulative pore volume, leading to a continuous decrease in the compressive strength of cement pastes. Compared to limestone-containing blends, the incorporation of magnesite was more beneficial to the compressive strength at 7 and 28 days. Additionally, limestone facilitated the precipitation of hemi- and mono-carboaluminate, whereas no hemicarbonate was observed in mixtures containing magnesite. The addition of magnesite promoted the formation of hydrotalcite-like phase, and the quantitative analysis revealed that the dissolution of magnesite primarily occurred in the first 7 days. The authors believed that the results obtained in this paper proposed new perspectives on utilizing magnesite as SCM in cement industry.

Links between soil pore structure, water flow and solute transport in the topsoil of an arable field: Does soil organic carbon matter?

An improved understanding of preferential solute transport in soil macropores would enable more reliable predictions of the fate of agrochemicals and the protection of water quality in agricultural landscapes. The objective of this study was to investigate how soil organic carbon (SOC) and soil texture shape soil pore structure and thereby determine the susceptibility to preferential transport under steady-state near-saturated flow conditions. To do so, we took intact topsoil samples from an arable field that has large variations in SOC content (1.1–2.7%) and clay content (8–42%). Soil pore structure was quantified by X-ray tomography and soil water retention measurements. Non-reactive solute transport experiments under steady-state near-saturated conditions were carried out at irrigation rates of 2 and 5 mm h−1 to quantify the degree of preferential transport. Near-saturated hydraulic conductivities at pressure heads of −1.3 and −6 cm were also measured using a tension disc infiltrometer. The results showed that larger abundances of small macropores (240–720 µm diameter) and mesopores (5–100 µm diameter) resulted in weaker preferential transport, due to larger hydraulic conductivities in the soil matrix that prevented the activation of water flow and solute transport in large macropores. In particular, the degree of preferential transport was most strongly and negatively correlated with the mesoporosity in the 30–100 µm diameter class. In contrast, the degree of preferential transport was not correlated with connectivity measures (e.g. the percolating fraction and critical pore diameter for the macropore network), probably because i.) the pore space of almost all samples was highly connected, being dominated by one percolating cluster, and ii.) only a part of this percolating macroporosity was active under the near-saturated conditions of the experiment. We also found that the degree of preferential transport was strongly and negatively correlated with clay content, whilst the effects of SOC were not significant. Nevertheless, macroporosity in the 240–720 µm diameter class and mesoporosity were positively correlated with SOC content in our soils and in some previous studies. Therefore, SOC sequestration in arable soils may potentially reduce the risk of preferential transport under near-saturated flow conditions through better developed networks of small macropores and mesopores.

Dependence of Pressure Characteristics of Pressurized Pulse Water Jet Chamber on Nozzle Diameter

The nozzle is the key element of the water jet generator for energy conversion. In order to explore the influence of the nozzle diameter on the pressure characteristics of the supercharged pulsed water jet plenum chamber, a supercharged pulsed water jet pressure acquisition system was established, and the equations of motion and theoretical pressurization ratio equations of the supercharged pulsed water jet generator were established. The pressurization chamber pressure acquisition experiments under different nozzle diameters were carried out. The research results show that the pressurized pulsed water jet generator has a critical nozzle diameter of 0.6 mm. When the nozzle diameter is less than the critical diameter, the pressure in the boost chamber is equal to the product of the driving pressure and the boost ratio. As the nozzle changes, there is no significant change in the peak pressure and frequency of the boost chamber. When the nozzle diameter is greater than the critical diameter, there is a non-linear relationship between the boost chamber pressure and the driving pressure. As the nozzle diameter gradually increases, the actual boost ratio gradually decreases, and the peak pressure of the boost chamber further decreases. The nozzle diameter can no longer provide a load for the establishment of fluid pressure in the boost chamber. The results of this research provide a research basis for further controlling the pressure characteristics of the boost pulse water jet.

CFD Research on Natural Gas Sampling in a Horizontal Pipeline

Accurately determining if the sample parameters from a natural gas pipeline’s sampling system reflect the fluid characteristics of the main pipe has been a significant industry concern for many years. In this paper, samples of natural gas in a horizontal pipeline are investigated. CFD is used in this work and the turbulence is considered in the simulation. Firstly, the critical diameter for particles affected by gravity within such pipeline is determined. And then, the effects of the operation pressure and velocity of sampling branches on sample parameters, and the influence of particle density on these sample parameters, are analyzed. Finally, four different structures of sample branches for natural gas in a horizontal pipeline are compared. It is found that 100 μm is the critical diameter at which particles are affected by gravity; the operating pressure of the sampling branch has a significant impact on the particle mass concentration. The particle density has little impact on the sampling system. Overall, the design of the sampling branches does not cause significant sampling errors. This study provides guidance for optimal sampling in existing natural gas pipelines and enables effective monitoring of particle impurity content and properties in natural gas.