Flow Density Research Articles

Stable bubble formations in a depth-perturbed Hele-Shaw channel

The propagation of polydisperse bubbles inside a rectangular Hele-Shaw channel by the constant volumetric flux flow of an ambient viscous liquid is generally unsteady; pairs of neighboring bubbles will either separate or coalesce because their propagation speeds increase monotonically with their sizes. Thus, any group of bubbles will eventually rearrange itself in order of decreasing size, individual bubbles will separate, and, crucially, there are no stable multiple-bubble states. Remarkably, the introduction of a small axially uniform elevation to the channel's lower boundary (on the order of a percent of the channel's depth) leads to the creation of stable multiple-bubble states and, thus, disrupts the usual reordering by bubble sizes. The constituent bubbles of such states lie in alternation on opposite sides of the elevation. The elevation provides a mechanism for the trailing bubbles to reduce their propagation speeds when approaching their preceding nearest neighbors. The stable multiple-bubble states are always led by the smallest bubble while the trailing bubbles can be arranged in any order and, thus, their number grows factorially as the number of bubbles increases. Published by the American Physical Society 2024

A Review of Research on the Stability of Fine-Grained Sediments in Debris Flows

Fine-grained sediments in debris flows refer to Quaternary sediments with grain sizes smaller than 2 mm. Their stability is closely related to the initial water threshold that triggers the debris flows and thus controls the density, scale, and damage of the debris flows. Based on this, they play a key “probe” role in early warnings of debris flows. Studies on fine-grained sediment stability are related to the accuracy and efficiency of early warnings of debris flows and thus play an important role in ensuring the safety of people and property. There have been some studies on fine-grained sediment stability in debris flows, but no one has carried out a systematic analysis and summary of this field. Therefore, in response to the urgent need for high-precision early warnings of debris flows, firstly, we review the current research on the aspects of fine-grained sediment stability, initiation, triggering, physical properties, hyperspectral remote sensing, and early warning systems; secondly, we summarize the main problems related to high-precision early warnings of debris flow hazards; and finally, we outline the future directions of research on fine-grained sediment stability in debris flows.

Heat Transfer Enhancement in a 3D-Printed Compact Heat Exchanger

The study describes experimental data on thermal tests during the condensation of HFE7100 refrigerant in a compact heat exchanger. The heat exchanger was manufactured using the additive 3D printing in metal. The material is AISI 316L steel. MPCM slurry was used as the heat exchanger coolant, and water was used as the reference medium. The refrigerant was condensed on a bundle of circular tubes made of steel with an internal/external diameter of di/de = 2/3 mm, while a mixture of water and phase change materials as the coolant flowed through the channels. Few studies consider the heat exchange in condensation using phase change materials; furthermore, there is also a lack of description of heat exchange in small-sized exchangers printed from metal. Most papers deal with computer research, including flow simulations of heat exchange. The study describes the process of heat exchange enhancement using the phase transition of coolant. Experimental data for the mPCM slurry coolant flow was compared to the data of pure water flow as a reference liquid. The tests were carried out under the following thermal and flow conditions: G = 10–450 [kg m−² s−1], q = 2000–25,000 [W m−²], and ts = 30–40 [°C]. The conducted research provided many quantities describing the heat exchange in compact heat exchangers, including heat exchanger heat power, heat exchange coefficient, and heat exchange coefficients for working media. Based on these factors, the thermal performance of the heat exchanger was described. External characteristics include the value of the thermal power and the heat exchange coefficient as a function of the mass flow density of the working medium and the average logarithmic temperature difference. The performance of the heat exchanger was presented as the dependencies of the heat exchange coefficients on the mass flux density and the heat flux density on the heat exchange surface. The thickness of the refrigerant’s condensate film was also determined. Furthermore, a model was proposed to determine the heat exchange coefficient value for the condensing HFE7100 refrigerant on the outer surface of a bundle of smooth tubes inside a compact heat exchanger. According to experimental data, the calculation results were in good agreement with each other, with a range of 25%. These data can be used to design mini condensers that are widely used in practice.

Investigating Molecular Adsorption on Graphene-Supported Platinum Subnanoclusters: Insights from DFT + D3 Calculations.

Platinum (Pt) subnanoclusters have become pivotal in nanocatalysis, yet their molecular adsorption mechanisms, particularly on supported versus unsupported systems, remain poorly understood. Our study employs detailed density functional theory (DFT) calculations with D3 corrections to investigate molecular adsorption on Pt subnanoclusters, focusing on CO, NO, N2, and O2 species. Gas-phase and graphene-supported scenarios are systematically characterized to elucidate adsorption mechanisms and catalytic potential. Gas-phase Pt n clusters are first analyzed to identify stable configurations and assess size-dependent reactivity. Transitioning to graphene-supported Pt n clusters, both periodic and nonperiodic models are employed to study interactions with graphene substrates. Strong adsorbate interactions predominantly occur at single top sites, revealing distinct adsorption geometries and stabilization effects for specific molecules on Pt6 clusters. Energy decomposition analysis highlights the paramount role of graphene substrates in enhancing stability and modulating cluster-adsorbate interactions. The interaction energy emerges as a critical criterion within the Sabatier principle, crucial for distinguishing between physisorption and chemisorption. Hybridization indices and charge density flow tendencies establish direct relationships with stabilization processes, underscoring graphene's influence in stabilizing highly reactive subnanoclusters. This comprehensive investigation provides critical insights into molecular adsorption mechanisms and the catalytic potential of graphene-supported Pt nanoclusters. Our findings contribute to a deeper understanding of nanocatalysis, emphasizing the essential role of substrates in optimizing catalytic performance for industrial applications.

Performance of combined organic precipitation, electrocoagulation, and electrooxidation in treating anaerobically treated palm oil mill effluents

Palm oil mill effluent (POME), wastewater generated from palm oil production, is known for its extremely high chemical oxygen demand and brownish color. Anaerobic digestion is the primary treatment method for POME in the palm oil industry; however, anaerobically treated POME has high concentrations of residual contaminants and color intensity. This study proposes an approach to treat anaerobically-treated POME in recycled water for industrial applications by integrating preliminary organic precipitation, electrocoagulation, and electrooxidation (EO). The EO process was optimized in terms of the current density, electrolysis time, electrode arrangement, and feed flow rate. At a current density of 60 mA/cm2 and an electrolysis time of 9 min, the EO process with a graphite anode and stainless-steel cathode in the monopolar electrode configuration reduced the phenolic concentration and color in the preliminary-treated POME from 8.95 mg/L and 317.19 ADMI to 0.25 mg/L and 26.10 ADMI, respectively. Additionally, the EO process exhibited a 92.26% efficiency in lowering the ammonium-nitrogen content.

Exergy Flow as a Unifying Physical Quantity in Applying Dissipative Lagrangian Fluid Mechanics to Integrated Energy Systems.

Highly integrated energy systems are on the rise due to increasing global demand. To capture the underlying physics of such interdisciplinary systems, we need a modern framework that unifies all forms of energy. Here, we apply modified Lagrangian mechanics to the description of multi-energy systems. Based on the minimum entropy production principle, we revisit fluid mechanics in the presence of both mechanical and thermal dissipations and propose using exergy flow as the unifying Lagrangian across different forms of energy. We illustrate our theoretical framework by modeling a one-dimensional system with coupled electricity and heat. We map the exergy loss rate in real space and obtain the total exergy changes. Under steady-state conditions, our theory agrees with the traditional formula but incorporates more physical considerations such as viscous dissipation. The integral form of our theory also allows us to go beyond steady-state calculations and visualize the local, time-dependent exergy flow density everywhere in the system. Expandable to a wide range of applications, our theoretical framework provides the basis for developing versatile models in integrated energy systems.

Comparative of OCT and OCTA parameters in patients with early chronic angle-closure glaucoma and early pituitary adenoma

Optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) have the potential application in evaluating pathological structural change of the optic nerve. We aimed to evaluate the value of the OCT and OCTA parameters of the optic disk and macular in differentiating early chronic primary angle-closure glaucoma (CPACG) and early pituitary adenoma (PA) in case of mild visual field defects (the mean defect (MD) > 6 dB). The results showed that regarding OCTA parameters, CPACG patients had lower retinal blood flow density of most layers of the optic disk and macular than PA patients. Regarding OCT parameters, CPACG patients had thinner circumpapillary retinal nerve fiber layer (CP-RNFL) in all quadrants and average CP-RNFL, ganglion cell layer (GCL) and macular ganglion cell complex (GCC) in each quadrant of macular inner and outer rings, and inner plexus layer (IPL) of macular inner ring, superior-outer ring and temporal-outer ring than PA patients. The Z test indicated that OCTA parameters and OCT parameters had similar value in the diagnosis of disease. In conclusion, in the case of similar visual field damage, early CPACG patients have smaller blood flow density and thinner optic disk and macular than early PA. OCTA has similar performance to OCT in diagnosing CPACG and PA.

The Retinal Blood Flow Density Is Related to the Pathological Severity of Diabetic Kidney Disease

Introduction: This study aimed to investigate the correlation between fundus blood flow parameters and the severity of pathological biopsy in patients with diabetic kidney disease (DKD). Methods: Data of patients with type 2 diabetes mellitus who completed renal pathology biopsies and optical coherence tomography angiography (OCTA) examinations, including renal function, 24-h urine protein quantification, and macular flow imaging, were collected. DKD pathology biopsies were graded as stages 1–4, and differences and correlations of the parameters were compared between groups. The grading was transformed into early (stage 1) and late (stages 2–4), and regression analyses were conducted to develop a model, draw a nomogram, and test efficacy. Results: This study included 157 eyes from 157 individuals in total. Urinary microalbumin and to urinary creatinine ratio (mALB/NCR) increased with pathological grading, whereas while glomerular filtration rate was decreased (p < 0.01). Corresponding retinal blood flow in superficial, deep, and full paracentral rings was decreased, which correlated with pathological grading (p < 0.01), with the highest blood flow density in the whole layer (r2 = −0.707). Meaningfully, in the early DKD model (area under the curve = 0.929 [0.889–0.970], p < 0.01), whole-layer blood flow density, mALB/NCR, and diabetes duration were statistically significant. Conclusions: The decrease in macular retinal blood flow density detected by OCTA is closely associated with the increase in pathological grading of DKD and can be used as a noninvasive parameter for monitoring early changes in DKD.

The preparation technology and catalytic mechanism of PVDF/PVP/a-MoSx porous membrane for water flow driven piezoelectric PMS activation

Piezoelectric catalysis couples with peroxymonosulfate (PMS) activation technology can efficiently increase the yield of reactive oxygen species (ROS). Herein, a novel flexible polyvinylidene difluoride/polyvinyl pyrrolidone/amorphous molybdenum sulfide (PVDF/PVP/a-MoSx) membrane with finger-like pore structure was prepared by non-solvent induced phase separation (NIPS) method. As a result, a-MoSx nanosheets can be exposed out of the pores to provide multiple active sites. The PVDF/PVP/a-MoSx with large dipole moment can form enhanced polarization field under water flow to accelerate the charges separation and transfer, thereby promoting the breakage of the OO bond of PMS. The mechanism of piezo-photocatalytic activated PMS was confirmed by COMSOL multiphysics simulations, electrochemical experiments, contribution of active species and DFT calculations. Moreover, a self-cycling degradation reactor was proved more effective in generating piezoelectric potential and improving the degradation efficiency, supporting the practical potential of this strategy. This study provides a new platform to develop piezoelectric porous membrane for enhanced PMS activation under low density flow water energy.

Relationship between the induced voltage of a rotor bar and the rotation characteristics of a high-temperature superconducting induction motor

Although high-temperature superconducting induction motors have a simple structure, they are distinguished by their high efficiency and high power density. However, an accurate theoretical model that defines the primary electrical characteristics controlling the motor has not been established because of the nonlinear characteristics of high-temperature superconducting squirrel-cage rotor winding. As part of establishing such a model, an experiment was conducted to analyze the relationship between the induced voltage of the rotor bar in a high-temperature superconducting squirrel-cage rotor winding and stator-side quantities (voltage and transport current), as well as its rotation characteristics. A subject was a 1.5 kW class induction motor using Bi–Sr–Ca–Cu–O high-temperature superconducting rotor bars and the experiment was performed at a temperature and a frequency of 77 K and 60 Hz, respectively. The induced voltages of the rotor bars were measured by applying a rotating magnetic field and exhibited a distorted waveform characterized by a third-order harmonic in a magnetic flux flow state. Despite the distorted voltage waveform of the rotor bar, the stator transport current responsible for driving the induction motor remained unaffected and the motor initiated rotation in a slip rotation mode. From the above results, it was experimentally clarified that a stator voltage exceeding the critical current of the rotor bar must be applied when starting the induction motor. It was also shown that the rotor bar can be regarded as a constant resistance for a constant effective value of the stator current when transitioning the motor into a slip rotation state.

Brain Microvascular Pericyte Pathology Linking Alzheimer's Disease to Diabetes.

The brain microvasculature, which delivers oxygen and nutrients and forms a critical barrier protecting the central nervous system via capillaries, is deleteriously affected by both Alzheimer's disease (AD) and type 2 diabetes (T2D). T2D patients have an increased risk of developing AD, suggesting potentially related microvascular pathological mechanisms. Pericytes are an ideal cell type to study for functional links between AD and T2D. These specialized capillary-enwrapping cells regulate capillary density, lumen diameter, and blood flow. Pericytes also maintain endothelial tight junctions to ensure blood-brain barrier integrity, modulation of immune cell extravasation, and clearance of toxins. Changes in these phenomena have been observed in both AD and T2D, implicating "pericyte pathology" as a common feature of AD and T2D. This review examines the mechanisms of AD and T2D from the perspective of the brain microvasculature, highlighting how pericyte pathology contributes to both diseases. Our review identifies voids in understanding how AD and T2D negatively impact the brain microvasculature and suggests future studies to examine the intersections of these diseases.

N6-methyladenosine modification of SLC38A7 promotes cell migration, invasion, oxidative phosphorylation, and mitochondrial function in gastric cancer

Solute carrier (SLC) 38 family responsible for trans-membrane transport of neutral amino acids, plays a role in the proliferation, invasion, and metastasis of cancer cells, but its role in gastric cancer (GC) progression remains unclear. This study aimed to explore the biological effects of SLC38A7 and its regulatory mechanisms in GC. RNA expression data, tumor tissue specimens, and GC cell lines were used for bioinformatics and experimental analyses. Cell Counting Kit-8 assay, wound healing assay, and Transwell invasion assay were used to evaluate cell viability, migration, and invasion, respectively. Oxidative phosphorylation, mitochondrial membrane potential and expression of the critical proteins in the mitochondrial respiratory chain were assayed using extracellular flux analysis, flow cytometry, and Western blot, respectively. RNA immunoprecipitation assay was used to explore the mechanisms of N6-methyladenosine (m6A) methylation. SLC38A7 was upregulated in GC tissue and cell lines. SLC38A7 silencing suppressed cell viability, migration, invasion, oxidative phosphorylation, and mitochondrial function in cancer cells. SLC38A7 overexpression had the opposite biological effects. Interactions between SLC38A7 and methyltransferase like 3 (METTL3) or insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2) were detected. SLC38A7 mRNA stability was maintained by METTL3/IGF2BP2 axis in an m6A-dependent manner. Our results suggest that SLC38A7, stabilized by METTL3 and IGF2BP2-mediated m6A methylation, enhances cell viability, migration, invasion, oxidative phosphorylation, and mitochondrial function in GC, highlighting its role as a potential therapeutic target for GC.

A High Current Density and Long Cycle Life Iron Chromium Redox Flow Battery Electrolyte

A High Current Density and Long Cycle Life Iron Chromium Redox Flow Battery Electrolyte

Modeling of particle migration in piping based on an improved discrete element method

Pore-scale particle migration in piping is the main reason of the suffusion-induced damage, which poses a significant threat to earth-rock dams. In order to investigate the micro-mechanism of piping seepage process, an improved fluid-solid coupling discrete element method is proposed in this paper. In this method, particles in a packed model are divided into coarse- and fine particle groups. Pores can be defined based on the coordinates of the coarse particles and the Delaunay triangulation algorithm. A pore density flow method is introduced to calculate the overall fluid pressure of each pore and the fluid flow via pore throats. Further, the drag force on fine particles inside a pore can be calculated according to the fluid velocities of the neighboring four pore throats. The proposed method was implemented in the discrete element software MatDEM, and was successfully used to simulate fine particle migration of piping, the particle loss process, and the related variation of permeability coefficient. The pore-jamming phenomenon during the fine particle migration is observed. The model provides an effective way for the numerical analysis and mechanism study of piping seepage process at the pore scale.

Nutritional status of the reservoir tributary backwater area and implications for nutrient control

Understanding the spatial and temporal distribution and driving factors of the nutritional status in the backwater area of typical tributaries in the Three Gorges Reservoir Region (TGRR) is important for the prevention and control measures. In this study, the Environmental Fluid Dynamics Code (EFDC) was used to extend in situ monitoring data, followed by the application of hydrogen and oxygen isotope data and scoring methods to predict the nutritional status in the backwater area of the Daning River. The results indicated that the nutritional status-sensitive period mainly ranged from May-October and was distributed at the end of the backwater area and tributary bay. The water temperature and intermediate density flow were identified as the key factors inducing deterioration in the nutritional status at the end of the backwater area and tributary bay, respectively. Nutrient reduction in the mainstream and tributary areas significantly affected the nutritional status in the backwater area. Notably, hydrodynamic adjustment under reservoir objectives is indispensable for improving the water environment in tributary bay after reaching the water quality standard. Our findings highlight the necessity of focusing on the upper reaches of the tributaries and reservoir for nutrient control and emphasize the importance of combining reservoir operation strategies to mitigate the deterioration in the nutritional status.

Phytohormones enhanced carbon fixation and biomass production in CO2 absorption-microalgae conversion system under light stress

CO2 absorption-microalgae conversion (CAMC) system can be a sustainable technology to achieve low-energy carbon capture and resource utilization in response to zero carbon. However, light stress could restrict the carbon utilization efficiency of CAMC system. In this study, melatonin (MT) and indole-propionic acid (IPA) as phytohormones, were used to promote the carbon fixation capacity and biomass yield of CAMC system under light stress, and the potential mechanism was also discussed. Both MT and IPA promoted the growth of Spirulina, and 10 mg-MT group obtained the highest biomass and carbon fixation capacity, which were 27.61 % and 30.62 % higher than control. MT and IPA promoted the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR), enhancing antioxidant activity to avoid oxidative damage. The results of transmission electron microscopy (TEM) and cell apoptosis showed MT and IPA reduced cell membrane damage and apoptosis. Phytohormones induced the carbon flux flow to the synthesis of carbohydrate and protein, and increased carbohydrate and protein productivity. Moreover, the maximum phycocyanin content and yield were 13.74 % and 43.25 % higher than the control. Therefore, adding phytohormones was an effective strategy to achieve high-value bioresources of microalgae in CAMC system under light stress.

Development of a transient analysis code for trans-critical simulation of SCWR

Supercritical water-cooled reactors (SCWR) experience pressure reductions below the critical point during a loss of coolant accident (LOCA). During the reactor depressurization, boiling crises may occur, leading to pressure fluctuations and significant increases in wall temperatures, posing a severe threat to the cladding. In this study, a one-dimensional transient analysis code has been developed to incorporate one-dimensional steady-state flow equations in the fluid domain and transient thermal conductivity equations in the solid domain. The code also includes a wall heat transfer model and a model for the velocity of the moving quench front to simulate transcritical depressurization transient processes. The simulation successfully predicts the typical experimental phenomena. It is reasonable to use the critical temperature as the demarcation point between the dry and wet conditions of the axial wall of the rod bundle under transcritical conditions. By combining the experimental data with the program calculations, the critical interface for the occurrence of boiling crisis under transcritical conditions is determined using mass flow rate, heat flow density and fluid temperature as inputs. The criterion for the occurrence of CHF under transcritical conditions is obtained, which provides a reference to the safety analysis of SCWRs.

Impact of initial outbreak locations on transmission risk of infectious diseases in an intra-urban area

Infectious diseases usually originate from a specific location within a city. Due to the heterogenous distribution of population and public facilities, and the structural heterogeneity of human mobility network embedded in space, infectious diseases break out at different locations would cause different transmission risk and control difficulty. This study aims to investigate the impact of initial outbreak locations on the risk of spatiotemporal transmission and reveal the driving force behind high-risk outbreak locations. First, we built a SLIR (susceptible-latent-infectious-removed)-based age-stratified meta-population model, integrating mobile phone location data, to simulate the spreading process of an infectious disease across fine-grained intra-urban regions (i.e., 649 communities of Shenzhen City, China). Based on the simulation model, we evaluated the transmission risk caused by different initial outbreak locations by proposing three indexes including the number of infected cases (CaseNum), the number of affected regions (RegionNum), and the spatial diffusion range (SpatialRange). Finally, we investigated the contribution of different influential factors to the transmission risk via machine learning models. Results indicate that different initial outbreak locations would cause similar CaseNum but different RegionNum and SpatialRange. To avoid the epidemic spread quickly to more regions, it is necessary to prevent epidemic breaking out in locations with high population-mobility flow density. While to avoid epidemic spread to larger spatial range, remote regions with long daily trip distance of residents need attention. Those findings can help understand the transmission risk and driving force of initial outbreak locations within cities and make precise prevention and control strategies in advance.

Balancing current density and electrolyte flow for improved zinc-air battery cyclability

Zinc-air batteries (ZABs), known for their high energy density and environmental friendliness, are emerging as promising solutions for sustainable energy storage. However, the irregular deposition of zinc on electrodes hinders the widespread utilization of rechargeable ZABs due to limited durability and stability. This study investigates the role of electrolyte flow in enhancing zinc electrodeposition and overall performance in zinc-air flow batteries (ZAFBs) at high current densities. We explore the interplay between current density, flow rate, and their influence on electrode surface morphology and the removal of the passivating zinc oxide layer to improve battery efficiency and lifespan. Using advanced in-situ synchrotron radiation x-ray tomography, we found that incorporating flowing electrolyte at specific current densities results in rounded dendrite tips, thinner and more uniform deposition layers, and improved zinc adhesion. Imaging and electrochemical analyses further reveal that flowing electrolyte enhances zinc morphology, reduces charge transfer resistance, diminishes passivation, and lowers galvanostatic charge/discharge polarization across various current densities, thereby improving battery cycling performance. Notably, the impact of flowing electrolyte is more pronounced at a moderate current density of 50 mA/cm2 compared to lower or higher currents. Our findings underscore the importance of electrolyte flow and current density management in developing high-performance ZAFBs, providing valuable insights for their future commercialization.

From Field to Pharmacy: Isolation, Characterization and Tableting Behaviour of Microcrystalline Cellulose from Wheat and Corn Harvest Residues.

A lack of strategies for the utilization of harvest residues (HRs) has led to serious environmental problems due to an accumulation of these residues or their burning in the field. In this study, wheat and corn HRs were used as feedstock for the production of microcrystalline cellulose (MCC) by treatment with 2-8% sodium hydroxide, 10% hydrogen peroxide and further hydrolysis with 1-2 M hydrochloric acid. The changes in the FT-IR spectra and PXRD diffractograms after chemical treatment confirmed the removal of most of the lignin, hemicellulose and amorphous fraction of cellulose. A higher degree of crystallinity was observed for MCC obtained from corn HRs, which was attributed to a more efficient removal of lignin and hemicellulose by a higher sodium hydroxide concentration, which facilitates the dissolution of amorphous cellulose during acid hydrolysis. MCC obtained from HRs exhibited lower bulk density and poorer flow properties but similar or better tableting properties compared to commercial MCC (CeolusTM PH101). The lower ejection and detachment stress suggests that MCC isolated from HRs requires less lubricant compared to commercial MCC. This study showed that MCC isolated from wheat and corn HRs exhibits comparable tableting behaviour like commercial sample, further supporting this type of agricultural waste utilization.