Multiple Flow Research Articles

Separations of meltwater discharge in a snowpack by artificial rain-on-snow experiments

In temperate regions, snow and its meltwater constitute primary freshwater resources and snowmelt isotopes offer valuable insights into understanding the snowmelt processes including the timing and contribution of snowmelt to the soil and watershed in spring. Assessing the storage and movement of liquid water within natural snowpacks, a previously unquantified aspect, holds significance for predicting natural hazards and managing water resources for agricultural purposes and ecosystem health. The escalating occurrence of rain-on-snow (ROS) events, attributed to winter warming, has the potential to trigger natural hazards and surface runoff into major river systems in temperate climate regions. End member mixing calculations (EMMC) based on isotopic and chemical tracers were employed to quantify the proportions of rainwater, meltwater, and pore water within the snowpack discharge. In this study, artificial rain-on-snow experiments involving conservative anions and stable water isotopes were conducted at the surface of snowpack to differentiate each component (rainwater, pore water, and snowmelt) within the discharge collected at the bottom of the snowpack. Pore water content exhibited a shift from 1.1 ± 1.1% (± 1σ, N = 23) after the initial artificial ROS event to 2.8 ± 1.2% (± 1σ, N = 19) following the spray in our experiment. Based on the EMMC, the contributions of rainfall, pore water, and snowmelt to the meltwater discharge were 2,620.2 L (63.3%), 829.0 L (20.0%), and 687.4 L (16.6%), respectively. Notably, contrary to prior studies, our experimental results suggest that rainwater reached the bottom through multiple rapid flow channels before matrix flow occurred. This experimental approach provides additional insights into the dynamics of water percolation in snowpacks during rain-on-snow events.

Study on characteristics and prediction of the pressure drag of the swept strut under supersonic wide-range conditions

In this paper, the numerical simulation of the swept strut ramjet combustor was carried out under wide-range conditions (Ma3 = 1.8 ∼ 5.0), and the pressure drag characteristics of the swept strut were discussed. The results show that the pressure drag characteristics of the swept strut are related to the Mach number of the combustor inlet and the swept angle of the strut. The decreased boundary of the strut pressure drag coefficient gradually advances with the decrease of the Mach number of the combustor inlet. When Ma3 = 1.8 ∼ 2.0, the pressure drag reduction boundary is α = 15°. When Ma3 = 2.2 ∼ 2.8, the pressure drag reduction boundary is α = 45°. When Ma3 = 3.0 ∼ 4.0, the pressure drag reduction boundary is α = 60°. When Ma3 = 5.0, the pressure drag reduction boundary is α = 65°. In addition, with the decrease of the Mach number of the combustor inlet, the pressure drag reduction performance benefit brought by increasing the swept angle of the strut will gradually increase. Furthermore, a pressure drag coefficient prediction model suitable for wide-range conditions and multiple configurations of swept struts was proposed based on deep learning. The prediction model consists of two parts in series, which includes the prediction model of the surface pressure coefficient of the swept strut based on multilayer perceptron (MLP) and the prediction model of the pressure drag coefficient of the swept strut based on convolutional neural network (CNN). To improve the prediction accuracy of the MLP model, new training samples were added based on the ensemble-based uncertainty quantification, and the improved MLP model was obtained by retraining. The results show that both the two prediction models have high prediction accuracy under the effect of multiple complex flow characteristics on the strut. The results of this study are helpful to provide a reference for the aerodynamic drag reduction design of the strut in the wide-speed supersonic combustor.

Numerical investigation of PEMFC performance based on different multistage serpentine flow field designs

The design of excellent flow fields can significantly enhance the output current density and improve the uniformity of reactant distribution in PEMFC (Proton Exchange Membrane Fuel Cell). Serpentine flow field has gained more attention due to its outstanding performance and simple structure, but there is little research on multi-channel serpentine flow field considering the consumption of reactant. In this paper, flow fields named multi-s and multi-pis were designed by considering reactant consumption, and compared with the traditional serpentine flow fields including 3 s, 5 s, 3pis and 5pis. Compared with 3 s and 5 s, the average power density of multi-s increased by 0.687 % and 1.256 %, respectively. The average power density of multi-pis increased by 0.326 % and 1.829 %, as compared to that of 3pis and 5pis. Moreover, the utilization of multiple serpentine and parallel flow fields enhances the uniformity of reactant distribution and current density. The paper further investigates the impact of inlet humidity, operating temperature and supply back pressure on the performance of these six flow fields at a working voltage of 0.45 V. The variations of operating parameters exert varying degrees of influence on the different flow fields, multi-s and multi-pis flow fields consistently demonstrating superior performance to the other four flow fields. The present study offers practical guidance for the implementation of PEMFCs, encompassing optimization strategies for flow field design, operation.

Multiple factor flows and heterogeneous premium of urban house prices: Empirical evidence from Chinese cities

Notable Regional heterogeneity is commonly observed in housing markets. This study examines how multiple factor flows affect urban house prices and the resulting premium. It utilizes over 100 million pieces of Chinese intercity factor flow data to construct a multi-layer network and introduces a new metric called multiple connectivity quality to measure a city's comprehensive factor connection capability. Empirical analysis reveals that cities with higher multiple connectivity quality tend to exhibit higher price premiums, making them more resilient to market fluctuations. This study offers fresh insight into regional heterogeneity within housing markets and holds practical significance for stabilizing these markets.

Solving optimal power flow frameworks using modified artificial rabbit optimizer

The present study introduces a nature inspired modified artificial rabbit optimizer (MARO) for solving the non-convex engineering optimization issues. The traditional artificial rabbit optimizer (t-ARO) reflects the survival strategies of the rabbits’ behaviors to avoid being hunted by the enemies, for which rabbits followed the detour scavenging and hiding strategies. However, the t-ARO still suffers from the stagnation complication and may cause of wrong in solution. To avoid early stagnation problem in t-ARO, the study proposes the three novel modifications in this approach. First modification is based on the fitness-distance balance (FDB) mechanism to boost up the searching capability of the rabbits’, while the second and third modifications are implemented to improve the exploitation strength of the t-ARO via prairie dogs (PD) and combination of quasi with opposite-based learning (QOBL) boosting mechanisms. To validate the effectiveness of the MARO, the statistical and non-parametric tests are conducted via standard benchmark functions. Furthermore, MARO is implemented to handle the single and the multiple objectives power flow frameworks using IEEE 30-bus and 57-bus standards. For authentication, the performance of proposed MARO is compared to the well-known techniques such as antlion optimizer (ALO), whale optimization algorithm (WOA), sine-cosine algorithm (SCA), dandelion optimizer (DO), artificial hummingbird algorithm (AHA), equilibrium optimizer (EO) and traditional artificial rabbit optimizer (t-ARO). The simulation outcomes declare that MARO establishes great superiority over the state-of-the-arts techniques.

Proposal of a facet-to-facet multiple flow direction algorithm based on geometrical and mathematical analysis of physical dispersion over triangle facet

Flow direction algorithms have been widely used to extract crucial terrain attributes of great hydrological and geomorphological significance. However, essential distinctions between the empirically-designed strategies of typical algorithms and the natural rules of physical dispersions bring various problems (e.g. parallel channel, artificial dispersion), leading to the low size and extent precisions of estimated results. In this work, geometrical and mathematical analysis is conducted on the inherent characteristics of physical dispersions along slope lines on local terrains. On each 3 × 3 window of digital elevation model (DEM), center pixel is divided into eight non-overlapping sub-facets. Necessary and sufficient (NS) conditions of size relationships between the elevations of adjacent pixels are summarized to directly identify the receiving facets of a sub-facet. Then, strict mathematical relations are derived between slope direction of a sub-facet and flow proportions allocated to receiving facets. A strategy is designed to re-adjust receiving facets and flow proportions for the boundary flow of adjacent facets. Lastly, a multiple-flow-direction algorithm called TFGA is proposed with the NS condition of size relationships, mathematical relation of slope direction with flow proportion, and adjustment strategy of boundary flow. Case studies are conducted for investigating the total contributing areas (TCA) and specific contributing areas (SCA) estimated by TFGA. Results reveal all-side superiorities of TFGA to typical algorithms in spatial patterns, error indicators and statistic characteristics of estimated TCAs and SCAs. Particularly, TFGA improves size precision of estimated results by approximately one order of magnitude. In a conclusion, we highly recommend TFGA for digital elevation analysis.

Net-zero carbon emission oriented Bi-level optimal capacity planning of integrated energy system considering carbon capture and hydrogen facilities

The integrated energy system (IES) is considered an efficient energy provision paradigm to improve the utilization efficiency of renewable generation (RG), reduce energy cost and improve energy supply reliability. However, the multi-dimensional uncertainties and the hydrogen utilization have posed enormous challenges to the optimal planning of the IES. This paper proposes a net-zero carbon emission oriented bi-level optimal planning model for the IES with full consideration of the multiple operational uncertainties in the IES (RG, multiple demands). The upper level is an optimal capacity configuration model, and the economic costs, energy selling profits, the penalty for power abandonment and energy supply shortage are settled as the objectives. The lower level is an optimal energy dispatch model with the objective function of minimizing the total operating cost of the IES on typical days. An integrated energy system framework consisting of multiple energy flows is formulated in the presence of carbon capture system (CCS) and hydrogen-to-power (H2P) facilities. To fully characterize the uncertainties of RG and multiple demands, a data-driven scenario generation method is adopted to expand the operational scenarios, in which probability distribution assumptions and prior knowledge are not necessary. Finally, the effectiveness of the proposed solution is extensively demonstrated through numerical simulation, and a sensitivity analysis is carried out to assess the impact of changes in electricity and gas prices on the IES planning results.

Coupled Modeling of Computational Fluid Dynamics and Granular Mechanics of Sand Production in Multiple Fluid Flow

Summary Sand production is a significant issue in oil and gas fields with poorly consolidated formations, often involving the multiphase flow of reservoir fluids and solid particles. The multiscale mechanisms of sand production, particularly fluid flow and particle movement, remain poorly understood. This study investigates these mechanisms using a coupled computational fluid dynamics and discrete element method (CFD-DEM) modeling approach. Single and multiple fluid flows of water and heavy oil were simulated with increasing fluid injection velocities, leading to different sand production patterns. The simulation results were compared with experimental results from a large cylindrical specimen of weak artificial sandstone under similar loading conditions. The multiphase conditions created various localized flow and deformation patterns that influenced both fluid and solid production, resulting in shorter transient sand production periods. Microstructures and phenomena such as fingering and water coning were observed, associated with a critical flow rate below which oil displacement was uniform and no water breakthrough occurred. Higher fluid injection velocities and fluid viscosities resulted in greater drag forces, leading to progressive damage zones and explaining the occurrence of single or multiple staged sand production events. The evolution of the microscopic granular structure was visualized under the effect of transient sand production.

Structural multistability for multi-speed wind energy harvesting from vortex-induced vibrations

Abstract Piezoelectric energy harvesters utilizing vortex-induced vibrations (VIV) have been extensively studied for converting wind energy into usable power for microelectronics. In this work, we explore the use of structural bistability to increase the range of flow speeds over which energy can be harvested without the need for complicated assemblies. We propose a harvester system featuring a piezoelectric transducer bonded to a cantilevered bistable composite laminate, which has two distinct equilibrium shapes at room temperature. To enhance the VIV, we attach a cylindrical bluff body to the free edge of the harvester. The structure’s inherent bistability allows for high power generation at two different flow speeds, contrasting with the single synchronization region typical of linear piezoelectric harvesters. We develop a reduced-order model to predict power output across varying flow speeds and validate these predictions through wind tunnel experiments, showing good agreement. Furthermore, we conduct a parametric study to optimize the model parameters for maximum power output. Our results demonstrate that the bistable harvester can generate up to 4.5 mW of power over a wind speed range of 9.3 m s−1–11.7 m s−1, outperforming the limited speed range of traditional linear VIV-based harvesters. This work underscores the potential to design VIV-based energy harvesters capable of operating efficiently across multiple flow speed ranges using a single structure with its dual stable configurations.

Coordination of energy loss and fish friendliness for a low-head tubular-pump blade based on a multi-objective optimization model

Tubular pumps and turbines are the water-to-electricity conversion devices widely used in pumped hydro storage systems for low heads and high flow rates. An ecological concern is the high proportion of fish injuries caused by the rotating blades. In this study, a tubular pump blade is retrofitted to balance the energy loss and fish friendliness through multi-objective optimization, combining computational fluid dynamics with a mathematical blade strike model. Sensitivity analysis identifies nine geometric variables out of thirteen for optimizing blade design. An approximation model is developed to implement optimization algorithm and achieve the objective function. By artificially assigning weights to targeted performance metrics, three scenarios are obtained: the optimal efficiency scheme (A), the optimal fish friendliness scheme (C) and the balanced scheme (B). Scheme C achieves a fish survival ratio of 100 % at multiple flow rates (for fish lengths of Lf/D=1/12), but results in a 6.4 % decrease in efficiency compared to scheme A. Additionally, a negative blade attack angle can improve flow pattern. Considerable reduction in fish mortality can be obtained by equipping the rotor with a larger size but lower shaft speed, while also limiting the fish size to pass through the pump running at a reduced flow rate.

De-risking Global Supply Chains: Looking Beyond Material Flows

executive summary: This essay examines supply chain de-risking driven by two forces: (1) the renewed concerns of the U.S. and its allies about supply chain resilience and (2) China's long-standing strategy to redefine the global order. main argument A defining feature of global supply chains is they are powered by material, information, financial, and human flows. By examining these multiple flows in the evolution of global supply chains, our analysis goes beyond the singular focus on material flows that is common in recent economic and foreign policy discourse. Another defining feature of global supply chains is the strategic interaction between different actors. Following this line of thinking, we argue that de-risking is not a unilateral option for the West and its developed economy partners but rather an interactive and fluid development taking place around the globe. This can be seen in the U.S.'s growing emphasis on improving supply chain resilience through reshoring, nearshoring, and friendshoring, as well as in China's diversification into markets such as Russia and the global South, with broader implications for major economies. Looking beyond material flows to information, financial, and human flows is important to monitor these indicators of the ongoing transitions in global supply chains. policy implications • Policymakers must recognize that de-risking is not a unilateral process but involves strategic interactions among multiple global actors. • It is imperative to consider the implications of information, financial, and human flows, in addition to material flows, to develop effective de-risking strategies. • Ensuring political stability and policy continuity is essential to effective de-risking, particularly in the context of changing administrations and economic policies. • In implementing de-risking, efforts should ensure coordination across the four types of flows while addressing the challenges of increased complexity and potential lack of visibility into operations. • The role of emerging economies in de-risking is critical, as they stand to benefit significantly but also play a key role in achieving diversified and resilient supply chains.

Topology optimization of regenerative cooling structures under high Reynolds number flow with variable thermo-physical properties

In the design of thermal protection system for hypersonic vehicles, the efficient convective heat transfer within regenerative cooling channels plays a critical role in maintaining their thermal performance. This study focuses on the topology optimization (TO) of the cooling channels that operate at high Reynolds number and have variable thermo-physical properties. A novel approach is introduced to enhance the density-based method by incorporating an effective artificial force correction and tabulating the temperature-dependent thermal properties. Several topology-optimized cooling layouts were generated to minimize the maximum temperature within the design domain while considering different power dissipation constraints. This confirms the validity of the proposed lumped correction term in momentum equation accounting both viscous and convective body forces. Regarding the thermal performance of the optimized layouts, the staggered arrangement of cellular ribs in the TO channel was found to induce multiple flow separations and promote turbulent mixing, thereby improving heat transfer efficiency and mitigating the thermal acceleration effect. Conjugate heat transfer calculations revealed that the optimal topology-optimized channel achieved a 24.3% improvement in overall thermal performance while being 15.3% lighter than the straight channel design. Furthermore, the optimal topology optimized layout consistently outperformed the straight channel design by 6.6% to 24.3% in terms of the overall thermal performance across a wide range of heat flux distribution and mass flow rate conditions. This investigation highlights the effectiveness of topology optimization in designing regenerative cooling structures featuring high Reynolds number hydrocarbon thermal fluid flow.

Simulation and performance characteristics of rock with borehole using Visual Finite Element Analysis

Purpose. This study aims to investigate fluid flow and heat transfer within rocks containing boreholes, focusing on the complex mechanisms within hot reservoirs. Non-commercial finite element (FE) software is used to visualize and present the results. Methods. The study involved the use of FE method with Visual Finite Element Analysis (VisualFEA) software to analyze the coupled phenomena of fluid flow and heat transfer in a rock sample. Special attention was given to incorporating material structure and geotechnical analysis in the software, as well as the treatment of cracked elements. In addition, the validation was done by comparing the current numerical solution using VisualFEA with the numerical solution using ANSYS Software. Findings. The study findings highlight the capabilities of VisualFEA software to accurately represent fluid flow, stress, and heat transfer in borehole-containing rocks. The results include insights into flow direction within the borehole, temperature distribution, and the validation of the software performance against expected system behavior. The study demonstrates the effectiveness of VisualFEA in handling complex loading and its ability to visualize multiple flow directions within a 2D model. The results are presented in the form of contours and curves. Originality. This study contributes to the field demonstrating the application of VisualFEA software in analyzing fluid flow and heat transfer in rocks with boreholes. The focus on incorporating material structure, geotechnical analysis, and treatment of cracked elements adds originality to the study, providing a comprehensive understanding of the coupled phenomena in hot reservoirs. Practical implications. The practical significance of this study is in the validation and benchmarking of VisualFEA software for studying fluid flow and heat transfer in geotechnical application. The findings can be utilized by geotechnical engineers and researchers to better understand the behavior of borehole-containing rocks under specific pressure and thermal loading conditions. The insights gained from this study can be used in decision-making processes related to resource mining, reservoir engineering, and geothermal energy use.

Day-ahead optimal dispatch method of integrated electric-heat-cool-gas energy system based on N-1 safety criterion

With the continuous development of integrated energy system and the deepening of the coupling relationship between multiple energy flows, the safe and stable operation of the system has received widespread attention. At present, the security of integrated energy system is mostly researched from the perspective of power grid and rarely researched from the perspective of equipment. This study proposes a day-ahead optimal dispatch method of integrated electric-heat-cool-gas energy system based on N-1 safety criterion, which ensures the normal operation of integrated energy system after the failure of a power supply equipment by increasing appropriate amount of power supply. In this study, the changes in equipment power and operating cost before and after equipment failure under the dispatch method considering N-1 safety criterion and the changes in equipment power and operating cost before and after equipment failure under the dispatch method without considering N-1 safety criterion are investigated by numerical simulation. The results show that when a power supply equipment fails, the average daily loss of load is 6139.99 kW for the dispatch method without considering the N-1 safety criterion and the average daily loss of load is 0 kW for the dispatch method considering the N-1 safety criterion. Therefore, the dispatch method considering the N-1 safety criterion performs better in terms of reliability. When a power supply equipment fails, the average operating cost is 5127.71 USD for the dispatch method without considering the N-1 safety criterion and the average operating cost is 4125.56 USD for the dispatch method considering the N-1 safety criterion. Therefore, the dispatch method considering the N-1 safety criterion performs better in terms of economy.

River-estuary continuum highlighted by variabilities in carbon and nitrogen stable isotope ratios of the catadromous eel Anguilla japonica.

Estuaries exhibit high physicochemical variability and the properties of estuaries and the constituent segments are not yet systematically understood. This study aims to reveal the spatial heterogeneity of predominant organic sources using carbon and nitrogen stable isotope ratios (δ13C and δ15N, respectively) of Japanese eels (Anguilla japonica), one of the ideal natural samplers. In the Miyakoda River, Japan, our study site, the effectiveness of eel δ13C and δ15N values as standard indices of predominant organic sources was tested by employing the River Continuum Concept. This study then extended the application of these indices to the estuary, i.e., the Hamana Lake system, into which the Miyakoda River flows. Once in the upper estuary, eel δ13C and δ15N values became high, with the latter peaking in this river-estuary continuum, indicating that artificial labile subsidies (nutrients and organic matter) with high δ15N values were rapidly assimilated into the food web. Eel δ15N values decreased again in the middle estuary. Nevertheless, the influence of terrestrial organic subsidies extended into this segment, as evidenced by the low δ13C values of eels. These results suggest that refractory organic matter with low δ15N values, such as plant-derived ones, is slowly assimilated into the food web in the downstream estuarine segments. The higher δ13C values in the lower estuary suggested that the contribution of eelgrass or macroalgae occurred in addition to benthic microalgae. Thus, our results emphasize the need to consider the multiple energy flows to understand the estuary as a continuum.

Evaluation Methods and Coupled Optimization at Macro- and Micro-Scales for Profiled Ring Rolling of Inconel718 Alloy.

The forming quality of profiled ring rolling not only encompasses macroscopic accuracy but also emphasizes the microstructure. Due to the multiple process parameters and complex metal flow during profiled ring rolling, the various forming defects are difficult to control and difficult to study theoretically. The objective of this study is to establish a comprehensive method for evaluating the forming quality of profiled rings, which considers both the macroscopic forming accuracy and the microstructure. Firstly, the synthetic size factor was defined, and the evolutionary relation between the section forming rate and the diameter growth rate of E-section ring rolling was analyzed in detail. The synthetic size factor can be used to describe the dimensional evolution and evaluate the forming accuracy of the profiled ring rolling process. Taking into full consideration the features of intermittent deformation in local areas, a microstructure evolution model of the Inconel718 alloy during E-section ring rolling, which can accurately predict the recrystallization volume fraction and average grain size of the final ring, was established. Then, combined with finite element simulation, the influence of the rotation speed of the driving roll on the macro-size evolution and microstructure was systematically analyzed. The results indicate that there is often a discrepancy between dimensional accuracy and microstructure uniformity in the optimization trend. For instance, the higher the rotation speed of the driving roll is, the more uniform the microstructure is, but the more difficult it is for the section profile to form. Finally, combined with response surface methodology (RSM), multi-parameter optimization was carried out with section forming accuracy and grain uniformity as the optimization objectives. By using the optimal parameters, an E-section ring with a complete profile and a uniform microstructure was obtained, with a maximum prediction error of the recrystallization volume fraction lower than 5%. The results show that the macroscopic and microscopic quality evaluation methods proposed in this study, as well as the optimization method combining RSM, can be effectively applied to the process optimization of profiled ring rolling.

Analysis of the influence of dust particles in the peanut pickup harvester with a self-designed axial-flow dust-fall box on its dust suppression performance

The atmospheric particulate pollution poses a serious threat to human health and ecological environment. The dust particle pollution caused by the operation of agricultural machinery is becoming increasingly severe and the peanut pickup harvesters are widely used in agricultural operation. Therefore, it is necessary to reduce the concentration of dust particles in the work of peanut pickup harvesters. In this study, a self-designed dust-fall box composed of multipleaxial flow cyclone tubes in parallel was integrated with the peanut pickup harvester. Based on the CFD-DPM model, simulation analysis was conducted to explore the effects of different inlet velocities, different numbers of swirling blades, and two types of exhaust port on the dust removal performance of the cyclone. The Box-Behnken design was used to determine the optimal structural parameters of the axial flow cyclone. The influence of the pressure distribution and velocity variations of the internal flow field on the dust removal efficiency of the two schemes was simulated and analyzed. Thereafter, a reasonable parallel scheme of multiple axial flow cyclone tubes in the dust-fall box was determined. The drone was used to monitor dust in peanut harvesting operations, and dust particle concentrations at 8 detection points under varying working conditions were recorded. The distribution and diffusion rules of dust in harvesting operations were explored through cluster analysis, and the test data obtained were compared with numerical calculation results to verify the accuracy of numerical calculation. The results showed that for a single axial flow cyclone, when the inlet wind speed was 6 m/s to 8 m/s and the number of swirling blades was 4, the structural parameters of the cyclone separator had significant influence on the separation efficiency. The influencing factors ranking in descending order were cylinder diameter, cylinder length, and exhaust pipe insertion depth, respectively. To be more precisely, the separation efficiency was best when the cylinder diameter was 60 mm, the cylinder length was 150 mm, the insertion depth of the exhaust pipe was 50 mm and the cone angle was 20°. It was more reasonable to use 8 axial flow cyclone tubes in parallel, and the maximum separation efficiency can reach 84.21 %. Field operations showed that the numerical calculation results were similar to the actual harvesting process. The dust particle concentration in the peanut harvesting operation equipped with a dust-fall box was always lower than 10 mg/m3. The dust particle concentration was the highest at the rear of the whole machine and the lowest near the cab. Compared conventional harvesters, the harvester with a dust-fall box reduced its dust particle concentration by 64.37 %; the concentration of 30 μm dust particles was reduced by 69.31 %; the dust particle concentration at the rear of the whole machine also effectively reduced. This study can provide reference for controlling dust emissions during peanut harvesting operations and agricultural machinery harvesting operations.

Effect of regenerated standpipe flow pattern on catalyst transport in fluid catalytic cracking unit

Standpipe is a pipeline that constitutes one of the components in the downstream portion of the catalyst circulation loop in a fluid catalytic cracking (FCC) unit, facilitates catalyst transportation between reactor and regenerator. This study measured pressures of the regenerated standpipe on a 1.0 Mt/a FCC unit to elucidate the underlying cause of the observed catalyst transportation. The results indicated that multiple flow patterns coexist within the standpipe, rather than a single dense-phase flow. The characteristic parameters of the static and dynamic pressure were intimately connected to the aforementioned flow patterns. The dynamic pressure data indicated that pressure dominant frequency and amplitude could employed in the identification of flow patterns. The packed bed flow had a pressure frequency ranging from 0 to 3.3 Hz, and a dominant frequency amplitude of 0.8, 1.8 and 2.2 Hz, allowed diagnosis of poor catalyst transport. The study demonstrated that the standpipe structure and catalyst mass flow rate were the key factors affecting gas-solid flow degassing by allowing for multiple flow patterns in the standpipe. The influence of aeration on the flow patterns was also discussed here, with an improper aeration rate resulting in reaction temperature fluctuations ranging from 0.5 to 23 °C.

Rooting meta-ecosystems with reciprocal lateral carbon and nitrogen flows in a Yangtze coastal marsh

Abstract The dynamics of lateral nutrient fluxes through hydrological movements are crucial for understanding ecological functions related to the flow of energy, materials, and organisms across various spatiotemporal scales. To investigate the connectivity of multiple spatial flow processes, we conducted a one-year field study to measure lateral hydrologic carbon (C) and nitrogen (N) fluxes across the continental shelf in the Yangtze estuary. We observed a significant correlation between the differences in remote sensing-based estimates of gross primary production (GPP) (ΔGPPMODIS) and the differences in eddy covariance (EC) tower-based GPP (ΔGPPEC) at both high-elevation and low-elevation sites. Our findings indicate that the saltmarsh acts as a net source of dissolved total C while serving as a net sink for dissolved total N. Furthermore, there was a significant correlation in the total dissolved stoichiometry of the C/N ratio between imports from and exports to adjacent aquatic systems. These findings highlight the importance of integrating ecological stoichiometric principles to improve our understanding of the complex relationships among physical, chemical, and ecological processes, particularly within the context of the meta-ecosystem framework. Additionally, when reciprocal hydrological lateral C and N flows are considered, a single ecosystem can function as both a source and sink within the meta-ecosystem framework.

Building-block-flow computational model for large-eddy simulation of external aerodynamic applications

Computational fluid dynamics is an essential tool for accelerating the discovery and adoption of transformative designs across multiple engineering disciplines. Despite its many successes, no single approach consistently achieves high accuracy for all flow phenomena of interest, primarily due to limitations in the modeling assumptions. Here, we introduce a closure model for wall-modeled large-eddy simulation to address this challenge. The model, referred to as the Building-block Flow Model (BFM), rests on the premise that a finite collection of simple flows encapsulates the essential missing physics necessary to predict more complex scenarios. The BFM is designed to: (1) predict multiple flow regimes, (2) unify the closure model at solid boundaries and the rest of the flow, (3) ensure consistency with numerical schemes and gridding strategies by accounting for numerical errors, (4) be directly applicable to arbitrary complex geometries, and (5) be scalable to model additional flow physics in the future. The BFM is utilized to predict key quantities in five cases, including an aircraft in landing configuration, demonstrating similar or superior capabilities compared to previous state-of-the-art models. The design of BFM opens up new opportunities for developing closure models that can accurately represent various flow physics across different scenarios.