Agglomerate Model Research Articles

Spatiotemporal Distribution and Fragmentation Driving Mechanism in Paddy Fields and Dryland of Urban Agglomeration in the Middle Reaches of the Yangtze River

The spatial-temporal distribution pattern of China’s cultivated land has changed dramatically from 1990 to 2020, and the problem of cultivated land fragmentation has become more prominent. However, the existing research lacks a focus on the two specific land use types, paddy fields and dryland. In this study, the spatiotemporal distribution pattern and the fragmentation driving mechanism of paddy field and dryland during the years 1990 to 2020 were identified by using the center of gravity center migration model, standard deviation ellipse, and land-use dynamic model for the urban agglomeration in the middle reaches of the Yangtze River as an example. The results show that there are significant differences in the spatiotemporal distribution characteristics of paddy field and dryland in the MRYRUA. Among the provinces and cities, Hubei province and its Xiangyang city showed the most obvious trend of change. The loss and gain of paddy fields and dryland is related to economic and policy contexts in each period. The main driving factor of paddy field and dryland fragmentation is natural condition, whereas a relatively important factor is the per capita disposable income of rural residents. The effects of each factor on paddy field and dryland fragmentation were not independent; any two factor interactions had a stronger effect on paddy field and dryland fragmentation than a single factor. In general, this study provides guidance and references for the main grain-producing areas undergoing rapid urbanization relating to cultivated land conservation, food security, and sustainable agricultural utilization.

Exploring migration dynamics and housing markets in transition countries: Recommendations for city management and public health

This article investigates the multifaceted challenges resulting from concentrated and unidirectional migration to Bishkek, the capital of the Kyrgyz Republic. The study addresses the urgent need to rectify disparities in internal migration patterns and housing opportunities within Bishkek. By analyzing the intricate relationship between housing dynamics and migration inflows, the research underscores the critical importance of these dynamics for effective urban planning. A novel approach is proposed, advocating for the creation of a Bishkek agglomeration model aimed at fostering more balanced urban development and creating an accessible environment for public health. The primary objective of this study is to elucidate the correlation between the construction of new housing infrastructure and the overall state of housing deprivation across the country. The findings provide valuable insights and recommendations for administrative bodies responsible for managing migration and housing policies aimed at creating a healthy living environment.

How does economic agglomeration affect carbon emissions at the county level in Liaoning China?

China's regional economic development has become a regional agglomeration model. The implementation of urbanization strategies promotes spatial concentration and catalyzes economic agglomeration. Due to the heterogeneity of economic development at various spatial scales, economic agglomeration has different environmental externalities. Peak carbon and carbon neutrality make it vital to explore these externalities in China's urbanization process, especially at smaller scales. This study uses a long time series of macro data for 42 counties in Liaoning Province and constructs a dynamic spatial panel Dubin model to assess the impact of economic agglomeration on carbon emissions, showing that agglomeration and emissions exhibit an “inverted N-shaped” curve at the county level. There is a threshold of emission increases and reductions for economic agglomeration. When economic agglomeration exceeds a threshold, it shows a significant emission reduction effect. After further decomposition of spatial effects, economic agglomeration affects carbon emissions through two channels: the direct and the indirect effect with urbanization as a mediator. There are also spillover effects of economic agglomeration on carbon intensity, meaning that economic agglomeration impacts carbon emissions in the region and surrounding areas. The results provide a reference for development guidelines and emission reduction policies at the county level, emphasizing the need to balance the economy and the environment in county regional development.

Comparison of Different Carbon Supports By Simulation of Agglomeration in Polymer Electrolyte Fuel Cell Catalyst Ink

Polymer electrolyte fuel cells (PEFCs) are one of the most possible power sources for heavy-duty vehicles like trucks due to their high conversion efficiency and low environmental impact. Since platinum which is often used as a catalyst is expensive, it is essential to reduce the amount of platinum by increasing the power density. Regarding materials, it was reported that the activity is increased by supporting platinum on porous carbon [1]. However, there is a voltage drop in the high current density region comparing non-porous carbon. This is caused by oxygen transport properties, but the relationship with the carbon structure is unknown. Oxygen moves through the voids in the catalyst layer, so it is necessary to control the porous structure that forms the voids. This porous structure depends on the conditions of the catalyst layer fabrication process. In particular, the dispersion process is important to determine the size of the carbon agglomerate, or the backbone of the catalyst layer. In this study, an agglomeration model in catalyst ink was developed, and the dispersion process was verified by simulation under various conditions to elucidate the factors that affect agglomeration.The discrete element method (DEM) was used for the simulation. In this study, aggregates were approximated into spheres, and the forces between the particles were the drag force from the fluid, Brownian motion, and particle-particle interactions. Based on DLVO theory, the particle-particle interactions were given as an attractive force due to the van der Waals interaction and a repulsive force due to the overlapping of the electric double layer. In addition, the effect of ionomer was considered. The ionomer effect was introduced as a repulsive force and modeled with the same equation as the repulsion due to the electric double layer. The dielectric dependence equation of the ionomer shape that Magnus et al. modeled [2] was incorporated. As the amount of ionomer added increases, a binder effect is observed between the particles. This effect was also introduced using the adsorption data of ionomers on carbon. The carbon was assumed to be non-porous (Vulcan) and porous (Ketjen). Considering the difference in the platinum ratio on the surface depending on the carbon porosity, the Hamaker constant, which affects the van der Waals force, was determined. Also, the zeta potential, which affects the electric double layer force, was used at different values for carbons. In this study, the calculations were started with the particles uniformly dispersed in the ink. Periodic boundary conditions were used as boundary conditions. Using the above numerical model, simulations were conducted with different water-alcohol ratios and ionomer carbon ratios (I/C).As a result, it was confirmed that differences in the agglomerate size for two carbon supports. This result implies that the composition of the ink and the type of carbon affect the catalyst layer structure and cell performance.AcknowledgmentThis study was carried out under the project of Development of Advanced PEFC Utilization Technologies supported by the NEDO.Reference[1] Y. C. Park et al., J. Pow. Sou r., 315, 179 (2016).[2] M. So et al., Int. J. Hydrog. Energy, 44, 28984 (2019).

Urbanization, economic agglomeration and economic growth

Are Chinese cities too agglomerated, and are production factors continuing to flow to cities?In recent years, research on this issue has attracted more and more attention from academics, for the research on this issue, academics generally believe that urbanization has a positive role in promoting economic growth, but whether urbanization will bring economic agglomeration and what is the role of economic agglomeration on the development of the economy? The research on this issue is still insufficient, therefore, Based on the panel data of 27 provinces from 2006 to 2020, it is generally believed that urbanization has a positive role in promoting economic growth. This paper adds economic agglomeration factors and uses a spatial econometric model to test the spillover effect of urbanization growth. The main conclusions are as follows: First, urbanization and economic agglomeration have a positive effect on economic growth, and there is a spatial spillover effect. Secondly, the advancement of urbanization is closely associated with economic growth, particularly in relation to the development of economic agglomeration. When economic agglomeration is based on a single-center model, it tends to impede urbanization and economic progress. In contrast, an economic agglomeration model with multiple centers has the potential to stimulate urbanization and further enhance economic growth. Thirdly, it is worth noting that the influence of urbanization on economic growth varies across different regions. Factors such as geographical location, resource availability, and local economic conditions contribute to this regional variation.

Population balance modeling of formation and breakage of nanoparticle agglomerates in a spouted bed

A population balance framework for fluidization of Al2O3 nano-agglomerates in a ProCell-type spouted bed considering agglomeration and breakage phenomena is developed. An equipartition of kinetic energy (EKE kernel) is used to model the agglomeration phenomena. For breakage, two different fragment distribution functions are considered, the Dirac delta function and a function with confined uniform binary breakage. The fractal dimension property is incorporated in both the agglomeration and breakage models. The model parameters are extracted from batch fluidization experiments conducted by varying the air pressure of the top nozzle. The developed model shows a good agreement with experimental observation in regard of the temporal change in the area and volume-weighted average size of nano-agglomerates and of their final size distribution. The developed population balance model is simulated to study the influence of model parameters on the evolution of average size and coefficient of variation of the nano-agglomerates.

Analysis method for aerosol deposition behavior under sodium spray fire

Sodium spray fire is a significant containment-related safety concern in sodium-cooled fast reactors (SFR). In a highly-energetic accident such as a core disruptive accident (CDA), the sodium spray fire not only poses a threat to containment integrity but also causes the generation and release of sodium aerosol source terms with strong radioactivity and chemical hazards. In our method, the sodium aerosol generation model, log-normal size distribution model, agglomeration models, and deposition models were applied. In particular, different turbulent energy dissipation rates were considered in the agglomeration models according to the different thermal-hydraulic states of containment and confinement, and the simplified Crump model and Beresnev models have been selected to describe the gravity-diffusion and the thermophoresis deposition behavior respectively, due to the specific conditions of sodium spray fires. Simulation studies have been divided into two categories based on a potential design concept: HTCA, AB5, and AB6 experiments were introduced to describe the drastic thermodynamic state variations caused by spray fires in the confinement, while ATF and AB7 experiments characterized a relatively stable environment similar to the containment. From the simulation results, the analysis method can be considered reasonable with respect to experimental values. Moreover, calculations have been performed for a hypothetical sodium spray fire caused by a rotator plug failure case in a paper-based European SFR.

Platinum loading and electrolyte volume fraction simultaneous gradient distributions in a proton exchange membrane fuel cell: Improving electrical performance and mass transfer

Platinum loading and electrolyte content affect the surface area of electrochemical reaction and proton conductivity, respectively, and protons and oxygen are not uniformly distributed in the catalyst layer. Therefore, platinum loading and electrolyte content can be set to be simultaneous non-uniform distributions to further enhance the species utilization and cell performance. In this study, a non-isothermal, two-dimensional, two-phase fuel cell model is set up and coupled with the catalyst layer agglomerate model. The electrolyte content and platinum loading uneven distributions influence on products and reactants transmission and electrical property is explored. Results indicate that electrolyte volume fraction and platinum loading coinstantaneous graded distribution is more helpful in the species transfer and electrical property improvement. The maximum power density of coinstantaneous graded distribution of platinum content and electrolyte loading along the channel direction is increased by 3.40% compared with the uniform distribution, and is 2.94% higher than the superposition of the maximum power density when the graded distributions of electrolyte volume fraction and platinum loading are separately set. Moreover, the platinum content and electrolyte content gradient distributions do not make liquid water saturation present an evident segment variation along the channel direction, while the opposite is true for oxygen concentration.

A conceptual, mathematical and quantitative reassessment of the Thin-film Flooded Agglomerate Model for air cathodes

Design, fabrication, scale-up, operation and degradation analysis of GDEs electrode are complex operations, requiring a precise knowledge-base and quantitative guidelines. Mathematical tools are strongly needed for this purpose, but often they exhibit conceptual, formal and computational complexities that - in practice - are manageable only by modelling experts. Consequently, models are, in fact, not sufficiently exploited to support systematically metal-air battery research, development and control, as they would have the potentialities to do. Sometimes, experiments are essentially used just to validate models, rather than using models to direct experimental work. In order to enable the concrete integration of mathematical modelling with experimental work on GDEs for ORR, in this paper we present a conceptual restatement of a state-of-the-art model for ORR GDEs, in view of physico-chemical and mathematical perspicuity. In addition, we provide a simplified analytical solution, that enables straightforward and physically transparent parametric analysis, and a detailed description of the numerical solution of the full problem.

Predicting Silica Deposition from Superheated, Pressurized Steam Using Numerical Modeling of Nucleation, Agglomeration and Deposition

A model that can be used to quantify silica deposition from superheated depressurized steam is developed. Classical nucleation theory, agglomeration and deposition onto a wall are combined in a numerical model that calculates the concentration profile, the particle size distribution and the deposition in a flow through a pipeline after a sudden increase in supersaturation. The work presented here is an important step in understanding the mechanisms governing precipitation from supercritical and superheated steam as produced by deep geothermal wells drilled in magmatic areas. The power potential in such systems can be significantly higher than for conventional systems if utilized efficiently. The presented results can be applied to improve industrial designs and decrease energy costs. The model predicts the amount of precipitation along a pipe at various supersaturations, and the resulting deposition velocity in a straight pipe correlates fairly well with recent experimental results. There is a high number of nanocolloids formed close to the pressure reduction position, where deposition is at its maximum. Downstream, larger agglomerates develop, and deposition decreases as the number of particles and the overall concentration decreases. The local maximum deposition rate increases with increasing supersaturation. The calculations show that deposition mechanisms are as important as the chemical process of solidification when estimating where and how most material will be deposited. The rapid formation and deposition of solids predicted indicate that depressurization along with solid capture could be used to rid fluid of silica.

Agglomeration factors and the geography of growing early‐stage businesses in Chile

AbstractNew models of agglomeration cast the urban productivity premium as the outcome of agglomeration economies, a spatial sorting of skilled entrepreneurs and greater selection effects leading to less, but more productive businesses. We provide descriptive evidence of the spatial distribution of growing early‐stage businesses in Chile that concurs with the theory. We show, first, that while business entry rates increase systematically with the size of a region, the rates of growing early‐stage businesses are not related to the levels of agglomeration. Second, we show that, on the contrary, average early‐stage business productivity, the levels of human capital and business exit rates all relate positively with agglomeration. Third, we estimate regression models that verify the expected relationships between agglomeration factors and regional growing early‐stage‐business activity. The results for Chile suggest that the disadvantages of agglomeration largely offset the benefits, and therefore there is no obvious location penalty to venturing in peripheral areas. Entrepreneurship policies in less‐developed countries should not target excessively to specific industries and regions, as they might curtail an entrepreneurial potential that is ubiquitous.

Green innovation ecosystems: Spatial organization mode and associated network renewal under coupling effect

The coupling effect of green innovation participants, elements, and environments directly reflects the operation and evolution of a green innovation ecosystem. This paper studies the spatial organization mode of green innovation ecosystems and the structural evolution and self-organization mode of their associated networks under this coupling effect. By selecting relevant data from 286 cities in China from 2010 to 2021, the green innovation ecosystem coupling coordination index (GIECCI) is calculated using a coupling coordination model. The calculation result is used as a weight to modify a gravity model to construct an innovation ecological network. After analyzing the calculation results, the findings are as follows. (1) The polarization effect of the GIECCI is significantly alleviated, presenting a quantitative structure close to the normal distribution; However, the existence of the Matthew effect trap leads to great resistance to green innovation in some cities. (2) Cities with the same or a similar GIECCI are more likely to form agglomerations, including mature, cross-distribution, and budding agglomeration models. (3) The connectivity status of urban nodes significantly varies, and the mismatch between connectivity symmetry and the total strength of green innovation gravity is widespread. These findings may provide a reference for government departments to plan the layout of green innovation industries and choose sustainable innovation strategies for enterprises.

Modeling of Cohesive Metal-induced Agglomeration in High Temperature Gas Fluidization: The Role of Particle Size

Modeling of Cohesive Metal-induced Agglomeration in High Temperature Gas Fluidization: The Role of Particle Size

Green technology diversification, technology vertical spillovers, and energy intensity in Chinese cities

Drawing from patent data spanning 2011-2016 in 249 Chinese prefecture-level cities and urban scale multi-region input-output (MRIO) table data, this paper empirically demonstrates that as green technological diversification levels escalate, the energy intensity of Chinese prefecture-level cities exhibits an initial increase followed by a decline. Green technological diversification indirectly influences urban energy intensity through vertical spillovers of green technology across the upstream and downstream sectors within the supply chain. Medium-sized cities, service industry-oriented cities, and those in the early stages of industrialization need to prioritize development of multiple green technologies to surpass the diversification turning point. The finding suggests a strategic transition for Chinese cities from a single green technology agglomeration model to a cluster model of collaborative development of multiple green technologies.

Numerical Simulation of the Collision Breakage Process between the Agglomerate and Hammer in a Hammer Crusher Using DEM

This paper focuses on simulating the collision breakage process between the agglomerate and hammer in a hammer crusher by the discrete element method (DEM) as the interaction between particles. This enables us to consider the energy change in the collision breakage process of the hammer. The agglomerate model is built by using the EDEM 2.7 software according to the principle of closest packing in crystallography, while the hammer model is modeled into an assembly of different sizes of spherical particles to make the collision breakage process between the agglomerate and hammer as the one of interrelation of particles. With these models, we mainly investigated collision force, collision impulse, energy breaking agglomerate, and the relationship between the specific breakage energy and agglomerate damage ratio. The collision force is represented as Gaussian function, the collision impulse is represented by the function of the mass ratio of agglomerate to hammer and the product of agglomerate mass and collision velocity, and the relationship between the specific breakage energy and agglomerate damage ratio is represented by exponential function. Finally, it can be seen from this study that, when crushing the agglomerate by hammer impact, it is necessary to increase the specific breakage energy by 1.75 times in order to increase the agglomerate damage ratio from 85% to 90% but 2.13 times in order to increase 95%. The proposed method can be used for the further development and design of the various types of crusher.

Modeling of aluminum agglomeration at solid propellant burning surface by combining aluminum ignition with LDP-SC cluster analysis

Aluminum particles at burning surface may agglomerate during the combustion process of composite solid propellant, involving the aggregation and ignition of aluminum particles as well as the secondary coalescence of agglomerates. So far it is still a huge challenge to capture the agglomeration process and obtain the size distribution of agglomerates accurately. Modeling of aluminum agglomeration was carried out by constructing several submodels, including propellant combustion, cluster analysis of aluminum particles, aluminum ignition and coalescence based on the packed three-dimensional propellant microstructure unit. Dynamic combustion process of propellant microstructure unit was simulated firstly, which characterizes the temperature distribution above the burning surface. Next, aluminum clusters were grouped using a new local density peaks-spectral clustering (LDP-SC) algorithm for initial aluminum particles in microstructure unit. The ignition of aluminum particles in clusters exposed from burning surface was then examined by considering their distributions in the flame of propellant. These exposed aluminum particles in a cluster yield an agglomerate once an aluminum particle is successfully ignited. Secondary mergence of multiple agglomerates was also considered when the distance between two particles in different agglomerates was less than a critical separation distance. With these submodels, the agglomeration process of a typical propellant and properties of aluminum clusters and agglomerates were estimated. The predicted size distribution of agglomerates shows reasonable agreement with experimental data, indicating that the present model is capable of predicting aluminum particle agglomeration during composite propellant combustion.

Understanding and optimizing water transport phenomena in the catalyst layer for anion exchange membrane fuel cells

Anion exchange membrane fuel cells (AEMFCs) are a promising power source due to zero emissions and high efficiency, and low precious metal loading. However, water management remains a significant issue affecting cell performance and durability. In this study, we develop a multi-physics model to investigate and optimize transport phenomena under various operational conditions and microstructure parameters. The agglomerate model is optimized to consider the influence of anode flooding and cathode drying in electrochemical reactions, and the simulation is validated with experimental results. Our findings indicate that an optimal anode inlet gas relative humidity of 80% achieved a tradeoff between anode flooding and ionic conductivity, resulting in a maximal power density of 758.9 mW/cm2. To alleviate anode flooding, we optimize the microstructure of the anode gas diffusion layer, significantly improving maximal power density to 833.4 mW/cm2 by increasing the contact angle to 130°. The optimal porosity achieves a balance between the transport of liquid water and electron. Large pore diameter and small thickness lead to a slighter anode flooding and higher maximal power density. In summary, our study provides insights into the transport behavior of multi-phase water, reactant gas, ion, and electron to guide the design of high-performance AEMFCs.

Urban administrative hierarchy and urban land use efficiency: Evidence from Chinese cities

The allocation of administrative resources is of vital importance, especially when discussing the process of urbanization in China. Under the unique political and administrative systems found in China, it is the urban administrative hierarchy (UAH) that determines both the agglomeration model and the allocation process of urban resources. Based on the panel data of 281 cities in China from 2003 to 2017, a dynamic spatial panel model (DSPM) and a mediation effect model are used to investigate the effect of the UAH on urban land use efficiency (ULUE), both from a theoretical and empirical point of view. The study finds not only the higher the administrative level, the higher the ULUE, but also that improvements to the UAH can significantly improve ULUE. After considering a series of robustness tests, the research conclusion is held to be valid. This paper also finds that both public services and investment environment have significant mediation effects with respect to the UAH and ULUE, but financial subsidies and infrastructure have significant suppressing effects. The paper promotes the understanding of ULUE and reveals the economic significance of the administrative hierarchy in resource allocation in a more general sense.

Modeling Nanoscale Ohmics in Carbon Supports of Fuel Cell Cathodes

Reducing platinum (Pt) loading in polymer electrolyte fuel cells (PEFCs) while meeting performace requirements is critical to their widespread deployment. However, significant polarization losses manifest at higher current densities in cathodes with lower Pt content. The morphology of the carbon supports in PEFC cathodes affects the location of Pt deposition into the micropits or onto the surface of the carbon support, translating into different kinetic and transport resistances. In this work, we derive an agglomerate scale model that differentiates the sink terms for Pt on the surface and in the pits of carbon supports. We develop an approach to assess the impact of nanoscale ohmic resistance to Pt in the micropits arising from weakly ionic solution in the carbon support on PEFC performance. Effectiveness factors relating the actual reaction rate to the maximum reaction rate (had all the Pt been exposed) are derived and embedded into a one-dimensional catalyst layer model. Parameters in the catalyst layer model are tuned based on experimental local oxygen transport resistances. Subsequently, we estimate bounds for the micropore resistances based on geometric and physical arguments. Lastly, polarization curves are simulated to assess the effect of the micropore resistance in fully-humidified and oxygen-rich environments.

Agglomerate Size Evolution in Solid Propellant Combustion under High Pressure

Solid propellant combustion and flow are significantly affected by condensed combustion products (CCPs) in solid rocket motors. A new aluminum agglomeration model is established using the discrete element method, considering the burning rate and formulation of the propellant. Combining the aluminum combustion and alumina deposition model, an analytical model of the evolution of CCPs is proposed, capable of predicting the particle-size distribution of completely burned CCPs. The CCPs near and away from the propellant burning surface are collected by a special quench vessel under 6~10 MPa, to verify the applicability of the CCP evolution model. Experimental results show that the predicted error of the proposed CCP evolution model is less than 8.5%. Results are expected to help develop better analytical tools for the combustion of solid propellants and solid rocket motors.