Microscale Effects Research Articles

Microstructural Evolution and Damage Mechanism of Water-Immersed Coal Based on Physicochemical Effects of Inorganic Minerals

Coal seam water injection technology enables seam permeability enhancement and facilitates outburst risk reduction. This study investigated the microscale effects of water infiltration on coal and the evolution mechanisms of its mechanical properties. To this end, we systematically analyzed dynamic changes (such as mineral composition, pore structure, and mechanical performance) in coal soaked for various durations using X-ray diffraction, low-field nuclear magnetic resonance (NMR), and uniaxial compression testing. The results indicate: (1) the coal NMR T2 spectrum displays three characteristic peaks, corresponding to rapid water absorption, uniform transition, and stabilization stages of soaking traditionally divided according to peak area variation trends. (2) The coal strength decreases with progressive soaking, influenced by water content, pore volume, mineral composition, etc. Its compressive strength and elastic modulus drop by 22.4% and 19.5%, respectively, compared to the initial values. (3) The expansion of clay minerals during immersion reduces average pore size. In contrast, quartz particle displacement, pore water movement, and soluble mineral dissolution increase pore volume, reducing the overall structure strength. (4) The dominant factors driving the degradation of mechanical properties vary across immersion stages, including water content and specific mineral concentration. This work offers new insights into how hydraulic technology alters coal seams, providing theoretical support for optimizing water injection strategies in the seam.

Micro-Scale Ice Shoveling Effect Induced by Magnetic-Responsive Microfins.

Icing is ubiquitous in nature and engineering applications, and imposes threats to road and air transportations, wind energy infrastructures, etc. However, current active de-icing solutions, especially the most popular one, i.e., heating, suffer from high energy consumption whilst passive methods are often ineffective at high-speed, long-term, or large-particle conditions. Herein, a promising strategy adopting magnetic-responsive microfins (MRS)featuring reversible deformations is developed for de-icing. A novel micro-scale ice shoveling effect induced by the localized destruction of the ice adhesion interface owing to the inhomogeneous deformation is demonstrated, and its dependence on the ice particle size and temperature is investigated. An analytical model is proposed to describe the mechanism of this effect, showing a linear relation between the position of the magnet and the induced force agreeing well with experiments, leading to a system straightforward to predict and control. Specifically, the de-icing capacity of the surface becomes prominent when small-scale ice particles merge to large ones, providing a promising solution for applications on aircraft, wind turbines, etc., as the first of its kind to remove large particles under high-speed conditions effectively.

Deep deoxidation of water in a miniaturized annular rotating device: Experimental investigation and machine learning modeling

Conventional gas–liquid devices exhibit limitations, including inadequate dispersion efficiency and significant backmixing, leading to low conversion and large equipment volume. Thus, a miniaturized annular rotating device (m-ARD) was proposed based on microscale effects and rotating flow field to achieve efficient gas–liquid mass transfer and high conversion. Nitrogen-oxygenated water was selected as the experimental system to evaluate the performance of the m-ARD. The gas–liquid flow characteristics were investigated. The analysis focused on examining the impact of different factors on deoxygenation efficiency. The deoxygenation performance was optimized and compared with different devices. The study found that the m-ARD enables a continuous counter-current gas–liquid flow mode, with superior mixing performance and a narrow residence time distribution. The deoxygenated water with an oxygen concentration as low as 0.14 ppm can be produced, with a volumetric mass transfer coefficient (kLa) of 0.26 s−1, a theoretical stage value of 4.22, and a handling capacity of 30 mL/min under optimized experimental conditions. In addition, kLa was predicted using an artificial neural network model and showed good agreement with the simulated values. This work provides a promising reactor for chemical reactions that require high conversions.

Research on the microscale effects of fuel pellets carrying chemical pesticide distillation residues

To effectively deal with organic hazardous wastes generated in the production processes of chemical pesticide industries. In this study, the strong shear force generated by high-speed rotating blades was utilized to fully mix and stir pasty or viscous liquid organic hazardous wastes with porous solid fuels. The wastes were broken down into small molecular clusters and evenly distributed on the surfaces of the pores of porous solid fuel particles. This study then investigated the thermal characteristics of fuel particles carrying the distillation residues of chemical pesticides under microscale effects, the volatilization and destruction removal characteristics, the formation of pollutants, and the migration and transformation of F and Cl elements. The results showed that when the average diameter of the fuel particles was 6 mm and the mass ratio of the chemical pesticide distillation residue to the fuel particles was 2:3, small molecular clusters of the residue were evenly distributed on the surfaces of the fuel particles, with a dispersity of 67 %. The volatilization rate of the irritating odors in the coated particles was less than 2 %. With an increase in the proportion of the chemical pesticide distillation residue, the ignition temperature of the particles decreased, the thermal stability increased, the burnout temperature rose, and the maximum weight loss rate first increased and then decreased. The Ca and alkali metal oxides in the fuel particles had a significant effect on fixing chlorine and fluorine.

Analytical analysis of 2D couple stress flow of blood base nanofluids with the influence of viscous dissipation over a stretching surface

This study examines the effects of viscous dissipation, thermal radiation, nanofluid over a stretched surface, and viscous dissipation on a two-dimensional couple stress blood base for the enhancement of heat transfer rate. Gold and multiwall carbon nanotubes are two forms of nanoparticles that are taken into consideration, with blood serving as the base fluid. The NLPDE controls the considering problem. The NLPDE was converted to NODEs using the mentioned similarity transformation. The analytical method known as HAM was used to analyze the transform NODE analytically. Graphs are used to illustrate the effects of many parameters, such as magnetic factors, nanoparticle volume friction, velocity power index, PN, thermal radiation factors, and EN, which are derived from TE and VE. The current research work highlights how important it is to include viscous dissipation in nanofluid dynamics. The results show complex interactions among stretching, thermal properties, and micro-scale effects. The results may have an impact on the development and enhancement of biomedical devices and treatments that use nanofluidic systems, especially those that deal with blood.

Liquid–liquid flow characteristics and mass transfer enhancement in a Taylor–Couette microreactor

AbstractThe liquid–liquid immiscible flow and mass transfer were investigated in a novel Taylor–Couette microreactor (TCMR). Due to the rotation shear and microscale effects, each phase flowed in the form of helical strips/bands, instead of dispersion droplets as in conventional equipment. Based on the movement and inclination of the bands, the helical vortex (HV), mixed helical vortex (MHV) and stationary helical vortex (SHV) were distinguished. The characteristics of the regimes were strongly influenced by rotation speed and flow rate, but the specific surface area only slightly varied. The flow regimes also influenced the two phase mass transfer. It was shown that the mass transfer coefficient kLa monotonically increased with the rotation speed in the HV regime, while it slightly decreased when the flow shifted into the MHV/SHV regime. According to the parametric studies, empirical correlations were developed for the flow regime transition and mass transfer prediction.

Optimized design of macro‐microreactor for scale‐up of liquid–liquid chemical processes

AbstractThe scale‐up of microreactor‐based flow chemical process represents a grand challenge in chemical engineering. The small characteristic size (<1000 μm) of a typical microreactor leads to not only microscale effect (process intensification) but also low throughput. Here, we report macro‐microreactor to achieve scale‐up of liquid–liquid chemical operation with process intensification. By incorporating the designed internals based on computational fluid dynamics, the characteristic size of the macro‐microreactor is expanded into 3000–4000 μm. The optimized design of macro‐microreactor with helical‐shaped internal exhibits both similar or even stronger microscale effect and high throughput in contrast to the typical microreactor. For the liquid–liquid chemical process, seven times higher mass transfer coefficient and about half reduction of the pressure drop are realized. These macro‐microreactors would find further applications in industrial chemical manufacturing.

Effect of strut microstructure on multiscale radiation properties of porous foams

Porous materials, widely used in engineering due to their excellent physical properties, have significant engineering and academic research value in their mechanism of radiation heat transfer. Micro-cellular foams are composed of a large number of struts and walls with micro-scale radiation effect, making it difficult to analyze the influence of strut micro-structure on radiation properties. In this study, the radiation parameters of the curved triangular prism-shaped struts are calculated using the finite element electromagnetic method, and the influence of the strut micro-structure parameters and the macroscopic parameters of the foam on the radiation characteristics is analyzed. The results demonstrate that the radiation properties of the equal-volume cylinder model, compared to the double-layer cylinder model, are closer to those of the curved triangular prism struts. The incidence angle has a negligible impact on the radiation parameter deviation of the struts. It is difficult to ignore the radiation parameter deviation of concave-curved triangular prism-shaped struts. The macroscale radiation properties of the foam are significantly influenced by the microscale radiation properties of the struts in the situation of low porosity, large pore size, and high strut volume ratio.

A micro-capillary jetting technology for liquid-liquid microdispersion with narrow size distribution

Liquid-liquid microdispersion is one of the key foundations for chemical process intensification. However, liquid-liquid microdispersion at the conditions of high phase ratio and high volume flow rate remains a problem and new microdispersion technology is highly required. Based on the microscale effect of the liquid jet, we developed the micro-capillary jetting technology. It can produce microdroplets (250–500 μm) with narrow size distribution (CV ≈ 10–20 %) in a wide range of physical properties with large capacity and little cost without the restriction of phase ratio. This paper reports the laws of the micro-capillary jetting technology. The liquid-liquid flow patterns and mechanism are studied, and a precise quantitative model to distinguish different jetting patterns is provided for the first time based on the energy analysis in the microscale. Then important factors including physical properties, dispersion mode and structural parameters are investigated. Accordingly, a mathematical model for the prediction of the average droplet size is established and the energy utilization in the jetting dispersion process is calculated.

A Modified Model of Micro-Scale Gas Seepage in Rock Porous Media

It is of significance to study the micro-scale gas seepage mechanism in rock porous media due to shale gas exploitation and prevention of tunnel gas explosion. However, current microscale seepage models have problems, such as poor accuracy or small computational domain. In this work, a representative volume element scale microscopic seepage model with high precision and large computational domain is established using the lattice Boltzamnn method. In the representative volume element scale model, micro-scale effect is considered by the Beskok-Karniadakis correction relationship. Then the accuracy of the representative volume element scale model is improved by proposing an equivalent resistance correction coefficient. The correction coefficient value is obtained by comparing the calculated result for the flow rate at a representative volume element scale and more precise pore scale. For example, when the porosity is 0.9 and the dimensionless specific surface area is 30, the corrected model can reduce the average deviation from 34.38 to 0.14%. Finally, to expand the applicability of the proposed model, a correlation for the correction coefficient is introduced as a function of the Knudsen number, porosity of porous media, and dimensionless specific surface area. The mean absolute percentage deviation of the correction coefficient correlation is 9.25%.

Nonlinear dynamics of three-layer microplates: simultaneous presence of the micro-scale and imperfect effects

Nonlinear dynamics of three-layer microplates: simultaneous presence of the micro-scale and imperfect effects

The multi-scale coupled model: a new framework capturing wind farm–atmosphere interaction and global blockage effects

Abstract. The growth in the number and size of wind energy projects in the last decade has revealed structural limitations in the current approach adopted by the wind industry to assess potential wind farm sites. These limitations are the result of neglecting the mutual interaction of large wind farms and the thermally stratified atmospheric boundary layer. While currently available analytical models are sufficiently accurate to conduct site assessments for isolated rotors or small wind turbine clusters, the wind farm's interaction with the atmosphere cannot be neglected for large-size arrays. Specifically, the wind farm displaces the boundary layer vertically, triggering atmospheric gravity waves that induce large-scale horizontal pressure gradients. These perturbations in pressure alter the velocity field at the turbine locations, ultimately affecting global wind farm power production. The implication of such dynamics can also produce an extended blockage region upstream of the first turbines and a favorable pressure gradient inside the wind farm. In this paper, we present the multi-scale coupled (MSC) model, a novel approach that allows the simultaneous prediction of micro-scale effects occurring at the wind turbine scale, such as individual wake interactions and rotor induction, and meso-scale phenomena occurring at the wind farm scale and larger, such as atmospheric gravity waves. This is achieved by evaluating wake models on a spatially heterogeneous background velocity field obtained from a reduced-order meso-scale model. Verification of the MSC model is performed against two large-eddy simulations (LESs) with similar average inflow velocity profiles and a different capping inversion strength, so that two distinct interfacial gravity wave regimes are produced, i.e. subcritical and supercritical. Interfacial waves can produce high blockage in the first case, as they are allowed to propagate upstream. On the other hand, in the supercritical regime their propagation speed is less than their advection velocity, and upstream blockage is only operated by internal waves. The MSC model not only proves to successfully capture both local induction and global blockage effects in the two analyzed regimes, but also captures the interaction between the wind farm and gravity waves, underestimating wind farm power by about only 2 % compared with the LES results. Conversely, wake models alone cannot distinguish between differences in thermal stratification, even if combined with a local induction model. Specifically, they are affected by a first-row overprediction bias that leads to an overestimation of the wind farm power by 13 % to 20 % for the modeled regimes.

Turbulence-induced droplet grouping and augmented rain formation in cumulus clouds

This paper provides the first observational analysis of how droplet separation is impacted by the flinging action of microscale vortices in turbulent clouds over a select radii range and how they vary over cloud cores and along the peripheral edges. It is premised that this mechanism initiates droplet separation within a cloud volume soon after condensational growth, largely in the cloud core, and operates until the cloud droplet radii exceed 20–30 µm when this effect fades rapidly. New observations are presented showing how microscale vortices also impact the settling rates of droplets over a critical size range (6–18 µm) causing them to sediment faster than in still air affecting swept volumes and thereby impacting the rain initiation and formation. Large-scale atmospheric models ignore these microscale effects linked to rapid droplet growth during the early stages of cloud conversion. Previous studies on droplet spatial organization along the cloud edges and inside the deep core have shown that homogeneous Poisson statistics, indicative of the presence of a vigorous in-cloud mixing process at small scales obtained, in contrast to an inhomogeneous distribution along the edges. In this paper, it is established that this marked core region, homogeneity can be linked to microscale vortical activity which flings cloud droplets in the range of 6–18 µm outward. The typical radius of the droplet trajectories or the droplet flung radii around the vortices correlates with the interparticle distance strongly. The correlation starts to diminish as one proceeds from the central core to the cloud fringes because of the added entrainment of cloud-free air. These first results imply that droplet growth in the core is first augmented with this small-scale interaction prior to other more large-scale processes involving entrainment mixing. This first study, combining these amplified velocities are included in a Weather Research and Forecasting- LES case study. Not only are significant differences observed in the cloud morphology when compared to a baseline case, but the ‘enhanced’ case also shows early commencement of rainfall along with intense precipitation activity compared to the ‘standard’ baseline case. It is also shown that the modelled equilibrium raindrop spectrum agrees better with observations when the enhanced droplet sedimentation rates mediated by microscale vortices are included in the calculations compared to the case where only still-air terminal velocities are used.

The Heterogeneous Effects of Microscale-Built Environments on Land Surface Temperature Based on Machine Learning and Street View Images

Global climate change has exacerbated alterations in urban thermal environments, significantly impacting the daily lives and health of city residents. Measuring and understanding urban land surface temperatures (LST) and their influencing factors is important in addressing global climate change and enhancing the well-being of residents. However, due to limitations in data precision and analytical methods, existing studies often overlook the microscale examination closely related to residents’ daily lives, and lack a deep exploration of the spatial heterogeneity of the influencing factors. This leads to these results being ineffective in guiding the planning and construction of cities. Taking Shenzhen as a case study, our study investigates the effects of various microscale build environment characteristics of LST using street view images and machine learning. A convolutional neural network model adopting the SegNet architecture is used to perform semantic segmentation on street view images, extracting features of the microscale urban-built environment. The LST is inverted through the Google Earth Engine (GEE) platform. By using Multiscale Geographically Weighted Regression (MGWR) models, our study reveals the comprehensive impact of the urban-built environment on LST and its significant spatial heterogeneity. The findings indicate that the proportions of sky, roads, and buildings are positively correlated with LST, while trees have a significant cooling effect. Although earth and water can reduce LST, their overall contribution is minimal due to limitations in their area and distribution patterns. This study not only reveals the key factors affecting urban LST at the microscale but also emphasizes the necessity of considering the spatial heterogeneity of these factors’ impacts. This suggests the need for targeted strategies for different areas to effectively improve the urban thermal environment and achieve sustainable urban development.

Effect of microscale C–S–H on the properties of Portland cement and hydration kinetics analysis at different curing temperatures

Microscale calcium–silicate–hydrate (C–S–H) is easily accessible and readily storable, enabling a cleaner production process of cement-waste grinding and simple chemical synthesis technology. However, the temperature effects of microscale C–S–H require further exploration. In this study, we evaluated the impact of microscale C–S–H admixture on the properties of Portland cement at different curing temperatures. Microscale C–S–H can not only increase the early strength of cement pastes, but also achieve high strength in the long term. Adding microscale C–S–H to cement can effectively reduce the apparent activation energy Ea of hydration products and accelerate the reaction of C3S and C2S with water and form more hydration products. At a curing temperature of 10 °C, the microscale C–S–H increased the 1 d compressive strength by 70.0% and shortened the hydration induction period by 1.2 h. Microscale C–S–H also increased the 12 h hydration degree by 38.1%. Microscale C–S–H promoted the formation of CH and xonotlite-like C–S–H and changed the composition of hydrates, although the effects diminished with increasing curing temperature. This paper offers theoretical and fundamental data on the usage of microscale C–S–H as an admixture in cement-based materials.

An electromechanical stimulation regulating model with flexoelectric effect of piezoelectric laminated micro-beam for cell bionic culture

Cell bionic culture requires the construction of cell growth microenvironments. In this paper, mechanical force and electrical stimulations are applied to the cells cultured on the surface of the piezoelectric laminated micro-beam driven by an excitation voltage. Based on the extended dielectric theory, the electromechanical microenvironment regulating model of the current piezoelectric laminated micro-beam is established. The variational principle is used to obtain the governing equations and boundary conditions. The differential quadrature method and the iterative method are used to solve two boundary value problems for cantilever beams and simply supported beams. In two cases, the mechanical force and electrical stimulations applied to the cells are analyzed in detail and the microscale effect is investigated. This study is meaningful for improving the quality of cell culture and promoting the cross-integration of mechanics and biomedicine.

Research on the thermal properties and interface resistance of multilayer multiscale semiconductor structures

The investigation of the thermal characteristics of high-power chips is mainly based on Fourier's law, and it does not adequately explore the microscale effects of the heat transfer process. In pursuit of a more profound comprehension of the size-dependent traits manifesting in the thermal conduction across multilayer, multiscale materials, this manuscript incorporates the phonon transport's scattering mismatch attributes, introducing a MBDE methodology aimed at delineating the thermal characteristics inherent to multilayer, multiscale structures. This approach was applied to elucidate the energy transfer dynamics among bi-layer (Si/Si, Diamond/Si, and Cu/Si) configurations of differing scales. To enhance thermal transfer efficiency, this work prioritizes the minimization of interface thermal resistance and system temperature gradients as optimization objectives, employing a genetic algorithm to identify scales favorable for energy transfer. The results indicate: 1) An increase in the Knudsen number (Kn) correlates with a more pronounced energy discontinuity at the interface, thereby elevating the interface thermal resistance; 2) The disparate material combinations exhibit varied energy transfer efficiencies, where the phononic compatibility between Cu/Si is inferior to that of Diamond/Si, culminating in a notably larger energy discontinuity and, consequently, augmented energy transfer losses for Cu/Si interfaces; 3) Through the application of a genetic algorithm, it was determined that transitioning from Kn1 to Kn2 yields an optimal thermal conduction scenario, characterized by an interface thermal resistance of 1.83 and a comprehensive temperature gradient of 6.69. This work holds significant implications for guiding the thermal design of high-power integrated chips.

Nonlinear Dynamic Analysis of FG Fluid Conveying Micropipes with Initial Imperfections

This paper investigates the nonlinear dynamics of FG-FCMPs with initial imperfections. Based on the MCST, the nonlinear equations of motion and the corresponding boundary conditions are established by applying Hamilton’s principle, the Euler–Bernoulli beam theory, and von-Kármán geometric nonlinearity. To describe the initial geometric imperfection of the FG-FCMP, the first-order vibrational mode is employed. Subsequently, in cases of primary parametric resonance, 1:2 subharmonic resonance for the first-order mode, as well as primary resonance for the second-order mode, Galerkin’s method, and the multiple scale method are utilized to analyze the amplitude–frequency responses of the imperfect FG-FCMP. The numerical simulations test the influence of flow velocity, micro-scale parameter, geometrical imperfections, and external loads on the nonlinear characteristics of a coupled system with two DOFs. It is found that, as the increase of flow velocity, micro-scale effect, and external load, the amplitude of the first two modes can be increased. The hardening characteristics are converted into the softening characteristics due to the imperfect effect. Furthermore, numerical results provide a more comprehensive understanding of the nonlinear dynamics of FCMPs for both periodic and chaotic motions.

Biomimetic hybrid porous microspheres with plant membrane-wall structure for evaluating multiscale mechanisms of ultrasound-assisted mass transfer

Determination of mass transfer during ultrasound-assisted extraction (UAE) has always been a challenge, not to mention the novel breakthrough of mechanisms for its positive effects. Herein, versatile porous microspheres (PM) with membrane-wall structure like plant tissues, which were made from sodium alginate/polyacrylamide dual crosslinking gels loaded with liposomes, were prepared to reveal the micro mass transfer effects during UAE. Results showed that prepared PM kept stable microstructure during extraction and ultrasound significantly accelerated the pore diffusion rather than surface diffusion. This effect resulted in higher UAE efficiency of PM with 60 % porosity than solid microspheres (143.72 to 155.47 mg/L), and the finding can be further explained as the accelerated internal diffusion (14.25 %) under ultrasound treatment. Moreover, multi-physics coupling simulations were performed to elucidate the enhanced pore flow and UAE efficiency. Acoustic streaming induced by cavitation effect increased the seepage velocity within the PM, and the pore structure would undergo compression and expansion deformation with alternated acoustic pressure due to its elastic characteristic. Both microscale effects improved the mass transfer and increase the UAE efficiency without structural damage from cavitation. This study fills the UAE mechanisms from micro view and provides a novel method for the study of vital micro processes.

The Impacts of Urban Morphology on Urban Heat Islands in Housing Areas: The Case of Erzurum, Turkey

The growing importance of climate change underlines the need to comprehend Urban Heat Islands (UHI), particularly those influenced by urban morphology. As progress has been made in understanding the macroscale relationship between urban morphology and UHIs, the microscale effects are often overlooked. This study, conducted in the city of Erzurum in Turkey, delves into the complex relationship between urban morphology and UHI intensity in different housing areas with distinct microclimates, focusing particularly on street networks, building systems, and land use. Pearson correlation analysis was performed to investigate the relationships between morphological indicators and UHIs in different housing areas. Key findings include that (1) noticeable UHI effects were observed, especially in dense areas with high-rise buildings. (2) UHIs reveal a strong correlation with both 2D and 3D urban morphological indicators. A moderate-to-high Sky View Factor (SVF) tends to reduce UHIs, while an extremely high SVF aggravates UHIs. (3) Enhancing street network integration emerges as a more effective strategy for mitigating UHI effects in mid-rise buildings compared to other morphological factors. The Normalised Difference Built-Up Index (NDBI) and Normalised Difference Vegetation Index (NDVI) may not reliably indicate UHIs in housing areas with a predominantly rural character. Consequently, this article recommends that urban morphology optimisation for UHI mitigation should prioritise spatial and indicator specificity in urban design and spatial planning for cities. Future research endeavours should investigate the influence of morphological indicators on UHI dynamics in different seasons, including various remote sensing indicators related to morphological structure, to enrich our understanding of daily UHI fluctuations within urban morphology research.