Microscale Effects Research Articles

Research on Boundary Layer Effect in Fractured Reservoirs Based on Pore-Scale Models

It is of great significance to study the seepage characteristics of heavy oil reservoirs, which are conducive to the efficient development of resources. Boundary layer effect (BLE) exists in the pore-scale flow process of macromolecular fluid media, which is different from the flow law of conventional fluid in the pore, yet the influence of BLE is ignored in the previous pore-scale simulation. Conventional porous media simulations have difficulty analyzing the mass transfer law of small-scale models under the influence of microfractures. Based on the CT scanning data and thin section data of the real core in the target area, the rock skeleton and flow space were extracted according to the maximum ball algorithm, and the pore network model representing the complex structure was constructed. The microscale effect of macromolecules in the flow process in the pores was characterized by modifying the effective flow. The effects of the BLE on the effective connectivity, displacement process, and oil distribution law were analyzed. The seepage characteristics of different wettability conditions and different water cut stages were compared. The results show that BLE reduces the effective flow space and leads to deviations in the relative permeability curve and capillary curve. For fractured porous media, the irregular shape of porous media was characterized by the morphological method, and the mass transfer process was analyzed by the equivalent flux method. The influence of the porous media shape on the macromass transfer process was compared. This study provides a solution to the problem of BLE in pore-scale simulation.

Epiphyton in Agricultural Streams: Structural Control and Comparison to Epilithon

Stream biofilms play an important role in the structure, functioning, and integrity of agricultural streams. In many lowland streams, macrophyte vegetation is abundant and functions as an important substrate for biofilm (epiphyton) in addition to the gravel and stone substrate for epilithon on the stream bed. We expect that reach-scale habitat conditions in streams (e.g., nutrient availability, hydraulic conditions) affect the epiphyton and epilithon biomass and composition, and that this effect will be substrate-specific (macrophytes and stones). The objectives of our study were (i) to describe concurrent changes in epiphyton and epilithon biomass and composition over a year in agricultural streams, and (ii) to determine the substrate specific reach-scale habitat drivers for the epiphyton and epilithon structure. We monitored epiphyton and epilithon biofilm biomass and composition at three-week intervals and reach-scale environmental conditions daily during a year for two agricultural steams. The results showed that epiphyton and epilithon communities differed in biomass, having high substrate specific biomass in epilithon compared to epiphyton. Epiphyton was mainly composed of diatom and green algae, while cyanobacteria were more important in epilithon, and the diatom species composition varied between the two biofilm types. Epiphyton structural properties were less influenced by reach-scale hydrology and nutrient availability compared to epilithon. The overall explanatory power of the measured environmental variables was low, probably due to micro-scale habitat effects and interactive processes within stream biofilms. Knowledge of biofilm control in agricultural streams is important in order to improve management strategies, and future studies should improve the understanding of micro-scale habitat conditions, interactive relationships within biofilms and between the biofilm and the substrates.

A separated representation involving multiple time scales within the Proper Generalized Decomposition framework

Solutions of partial differential equations can exhibit multiple time scales. Standard discretization techniques are constrained to capture the finest scale to accurately predict the response of the system. In this paper, we provide an alternative route to circumvent prohibitive meshes arising from the necessity of capturing fine-scale behaviors. The proposed methodology is based on a time-separated representation within the standard Proper Generalized Decomposition, where the time coordinate is transformed into a multi-dimensional time through new separated coordinates, each representing one scale, while continuity is ensured in the scale coupling. For instance, when considering two different time scales, the governing Partial Differential Equation is commuted into a nonlinear system that iterates between the so-called microtime and macrotime, so that the time coordinate can be viewed as a 2D time. The macroscale effects are taken into account by means of a finite element-based macro-discretization, whereas the microscale effects are handled with unidimensional parent spaces that are replicated throughout the time domain. The resulting separated representation allows us a very fine time discretization without impacting the computational efficiency. The proposed formulation is explored and numerically verified on thermal and elastodynamic problems.

Analytical and mathematical simulation for nonlinear stability of scale-dependent magneto-electro-elastic system

By using differential quadrature method (DQM), a numerical investigation was provided for nonlinear stability behavior of magneto-electro-elastic (MEE) cylindrical shells at microscale. It is assumed that the cylindrical shell has been subjected to compressive loads leading to buckling phenomena in geometrically nonlinear regime. The non-uniformity of strain field has been inserted in the formulation for considering the microscale effects. The material properties of the shell are considered to be inhomogeneous with graded distribution. After solving the governing equations using DQM, it is realized that if the nanoscale shell is subjected to electrical and magnetic fields, the post-buckling path may be changed with the value of electrical voltage and magnetic potential. Also, strain gradient effects have remarkable influence on post-buckling curves and critical voltages.

Nonlinear electromechanical dynamics of piezoelectric doubly-curved microsystem using modified strain gradient theory

This paper is devoted to investigate the nonlinear free vibrations of multi-phase piezoelectric doubly-curved microshells in the context of modified strain gradient elastic (MSGT). The microshell has been made from two constituents for which different compositions have been considered by defining a piezoelectric phase percentage. The microscale effects have been described with the incorporation of three scale coefficients involved in MSGT. With the use of suitable Fourier series and the concept of Galerkin's method, the solution for the governing equations of double-curvature microshell have been provided. The calculated frequencies are dependent on the piezoelectric phase percentage, scale coefficients, curvature radius and applied electric voltage.

A Micron-Sized Laser Photothermal Effect Evaluation System and Method.

The photothermal effects of lasers have played an important role in both medical laser applications and the development of cochlear implants with optical stimulation. However, there are few methods to evaluate the thermal effect of micron-sized laser spots interacting with other tissues. Here, we present a multi-wavelength micro-scale laser thermal effect measuring system that has high temporal, spatial and temperature resolutions, and can quantitatively realize evaluations in real time. In this system, with accurate 3D positioning and flexible pulsed laser parameter adjustments, groups of temperature changes are systematically measured when the micron-sized laser spots from six kinds of wavelengths individually irradiate the Pd/Cr thermocouple junction area, and reference data of laser spot thermal effects are obtained. This work develops a stable, reliable and universal tool for quantitatively exploring the thermal effect of micron-sized lasers, and provides basic reference data for research on light-stimulated neuron excitement in the future.

A FRACTAL MODEL FOR PREDICTING THE EFFECTIVE THERMAL CONDUCTIVITY OF ROUGHENED POROUS MEDIA WITH MICROSCALE EFFECT

The effective thermal conductivity (ETC) of roughened porous media (RPM) is of interest in a number of applications of heat transfer. In this work, a fractal analytical model for the ETC of RPM with microscale effect is proposed. The proposed fractal model is expressed in terms of relative roughness, the molecular mean free path, porosity, fractal dimensions (pore area fractal dimension and tortuosity fractal dimension), maximum pore diameter, capillary straight length, and the thermal conductivity of the solid matrix and gas. It is observed that the dimensionless ETC of RPM decreases with increasing relative roughness, pore area fractal dimension and tortuosity fractal dimension. Besides, it is found that the dimensionless ETC of RPM increases with thermal conductivity ratio of gas phase over solid phase. In addition, it is found that the dimensionless ETC of RPM is slightly dependent on the relative roughness and tortuosity fractal dimension when [Formula: see text]. The determined dimensionless ETC of RPM is in good agreement with experimental data and existing models reported in the literature. With the proposed fractal model, the physical mechanisms of heat transport through RPM with microscale effect are better elucidated. Every parameter in the fractal analytical model has clear physical meaning, with no empirical constant.

Direct observation of wetting behavior of water drops on single micro-scale roughness surfaces of rose petal effect

Hypothesis: It has been verified that a surface of single micro-scale structures with certain roughness could exhibit petal effect. That is, water drops with a contact angle larger than 150° would pin on the petal effect surface. It is conjectured that the water drop could pin on the single micro-scale roughness petal effect surface by totally infiltrating into spaces (or grooves) between micro-pillars.Experiments: An inverted optical microscopy system is synchronically applied in the process of advancing/receding contact angle (ACA/RCA) measurements to directly observe the wetting behavior of water droplets on hydrophobic patterned surfaces with regular arrays of square micro-pillars.Findings: A sequence of wetting behavior evolution, Wenzel → petal → pseudo-lotus → lotus, is observed on the hydrophobic patterned surfaces along with increasing surface roughness. It is interesting to observe a Cassie-Wenzel transition for water drops on a petal substrate during the ACA measurement (embedded needle method), leading to two ACAs, one before (in Cassie state) and one after the transition (in Wenzel state). Thus, the petal substrates have large contact angle hysteresis (CAH) (with both ACA and RCA in Wenzel state) to pin the water drop in Wenzel state. A Cassie-Wenzel transition is consistently observed during the evaporation process of water drops on pseudo-lotus substrates, leading to two RCAs: one in Cassie state and one in Wenzel state. The pseudo-lotus substrates have CAH (with both ACA and RCA in Cassie state) small enough to make water drops easily slide off.

Flow field characteristics of micro-scale textured surfaces of water-lubricated bearings using lattice Boltzmann method

PurposeThe purpose of this paper is to study the flow field characteristics of the micro-scale textured bearing surfaces using the lattice Boltzmann method based on the microscopic dynamics of the fluid.Design/methodology/approachConsidering the inertia effects and the micro-scale effects, the models of a single micro-scale texture unit cell with different shapes and different film thickness ratios are established. The influence of pressure difference between inlet and outlet of the unit cell on flow characteristics is studied.FindingsThe surface pressure distribution, flow patterns and pressure contours in the flow field are obtained. The results reveal that the pressure difference has a significant influence on the characteristics of the micro-textured flow field.Originality/valueThe results have certain guiding significance for further step investigation on microscopic lubrication mechanism of the water-lubricated polymer bearings.

Theoretical and experimental exploration on the micro asperity contact load ratios and lubrication regimes transition for water-lubricated stern tube bearing

The paper investigates the micro asperity contact load ratios and lubrication states of the water-lubricated bearing. New coupled models with consideration of micro-scale asperity contact effects are put forward. The relevance of load ratio with transition of lubrication regimes under multi coupled structural parameters and operating conditions are established. The three-dimensional relationships between typical parameters and contact ratio under typical working conditions have been further studied. Characteristic parameters of lubrication regimes transition under multi coupled factors are investigated. The mechanism of regimes transition is revealed at the micro level. Experimental measurements verify the correctness of the revised model. Researches are beneficial for the definition of micro asperity contact load ratio and lubrication regimes transition for such bearings.

Gas–Liquid Taylor Flow Characteristics in a Fractal Microchannel Network during Numbering-up and Sizing-up

In the present study, the characteristics of gas-liquid Taylor flow in a fractal microchannel network were investigated by numerical modeling and experiments. With perpendicular gas intake, the fractal design methodology resulted in uniform flow distribution. Unstable Taylor flow and saddle-shaped velocity profile were observed in a high-level branch with 0.3 mm width. The liquid slug exhibited different flow fields during splitting in the bifurcations of different levels. The significant size effects were further investigated in four channels representing different sizes (0.3, 0.6, 1.2, and 2.4 mm) via a μ-PIV and high-speed camera. The normalized slug length (LS/W) increased with the increasing gas-liquid flow rate ratio (jG/jL), while the bubble length (LB/W) followed an opposite trend. The stability of the gas-liquid Taylor flow pattern became worse when the gas velocity increased beyond a certain value (Reynolds number Re > 220) under the microscale effect. Two typical counter rotating vortices were observed in the liquid slug, and the swirling strength increased exponentially with the jG/jL. It was found that both the velocity profile in the 0.3 mm channel deviated from the laminar flow. Particularly, a flow field similar to turbulence was observed in the 0.3 mm channel when the jG/jL reached 4. This work quantified the significant size effect in micro- and millichannels, providing theoretical basis for the effective scale-up of the microreactor.

Nusselt number-turbulent strain rate relationship: Forced convection of a flat surface downstream of a pair of side-by-side rectangular strips

The turbulent strain rate generated by a pair of 25.4 mm tall and 12.7 mm wide (W) rectangular strips at a Reynolds number based on the strip width of 8500 was measured using a 3D hotwire probe in a wind tunnel. The strips were placed side-by-side separated by 3 W, 2 W, and 1 W. The convective heat transfer enhancement, denoted by the normalized Nusselt number (Nu/Nu0), was correlated with turbulence fluctuation, Taylor microscale, turbulent strain rate and integral-Taylor scale ratio. With the effects of both turbulence fluctuation and eddy scale incorporated, the turbulent strain rate correlated most strongly with Nu/Nu0, with an R-square value of 0.82. Comparatively, the R-square for Nu/Nu0 - velocity fluctuation and Nu/Nu0 - Taylor microscale were 0.77 and 0.64, respectively. Furthermore, the turbulent strain rate was found to have the most significant impact on heat transfer augmentation, more so than the individual effects of turbulent fluctuation and Taylor microscale.

Effects of long-term ethanol storage on muscle architecture.

Muscle excursion and force potential can be estimated from architectural variables, including mass, volume, fascicle length, and density. These have been collected from fresh specimens, preserved specimens, and sometimes mixed samples of both. However, preservation alters the gross morphology of muscles. This study aims to quantify the effects of long-term storage on myological properties across a sample of fresh and ethanol preserved Mus musculus specimens ranging in storage time from 16 to 130 years. Masses, volumes, and densities of biceps femoris, quadriceps femoris, and triceps surae were measured, and histological cross-sections of some specimens were used to evaluate the microscale effects of long-term fluid preservation. For the remainder of thesample, chemically dissected fascicle lengths were measured to evaluate the fixation effects on the linear dimensions of muscle architecture. Relative muscle mass, volume, fascicle length, average fiber area, and density, and percent fiber area were regressed against years stored in ethanol. Muscle size dropped steeply between fresh and stored samples, ultimately decreasing by 62 and 60%, respectively. These losses correlate with histologically measured shrinking of average muscle fiber area. Density of stored specimens plateaued 5% below that of fresh ones. Although muscles lost mass and volume during ethanol storage, fascicle lengths did not shorten significantly (presumably because they were preserved attached on either end to bone). This study demonstrates that muscle mass, volume, and density of specimens stored long-term in ethanol should be corrected by factors of 2.64, 2.49, and 1.054 respectively for comparability to fresh specimens.

Transient thermo-mechanical analysis of FGM hollow cylindrical structures involving micro-scale effect

Thermo-mechanical properties of the functionally graded materials (FGMs) are the pivotal role to improve their service lives exposed to some extraordinary thermal circumstances. An analytical procedure to explore the thermo-mechanical interaction involving the micro-scale effect is proposed for the first time in this work. The governing equations are firstly constructed in a cylindrical coordinate in the context of the generalized Chandrasekharaiah–Tzou theory (C–T theory). An asymptotic approach, based on the Laplace transform technique and its limit theorem, is then employed to solve these equations analytically, in which a common linearization technique is prior to introduce to disperse the non-linear terms involving variable material properties with different gradient patterns. The layer-formed solutions of a typical FGM hollow cylindrical structure with its inner boundary subjected to a sudden temperature rise is finally obtained and validated. A detailed parametric study has been conducted to explore the effect of the micro-structure interaction, physical properties distribution patterns, and the structure size on the thermo-mechanical response. The results state that the effect of micro-structure interaction mainly focuses on the thermal wave propagation and is more significant for the ceramic-rich case. The delay effect on the heat transport induced by thermal inertia is also wakened significantly by the micro-structure interaction, which leads to a larger range of thermo-elastic response and smaller peak stress.

Three-Dimensional Elastoplastic Contact Analysis of Rough Surface Considering a Micro-Scale Effect

Abstract The micro-surface asperity scale of grinding metal parts is within several microns. When two grinding surfaces are in contact, the unevenness of the plastic deformation of the asperities at the micro-scale leads to greater plastic hardening strength of the material. The results of the nano-indentation experiment conducted in this paper confirmed this phenomenon. Based on conventional mechanism-based strain gradient (CMSG) plasticity theory, the micro-scale plastic constitutive equation of materials is given and then is verified by the nano-indentation experiment. Finite element software abaqus and the user-defined element (UEL) subroutine are used to build three-dimensional rough surface elastoplastic contact models. By calculating the grinding rough surface contact in the macro-scale constitutive model based on J2 theory and in the CMSG plasticity constitutive model, the influence law of plastic micro-scale effect on contact performance is obtained.

IMPACT OF NANOFLUIDS ON EXTERNAL AND INTERNAL FLOW VIA NAVIER-STOKES AND CONVECTIONDIFFUSION EQUATIONS FOR PARALLEL PLATES WITH SLIP BOUNDARY CONDITIONS

With the modernization and miniaturization of equipment and systems toincrease the overall efficiency in smaller spaces, new cooling solutions needto be developed. Microfluidic in the last decades becomes a new way to getthis. Nanofluids are used to attend this demand to optimize efficiency, withtheir improved thermohydraulic properties, especially different thermalconductivities. To determine the advantages of using a nanofluid for thermalexchange, the properties, parameters and modelling will be presented, and thedifferential equations necessary to obtain the results. In that sense, the basictheory of fluid mechanics and heat transfer, through the Navier-Stokes andConvection-Diffusion equation, is used in the two-dimensional steady-stateformulation. Slip boundary conditions for the velocity field. Constant heat fluxand constant temperature at the surface are used for the temperature field,initially without the flow’s microscale effects. The external flow over a flatplate and internal flow between parallel plates will be studied. Considering alaminar flow, with the base fluid being water and engine oil, with variousvolumetric fractions of Single Wall and Multiple Wall Carbon Nanotubes. Todetermine the results and create the comparative graphs, the WolframMathematica v.11 software will be used for solving the remaining partialdifferential equations.

Effect of temperature on the nonlinear dynamic behavior of two-lobe non-circular gas-lubricated micro-bearings

In this paper, the molecular gas lubrication model was used to analyze the nonlinear dynamic behavior of two-lobe non-circular gas-lubricated micro-bearings. The effects of temperature rise are taken into account. At high temperatures, in addition to gas rarefaction, its viscosity and friction will also change, and slip across boundaries will occur. The rarefaction of the lubricating gas film caused by the microscale effect at high temperatures was considered. The effects of temperature and rotation speed (with and without rarefaction effect) on the dynamic behavior of the non-circular micro gas bearing were studied. The nonlinear equation governing the gas behavior is discretized using the finite-element method and then solved simultaneously with the dynamic equations of rotor motion using the fourth-order Runge–Kutta method. Center orbit diagrams, phase portraits, Poincare maps, power spectrum, and bifurcation diagrams are used to investigate the dynamic behavior of two-lobe non-circular gas-lubricated micro-bearings. Some results show that with increasing temperature, the rotor behavior changes from T-periodic to quasi-periodic. It was also observed that at high temperatures, with increasing rotational speed, the behavior of the system changes from T-periodic to quasi-periodic, but if the gas is rarefied, this change occurs at a slower speed.

Nonlinear pull-in analysis of LASMP laminated micro-plate considering micro-scale effect

This research concentrates on pull-in behavior of a micro-plate laminated with a novel material: light activated shape memory polymer (LASMP). Under light exposure, this material can realize dynamic Young’s modulus. With this feature, a LASMP laminated micro-plate model considering micro-scale effect and geometric nonlinearity is proposed. Dynamic equations of the micro-plate system are derived via Hamilton principle and solved by Galerkin method whose accuracy is validated by FEM. Effect of size dependency and dynamic Young’s modulus of LASMP on pull-in behavior of the micro-plate are studied. Present study provided a technique to manipulate pull-in phenomenon of electrically actuated micro-plate.

Effect of Micro-Scale and Nano-Scale Boron Nitride on Thermal Property of Silicone Rubber Via Experimental and Simulation Method

With the development of electronic integration, excellent insulation and high thermal conductivity thermal interface materials (TIMs) are needed to be used. Most of currently reported TIMs have high thermal conductivity, but their processing is complex and not suitable for industrial application. In this work, a simple method is provided to prepare thermally conductive silicone rubber (SR) composites. Effects of size and ratios of micro-scale boron nitride (BN) and nano- scale BN on mechanical properties, thermal conductivity and thermal stability of SR/BN composites are investigated. Results show that when the ratio of micro-scale BN loading to nano-scale BN loading is equal and the loading of BN are 60 phr, the thermal conductivity of SR/BN composites reaches to 2.632 W/(m·K), which is 18 times higher than that of SR. Meanwhile, when the loading of micro-scale BN is twice than that of nano-scale BN, the SR/BN composites maintain good mechanical properties (the tensile strength reaches to 6.2 MPa). In addition, the SR/BN composites exhibit excellent thermal stability and the heat loss of all samples are nearly 45%. This can provide a new idea for a simple and effective preparation of the SR/BN composites with a high thermal conductivity and insulating.

Impact of Zero-Valent Iron on Freshwater Bacterioplankton Metabolism as Predicted from 16S rRNA Gene Sequence Libraries.

The application of zero-valent iron particles (ZVI) for the treatment of heavily polluted environment and its biological effects have been studied for at least two decades. Still, information on the impact on bacterial metabolic pathways is lacking. This study describes the effect of microscale and nanoscale ZVI (mZVI and nZVI) on the abundance of different metabolic pathways in freshwater bacterial communities. The metabolic pathways were inferred from metabolism modelling based on 16S rRNA gene sequence data using paprica pipeline. The nZVI changed the abundance of numerous metabolic pathways compared to a less influencing mZVI. We identified the 50 most affected pathways, where 31 were related to degradation, 17 to biosynthesis, and 2 to detoxification. The linkage between pathways was two times higher in nZVI samples compared to mZVI, and was specifically higher considering the arsenate detoxification II pathway. Limnohabitans and Roseiflexus were linked to the same pathways in both nZVI and mZVI. The prediction of metabolic pathways increases our knowledge of the impacts of nZVI and mZVI on freshwater bacterioplankton.