Microscopic Flow Research Articles

Effect of geometrical parameters of air-induction nozzles on droplet characteristics and behaviour

Delivering pesticide droplets accurately to a target has always been a challenge for crop spraying. Pesticide spray that drifts or runs-off the crop are major sources of soil and groundwater pollution and encourage pesticide overuse. This study optimised an agricultural air-induction nozzle to overcome these difficulties. Various configurations were designed and manufactured to investigate the geometrical parameters. A range of experiments were designed and carried out to simulate field conditions and examine spray structure, stability, droplet size range, and the probability of microbubbles to determine correlations between droplet size and spray drift and droplet rebound potential with or without entrained microbubbles. The performance of the designed nozzle was compared to that of commercial nozzles. Optical diagnostic methods, including high-speed photography, laser diffraction-based droplet sizing, and microscopic flow visualisation, were employed to perform accurate investigations of droplet size range and microbubble presence potential. In addition, the spatial distribution of spray influenced by lateral wind was investigated in an open-type wind tunnel and measured using a 2-dimensional patternator and water-sensitive papers. The rebound potential of the droplets was investigated using high-speed photography for artificial leaves. The results demonstrate the significance of geometrical design factors on the performance of nozzles and the effectiveness of induced air on the reduction of drift and rebound potential. Droplets including microbubbles were found to distribute across the surface of the target leaves on impact and exhibit increased rebound resistance. • Agricultural nozzles with coarser sprays have less drift potential. • Jet pump geometry controls ALR where the tip V-cut angle controls the spray angle. • Injection pressure enhances the atomization quality and degrades the uniformity. • Droplet air inclusion leads to better coverage. • Larger droplets including air bubbles have less rebound potential.

Utilizing UAVs Technology on Microscopic Traffic Naturalistic Data Acquirement

Research into collecting and measuring reliable, accurate, and naturalistic microscopic traffic data is a fundamental aspect in road network planning scientific literature. The vehicle trajectory is one of the main variables in traffic flow theory that allows to extract information regarding microscopic traffic flow characteristics. Several methods and techniques have been applied regarding the acquisition of vehicle trajectory. The forthcoming applications of intelligent transport systems on vehicles and infrastructure require sufficient and innovative tools to calibrate existing models on more complex situations. Unmanned aerial vehicles (UAVs) are one of the most emerging technologies being used recently in the transportation field to monitor and analyze the traffic flow. The aim of this paper is to examine the use of UAVs as a tool for microscopic traffic data collection and analysis. A comprehensive guiding framework for accurate and cost-effective naturalistic traffic surveys and analysis using UAVs is proposed and presented in detail. Field experiments of acquiring vehicle trajectories on two multilane roundabouts were carried out following the proposed framework. Results of the experiment indicate the usefulness of the UAVs technology on various traffic analysis studies. The results of this study provide a practical guide regarding vehicle trajectory acquirement using UAVs.

MTT Heterogeneity in Perfusion CT Imaging as a Predictor of Outcome after Aneurysmal SAH.

Impairment of tissue oxygenation caused by inhomogeneous microscopic blood flow distribution, the so-called capillary transit time heterogeneity, is thought to contribute to delayed cerebral ischemia after aneurysmal SAH but has so far not been systematically evaluated in patients. We hypothesized that heterogeneity of the MTT, derived from CTP parameters, would give insight into the clinical course of patients with aneurysmal SAH and may identify patients at risk of poor outcome. We retrospectively analyzed the heterogeneity of the MTT using the coefficient of variation in CTP scans from 132 patients. A multivariable logistic regression model was used to model the dichotomized mRS outcome. Linear regression was used to eliminate variables with high linear dependence. T tests were used to compare the means of 2 groups. Furthermore, the time of the maximum coefficient of variation for MTT after bleeding was evaluated for correlation with the mRS after 6 months. On average, each patient underwent 5.3 CTP scans during his or her stay. Patients with high coefficient of variation for MTT presented more often with higher modified Fisher (P = .011) and World Federation of Neurosurgical Societies grades (P = .014). A high coefficient of variation for MTT at days 3-21 after aneurysmal SAH correlated significantly with a worse mRS score after 6 months (P = .016). We found no correlation between the time of the maximum coefficient of variation for MTT after bleeding and the patients' outcomes after 6 months (P = .203). Heterogeneity of MTT in CTP after aneurysmal SAH correlates with the patients' outcomes. Because the findings are in line with the pathophysiologic concept of the capillary transit time heterogeneity, future studies should seek to verify the coefficient of variation for MTT as a potential imaging biomarker for outcome.

Potential Anti-leishmanial Activity of a Semi-purified Fraction Isolated from the Leaves of Parthenium hysterophorus.

In the present perspective, emergence of resistant strains of Leishmania donovani and severe side effects resulting from the use of conventional anti-leishmanial therapies present an urgent need for developing novel agents against this parasite. We have explored the effectiveness of secondary plant metabolites as alternative choices in the treatment for visceral leishmaniasis (vl). The plant Parthenium hysterophorus L. (Asteraceae) was collected from the West Bengal State University Campus, Barasat, West Bengal, India. The leaves of this plant were extracted by different solvents, such as ethyl acetate, water, petroleum ether and hexane. Gas chromatography-mass spectrometry (GC-MS) analysis was also carried out for the identification of compounds in the hexane soluble fraction (PHFd) with substantial anti-leishmanial activities. The antipromastigote activity and cytotoxicity of this fraction were evaluated by the tetrazolium MTT assay. Other biochemical and physiological parameters were studied by microscopic observation and flow cytometric analyses. PHFd showed considerable activity against L. donovani promastigotes (IC50: 20 µg/ml). The PHFd also inhibited in vitro growth of L. major LV39 promastigotes dose dependently with an IC50 of 40 µg/ml. The GC-MS studies of this particular fraction revealed the presence of four major compounds with different retention times (RT) of 26.08, 33.11, 36.41, and 41.20 min. In this study, we also established that PHFd could induce DNA damage and subsequent apoptosis of L. donovani promastigotes with a concomitant increase in generations of reactive oxygen species (ROS) in a time-dependent manner. This fraction was also found to be effective in nitric oxide-mediated inhibition of intracellular amastigotes (IC50:12.5 µg/ml) without any noticeable cytotoxicity towards murine splenocytes in vitro. This study provides the basis for additional phytochemical and pharmacological studies on the antiprotozoal applications of P. hysterophorus.

Analysis of the frequency dependence characteristics of wave attenuation and velocity dispersion using a poroelastic model with mesoscopic and microscopic heterogeneities

ABSTRACTSeismic waves passing through partially saturated porous rocks produce pressure gradients in the fluid phase, and, hence, the resulting fluid flow is accompanied by various length scales. The major mechanism responsible for seismic attenuation and dispersion is arguably known as wave‐induced fluid flow between inhomogeneities of microscopic, mesoscopic and macroscopic scales. Previous studies have revealed that differentiating the influence of heterogeneities at various scales on wave attenuation within seismic exploration and sonic frequencies, nevertheless, is very difficult. This is because wave attenuation mechanisms due to different heterogeneities are practically impossible to be unrelated. Therefore, it is important for a more quantitative interpretation of the relative contribution of inter‐dependent energy loss mechanisms through improved understanding of the combined influences associated to the microscopic squirt flow and mesoscopic fluid flow. We introduce a scaled poroelastic model to evaluate frequency‐dependent attenuation and velocity dispersion characteristics by considering the combined presence of microscopic and mesoscopic heterogeneities. To do so, the capillarity effects are incorporated into the poroelastic model with random distributions of the sizes of mesoscopic‐scale heterogeneities. A range of pertinent scenarios are calculated, and the acoustic properties indicate wave attenuation decreases whereas the phase velocity increases corresponding to additional capillary forces. Meanwhile, numerical results of the proposed model were compared with experimental measurements of a tight sandstone to examine its validity. Results of numerical simulations suggest that seismic reflections produce more complicated signatures in the presence of an interbedded structure of a reservoir exhibiting velocity dispersion. Therefore, the proposed procedure can help in assessing the sensitivities of frequency‐dependent seismic signatures to reservoir fluid mobility and patch heterogeneities.

The transient flow mechanism and intermittent film thickness evolution regulation of droplet mode for horizontal tube falling film

The behavior of falling film over horizontal has significant impacts on the efficiency of heat and mass transfer for the horizontal tube evaporators and absorbers especially for intermittent droplet model at low spray density, which has lower heat and mass transfer resistance. Thus it is critical to illuminate transient and intermittent flow mechanism of droplet dynamic behavior and film thickness evolution regulation over horizontal tube falling film at low spray density. A two dimension multi-phase flow mode for superhydrophilic surface was established to capture the microscopic flow mechanism. The results indicated that droplet generation and growth stages accounted for more than half of the droplet life cycle and an obvious droplet retraction and pulsation were first observed during droplet generation due to surface tension and local additional pressure. Further, the whole life cycle transient and intermittent film thickness map of droplet mode was depicted. And found that the liquid film thickness transient evolution regulation of droplet mode could be split into two zones: impact zone and stable zone. For impact zone, the film thickness was rapidly decreased with the spreading of the liquid film from the millimeter level to 200 μm within 0.2 s. While for stable zone, film thickness almost maintained stable over a long period time until the next droplet impacted. Because of the intermittent of droplet generation and movement, the change of film thickness of droplet mode with spray Reynolds was achieved by increasing impact frequency of droplet impact instead of the volume of a single droplet.

Intra-pore tortuosity and diverging-converging pore geometry controls on flow enhancement due to liquid boundary slip

The liquid boundary slip, in contrast to the conventional no-slip boundary condition, exists due to a less wetting or the non-wetting nature of sediment grains, which can significantly control fluid hydraulics of porous media, specifically which consists of smaller pore-throats, e.g., siltstones and mudstones. Most studies to date presume a no-slip boundary condition and a few who have investigated the aspects of slip-boundary presume a simplified straight tube or a non-tortuous pore shape. Therefore, how the degree of tortuosity and pore-geometry control flow enhancement in porous media remains underexplored. In this computational study, we design a set of diverging-converging staggered tortuous (DCST) pores, which account for a variable amount of intra-pore tortuosity. To compare, a set of capillary pores are designed that can account for tortuosity by taking the form of sinusoidal and helical shapes. Our results quantify how the diverging-converging nature of pore geometry and its intra-pore tortuosity alone have a significant impact on modifying the microscopic flow behavior -accounting of which is a key in upscaling these effects to a macroscopic continuum or the Darcy-scale. We find, DCST pores contribute to an asymptotic flow enhancement behavior in response to boundary slip.In comparison, capillary pores lead to a linearly ‘unlimited’ flow enhancement. This unlimited nature of flow enhancement can lead to differences over several orders in magnitude. We test theoretical models to predict flow enhancement from all pores. We determine constitutive relations that can predict flow enhancement as a function of intra-pore tortuosity and hydraulic shape factor. We examine the physical mechanisms of energy dissipation and find that the microscopic fluid-structure interactions can contribute to significant variation in how intra-pore geometry and boundary slip manifest as the flow enhancement factor relevant to the continuum-scale. We find that the ‘asymptote’ in the flow enhancement factor of DCST pores manifests as a result of an equilibrium between energy dissipation and enhancing flow due to boundary slip, at least in the laminar flow regime.

Modeling the Operation of Left-Turn Vehicles at Exit Lanes for Left-Turn Intersections

AbstractThis study aimed to describe the operation of left-turn vehicles under the impact of exit lanes for left-turn (EFL) control. A microscopic traffic flow model was proposed, in which a multiv...

Investigation of Post-Darcy Flow in Thin Porous Media

We present numerical simulations of post-Darcy flow in thin porous medium: one consisting of staggered arrangements of circular cylinders and one random distribution of cylinders bounded between walls. The simulations span a range of Reynolds numbers, 40 to 4000, where the pressure drop varies nonlinearly with the average velocity, covering nonlinear laminar flow to the fully turbulent regime. The results are compared to those obtained by replacing the bounding walls with symmetric boundaries with the aim to reveal the effect of bounding walls on microscopic characteristics and macroscopic measures, i.e., pressure drop, hydrodynamic dispersion and Reynolds stresses. We use large eddy simulation to directly calculate the Reynolds stresses and turbulent intensity. The simulations show that vortical structures emerge at the boundary between the cylinders and the bounding walls causing a difference between the microscopic flow in the confined and non-confined porous media. This affects the averaged values of pressure drop, the hydrodynamic dispersion and the Reynolds stresses. Finally, the distance between the bounding walls is altered with the particle Reynolds number kept constant. It is observed that the difference between results calculated in confined and non-confined cases increases when the bounding walls are narrower.

Internet connected vehicle platoon system modeling and linear stability analysis

The fast development of communication technique builds an era of Internet of Everything. In the automobile world, Internet-Connected Vehicle (CV), also called IntelliDrive, will accelerate the autonomous driving era’s coming. And the traffic flow theory will undergo major changes as CV platoon becomes common way for our travel. As we know that the CV has different driving decision mechanisms from human-driven vehicles, such as an CV can receive more information and make much faster decision than a human-driven vehicle. Only if we fully understand the autonomous traffic flow’s characteristics, then we can improve the level of traffic engineering study and management in the future. On the thought of building autonomous traffic flow theory, we present CV platoon car-following model as the theoretical microscopic traffic flow model. The model is described by a mathematical differential-difference equation, which has a synthesized optimal velocity differential function and a full platoon with weighted relative velocity difference function. There are three main factors in the model, which are the optimal velocity difference impact factor p and action related vehicle number l, and weighted velocity difference sum coefficient λ. The model reflects the effects of front interactions between every two adjacent CV instead of the weighted average headway in the platoon. We deduce the model’s stability conditions with linear system stability theory and do some computer numerical simulations to verify our suppositions. Simulation results show that the more information broadcasting among CV, the more stable of the traffic flow system is. At last, we discuss our study’s contributions from the viewpoint of theoretical and practical value, and point out future research directions. In a word, the highlight of the paper is that we find the CV platoon system’s running mechanism by building an CV platoon car-following model under connected environment and give its linear stability condition, which is great value for advanced traffic management in autonomous driving era.

Lattice dynamics and ultrafast energy flow between electrons, spins, and phonons in a 3d ferromagnet

The ultrafast dynamics of magnetic order in a ferromagnet are governed by the interplay between electronic, magnetic and lattice degrees of freedom. In order to obtain a microscopic understanding of ultrafast demagnetization, information on the response of all three subsystems is required. A consistent description of demagnetization and microscopic energy flow, however, is still missing. Here, we combine a femtosecond electron diffraction study of the ultrafast lattice response of nickel to laser excitation with ab initio calculations of the electron-phonon interaction and energy-conserving atomistic spin dynamics simulations. Our model is in agreement with the observed lattice dynamics and previously reported electron and magnetization dynamics. Our approach reveals that the spin system is the dominating heat sink in the initial few hundreds of femtoseconds and implies a transient non-thermal state of the spins. Our results provide a clear picture of the microscopic energy flow between electronic, magnetic and lattice degrees of freedom on ultrafast timescales and constitute a foundation for theoretical descriptions of demagnetization that are consistent with the dynamics of all three subsystems.

Scale-independent relationship between permeability and resistivity in mated fractures with natural rough surfaces

Geothermal systems consisting of fractures in impermeable rocks are difficult to characterize by in situ methods. In an effort to link characteristics of small-scale and large-scale fractures, this study investigated possible relations between their geophysical parameters. We upscaled the relationship between fracture permeability and formation factor in a laboratory specimen to larger fracture dimensions. Microscopic flow characteristics indicate that this relationship is related to the tortuosity of flow paths. We derived an empirical formula that directly predicts changes in fracture permeability from changes in formation factor. This relation may make it possible to monitor subsurface hydraulic activities through resistivity observations.

Laws of gas and water flow and mechanism of reservoir drying in tight sandstone gas reservoirs

The reservoir permeability of tight sandstone gas reservoirs is low, which makes it difficult to carry out displacement flow experiments on real cores underground conditions, so the microscopic flow mechanism can be hardly studied. Based on the lattice Boltzmann method (LBM), this paper simulated the flow process of formation water displaced by tight gas under the simulated reservoir conditions of high temperature and high pressure to clarify the distribution of bound water in the reservoir. Then, reservoir drying was experimentally studied using the laser etching model, and numerical simulation of reservoir drying was simplified by referring to the visualization results of the experiment. Finally, the influence of reservoir drying on the seepage capacity of tight gas was studied by means of numerical simulation. And the following research results were obtained. First, when the lattice Boltzmann model is used for high temperature and high pressure reservoirs, it satisfies the Laplace law and its numerical solution of two-phase Poiseuille flow rate is basically consistent with the analytical solution, which indicates that this model can be used to simulate gas–water immiscible displacement under reservoir conditions. Second, tight gas preferentially breaks through in large porous media connected channels, and after the breakthrough, the displacement rate of formation water decreases significantly. Third, the contact angle between formation water and rock wall has a significant influence on gas–water two-phase flow. The stronger the water wettability of the rock is, the lower the displacement rate is. Fourth, the bound water in tight sandstone gas reservoirs can be classified into four types, including adsorbed water film, blind end pore water, dead pore water and trapped water. In porous media, a large number of connected micro-channels are occupied by trapped water and adsorbed water film and the phenomenon of “water lock” is obvious, which seriously influences the seepage capacity of tight gas in the porous media of reservoir. Fifth, drying agent can react with bound water to produce a large number of bubbles, which will consume adsorbed water film, trapped water and blind end pore water, so as to improve the gas seepage capacity. Sixth, in the “water lock” regions formed by trapped water, the gas seepage capacity can be effectively improved by increasing the drying strength. On the whole, the tight gas permeability increases with the increase of drying strength, but its increase amplitude decreases gradually when the drying strength exceeds a certain degree.

Supersonic needle-jet generation with single cavitation bubbles

Collapsing cavitation bubbles produce intense microscopic flows. Here, in an aqueous environment, we seed single laser-induced bubbles (diameter about one millimeter) in proximity to a solid surface, in a regime that has not been well explored before in order to generate a “needle jet.” The needle jet propagates at supersonic speed through the gas phase toward the solid. It reaches average velocities of more than 850 ms−1 and thus is an order of magnitude faster than the regular jets that have frequently been observed in cavitation bubbles. The dynamics leading to the needle jet formation are studied with high speed imaging at five million frames per second with femtosecond illumination. This highly repeatable, localized flow phenomenon may be exploited for injection purposes or material processing, and it is expected to generate significantly larger water hammer pressures and may also play a role in cavitation erosion and peening.

Elevated temperature results in higher compositional variability of pioneer phytoplankton communities in a mesocosm system

AbstractA crucial point in current research on plankton ecology is how global warming will change community functioning, which has led to numerous studies addressing the question with a variety of conclusions. We previously observed a long-term increase in the compositional variability of phytoplankton in a large shallow lake with a concurrent rise in mean temperature, and we conducted an experimental test of this hypothetical link in a mesocosm system. Following predictions of water temperature for the end of the century, 12 mesocosms were filled with prefiltered and sterilized lake water with six of the tanks kept 3°C above ambient levels. Phytoplankton colonization and subsequent changes in its composition were monitored using microscopic analysis and flow cytometry. Chlorophytes were the most successful colonizers, with no treatment-specific effect on dominant taxa. However, heated mesocosms showed higher variation in community structure (distance-based beta diversity), due to higher variability in subdominant species, a considerable portion of which were flagellated taxa. Our hypothesis of temperature-driven compositional variation was supported by both cytometric and taxonomic data, implying that higher spring temperatures can enhance variability in phytoplankton, which might increase the chance of alternate pathways during succession and reduce the predictability of its annual cycle.

Experimental Investigation of Polymer-Coated Silica Nanoparticles for EOR under Harsh Reservoir Conditions of High Temperature and Salinity

Laboratory experiments have shown higher oil recovery with nanoparticle (NPs) flooding. Accordingly, many studies have investigated the nanoparticle-aided sweep efficiency of the injection fluid. The change in wettability and the reduction of the interfacial tension (IFT) are the two most proposed enhanced oil recovery (EOR) mechanisms of nanoparticles. Nevertheless, gaps still exist in terms of understanding the interactions induced by NPs that pave way for the mobilization of oil. This work investigated four types of polymer-coated silica NPs for oil recovery under harsh reservoir conditions of high temperature (60 C) and salinity (38,380 ppm). Flooding experiments were conducted on neutral-wet core plugs in tertiary recovery mode. Nanoparticles were diluted to 0.1 wt.% concentration with seawater. The nano-aided sweep efficiency was studied via IFT and imbibition tests, and by examining the displacement pressure behavior. Flooding tests indicated incremental oil recovery between 1.51 and 6.13% of the original oil in place (OOIP). The oil sweep efficiency was affected by the reduction in core’s permeability induced by the aggregation/agglomeration of NPs in the pores. Different types of mechanisms, such as reduction in IFT, generation of in-situ emulsion, microscopic flow diversion and alteration of wettability, together, can explain the nano-EOR effect. However, it was found that the change in the rock wettability to more water-wet condition seemed to govern the sweeping efficiency. These experimental results are valuable addition to the data bank on the application of novel NPs injection in porous media and aid to understand the EOR mechanisms associated with the application of polymer-coated silica nanoparticles.

An Automated Microscopic Malaria Parasite Detection System Using Digital Image Analysis.

Rapid diagnosis and parasitemia measurement is crucial for management of malaria. Microscopic examination of peripheral blood (PB) smears is the gold standard for malaria detection. However, this method is labor-intensive. Here, we aimed to develop a completely automated microscopic system for malaria detection and parasitemia measurement. The automated system comprises a microscope, plastic chip, fluorescent dye, and an image analysis program. Analytical performance was evaluated regarding linearity, precision, and limit of detection and was compared with that of conventional microscopic PB smear examination and flow cytometry. The automated microscopic malaria parasite detection system showed a high degree of linearity for Plasmodium falciparum culture (R2 = 0.958, p = 0.005) and Plasmodium vivax infected samples (R2 = 0.931, p = 0.008). Precision was defined as the %CV of the assay results at each level of parasitemia and the %CV value for our system was lower than that for microscopic examination for all densities of parasitemia. The limit of detection analysis showed 95% probability for parasite detection was 0.00066112%, and a high correlation was observed among all three methods. The sensitivity and specificity of the system was both 100% (n = 21/21) and 100% (n = 50/50), respectively, and the system correctly identified all P. vivax and P. falciparum samples. The automated microscopic malaria parasite detection system offers several advantages over conventional microscopy for rapid diagnosis and parasite density monitoring of malaria.

Adaptations in driver deceleration behaviour with automatic incident detection: A naturalistic driving study

Traffic congestion and crash rates can be reduced by introducing variable speed limits (VSLs) and automatic incident detection (AID) systems. Previous findings based on loop detector measurements have revealed that drivers reduce their speeds while approaching traffic congestion when the AID system is active. Notwithstanding these behavioural effects, most microscopic traffic flow models assessing the impact of VSLs do not describe driver response accurately.This study analyses the main factors that influence driver deceleration behaviour while approaching traffic congestion with and without VSLs. The Dutch VSL database was linked to the driver behaviour data collected in the UDRIVE naturalistic driving study. Driver engagement in secondary tasks and glance behaviour were extracted from the video data. Linear mixed-effects models predicting the characteristics of deceleration events were estimated.The results show that the maximum deceleration is high when approaching a slower leader, when driving at high speeds and short distance headways, and close to the beginning of traffic congestion. The minimum time headway is short when driving at high speeds and changing lanes. Certain drivers showed higher decelerations and shorter time headways than others. Controlled for these main factors, smaller maximum decelerations were found when the VSLs were present and visible, and when the gantries were within close proximity. These factors could be incorporated into microscopic traffic simulations to evaluate the impact of AID systems on traffic congestion more realistically. Further research is needed to clarify the link between engagement in secondary tasks, glance behaviour and deceleration behaviour.

Spontaneous imbibition in tight porous media with different wettability: Pore-scale simulation

Spontaneous imbibition is significantly influenced by rock wettability, and it has been extensively studied in core-based experiments and numerical simulations owing to its important role in the development of oil/gas reservoir. Due to the fine pore structure and complex wettability of tight sandstone, an in-depth exploration of the effects of wettability on the pore-scale flow physics during spontaneous imbibition is of great value to complement traditional experimental studies and enhance the understanding of microscopic flow mechanisms during the development of tight oil reservoirs. Based on a X-ray computed tomography scanning experiment and a lattice Boltzmann multiphase model, in this work, we systematically investigate the effects of different hydrophilic strengths on the evolution of the imbibition fronts within the micropores and the degree of nonwetting fluid recovery during spontaneous imbibition of tight sandstone. The results show that the wettability significantly affects the morphological characteristics of the imbibition fronts. Under strong hydrophilic conditions, the wetting fluid preferentially invades the pore corner in the form of angular flow. As the contact angle increases, the hysteresis effect at the main terminal interface decreases, and the two-phase interface becomes regular and compact. Wettability also significantly affects the imbibition rate and the nonwetting fluid recovery degree. The smaller the contact angle, the faster the imbibition rate and the higher the recovery degree of nonwetting fluids during the cocurrent spontaneous imbibition.

Multiscale Simulations of Polymer Flow Between Two Parallel Plates

Abstract A modified multiscale method without constitutive equation is proposed to investigate the microscopic information and macroscopic flow properties of polymeric fluid with the memory effect between parallel plates. In this method, the domain is entirely described by macromodel with isolated molecular dynamics simulations applied to calculate the necessary local stresses. The present method is first verified by the creep-recovery motion and pressure-driven flow, and all results are in excellent agreement with the available numerical solutions in literature. Then, the method is extended to simulate two typical problems of relatively large spatial scale in general beyond the capability of molecular dynamics simulations. In the planar Couette flow, the relationship between macroscopic properties and the time evolution of local molecular information is investigated in detail without long time averaging. All results that are consistent with nonequilibrium molecular dynamics and literature qualitatively or quantitatively demonstrate the validity of present multiscale method in simulating transient viscoelastic flows and the capacity to obtain the polymer information. In the pressure-driven flow, a general monotonically decreasing relationship between the maximum or average velocities and the polymer concentrations has been found regardless of the polymer chain length. Particularly, the reference concentration that satisfies a power law with chain length is closely related to the overlap concentration, and the reference velocity is exactly the relevant velocity of Newtonian fluid with corresponding zero shear rate viscosity.