Deposition Rate Coefficient Research Articles

Optimization of Operational Parameters of Plant Protection UAV.

The operational parameters of plant protection unmanned aerial vehicles (UAVs) significantly impact spraying effectiveness, but the underlying mechanism remains unclear. This paper conducted a full factorial experiment with varying flight speeds, heights, and nozzle flow rates to collect parameter space data. Using the Kriging surrogate model, we characterized this parameter space and subsequently optimized the average deposition rate and coefficient of variation by employing a variable crossover (mutation) probability multi-objective genetic algorithm. In the obtained Pareto front, the average sedimentation rate is no less than 46%, with a maximum of 56.08%, and the CV coefficient is no more than 13.91%, with a minimum of only 8.42%. These optimized parameters enhance both the average deposition rate and spraying uniformity compared to experimental data. By employing these optimized parameters in practical applications, a balance between the maximum average deposition rate and minimum coefficient of variation can be achieved during UAV spraying, thereby reducing pesticide usage, promoting sustainable agriculture, and mitigating instances of missed spraying and re-spraying.

Role of flow structures on the deposition of low-inertia particles in turbulent pipe flow

We analyze the effect of large-scale coherent structures on the deposition of low-inertia particles in a turbulent pipe flow using extended proper orthogonal decomposition (EPOD) and spectral analysis. We perform direct numerical simulations (DNSs) at two the Reynolds numbers 5300 and 10 300 (based on bulk parameters) with the particles released at the pipe inlet. The equilibrium Eulerian model is employed for calculating particle velocity, and the analysis is limited to particles with Stokes number (based on wall units) less than 1. Increasing the Stokes number increases the energy at small streamwise wavelengths (due to inertial clustering), and the spectral energy peak moves from λz+≈1000 to λz+≈150. The spectral peak in the (λz+,y+) plane, where y+ is the wall-normal distance, moves from the buffer layer to the logarithmic region. Gravity has a substantial effect on the POD mode shapes. For the downward flow, a second peak appears closer to the center. A new Fukagata-Iwamoto-Kasagi (FIK) identity is derived for the wall deposition rate coefficient (Sherwood number, Sh) and employed to quantify the contributions of the mean and fluctuating velocity and particle concentration fields for different Stokes, Froude, and Reynolds numbers. Modes with azimuthal wave numbers kθ equal to three or four are found to contribute most to deposition. Application of the developed methodology to higher Reynolds number can elucidate the role of large- and very-large-scale flow structures on particle deposition to the wall. It is well known these structures leave their footprint at the wall but their contribution to deposition is not well understood. Published by the American Physical Society 2024

Modeling the Transport and Retention of Nanoparticles in a Single Partially Saturated Pore in Soil

AbstractPore‐network models are powerful tools for studying particle transport in complex porous media, and investigating the role of interfaces in their fate. The first step in simulating particle transport using pore‐network models is to quantitatively describe particle transport in a single pore, and obtain relationships between pore‐averaged deposition rate coefficients and various pore‐scale parameters. So, in this study, a three‐dimensional (3D) mathematical model is developed to simulate the transport and retention of nanoparticles within a single partially saturated pore with an angular cross‐section. The model accounts for particle deposition at solid‐water interfaces (SWIs), air‐water interfaces (AWIs), and air‐water‐solid (AWS) contact regions. We provide a novel formulation for particle diffusive transport from AWI to AWS, where particles are assumed to be retained irreversibly by capillary forces. The model involves 12 dimensionless parameters representing various physicochemical conditions. The 3D model results are averaged over the pore cross‐section and then fitted to breakthrough curves from one‐dimensional (1D) advection‐dispersion‐sorption equations with three‐site kinetics to estimate 1D‐averaged deposition rate coefficients at interfaces. We find that half‐corner angle, particle size, radius of curvature of AWI, and mean flow velocity have a significant effect on those coefficients. In contrast, chemical parameters such as ionic strength and surface potentials of particles and interfaces have negligible effects. AWS is found to be the major retention site for particles, especially for hydrophobic particles. We develop algebraic relationships between 1D‐averaged deposition rate coefficients at interfaces vis‐à‐vis various pore‐scale parameters. These relationships are needed for pore‐network models to upscale nanoparticle transport to continuum scale.

Capture of colloidal fine suspended particle by aquatic vegetation under rainfall

The capture of colloidal fine suspended particles by vegetation plays an important role in water quality of the shallow aquatic system under rainfall. Quantifying impact of rainfall intensity and vegetation condition on this process remains poorly characterized. In this study, the colloidal particle capture rates under three rainfall intensities, four vegetation densities and with submerged or emergent vegetation were investigated in different travel distance in a laboratory flume. Considering vegetation as porous media, non-Darcy's law with rainfall as a source term, was coupled with colloid first-order deposition model, to simulate the particle concentration changes with time, determining the particle deposition rate coefficient (kd), representing capture rate. We found that the kd increased linearly with rainfall intensity; but increased and then decreased with vegetation density, suggesting the existence of optimum vegetation density. The kd of submerged vegetation is slightly higher than emergent vegetation. The single collector efficiency (η) showed the same trend as kd, suggesting colloid filtration theory well explained the impact of rainfall intensity and vegetation condition. Flow hydrodynamic enhanced the kd trend, e.g., the theoretical strongest flow eddy structure represented in the optimum vegetation density. This study is helpful for the design of wetland under rainfall, to remove colloidal suspended particles and the hazardous material, for the protection of the downstream water quality.

Impacts of Nanobubbles in Pore Water on Heavy Metal Pollutant Release from Contaminated Soil Columns.

This study investigated the release of heavy metals from polluted soil under the pore water flow containing nanobubbles (NBs) to simulate natural ebullition. Three types of NBs (CH4, H2, and CO2) were generated in water and characterized, including bubble size, zeta potential, liquid density, and tension. The flow rate used in column tests was optimized to achieve proper soil fluidization and metal desorption or release. The leachate chemistries were monitored to assess the effect of NBs on conductivity, pH, oxidation-reduction potential (ORP), and dissolved oxygen (DO). The results showed that NBs in the pore water flow were significantly more effective in releasing Pb compared to DI water, with CO2 NB water being the most effective and H2 NB water being the least effective. CO2 NB water was also used to rinse column soil contaminated with four different metals (Pb, Cu, Zn, and Cr), which exhibited different leaching kinetics. Moreover, a convective-dispersion-deposition equation (CDDE) model accurately simulated the leaching kinetics and explained the effects of NBs on the key parameters, such as the deposition rate coefficient (Kd), that affect the released metal transport. The findings could provide new insights into soil pollutant release under ebullition and soil remediation using water wash containing NBs.

Numerical investigation of nanofluid deposition in a microchannel cooling system

Nanofluid-microchannels (NF-MCs) have emerged as an important topic for thermal management of electronic devices. However, deposition of nanoparticles is a tricky problem, and this paper conducts a numerical study to identify the best working conditions to prevent deposition of nanofluids in a microchannel cooling system. According to the findings, large nanoparticles, high velocity, low inlet temperature, high nanoparticle density, low nanofluid density, and high base fluid viscosity are the best working conditions for improving nanofluid stability. However, heat transfer rates and pressure drop must also be taken into account. The nanoparticle deposition rate and average heat transfer coefficient only increase by 2.71% and 0.92% respectively as the heat flux increases from 20 kW/m2 to 100 kW/m2, but the pressure drop decreases by 10.57%. Therefore, changing the heat flux is not the best option. Moreover, the inlet temperature has only a minor effect on the heat transfer coefficient, so it is crucial to balance the pressure drop and nanoparticle deposition when designing systems.

MODELING THE EFFECT OF PHYSICAL AND CHEMICAL HETEROGENEITY OF GRAIN SURFACE ON NANOPARTICLE TRANSPORT IN A SINGLE PORE IN SOIL

The physical and chemical heterogeneity of soil grains significantly affects nanoparticle transport. However, no quantitative relationships exist for particle deposition rates accounting for grain-surface heterogeneity. This study quantifies the effect of various physicochemical parameters on the nanoparticle deposition rate coefficients in a single heterogeneous pore in soil. A mathematical model is developed to simulate the transport of nanoparticles through an idealized pore of cylindrical shape with rings of the same height on the wall representing roughness. Chemical heterogeneity is considered by assigning positive and negative charges to the top of the ring elements and the remaining area of the pore wall, respectively. Particle transport is simulated by solving the advection-diffusion equation with first-order sorption at the pore wall. Nanoparticle breakthrough curves obtained from simulations are fitted with a 1D advection-dispersion-sorption equation. The pore-averaged deposition rate coefficients obtained thus are satisfactorily described using a power-law relationship vis-a-vis pore-scale parameters. The Damkohler number for nanoparticle attachment to the pore wall is significantly affected by parameters representing pore and particle radii, flow velocity, surface potentials of nanoparticles, and regions of the pore wall having positive and negative charges, and Hamaker constant. However, the Damkohler number for nanoparticle detachment from the pore wall is predominantly influenced by parameters representing particle size, roughness height, surface potentials of nanoparticles, and regions of the pore wall having positive and negative charges, Hamaker constant, and ionic strength. Chemical heterogeneity plays a dominant role in nanoparticle retention than wall roughness. The above relations can be incorporated into a pore-network model to quantify the effect of grain-surface heterogeneity on nanoparticle deposition at the continuum scale.

Predicting colloid transport and deposition in an array of collectors

Colloid transport and deposition are influenced by pore structures and transport history. In contrast to the homogeneous single-collector efficiency assumption in the classical colloid filtration theory (CFT), it is realized that for accurate prediction of deposition the pore geometry and variation of single-collector efficiency along the transport direction need to be carefully considered. The axisymmetric Happel sphere-in-cylinder array models are developed. Comprehensive sets of numerical simulations are performed covering a wide range of parameters. We propose an upscaling equation of deposition rate coefficient by adopting the average collector efficiency and the array geometric model. The predictions based on the proposed model are compared with those from the classical CFT and previous experiments. We find that the collector efficiencies decrease substantially along the array in most natural conditions, especially within the first few collectors, which is attributed to the gravitational sedimentation and interception mechanisms. Detailed comparison with existing experimental data demonstrates that the upscaled model more accurately predicts the deposition rate than the equations based on single-collector efficiencies, especially for small and large colloids. Our work suggests the significance of considering array packing structures in CFT and can have implications for predicting colloid transport in industrial and field applications.

Cotransport of microplastics and sulfanilamide antibiotics in groundwater: The impact of MP/SA ratio and aquifer media

The aim of this study was to investigate the effects of the aquifer media, structure type, and initial concentration ratio of contaminants on the cotransport behavior of microplastics (MPs) and sulfanilamide antibiotics (SAs) through a series of one-dimensional column experiments in groundwater. Under a single suspension system, the relative mass recovery rates of fine sand, medium sand, and coarse sand were 25.65%, 37.50%, and 57.91%, respectively. The breakthrough curve of MPs showed a weak and slow upward trend, indicating that the migration of MPs in aqueous media is mainly blocked by the surface. The migration results of different structure type on SAs (ST, SM, SM2, SMX) in a single suspension system indicated that the deposition rate coefficients (kc) of the four SAs were 1.23 × 10−1, 9.09 × 10−2, 1.11 × 10−1, and 8.87 × 10−2. Under a binary suspension system (MPs:ST = 1:1), the maximum effluent concentration (MEC) of MPs in fine sand, medium sand, and coarse sand increased to 0.52, 0.64, and 0.88, respectively, and the relative mass recovery rates of ST were 22.79%, 23.59%, 20.25%. This results show that the coexistence of MPs and SAs significantly promotes the migration of MPs and inhibits that of SAs. It is mainly because of their carrier action, adsorption sites and additional deposit sites for MPs through SAs pre-deposition on media. When the initial concentration ratio was 2:1, the particles had the highest Zeta potential (−48.3 mV) and the highest potential barrier (3200 kBT), leading to the formation of complex aggregates (MPs-SAs-MPs) owing to the aggregation of colloidal MPs. The increase in the volume and number of MPs-SAs co-aggregates on the surface of the media as the initial concentration of MPs increases, which was mainly due to the disappearance of surface blocking effect and the occurrence of filtering maturation effect.

Effects of clay minerals on the transport of polystyrene nanoplastic in groundwater

Microplastics are widely detected in the soil-groundwater environment, which has attracted more and more attention. Clay mineral is an important component of the porous media contained in aquifers. The transport experiments of polystyrene nanoparticles (PSNPs) in quartz sand (QS) mixed with three kinds of clay minerals are conducted to investigate the effects of kaolinite (KL), montmorillonite (MT) and illite (IL) on the mobility of PSNPs in groundwater. Two-dimensional (2D) distributions of DLVO interaction energy are calculated to quantify the interactions between PSNPs and three kinds of clay minerals. The critical ionic strengths (CIS) of PSNPs-KL, PSNPs-MT and PSNPs-IL are 17.0 mM, 19.3 mM and 21.0 mM, respectively. Experimental results suggest KL has the strongest inhibition effect on the mobility of PSNPs, followed by MT and IL. Simultaneously, the change of ionic strength can alter the surface charge of PSNPs and clay minerals, thus affecting the interaction energy. Experimental and model results indicate both the deposition rate coefficient (k) and maximum deposition (Smax) linearly decrease with the logarithm of the DLVO energy barrier, while the mass recovery rate of PSNPs (Rm) exponentially increases with the logarithm of the DLVO energy barrier. Therefore, the mobility and associated kinetic parameters of PSNPs in complex porous media containing clay minerals can be predicted by 2D distributions of DLVO interaction energy. These findings could help to gain insight into understanding the environmental behavior and transport mechanism of microplastics in the multicomponent porous media, and provide a scientific basis for the accurate simulation and prediction of microplastic contamination in the groundwater system.

Investigation of Electrophoretic Deposition of PANI Nano fibers as a Manufacturing Technology for corrosion protection

In this study, the process of electrophoretic deposition (EPD) of polyaniline (PANI) film was described kinetically via utilizing three models; Hamaker, Zhang, and Baldisseri for both quantitative and statistically employing the response surface method (RSM). Zeta potential and particle analyzer were used to determine the electrostatic force existing between particles of the suspension. Nevertheless, to demonstrate the parameters of EPD and its effects on the properties of the films deposited at a time interval of (180–600 s), in-depth research on the fundamentals of the kinetics of PANI-EPD is necessary. Erstwhile, researchers reported a cathodic reduction of the PANI during EPD simultaneously, entangling the process and control of kinetics. Consequently, in this work, low voltages were accustomed to avert an important PANI, reducing during the process of EPD, established via SEM, XRD, and FT-IR. Therefore, the kinetics of PANI-EPD was initiated as a function of voltage and time of deposition, followed by deposited films characterization microscopically. The results of the experiments indicated that it follows a linear deposition growth law, which agrees with the predictions of Hamaker's law. In comparison, the profilometry and optical absorbance provide an estimate of PANI deposition rate, density, and extinction coefficient. Baldisseri model was also shown to reproduce the data of the experiment among other kinetics of semi-empirical equations. Transition in the mechanism of deposition from linear mode to parabolic was also observed. This study shall help in comprehending the process of thermal degradation in-depth and also be a useful tool in anticipating thermal stability, which can also assist in bypassing unintended thermal degradation of polymeric products in various industries.

Colloid‐Pollutant Migration through Saturated Vegetative Filter Strips with Various Hydrodynamics Condition under Rainfall

AbstractFlow hydrodynamic condition impacts the deposition process on vegetation and removal of colloid and colloid‐associated contaminants in saturated vegetative filter strips (VFSs) under rainfall. A 9.6‐m‐long flume was constructed to investigate the retention of colloids through VFSs, with saturated soil and simulated rainfall. Colloidal filtration theory was applied to calculate the colloid deposition rate coefficient (kd) on vegetation surface. The result showed that removal efficiencies (η) of the single‐stem decreased, but colloid kd on the flume scale vegetation increased with increased Reynolds number (Re). Flume experiment found that the colloid retention rate in VFSs decreased as the Re increased. Since deposition on vegetation surface and diffusion into saturated soil are two main removal mechanisms, the discrepancy between kd and retention rate suggests that colloid diffusion into the soil was the dominant process of colloid removal in saturate VFSs. The research deepens the understanding of colloid transport mechanism in VFSs, and provides theoretical basis for the design of VFSs.

Predicting the Rate Coefficients of Attachment and Detachment of Colloids in Saturated Porous Media

The transport behavior of pathogenic microorganisms and nanoparticles (NPs) in the subsurface is usually studied by performing laboratory soil column experiments. Parameters describing colloid deposition on grain surfaces are estimated by fitting observed breakthrough curves with an appropriate one-dimensional model. However, predictive tools to estimate colloid deposition parameters, knowing the system properties such as soil type, colloid type, solution chemistry, and flow velocity, are useful in estimating the travel distances of pathogenic microorganisms in the subsurface. Such predictive models are rare, except the colloid attachment rate coefficient predicted by colloid filtration theory (CFT) under favorable conditions. Although a couple of theoretical and empirical predictive models are available for estimating the deposition parameters under unfavorable conditions, they were developed for a small set of data, and their applicability to a wide range of conditions is unexplored. In this study, several sets of column-experimental data from literature, covering a wide range of experimental conditions, were analyzed to understand key factors that control colloid deposition. Empirical relationships were developed for deposition rate coefficients and sticking efficiency of various colloidal types [viruses, bacteria, graphene oxide (GO) NPs, silver (Ag) NPs, titanium dioxide (TiO2) NPs, and carboxylate-modified latex (CML) colloids] vis-à-vis 11 physicochemical parameters such as porosity, mean pore-water velocity, median grain size, colloid radius, solution ionic strength, surface potentials of colloids and grains, Hamaker constant, temperature, viscosity of water, and dielectric constant. While deposition of viruses and CML colloids on grain surfaces was found to be reversible, deposition of bacteria, GO NPs, Ag NPs, and TiO2 NPs was found to be irreversible. The empirical equations proposed in this study can predict deposition rate coefficients more closely (p < .001, R2 = 0.69−0.85) than CFT (p < .7, R2 ≤ 0.41). The performance of CFT in predicting the attachment rate coefficients of viruses, bacteria, GO NPs, TiO2 NPs, and CML colloids was found to improve significantly when estimated rate coefficients were multiplied by the sticking efficiency calculated using the empirical expression proposed in this study (p < .001, R2 = 0.65−0.95).

Prediction of collector contact efficiency for colloid transport in porous media using Pore-Network and Neural-Network models

Conventional colloid filtration theory (CFT) uses the single collector contact efficiency (η) to describe the mass transfer of colloids to a collector surface. However, this approach neglects the full complexity of the pore structure and flow field of real porous media. In this study, the porous medium geometry, flow field, and colloid mass transfer are quantified using a pore-network model (PNM). A database of pore scale η is established by finite-element method to train a Neural-network model (NNM). The reasonable prediction of η indicates the potential of using the developed NNMs as an alternative to correlation equations, which can free the users from repeated numerical simulation. In contrast to the prediction by conventional CFT, the value of η in the PNM occurs as a distribution, which is dependent upon the geometry parameters of the PNM. The mean value of η increases with the standard deviation of pore radius and decreases with the curvature number, but the dependency on coordination number is more complex. Upscaled values of the deposition rate coefficient (kd) corresponding to the distribution of η are calculated by the breakthrough curves by PNMs. The prediction of kd by PNM is then compared with that by CFT. Results show that kd predicted by PNM shows more significant response to velocity change, and less remarkable response to colloid density change than kd predicted by CFT. The comparison between the flow velocity distribution between PNM and CFT shows that the high-velocity region of the flow field in the porous media has been neglected in CFT, which can lead to insufficient consideration of convection. The results of this work imply that it is necessary to consider the influence of the complex pore structure of porous media on the collection of colloids.

Colloidal transport and deposition through dense vegetation

The effectiveness of submerged synthetic aquatic vegetation on removal of colloids from flowing water was investigated to explore retention of particulate nonpoint source pollutants in aquatic systems. In colloid transport experiments, the deposition rate coefficient of colloids in dense vegetation is often taken as spatially constant. This assumption was tested by experiments and modeling aimed at quantifying changes in colloid retention with travel distance in submerged synthetic aquatic vegetation. Experiments were performed in a 10-m long, 0.6-m wide flume with a 5-cm water depth under different fluid velocities, initial colloid concentrations, and solution pH values. A model accounting for advection, dispersion and first-order kinetic deposition described the experimental data. The colloid deposition rate coefficient showed a power-law decrease with travel distance, and reached a steady state value before the end of the flume. Measured changes in colloid properties with transport distance (ζ potential and size) could not explain the observed decrease. While gravity was shown to contribute to the decrease, its impact was too weak to explain the decreasing power law trend, suggesting that processes operating in granular media to produce similar outcomes may also apply to submerged vegetation.

Effects of Proppant Wettability and Size on Transport and Retention of Coal Fines in Saturated Proppant Packs: Experimental and Theoretical Studies

Hydraulic fracturing is the main stimulation technique that enables the economic production of coalbed methane reservoirs. However, massive invasion and retention of coal fines in proppant packs can clog the pore spaces and lead to an impairment of fracture conductivity. In this study, the effects of proppant wettability and size on retention of coal fines in proppant packs during the dewatering stage were investigated, for their optimization to achieve a long-term and effective control of fines retention. First, a series of transport and retention experiments of coal fines were performed on saturated proppant packs with different proppant sizes and wettabilities. Herein, standard quartz sand was used as the proppant carrier, and its surface wettability was modified to either hydrophobicity or stronger hydrophilicity by treatment with fluorocarbon resin and piranha solution, respectively. The experimental results indicated that both the retained amount and the deposition rate coefficient of coal fines decreased with increasing proppant hydrophilicity (or decreasing proppant hydrophobicity) and size. For the proppants treated with piranha solution, almost no coal fines were retained in proppant packs. Second, the forces/torques acting on coal fines in the vicinity of proppants were analyzed to elucidate the underlying mechanisms responsible for the influence of proppant wettability and size on fines retention. The effective filter surface (EFS) parameter was estimated by analyzing forces/torques to evaluate the filtration performance of proppant packs. Theoretical results illustrated that the EFS value decreased with increasing proppant hydrophilicity and size. The EFS value for proppants treated with piranha solution was near zero, which was due to the chemically “unfavorable” retention condition induced by piranha solution treatment. The EFS exhibited a similar tendency to the retention of coal fines observed in experiments, which validated the model. Finally, the recommendations on fines retention control in proppant packs were provided.

Real-time bioluminescent imaging of spatiotemporal variation of microbial retention during transport through porous media under variably saturated flow conditions

This study investigated the transport and retention of bioluminescent Escherichia coli strain 652T7 under different pore water velocities (8.7 cm h−1 and 13.0 cm h−1) and pore water saturations (85% and 100%) utilizing a non-invasive, real-time bioluminescent imaging technique. Under saturated flow conditions, the concentrations of retained bioluminescent E. coli 652T7 decreased exponentially with distance from the source at the lower velocity but decreased non-exponentially at the higher velocity. Under unsaturated flow conditions, pore water velocity had no significant effect on bacterial breakthrough concentration; however, the concentrations of retained cells were maximal at a significant distance from the source (non-monotonic). The distance from source of the maximum concentration increased from 2.4-cm at 1.05 pore volumes to 4.3-cm at 3.15 pore volumes, indicating slow translation of bacterial down-gradient under unsaturated flow conditions. That conditions were modestly unfavorable to attachment at the solid-water interface (SWI) was indicated by deposition rate coefficients being greater (by a factor of four) for simulations versus experiments, and by significant repulsive barriers to attachment at both the SWI (260 kT) and the air–water interface (AWI, fully repulsive). The inferred slow translation under unsaturated flow conditions therefore reflects either accumulation without arrest in the secondary minimum at the SWI and/or capillary interaction at the AWI. This non-invasive bioluminescence method yielded real-time quantitative observation of bacterial distribution from source and demonstrated contrasting transport behaviors previously obtained solely via more laborious methods with limited spatio-temporal observation.

Full factorial sensitivity analysis of asphaltene precipitation and deposition in CO2 and CH4 coreflooding

Modelling of asphaltene precipitation and deposition in petroleum reservoirs requires adjustable parameters and introduces uncertainty sources. To address the main sources of uncertainty, a two-level full factorial sensitivity analysis was applied to asphaltene precipitation and deposition. Six factors were critically evaluated in the models, three concerning the precipitation phenomenon and the others related to the asphaltene deposition: asphaltene molar content, binary interaction parameters, reference pressure, asphaltene molar volume, surface deposition rate coefficient and flocculation parameters. The effect of these factors on the average of permeability reduction is assessed and their relative importance and relevant interactions were analyzed. Curves of precipitated, flocculated and deposited asphaltene showed that asphaltene deposition caused permeability reduction. Results showed that thermodynamic sources of uncertainty have a more significant effect on the model performance compared to the kinetics parameters ones. This suggests that fitting deposition parameters using experimental permeability reduction data may jeopardize the applicability of these parameters in real field conditions. The aggregation of asphaltene precipitates to form larger particles is modelled using the Kohse and Nghiem flocculation model, one of the most used. Simulations for different conditions were also performed to improve the reliability of the findings. We conclude that reestimation of these model parameters using experimental data of kinetics of asphaltene aggregation is required to provide acceptable description of the aggregation phenomenon.

Deposition mechanism of polydisperse xanthan gum-stabilized graphene oxide/nano-iron composites in saturated porous medium

Engineered materials (EMs) have shown promise for remediation of groundwater contaminants and the potential application relies on the delivery of aqueous solutions of EMs to a targeted subsurface location or region. Thus, the ability to accurately predict nanoparticle transport and retention in saturated porous media is one of the most technical challenges faced by the design and assessment of potential field-scale environmental applications. Here, a prior prediction model was presented by coupling the effect of Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction, Brownian diffusion, hydrodynamics and interception. Characteristics used in the model were medium size, porosity, injection velocity, size distribution of particles, attachment efficiency, single-collector contact efficiency. The direct comparison of parameterized prior model predictions to experimental measurements was proposed to thoroughly understand deposition mechanism of polydisperse xanthan gum-stabilized graphene oxide/nano-iron composites (XG-nZVI/rGO). The model predicted deposition rate coefficient quantitatively very close to measured rates. When the particle diameter (dp) of XG-nZVI/rGO excessed 1.2080 μm, it was retained in the porous medium by interception; When dp < 0.1737 μm, XG-nZVI/rGO would deposite in the porous medium if the kinetic energy (Ek) it possessed is less than the depth of the secondary energy minimum; When 0.1737 μm < dp < 1.2080 μm, deposition occurred where adhesive torques (TA) was in excess of hydrodynamic drag torgues (TH) particles subject to. Further, deposition rate was positive correlated with injection concentrations among the range of 0.34–1.70 g/L. Besides, low deposition rates were observed with injection velocities around 0.69 cm/min.

A mathematical model for predicting indoor PM2.5 concentration under different ventilation methods in residential buildings

Experiments and theoretical analyses are conducted in a residential building in Changzhou to study indoor PM2.5 concentrations by establishing a combined parameter model. An alternative method for predicting the particle deposition rate and penetration coefficient is proposed, and its accuracy is tested and verified by experiments using time-dependent concentrations and air exchange rate measurements. The predicted PM2.5 penetration coefficient increased from 0.70 to 0.88 when the air exchange rates were varied from 0.2 h−1 to 0.5 h−1. In addition, outdoor sources of PM2.5 dominantly contributed approximately 90% to 98% to the indoor concentrations for both mechanically and naturally ventilated structures. Finally, a mathematical model for predicting the indoor concentration is presented using a mass balance equation, which estimates the parameter values in the building. The indoor PM2.5 concentrations ranged from 40 to 46 µg/m3 by using a fresh air system with 82% filtration efficiency, while those by using open windows for natural ventilation ranged from 105 to 118 µg/m3 when the outdoor PM2.5 concentration ranged from 115 to 137 µg/m3. The results of this study can be used to estimate the indoor particle level. Practical application: By applying the ventilation criteria for acceptable indoor air quality in ASHRAE Standard 62.1, the indoor PM2.5 monitoring results show serious pollution in dwellings in 2018. More dwellings are expected to maintain a clean indoor environment in the future. Thus, it is crucial to consider the indoor PM2.5 pollution risk in the building design to prevent the possible consequences of unsafe high indoor concentrations. The use of this prediction model, as discussed in this article, will provide further information on the influence of the particle deposition rate ( K) and penetration coefficient ( P) on indoor PM2.5 concentrations.