Deposition Coefficient Research Articles

Numerical Study of Particle Concentration Effect on Deposition Characteristics in Turbulent Pipe Flows

The present study focuses on the particle concentration effect on the particle deposition onto a channel wall in numerically simulated turbulent pipe flows. Large eddy simulation of the incompressible Navier-Stokes equations was performed to calculate the time-dependent turbulent flow field of continuous gas phase. Considering the technical application to the droplet motion in boiling water reactor subchannels, the flow direction was set to be vertically upward. The particles were placed at random initial locations in the pipe. The subsequent particle motion was tracked individually using a simple Lagrangian equation. To investigate the particle concentration effect on the rate of particle deposition, “two-way method” was applied, in which the two-way interactions between the continuous phase and the particles were taken into consideration. The calculated results showed that the mass transfer coefficient of particle deposition decreased noticeably with an increase in the particle concentration. This tendency was consistent with the experimental observations and empirical correlations. The present numerical results indicated that the turbulence modulation in the continuous gas phase is one of the primary causes of the reduction of the deposition mass transfer coefficient observed under high-droplet-concentration conditions.

TU-E-BRB-05: Real-Time Dose Reconstruction for Treatment Monitoring

Purpose: To reconstruct in real‐time the dose distribution of intensity‐modulated radiation therapy(IMRT)delivered to a patient during treatment.Method and Materials: First, we use a GPU‐based FSPB algorithm to calculate the dose deposition coefficients Dij for all IMRT field. Dij is the dose contribution of the ith beamlets to the jth voxel on the patient image, and it is pre‐computed and stored in the memory. During the treatmentdelivery,MLC leaf positions will be read in real‐time from either the MLC controller or the cine EPIDimages. Then the delivereddose distribution is generated using the Dij matrix and the leaf positions. In this work, we simulate this process using the MLC DynaLog files in retrospective. We extract the leaf positions and fractional MU every 50 ms from the MLC DynaLog files and converted them to a beam mask Bi using an in‐house software based on MATLAB. The accumulated dose distribution delivered up to a time point is then computed by convolving Dij with Bi. Results: It takes on average less than 1 s to pre‐calculate Dij for each beam. It takes on average 0.2 s to update the accumulative dose distribution on patient's geometry. It is expected that this time can be further reduced by 10 to 20 times when we implement it on GPUs to meet the real‐time requirement. Conclusion: We have developed a dose reconstruction algorithm with pre‐calculated dose deposition coefficients using GPU‐based FSPB algorithm. The results indicate that real‐time dose reconstruction during treatmentdelivery is feasible, enabling dose‐based real‐time treatment monitoring.

Removal of carbonyl sulfide at low temperature: Experiment and modeling

A mathematic model of carbonyl sulfide (COS) removal at low temperature with fouling of catalyst has been developed based on experimental results. Kinetic studies were conducted in a fixed bed reactor under atmospheric pressure and at low temperature (40-70 °C). Experimental results of breakthrough curves were used to obtain kinetic parameters accounting for axial dispersion, external and internal mass-transfer resistances as well as the sulphur deposition on inner-face of catalyst. Initial bulk porosity of particle ( ɛ P0 ), deactivation coefficient ( α), sulfide deposition coefficient ( β) were used to quantify the behavior of COS removal at different operating conditions. Adsorption heat of H 2O and activation energy of COS removal was 21.5 and 62.4 kJ/mol respectively. The effects of flow rate, COS inlet concentration, temperature and relative humidity(RH) were analyzed, and it was found that relative humidity carried a heavier weight than temperature on ε P0 , α, β within our experimental conditions. The model agreed well with the experimental breakthrough curves and satisfactorily predicted the fixed-bed reactor performance, and this model can be used as a reliable tool for process design and scaling-up of similar system.

An aerosol chamber investigation of the heterogeneous ice nucleating potential of refractory nanoparticles

Abstract. Nanoparticles of iron oxide (crystalline and amorphous), silicon oxide and magnesium oxide were investigated for their propensity to nucleate ice over the temperature range 180–250 K, using the AIDA chamber in Karlsruhe, Germany. All samples were observed to initiate ice formation via the deposition mode at threshold ice super-saturations (RHithresh) ranging from 105% to 140% for temperatures below 220 K. Approximately 10% of amorphous Fe2O3 particles (modal diameter = 30 nm) generated in situ from a photochemical aerosol reactor, led to ice nucleation at RHithresh = 140% at an initial chamber temperature of 182 K. Quantitative analysis using a singular hypothesis treatment provided a fitted function [ns(190 K)=10(3.33×sice)+8.16] for the variation in ice-active surface site density (ns:m−2) with ice saturation (sice) for Fe2O3 nanoparticles. This was implemented in an aerosol-cloud model to determine a predicted deposition (mass accommodation) coefficient for water vapour on ice of 0.1 at temperatures appropriate for the upper atmosphere. Classical nucleation theory was used to determine representative contact angles (θ) for the different particle compositions. For the in situ generated Fe2O3 particles, a slight inverse temperature dependence was observed with θ = 10.5° at 182 K, decreasing to 9.0° at 200 K (compared with 10.2° and 11.4° respectively for the SiO2 and MgO particle samples at the higher temperature). These observations indicate that such refractory nanoparticles are relatively efficient materials for the nucleation of ice under the conditions studied in the chamber which correspond to cirrus cloud formation in the upper troposphere. The results also show that Fe2O3 particles do not act as ice nuclei under conditions pertinent for tropospheric mixed phase clouds, which necessarily form above ~233 K. At the lower temperatures (<150 K) where noctilucent clouds form during summer months in the high latitude mesosphere, higher contact angles would be expected, which may reduce the effectiveness of these particles as ice nuclei in this part of the atmosphere.

Numerical Study of Particle Concentration Effect on Deposition Characteristics in Turbulent Pipe Flows

The present study focuses on the particle concentration effect on the particle deposition onto a channel wall in numerically simulated turbulent pipe flows. Large eddy simulation of the incompressible Navier-Stokes equations was performed to calculate the time-dependent turbulent flow field of continuous gas phase. Considering the technical application to the droplet motion in boiling water reactor subchannels, the flow direction was set to be vertically upward. The particles were placed at random initial locations in the pipe. The subsequent particle motion was tracked individually using a simple Lagrangian equation. To investigate the particle concentration effect on the rate of particle deposition, “two-way method” was applied, in which the two-way interactions between the continuous phase and the particles were taken into consideration. The calculated results showed that the mass transfer coefficient of particle deposition decreased noticeably with an increase in the particle concentration. This tendency was consistent with the experimental observations and empirical correlations. The present numerical results indicated that the turbulence modulation in the continuous gas phase is one of the primary causes of the reduction of the deposition mass transfer coefficient observed under high-droplet-concentration conditions.

Effects of feeding levels on growth performance, feed utilization, body composition and apparent digestibility coefficients of nutrients for juvenile Chinese sucker,Myxocyprinus asiaticus

An experiment was conducted to determine effects of feeding levels on growth performance, feed utilization, nutrient deposition, body composition and apparent digestibility coefficients (ADCs) of nutrients for juvenile Chinese sucker (initial weight, 11.77±0.22 g). Chinese sucker were fed a practical diet from 0% (starvation) to 4.0% (at 0.5% increments) body weight (bw) day−1 for 8 weeks. The results showed that growth performance, feed utilization, nutrient deposition, body composition and ADCs of dry matter, protein and energy were significantly (P<0.05) affected by feeding levels. Survival was the lowest for the starvation group. Final mean body weight, growth rate, thermal-unit growth coefficient (TGC) increased with feeding rate from 0% to 3.0% bw day−1 (P<0.05) and showed no significant differences above the level (P>0.05). Feed conversion rate was significantly lower at a feeding level of 2.5% bw day−1 than above and below the level (P<0.05). Protein efficiency ratio was markedly highest at the 2.5% bw day−1 ration level (P<0.05). Fish fed at the feeding level (1.0% bw day−1), which represented a maintenance ration (energy gain was less than 2.27 kJ fish−1 day−1), showed positive protein deposition but negative lipid deposition. This indicates that fish fed a maintenance ration mobilize body lipid reserve to support protein deposition. Lipid contents of whole body, muscle and liver increased with increasing feeding rates from 0.5% to 3.0% bw day−1 and showed no significant differences above the level (P>0.05). Protein contents of whole-body composition increased with feeding rate from 0.5 to 3.0% bw day−1 (P<0.05) and showed no significant differences above the level (P>0.05), whereas muscle and liver remained relatively stable with the different ration amount with the exception of fish fed a ration of 0.5% bw day−1, at which Chinese sucker possessed significantly lower body protein concentration (P<0.05). The ADCs of dry matter, protein and energy decreased with increasing feeding levels from 0.5% to 3.0% bw day−1 and then remained relatively constant over the level. Based on the broken-line regression analysis using WG data, the optimum and maintenance feeding levels for Chinese sucker were 3.10% bw day−1 and 0.45% bw day−1 respectively.

GPU-based ultra-fast dose calculation using a finite size pencil beam model

Online adaptive radiation therapy (ART) is an attractive concept that promises the ability to deliver an optimal treatment in response to the inter-fraction variability in patient anatomy. However, it has yet to be realized due to technical limitations. Fast dose deposit coefficient calculation is a critical component of the online planning process that is required for plan optimization of intensity-modulated radiation therapy (IMRT). Computer graphics processing units (GPUs) are well suited to provide the requisite fast performance for the data-parallel nature of dose calculation. In this work, we develop a dose calculation engine based on a finite-size pencil beam (FSPB) algorithm and a GPU parallel computing framework. The developed framework can accommodate any FSPB model. We test our implementation in the case of a water phantom and the case of a prostate cancer patient with varying beamlet and voxel sizes. All testing scenarios achieved speedup ranging from 200 to 400 times when using a NVIDIA Tesla C1060 card in comparison with a 2.27 GHz Intel Xeon CPU. The computational time for calculating dose deposition coefficients for a nine-field prostate IMRT plan with this new framework is less than 1 s. This indicates that the GPU-based FSPB algorithm is well suited for online re-planning for adaptive radiotherapy.

Film growth by polyatomic C2H5+ bombarding a diamond (1 0 0) surfaces: Molecular dynamics study

The deposition of polyatomic C2H5+ ions is studied using classical molecular dynamics simulations with a new improved Brenner potentials developed by Brenner. The simulation results show that when the incident energy is less than 65eV, the deposition coefficient of H is larger than that of C atoms. When the incident energy is larger than 65eV, the deposition of H is less than that of C atoms. With increasing incident energy, a transition from Csp3-rich to Csp2-rich in the grown films is found.

Deposition rates of unattached and attached radon progeny in room with turbulent airflow and ventilation

In this paper deposition rate coefficients for unattached and attached radon progeny were estimated according to a particle deposition model for turbulent indoor airflow described by Zhao and Wu [2006. Modeling particle deposition from fully developed turbulent flow in ventilation duct. Atmos. Environ. 40, 457–466]. The parameter which characterizes turbulent indoor airflow in this model is friction velocity, u*. Indoor ventilation changes indoor airflow and friction velocity and influences deposition rate coefficients. Correlation between deposition and ventilation rate coefficients in the room was determined. It was shown that deposition rate coefficient increases with ventilation rate coefficient and that these parameters of the Jacobi room model cannot be assumed to be independent. The values of deposition rate coefficients were presented as functions of friction velocity and ventilation rate coefficient. If ventilation rate coefficient varies from 0.1 up to 1 h −1, deposition rate coefficients for unattached and attached fractions were estimated to be in the range 3–110 h −1 and 0.015–0.35 h −1, respectively.

Energy Absorption Buildup Factors and Energy Conservation

The ANSI/ANS energy absorption buildup factors (ANSI/ANS-6.4.3–1991) were used to determine if they conserve absorbed energy from a point source of monoenergetic photons in an infinite, absorbing medium. Air, water, concrete, iron, lead, and uranium were considered for photon energies ranging from 0.015 to 15 MeV. The primary calculations were based on fitting natural cubic splines to the energy absorption buildup factors and analytical integration of the energy absorbed using the cubic spline curve fit. This method was supplemented by linear spline interpolation. For air, water, concrete, and iron, the ANSI/ANS energy absorption buildup factors were determined using the method of moments with theenergy attenuation and deposition coefficients of Hubbell (NSRDS-NBS 29). The results of this study essentially confirmed energy conservation for these four materials using the energy attenuation and deposition coefficients of Hubbell. For lead and uranium, the ANSI/ANS energy absorption buildup factors were determined using the discrete ordinates-integral transport method with PHOTX energy attenuation and deposition coefficients that are essentially the same as those in the ANSI/ANS report. The calculations in this study could not confirm energy conservation for these two materials.

Effects of Particle Relaxation Time and Continuous-Phase Reynolds Number on Particle Deposition in Vertical Turbulent Pipe Flows

The present study focuses on the mechanism of particle deposition onto a channel wall in numerically simulated turbulent pipe flows. Large eddy simulation of the incompressible Navier-Stokes equations was performed to calculate the time-dependent turbulent flow field of continuous gas phase. Considering the engineering application to the droplet motion in boiling water reactor subchannels, the flow direction was set to be vertically upward. The particles were placed at random initial locations in the pipe, assuming that the initial velocities in the lateral direction are equal to zero. The subsequent motion of particles was tracked individually using a simple Lagrangian equation. It was shown that small particles tended to accumulate in the viscous sublayer while large particles moved parallel to the pipe wall. The deposition coefficient was hence highest when the particles were intermediate in size or in relaxation time. The calculated results indicated that the effect of the continuous-phase Reynolds number on the deposition mass transfer coefficient was not negligible since it affected the drag and the lift coefficients and, consequently, the particle motion in the lateral direction.

Parameterization of surface kinetic effects for bulk microphysical models: Influences on simulated cirrus dynamics and structure

A parameterization for the influences of the deposition coefficient (αd) and, therefore, surface kinetics on ice crystal vapor growth in bulk microphysical models is derived. The parameterization is developed by considering three distinct growth regimes, each of which depends on the mean size of the ice crystals: inefficient growth in which surface kinetics dominate vapor growth, efficient growth in which diffusion dominates vapor growth, and an intermediate regime in which both surface kinetics and diffusion are important. Analytical solutions to the distribution‐integrated vapor growth equations are derived for the inefficient and efficient growth regimes, whereas a plausible approximation is suggested for the intermediate growth regime. Use in a numerical cloud model requires a method to choose between the growth regimes, and we show that the kinetic length scale can be used for this purpose. The parameterization is used in eddy‐resolving simulations of a warm and unstable cirrus case. Simulation results tend to match prior microphysical studies: cirrus microphysics are insensitive to αd if αd &gt; 0.1, whereas lower values of αd produce relatively high ice concentrations and ice supersaturations. Our simulations suggest that large changes in cirrus structure and dynamics occur when αd becomes lower than ∼0.05. When growth is this inefficient, ice concentrations are high and precipitation rates are low, which leads to a cirrocumulus‐like structure over time. The dynamic motions in these clouds are driven primarily by infrared cloud top cooling and cloud base warming. At larger values of αd (&gt;0.05), the more efficient vapor growth leads to lower ice concentrations and larger precipitation rates. This causes the initially layered cirrus to transition into cirrus uncinus with precipitation tails. The cloud fraction in this case is low, with lifetimes almost 6 hours less than in the cases with inefficient growth (αd &lt; 0.05).

Energy Absorption Buildup Factors and Energy Conservation

The ANSI/ANS energy absorption buildup factors (ANSI/ANS-6.4.3–1991) were used to determine if they conserve absorbed energy from a point source of monoenergetic photons in an infinite, absorbing medium. Air, water, concrete, iron, lead, and uranium were considered for photon energies ranging from 0.015 to 15 MeV. The primary calculations were based on fitting natural cubic splines to the energy absorption buildup factors and analytical integration of the energy absorbed using the cubic spline curve fit. This method was supplemented by linear spline interpolation. For air, water, concrete, and iron, the ANSI/ANS energy absorption buildup factors were determined using the method of moments with theenergy attenuation and deposition coefficients of Hubbell (NSRDS-NBS 29). The results of this study essentially confirmed energy conservation for these four materials using the energy attenuation and deposition coefficients of Hubbell. For lead and uranium, the ANSI/ANS energy absorption buildup factors were determined using the discrete ordinates-integral transport method with PHOTX energy attenuation and deposition coefficients that are essentially the same as those in the ANSI/ANS report. The calculations in this study could not confirm energy conservation for these two materials.

Studying colloid transport in porous media using a geocentrifuge

Movement of colloids in the subsurface is a concern because mobile colloids may enhance the transport of contaminants. The excessive time required to conduct flow and transport experiments in porous media led to the use of centrifuges to evaluate subsurface transport processes. The objective of this study was to determine the suitability of centrifuges to study colloid transport in saturated porous media. We used a geocentrifuge to run colloid transport experiments under different centrifugal accelerations up to 20 g. Colloids of different densities were used: polystyrene (1.05 g/cm3), silica (2 g/cm3), and hematite (5.26 g/cm3). Deposition coefficients were obtained from the colloid breakthrough curves. We used filtration theory and a theory based on sedimentation‐diffusion to derive functional relationships between centrifugal acceleration and colloid and porous media properties, which allow us to predict the effect of acceleration on colloid transport. Comparison of experimental deposition coefficients with predictions based on filtration theory showed that filtration theory accurately predicted the behavior of polystyrene at higher accelerations but underpredicted colloid deposition for silica and hematite at accelerations higher than ∼10 g. The sedimentation‐diffusion theory allows us to determine whether a system is dominated by sedimentation or diffusion, or is in a transitional state. Theoretical predictions of colloid deposition in a porous medium agreed well with experiments, suggesting that the theory can be used to delineate when centrifugal acceleration will alter colloid transport in flow through column studies conducted in a centrifuge. Common subsurface colloids, such as iron oxides and aluminosilicates, can be affected at accelerations that are used in geocentrifuge transport studies (5 to 300 g). Even colloids with low specific densities, such as polystyrene, will be affected by centrifugal accelerations if their size is large.

Parameterization of cirrus cloud formation in large‐scale models: Homogeneous nucleation

This work presents a new physically based parameterization of cirrus cloud formation for use in large‐scale models which is robust, computationally efficient, and links chemical effects (e.g., water activity and water vapor deposition effects) with ice formation via homogenous freezing. The parameterization formulation is based on ascending parcel theory and provides expressions for the ice crystal size distribution and the crystal number concentration, explicitly considering the effects of aerosol size and number, updraft velocity, and deposition coefficient. The parameterization is evaluated against a detailed numerical cirrus cloud parcel model (developed during this study), the equations of which are solved using a novel Lagrangian particle‐tracking scheme. Over a broad range of cirrus‐forming conditions, the parameterization reproduces the results of the parcel model within a factor of 2 and with an average relative error of −15%. If numerical model simulations are used to constrain the parameterization, error further decreases to 1 ± 28%.

Bacteria Transport and Deposition under Unsaturated Flow Conditions: The Role of Water Content and Bacteria Surface Hydrophobicity

Column experiments were conducted to investigate the transport and deposition behavior of representative hydrophobic and hydrophilic bacteria strains in sand at different water saturations. These strains are similar in surface charge, shape, and size, and differ primarily in their surface hydrophobicity and tendency to form aggregates. The amount of bacteria that were retained in the sand increased with decreasing water saturation, especially for the more hydrophobic strain that formed larger cell aggregates. Most of the cells were retained close to the column inlet, and the rate of deposition rapidly decreased with depth. The experimental data were analyzed using a mathematical model that accounted for deposition on two kinetic sites. Consideration of depth‐dependent deposition in the model formulation significantly improved the description of the data, and the amount of cell retention was typically dominated by this site. The depth‐dependent deposition coefficient tended to increase with decreasing water content, especially for the hydrophobic bacteria. Straining is believed to account for these observations because it increases in magnitude with increasing cell and aggregate size and when a greater fraction of the water flows through a larger number of small pore spaces with decreasing water content. Cell retention on the other kinetic deposition site was well described using a conventional model for attachment and detachment. Consistent with interaction energy calculations for bacteria attachment, however, low amounts of cell retention occurred on this site. Attempts to separately determine the amounts of attachment to solid–water and air–water interfaces were confounded by the influence of straining.

Timescale analysis of aerosol sensitivity during homogeneous freezing and implications for upper tropospheric water vapor budgets

Using timescales for the generation and depletion of water vapor, we predict aerosol sensitivity in clouds formed by homogeneous freezing. Our timescale analysis explains why aerosol sensitivity increases dramatically with ice deposition coefficients (αi) ≪ 0.1, and also why aerosol sensitivity increases as vertical velocity increases, temperature decreases, aerosol number decreases, and aerosol size decreases. We combine existing in‐situ observations with adiabatic parcel modeling to constrain αi ≥ 0.1 for small ice crystals forming at high ice supersaturations. Two important implications for understanding and modeling upper tropospheric water vapor budgets emerge from our results: 1) aerosol sensitivity can be appreciable at low temperatures and moderate updrafts (∼5 cm/s) in the upper tropical troposphere, 2) reconciling our results with recent laboratory measurements supports theory that αi increases with ice supersaturation and/or decreases with ice crystal size.

Nonuniform deposition of particles inside the pores of a semipermeable membrane

Macroscopic equations of the theory of filtration through granular beds are used to consider the spatial nonuniformity of particle deposition on pore walls during the standard blocking of the pores of ultrafiltration (UF) and microfiltration (MF) membranes. It is shown that the thickness of the layer of particles deposited inside the pore is characterized by a high degree of nonuniformity, which considerably affects the values of membrane permeate flux and selectivity. The effect of pore diameter, pore length, transmembrane pressure, and the coefficient of particle deposition onto the inner pore surface on the performance of standard blocking is studied. A dimensionless number representing the combination of the above parameters is proposed. The number can be used for optimizing the choice of membranes and process parameters for the UF and MF processes using standard blocking.

Impact of lux gene insertion on bacterial surface properties and transport

Genetic markers have been in popular use for tracing microbial movement in the environment. However, the impact of genetic marker insertion on microbial surface properties and consequent transport is often ignored. For this research, we investigated the impact of luminescence-based genetic marker insertion on bacterial surface properties and transport. Typical Gram-positive bacterial strains of Lactobacillus casei, Streptococcus mitis and Micrococcus luteus were used as model bacterial strains in this research. We manipulated gene transfer to observe the impact of lux gene insertion on bacterial surface properties based on contact angle measurements, and we conducted column experiments to evaluate the impact of lux gene insertion on bacterial transport. After lux gene insertion, bacterial interactions with the porous media increased, demonstrating stronger deposition potential in the porous media. Accordingly, retention of the daughter strains increased. Lux gene insertion also resulted in an increase in bacterial dispersion and equilibrium adsorption in the porous media. The bacterial deposition coefficient was found to correlate with the free energy of interactions between bacteria and the porous media.

A Stochastic Model for Colloid Transport and Deposition

Profiles of retained colloids in porous media have frequently been observed to be hyper-exponential or non-monotonic with transport depth under unfavorable attachment conditions, whereas filtration theory predicts an exponential profile. In this work we present a stochastic model for colloid transport and deposition that allows various hypotheses for such deviations to be tested. The model is based on the conventional advective dispersion equation that accounts for first-order kinetic deposition and release of colloids. One or two stochastic parameters can be considered in this model, including the deposition coefficient, the release coefficient, and the average pore water velocity. In the case of one stochastic parameter, the probability density function (PDF) is characterized using log-normal, bimodal log-normal, or a simple two species/region formulation. When two stochastic parameters are considered, then a joint log-normal PDF is employed. Simulation results indicated that variations in the deposition coefficient and the average pore water velocity can both produce hyper-exponential deposition profiles. Bimodal formulations for the PDF were also able to produce hyper-exponential profiles, but with much lower variances in the deposition coefficient. The shape of the deposition profile was found to be very sensitive to the correlation of deposition and release coefficients, and to the correlation of pore water velocity and deposition coefficient. Application of the developed stochastic model to a particular set of colloid transport and deposition data indicated that chemical heterogeneity of the colloid population could not fully explain the observed behavior. Alternative interpretations were therefore proposed based on variability of the pore size and the water velocity distributions.