Sheldon Green


Research Classification

Fluid Mechanics
Biological and Biochemical Mechanisms

Research Interests

building ventilation

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Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Liquid jet impingement on a moving wall (2023)

This research studies the impingement of a free surface Newtonian liquid jet on a dry solid moving wall using theoretical, numerical and experimental methods. The study focus mainly on the parameter range of jet Reynolds numbers 100
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Lubricated rolling over a pool (2022)

The focus of this research is the rolling of a cylinder over a pool of viscous fluid. This process has many industrial applications such as roll coating, lubrication of bearings, and rail transport (the primary motivator of this research). The problem is studied for Newtonian and shear-thinning fluids. The speed, width and loading of the cylinder are varied as are the initial depth and length of the viscous pool. Depending on the operating conditions, the cylinder will either ride on a lubrication film or remain in solid contact with the underlying substrate (although in the wheel/rail interface, there could also be a mixed or boundary lubrication regime). For the former situation, a lubrication theory is provided to predict the pressure underneath the cylinder and the film thickness deposited on the substrate. To account for the flux of fluid escaping towards the cylinder edges (3D effects), an approximation of the lubrication theory is used that includes an adjustable parameter. Once this single parameter is calibrated against experiment, the theory predicts peak lubrication pressures, gap sizes and film thicknesses to within about ten percent. The printer's instability arises during the splitting process, patterning the residual fluid films on the substrate and cylinder. If the pool length is less than the cylinder circumference, the fluid adhering to the cylinder is rotated back into contact with the substrate, and when there is sufficient adhered fluid a lubrication film forms that can again be modelled by the theory. Conversely, if there is insufficient adhered fluid, no contiguous lubrication film is formed; instead the pattern from the printer's instability "prints" from the cylinder to the substrate. A field experiment was conducted to understand the initial pickup of the liquid by the train wheel and subsequent carrydown along the track. Due to the high wheel-rail contact pressure, the liquid failed to form a lubrication layer (not the preferred outcome) and was squeezed out laterally, adhering to the edges of the wheel contact band. This edge liquid, however, provides tribological benefits on the curved track due to movement of the contact band as the train rounds a curve.

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Modeling the creping process in tissue making (2019)

Creping is a key operation in the manufacturing of low-density tissue paper. In this process, a wetweb is pressed and adhered onto a drying cylinder (Yankee) rotating at a high speed, dried onYankee, and then scraped off by a doctor blade. This controlled and violent interaction betweenthe web moving at a high speed with the stationary blade creates a series of invisible micro-folds,and explodes the thickness of the web through inter-fiber debonding. Various parameters governcreping and finding their optimal combination is currently limited to experience or costly trials. Aone-dimensional particle dynamics model is developed to study nonlinear deformations in thecreping process, and to understand the underlying mechanisms. Specifically, the web is modeledas a single layer of discrete particles connected by visco-elasto-plastic elements. A mixed-modediscrete cohesive zone model is embedded to represent the adhesive layer. Self-contact of the webis incorporated by a penalty method. First, a systematic parametric study is reported to assess therelative impact of various process parameters on the crepe structure and hence the tissue quality.Then, the model is extended to a multi-layered web to investigate the “sheet explosion”. A phasediagram for the creping regimes is constructed. Next, the effects of inhomogeneities on the crepingprocess are investigated. Three common inhomogeneities are considered separately: the formingfabric pattern; the non-uniform basis weight; and the non-uniform adhesion. Finally, a series ofexperiments have been conducted on an existing lab-scale creping apparatus to validate theproposed model, and qualitative agreement is observed. The model can serve as a tool toinvestigate the process-structure-property correlation in tissue making, and the findings in thisthesis offer practical guidance to the industry in the choice of forming and creping processparameters.

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Impact of humidity, temperature, and particulate fouling on membrane-based energy exchangers (2018)

Membrane-based energy recovery ventilators (ERVs) improve building energy efficiency by transporting heat and moisture between incoming and outgoing air streams. Although long-term studies are not available due to the recent implementation of this technology, there are preliminary indications that moisture transport might degrade with the extended operation, possibly as the result of exposure to air pollution or other environmental stresses. The scope of this dissertation is to quantify the influence of environmental factors on the permeation properties of current-generation composite membranes and the overall performance of ERV exchanger cores.First, the impact of particulate fouling was investigated via accelerated membrane- and core-level fouling experiments. The core-level experiments showed minimal impact on the effectiveness of ERV cores from coarse dust loadings. However, membrane-level examination with aerosol nanoparticles indicated that moisture transport through membranes was especially impaired when particles were hygroscopic or contained liquids. These results suggest that the optimal protection by filters and the orientation of the membrane would depend on the nature of the indoor and outdoor aerosols.Second, the effects of relative humidity and temperature on the transport of water vapor and CO₂ (as a surrogate for indoor air pollutants) was evaluated through a systematic study of some standard polymers suitable for ERV use. It was shown that the permeability and selectivity of membranes could vary up to an order of magnitude depending on the membrane material, the temperature and relative humidity on both feed and permeate sides of the membrane, as well as orientation in asymmetric composite membranes. A theoretical model for predicting permeability of composite membranes, based on a limited number of kinetic water vapor sorption tests of the selective coating polymer, was successfully developed and validated for a commercial membrane. This model was then coupled with a heat and mass transfer model of cross-flow ERV exchanger cores to interpret the membrane-level variations regarding ERV exchanger core performance. A study of the effects of outdoor air parameters showed that the effectiveness of ERV exchangers could increase or decrease significantly with outdoor air relative humidity, while outdoor air temperature had only a minimal influence on effectiveness parameters.

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Paper drying - experimental studies on the influence of dryer fabric (2018)

This research is an experimental investigation on paper drying that primarily focuses on the effects of the dryer fabric on the drying process of paper. A novel method for moisture content measurement is presented. The working principle of this method is the strong correlation between the optical transparency of paper and its moisture content due to the refractive index matching role of water in wet paper. Spectrographic and microscopic measurement techniques were employed to characterize the relation of moisture content and relative transparency of paper. As optical access to the paper is restricted by the dryer fabric, the optical transparency of paper should be measured only with one-sided optical access. To achieve this goal, a novel technique of transmittance measurement is developed that is able to determine the transparency of thin film objects (i.e. paper) with only one-sided optical access. Employing a fluorescence imaging method, this optical configuration eliminates the spurious effect of reflection of the incident light by filtering the excitation wavelength before reaching the optical detector.To study the paper drying process in a multi-cylinder dryer, an experimental setup is designed to simulate realistic conditions of a typical paper dryer while providing optical access for the measurement system. Ten commercially available fabric types manufactured by weaving synthetic filaments are used in the investigations. It is shown that the fabric structure affects the drying progression and the drying time significantly. The contact area and three-dimensional arrangement of the filaments have the greatest impact on the drying process. To study through air drying (TAD), another experimental apparatus is designed to perform drying under controlled conditions of air temperature and mass-flowrate. Four commercially available TAD fabrics with different structural designs and characteristics are used in the investigations. It is shown that the geometry of the contact spots of the fabrics has a significant impact on the drying time at high drying intensities. Comparing the spatial maps of moisture content with the paper grammage distribution reveals that there is a correlation between the local grammage and the local moisture in a paper sheet during the drying process.

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A novel SPH method for investigating the role of saliva in swallowing using 4D CT images (2017)

The thesis presents novel computer methods towards simulation of oropha-ryngeal swallowing. The anatomy and motion of the human upper airwaywas extracted from dynamic Computed Tomography (CT) data using a noveltool and workflow. A state-of-the-art SPH method is extended to accommo-date non-Newtonian materials in the extracted geometries. A preliminarynumerical experiment of six human oropharyngeal swallows using SmoothedParticle Hydrodynamics (SPH) demonstrates that the methods are robustand useful for simulation of oropharyngeal swallowing.The presence of saliva is well known to be important for mastication,swallowing, and overall oral health. However, clinical studies of patientswith hyposalivation are unable to isolate the effect of saliva from other con-founding factors. The simulation presented in this thesis examines fluidboluses under lubricated and non-lubricated boundary conditions. Upon comparison with medical image data, the experiments suggest that salivadoes not provide a significant lubricative effect on the bolus transit times,but it may serve to reduce residue and therefore improve overall swallowingefficacy. Our findings, while preliminary, corroborate with existing clinicalresearch that finds that groups with hyposalivation do not have significantlydifferent transit times with control groups, but that residue may be increased in the hyposalivation group.Previous studies using computer simulation of fluid flow in the orophar-ynx typically make use of simplified geometries. Our work uses dynamic320-row Area Detector Computed Tomography (ADCT) images as the ba-sis for the simulations, and therefore does not require simplifying geometricassumptions. Since the data are dynamic, motion trajectories are all sup-plied by the ADCT data, and extrapolation from 2D sources such as bi-planevideofluoroscopy is not required. Processing the image data required the de-velopment of a novel workflow based on a new tool, which we call BlendSeg.We utilize and extend Unified Semi-Analytic Wall (USAW) SPH methodsso that orophrayngeal swallowing simulations may be performed. Theseextensions include the simulation of non-Newtonian boluses, and moving3D boundaries. Partial validation of the extended USAW SPH method isperformed using canonical flows.

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Air filtration: predicting and improving indoor air quality and energy performance (2015)

Air filtration is used to reduce particle concentrations in the indoor environment to provide improved occupant health due to reduced exposure. Increased focus on occupant health in emerging design standards is leading to the installation of higher efficiency filtration systems. These systems generally have higher resistance to flow and therefore impose a greater energy penalty. Previous air filter models have used simplified assumptions with regards to the dynamics of filter operation, which have limited the potential to determine energy efficiency or optimization approaches to system design and operation. This dissertation focuses on developing an improved air filter model to investigate the potential for system modifications to reduce energy consumption and improve indoor air quality (IAQ) within commercial buildings.A new air filter performance model was developed using generalizable results from ASHRAE Standard 52.2-2012 and validated against laboratory and real-world experiments. The results showed better agreement with laboratory tests than with real operation. The filter model was combined with existing indoor particle dynamics and epidemiological models to determine the impacts of changes to system operation through monetization of operation costs and health benefits. Laboratory experiments were performed to evaluate the role that particle properties and relative humidity play in determining the filter performance changes with the aim of better understanding the reasons for discrepancies in operation between laboratory and field filter tests.Operation can now be optimized by accounting for dynamic characteristics of filter performance. Benefits of improved filtration efficiency were found to outweigh added costs. Adopting specific indoor particle concentration limits is recommended to replace existing specifications relying on filter efficiency. System designs can then be optimized to account for local particle concentration and energy costs. A number of system design changes have been highlighted that allow for simultaneous reduction in operation cost and indoor particle concentrations. Relative humidity has been identified as a critical parameter in filter performance and standardized tests should be modified to account for variability in relative humidity and particle characteristics typical of real operation to allow for improvements to future model predictions.

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Modeling the Fluid-Structure Interaction of the Upper Airway: Towards Simulation of Obstructive Sleep Apnea (2014)

Obstructive Sleep Apnea (OSA) is a syndrome in which the human Upper Airway (UA) collapses during sleep leading to frequent sleep disruption and inadequate air supply to the lungs. OSA involves Fluid-Structure Interaction (FSI) between a complex airflow regime and intricate mechanics of soft and hard tissue, causing large deformation of the complicated UA geometry. Numerical simulations provide a means for understanding this complex system, therefore, we develop a validated FSI simulation, composed of a 1D fluid model coupled with a 3D FEM solid solver (Artisynth), that is applied to a parameterized airway model providing a fast and versatile system for researching FSI in the UA.The 1D fluid model implements the limited pressure recovery model of Cancelli and Pedley [28] using a dynamic pressure recovery term, area function corrections allowing complete closure and reopening of fluid geometries, and discretization schemes providing robust behavior in highly-uneven geometries. The fluid model is validated against 3D fluid simulations in static geometries and simple dynamic geometries, and proves reliable for predicting bulk flow pressure. Validation of simulation methods in Artisynth is demonstrated by simulating the buckling, complete collapse, and reopening of elastic tubes under static pressure which compare well with experimental results.The FSI simulation is validated against experiments performed for a collapsible channel (a "2D" Starling resistor) designed to have geometry and characteristics similar to the UA. The observed FSI behaviors are described and compared for both experiment and simulation, providing a quantitative validation of the FSI simulation. The simulations and experiments agree quite well, exhibiting the same major FSI behaviors, similar progression from one behavior to another, and similar dynamic range.A parameterized UA model is designed for fast and consistent creation of geometries. Uniform pressure and dynamic flow FSI simulations are performed with this model for numerous parameters associated with OSA. Uniform pressure simulations compare well to clinical data. Dynamic flow results demonstrate airflow limitation and snoring oscillations. The simulations are fast, simulating 1 s of FSI in 30 minutes. This model is a powerful tool for understanding the complex mechanics of OSA.

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Dispersion of expiratory droplets in a model single patient hospital recovery room with stratified ventilation (2013)

Concerns about the environment, energy costs, and airborne infection risk have revived interest in ventilation systems for health care facilities. Low energy ventilation systems (e.g. stratified air ventilation) have received attention as a means of providing a better air quality at a lower energy cost. The sensitivity of such ventilation systems to boundary conditions in removing airborne contaminants produced by expiratory injections is of concern and studied experimentally and numerically in this work. A three step methodology is adopted. First, an air-assist internally mixing atomizer is developed to generate a poly-disperse distribution of droplets for ventilation testing. A series of near-field experiments reveal droplet size, velocity, and diffusivity in radial and axial directions for steady and transient atomization. Second, the atomizer is used to inject droplets into a mock-up of a patient recovery room with an underfloor air distribution ventilation system. A series of far-field size-resolved concentration measurements are conducted at locations representative of an occupant (receptor). Third, Computational Fluid Dynamics (CFD) simulations are used to predict airborne droplet exposure among various cases in the far-field experiments. Both tracer gas and discrete phase approaches are implemented. Based on the findings we recommend guidelines for ventilation design and room usage in real single patient hospital recovery rooms with stratified ventilation systems. It is desired to have expiratory injections at low momentum, preferably directed towards the walls or upwards. It is also advisable that occupant suspects spend most of their time away from the injection source, possibly at the corner of the room or behind the source. The variations in occupant thermal plume is not likely to affect exposure to airborne droplets in statistically significant ways. It is advisable to used air change rates greater than four since expiratory injections are likely to break down the vertical contaminant stratification. It is likely that dispersion rates be higher for sub micrometer droplets but lower for larger droplets. This has implications for ventilation design strategy as a function of pathogen or pathogen carrying droplet size.

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Investigation of fibre interaction with a forming fabric (2013)

The forming stage of the papermaking process plays an important role in shaping the quality of final paper sheets. This thesis focuses on studies of fibre motion in the forming section. Wire mark was investigated both numerically and experimentally. Initial sheet forming was simulated with hundreds of fibres of random initial distribution placed into the flow above the fabric and advected onto the fabric. The surface roughness of the resulting fibre mat was calculated. The results show that during initial formation, topographic wire mark is caused in part by fibre bending and in part by the geometry of the fabric. For the specific fibres and sinusoidal forming fabric examined, more than 50% of topographic wire mark was caused by fabric geometry, with the remainder caused by fibre bending. In the experiments, the surface roughness of paper sheets made from different fibre properties was studied using an X-ray tomography device. Light-weight fibre mats were made in a handsheet former machine. A surface map of the wire side of the paper was produced via image analysis. The results reveal that increasing fibre coarseness decreases the surface smoothness of paper. As fibre length increases, surface roughness decreases slightly. Both fine and coarse forming fabrics were used in the sheet forming section. The surfaces of fibre mats made from finer forming fabrics were found to be smoother.The fibre orientation distribution of final paper sheets is closely dependent on the physical properties of the sheets. Fibre orientation in the forming section was studied numerically. In the simulations, one end of each fibre was held by the wire/fibre mat, with the other end carried in the flow. In the uniform flow, analyzed solution from the analysis was obtained. The fibre angle after deposition was only found to be a function of flow direction and initial fibre position. In the shear flow, a dimensionless group of γL/u_z was defined. As the value of γL/u_z increases, fibre mats increase in anisotropy. Fibre properties such as flexural rigidity and aspect ratio were found to have a insignificant effect on fibre orientation.

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Three-dimensional flow through forming fabrics and the motion of flexible fibres in flow (2010)

This dissertation addresses the 3D flow through forming fabrics. In the first part of this thesis, the single phase 3D flow through certain specific fabrics was modeled. In practice, the Reynolds number of the fabric flow, based on paper-side filament diameter, is around 100. Consequently, it is not too surprising that the permeability of the fabrics was found to vary approximately as Re ⁻⁰˙⁴, which is intermediate between the expected low Re (Re⁻¹) and high Re (Re⁰) limits. The resistance of a multilayer fabric was found to be nearly equal to the sum of the resistance of each layer considered in isolation. The effect of filament-scale and weave-scale flow non-uniformity on the fiber distribution in the finished paper was considered. For one specific fabric, there was 3 times more chance for short fibers to accumulate initially over openings than blockages of the fabric. Jet-to-wire speed ratio was found to have an insignificant effect on permeability results, but a marked effect on the Machine Direction shear stress in the vicinity of the paper-side filaments. In an attempt to model sheet formation, numerical simulations of the motion of a single fiber in the flow field of a cylinder was carried out as a canonical test case of the fiber/filament interaction system. Seven dimensionless groups govern the problem. A range of dimensionless groups were found for which the fiber hung up on the cylinder, whereas for other values of the dimensionless groups the fiber slid over the cylinder. In general, longer and more flexible fibers had a greater likelihood to be caught by the filament. Yawed finite aspect ratio cylinders at moderate Reynolds numbers are approximate representations of fibers in the flow field of forming fabrics. No analytical solution or any experimental data are reported in the literature to predict the drag and lift force on such particles in such flows. Computational Fluid Dynamics (CFD) simulations were conducted to find the drag and lift coefficients of inclined finite circular cylinders at Reynolds numbers in the range 1-40. The simulations showed that the Independence Principle was highly inaccurate for low inclination angles.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Optical measurement of paper moisture content with application in paper pressing (2023)

The measurement of moisture content (MC) distribution in the paper is important as it affects the overall quality of the paper. It is common practice to measure the moisture content distribution at the end of the forming section of the paper machine, in order to control the papermachine headbox slice gap distribution. However, there exists no equivalent measurement technique to measure the moisture distribution downstream of the press section in real-time.This thesis presents a novel non-contact method for measuring moisture content. The method is based on the high light absorptivity of liquid water in the 1400-1500 nm wavelength range. By using a short-wave infrared (SWIR) camera and an infrared LED to illuminate the paper, the relationship between moisture content and relative intensity RI was investigated for four different samples (Whatman paper, NBSK, NBHK, tissue paper), where RI corresponds to the measured light intensity due to wet paper normalized by the intensity due to dry paper. The results show that for all samples, RI decreases as moisture content increases, and it is possible to measure the spatial moisture content distribution using this relationship. The value of this measurement technique was demonstrated by using it to measure the moisture distribution in the paper during a simulated pressing operation.

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Particulate laden spray deposition on moving surfaces (2023)

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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Concentration and mass deposition measurements in two-phase jet flow with applications to railroad friction management systems (2021)

This work presents initial results of a new method to apply friction modifier materials for railroad applications along with a novel particle concentration measurement method for two-phase flows. Until now, railroad friction management systems used liquid friction modifiers or solid sticks to apply the material to the top of the rail or to a moving train’s wheel to reduce the friction. We investigate in lab experiments a new method of applying solid lubricant powders such as molybdenum disulfide (MoS2) and graphite directly on top of the rail using electrostatic powder coating. To design and assess the performance of an applicator for spray or powder coating, it is useful to know the particle concentration in the particle jet. The concentration distribution data will aid in modifying the design of the applicator to achieve the desired deposition pattern. Current methods of concentration measurements such as laser Doppler anemometry (LDA)/phase Doppler anemometry (PDA) and planar nephelometry are excellent to provide accurate local measurements of concentration but are expensive and complicated to set up and operate. Our proposed measurement method is based on light extinction and is much easier to set up and use. This method is capable of providing particle concentration statistics for axisymmetric distributions. We show that the extinction efficiency measured with this method for a given particle agrees with known values (of somewhat less than two) for a non-ideal imaging setup. Furthermore, we demonstrate that the concentration distribution of a jet at the exit of a pipe nozzle as well as downstream is similar to that observed by previous researchers. We also present data on the deposition efficiency of electrostatic powder coating for railroad friction management systems under different test conditions. The results show that applying pure MoS2 or graphite achieves low deposition efficiencies and these materials should be surface treated with a non-conductive coating before being applied. We also discuss how the newly developed particle concentration measurement method can be used to design and monitor the performance of the new railroad friction modifier applicator.

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Experimental investigations of the effect of surface roughness on high-acceleration film splitting between two substrates (2021)

Thin liquid film separation is an important part of many industrial processes and is relevant to “rewet” that can occur in the press section of a papermachine. The separation ratio, the mass of the remaining liquid on one (“the moving”) substrate after separation to the total mass of the initial liquid film between two substrates, is of particular interest in this thesis because reducing rewet reduces the energy consumption in the dryer section of a paper machine significantly. The focus of this study is the experimental measurement of high-acceleration separation of Newtonian liquid films trapped between two substrates. The behavior of the liquid bridges between smooth separating substrates has been a subject of past studies at low separation rates. A distinction of this study is the investigation of high-acceleration separation of the thin liquid bridging the gap between rough as well as smooth substrates. An experimental apparatus has been designed and manufactured that can produce average separation accelerations of up to 325 m/s2, initial bridge heights starting from 10 µm, and average surface roughness values of up to 86 µm.When the distance between substrates increases, a viscous fingering region is observed along the perimeter of the wetted area where air fingers grow radially inward, while in the center region, cavitation bubbles can emerge and grow until the two substrates are sufficiently separated such that the liquid bridges between them break. The separation ratio is meaningfully affected by the surface roughness, viscosity, and acceleration, creating variations of up to 20% in the separation ratio. It is hypothesized that the separation ratio is affected by the relative amounts of the flow field that are subject to viscous fingering and liquid cavitation. Two distinct separation processes, residual layer formation and fibrillation, corresponding to the two flow regimes have been suggested to explain the difference in the measured separation ratios of different cases. A laser-induced fluorescence (LIF) measurement system has been developed to measure the thickness distribution of the liquid bridges during the separation process, and the results of the LIF measurements are consistent with the suggested hypothesis.

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CFD-DEM simulation of locomotive sanders (2018)

This study presents the development and results of a numerical model of a locomotive sander system. Locomotive sanders are used to optimize traction between the train wheels and railhead by spraying sand into the interface. It has been previously shown that a large fraction of sand sprayed by the sanders does not make it through the wheel-rail nip, leading to sand wastage and thereby increasing the cost and refilling effort.In this project, pneumatic conveying of sand through the wheel-rail nip is numerically modelled through coupled Computational Fluid Dynamics and Discrete Element Method simulations. The gas phase, discrete phase and coupled two-phase flows are separately validated against literature, and the parameters effecting the deposition of sand through the nip- relating to both aerodynamics of the particle laden jet and interaction with geometry are independently analyzed pertaining to their effects on sander efficiency. The aerodynamics associated with the particle laden jet play a critical role in optimizing the amount of sand going through the wheel-rail interface, with the particle velocities being directly correlated with the sander efficiency. Particle-geometry interactions are found to have a negligible effect on the deposition. In the absence of crosswinds, it is recommended to either employ smaller particles, or particles with a higher surface area to volume ratio to enhance the sander efficiency. Furthermore, a larger airflow rate through the nozzle is suggested. It is also found that the presence of crosswinds strongly negatively affects sander efficiency, which can be mitigated, to some extent, by reducing the nip-nozzle distance as much as safety regulations will allow, and using coarser grain particles.

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Cold flow simulation of gas flare auxiliary air (2018)

Flaring in oil and gas production is the controlled burning of unwanted exhaust gases to enhance safety. During flaring, there are two important concerns. The first is to prevent the flame from accumulating on the flare tip, which occurs during periods of high crosswinds. Such flame accumulation, which is known as flame capping, can cause premature failures and structural damage of the flare tip if sustained for long period of time. Excluding the combustion physics, a gas flare can be simplified as a jet in a crossflow (JICF). To avoid the considerable complexity associated with simulating a combusting flow, cold flow modeling can be used to investigate the critical flow conditions that would result in flame capping. The second concern is to avoid excessive smoke during combustion, which is important to meet the environmental regulations. Saudi Aramco has therefore developed a flare system that ameliorates both concerns. The system uses supersonic air nozzles that are distributed evenly around the flare exit. Besides preventing flame capping, the high-speed jets of these nozzles introduce extra oxygen and improve mixing in the combustion zone, which reduces flare smoking. The focus of this thesis is the cold (non-combusting) flow in one of these flare systems. Computational Fluid Dynamics (CFD) was used to study the flow within a gas flare. The capabilities of different turbulence models to simulate the flare flow field, particularly Large Eddy Simulation (LES) and Shear Stress Transport (SST) k-ω model, were tested by reproducing previous JIFC experimental data. The flow within the auxiliary air nozzles was studied by computing several parameters such as the mass entrainment, axial velocity, turbulent kinetic energy and Mach number in different flow regimes. Additionally, the differences between the results from different Reynolds-Averaged Navier–Stokes (RANS) models (including the SST k-ω and the Realizable k-ε) are investigated. For fixed mass flow rate, the detailed geometry of these nozzles is shown to have little impact on the mass entrainment rate, and therefore is expected to have little impact on the flare combustion characteristics. Finally, this work presents a preliminary study of a simplified full flare system.

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Particle Impingement onto a Moving Substrate (2018)

Particle sprays are salient in processes such as erosion in turbomachinery and traction enhancement in the railroad industry. In this study, particles with a Stokes number at the nozzle much larger than unity were sprayed at an acute angle between a horizontal, flat, moving substrate, representing the rail, and a wheel. A device was created that contained a sprayer aimed between the wheel and moving substrate, with the rim of the wheel hovering above the flat substrate. The particles form a spray into the nip that can ricochet between both the wheel and substrate. The standard deviation of the angle that the particle trajectories make as they exit the nozzle can be used to describe the geometry of the spray. Similarly, the normal and tangential coefficients of restitution describe ricochet effects by quantifying the amount of energy dissipated through the particle-substrate interaction. Initial work in this study focuses on the spray and bounce properties to determine their correlation to the particle’s efficiency, which was defined as the percentage of particles leaving the nozzle that make it into the nip. Next, the effects of shape and size were determined using particles with similar compositions. Then, the effect of coating the particles and substrate speed was determined. For silica sand with diameters from 0.2-0.6 mm, the typical efficiency was 68% with a flat wheel and rail profile. The larger and rounder particles were found to deposit the best, with coated sand having an efficiency of 91%. It was discovered that the improvement in the efficiencies may be from reducing the spread of the particle spray from the nozzle from 8° to 3°, which increased the likelihood that the particles make it between the wheel and belt. Lastly, decreasing the substrate speed below 18 km/h produced lower efficiencies due to the particle-particle interactions as they approach the wheel-substrate interface unless the mass flowrate of the particles was reduced.

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Understanding the wheel/rail transfer mechanism in liquid friction modifier carry-down (2017)

In the rail road industry liquid friction modifiers (LFM’s) are used on thetop of rail (TOR) between the wheel/rail interface to reduce curve noise,lateral forces, rail wear and fuel consumption. The friction modifier may beapplied to the rail via a track side applicator and is carried down by thetrain into curved sections of the track where the greatest benefit is seen.A custom laboratory scale machine was designed and built for the purpose of conducting experiments to study the behaviour of LFM carry-downover a large number of wheel/rail interactions. The machine was also designed so that the film transfer at the wheel/rail interaction location couldbe studied.The use of a fluorescent agent to enhance the ability to visualize LFMcarry-down showed promising results, enabling small amounts of carry-downthat couldn’t otherwise be seen under ambient light conditions to now beseen under fluorescence.Qualitative experiments using the machine were performed showing thatan increase in the wheel speed results in an increase in the amount of frictionmodifier transferred from the rail to the wheel at the initial pickup location,thus increasing the carry-down. Increasing the applied load had the oppositeeffect and reduced the amount of friction modifier initially transferred fromthe rail to the wheel, and thus reducing the carry-down. The profile of thewheel was observed to effect the initial transfer amount and the ensuingcarry-down due to high/low pressure zones along the wheel/rail interface.

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An assessment of lattice Boltzmann method for swallowing simulations (2016)

Lattice Boltzmann is a fixed grid particle based method originated from molecular dynamics which uses a kinetic-based approach to simulate fluid flows. The fixed grid nature and simplicity of lattice Boltzmann algorithm makes it an appealing approach for preliminary swallowing simulations. However, the issues of compressibility effect and boundary/initial condition implementation can be the source of instability and inaccuracy especially at high Reynolds simulations. The current work is an assessment of the lattice Boltzmann method with respect to high Reynolds number flow simulations, compressibility effect of the method, and the issue of boundary and initial condition implementation. Here we investigate the stability range of the lattice Boltzmann single relaxation and multi relaxation time models as well as the issue of consistent boundary/initial condition implementation. The superior stability of multi relaxation time (MRT) model is shown on the lid-driven cavity flow benchmark as a function of Reynolds number. The computational time required for the SRT model to simulate the li-driven cavity flow at Re=3200 is about 14 times higher than the MRT model and it’s shown that computational time is related to the third power of lattice resolution. It is suggested that single relaxation time model is inefficient for simulations with moderately high Reynolds number Re>1000 and the use of multi relaxation time model becomes necessary. Compressibility effect is the next topic of study where the incompressible lattice Boltzmann method is introduced. The compressibility error of the method surpasses the spatial discretization error and becomes the dominant source of error as the flow Reynolds number increases. It is shown on a 2D Womersley flow benchmark that the physical time step required for LBM is about 300 times larger than the physical time step of the finite volume implicit solver while generating results with the same order of accuracy at Re=2000. Due to the compressibility error inherent to the method, lattice Boltzmann is not recommended for preliminary swallowing simulations with high Reynolds number, since implicit time advancement methods can generate results with the same order of accuracy in noticeably less computational time.

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Numerical simulation of particle separation in centrifugal air classifiers (2016)

The demand for fine mineral powder in various industries has stimulated creative methods for separating the fine portion of particles from a mixture. Among the many different types of classifiers invented, centrifugal rotor air classifiers are characterized by their capability in producing ultra-fine products with a cut-size as low as 3um.Classification occurs due to the size-dependence of aerodynamic and inertial forces acting on particles: coarse particles have a higher ratio of centrifugal force to aerodynamic drag than do fine particles, and therefore are preferentially ejected to the classifier perimeter. Therefore, the high speed rotor located inside the classifier is key to classification. Computational fluid dynamics (CFD) is utilized in this study to investigate the motion of calcium carbonate particles in a rotor classifier. The single phase flow in two- and three-dimensional models of the rotor is computed. Two turbulence models, namely K-Omega and RSM, are applied to close the Reynolds-averaged Navier-Stokes equations. Once the single phase flow has been computed the motion of solid particles is simulated using the Discrete Phase Model. This model ignores particle-particle interactions and the influence of the particles on the air flow. The motion of the particles is coupled to a statistical model of the turbulent velocity fluctuations. By tracking hundreds of particles, the efficiency for a variety of hypothetical classifiers is estimated. Though the CFD models, in comparison with experiments, cannot accurately predict the absolute cut-size values, they have proved effective in predicting cut-size shifts as a result of rotor geometry modification or alternative operating conditions. Based on these simulations two new rotors were built and the change in cut-size was predicted within 30% accuracy. Based on the paths of a large number of particles tracked in various operating conditions, regions in the rotor with very high particulate concentrations are identified. We speculate that this elevated concentration makes particle-particle interactions much more important than would be expected based on the feed concentration, which could in turn reduce the acceptance of the smallest particles.

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Particle-Laden Liquid Jet Impingement on a Moving Surface (2016)

In the railroad industry, coating of the rail with liquid changes the forces at the wheel-rail interface. Wet leaves on rail tracks can reduce the wheel-rail traction to dangerously low levels. To enhance wheel traction, railroads spray sand on the tracks. The sand may be applied in the form of a particle-laden jet. The impingement of high-speed liquid jets on a moving surface was studied. The jet fluids were dilute suspensions of neutrally buoyant particles in water-glycerin solutions. At the low concentration studied, the suspension has a Newtonian fluid viscosity. A variety of jet and surface velocities, liquid properties, mean particle sizes, and volume fractions were studied. It was observed that for jets with very small particles, the addition of solids to the jet enhances deposition. In contrast, jets with larger particles in suspensions were more prone to splash than single phase jets of the same viscosity. It is speculated that the non-monotonic dependence of the splash threshold on the particle size occurs when the particle diameter is comparable to the lamella thickness. Additionally, volume-of-fluid (VOF) CFD simulations were carried out to provide a full description of the flow field of a particle-free Newtonian jet spreading over a moving surface. The jet Reynolds number and Weber number of the simulations were in the range of 50-1000 and 100-8000, respectively. The simulations were generally in good agreement with experiments and they could successfully predict the lamella dimensions and velocity profiles.

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Full Scale Train Underbody Aerodynamic Evaluation for Top of Rail Friction Modifier Application (2015)

Liquid jet impingement is employed in the rail industry to apply friction modifier to the rail surface. Use of the friction modifier is known to reduce wear and improve fuel efficiency. L.B. Foster ® deploys friction modifier using a nozzle located downwind of the wheels on freight trains. Understanding the aerodynamic environment of the nozzle is important for researching how to maximize the deposition of the liquid friction modifier from the nozzle to the tracks. The air pressure and velocity at the location of the nozzle was evaluated experimentally at full scale in field trials. The pressure at a fixed ground location was measured by transducers as the train passed. The air velocity in the reference frame of the moving vehicle was measured using a fiber-film anemometer at the location of the liquid-friction-modifier spray nozzle, 0.4 wheel diameters downwind of the wheel center.The measured air speeds scales linearly with the train speed, and the measured pressure scales linearly with the dynamic pressure, implying that Reynolds number effects are negligible. The pressure distribution showed an initial pressure increase just downwind of the leading edge of the vehicle followed by a spike in suction. The pressure distribution was found to depend on the orientation of the vehicle. With a rail car leading the vehicle, the spike in suction produced was about 50% larger than the suction spike produced when a locomotive, lower to the ground, was leading the vehicle. The mean air speed was measured to be approximately 29% of the train speed. The mean air speed the same distance upwind of the wheel was measured to be approximately 38% of the train speed. Turbulence intensity levels were measured to be about 0.15. Cross wind effects became much less significant when the train speed was equal to or greater than the cross wind speed.The train undercarriage airflow was modeled numerically using Autodesk Simulation CFD™ software. The CFD simulations were in approximate agreement (typically, within 2%) with experimental measurements and confirmed that the presence of the support bracket for the anemometer had limited impact on the measured wind speed.

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Newtonian and Viscoelastic Liquid Jet Impingement on a Moving Surface (2015)

Motivated by the need to improve transfer efficiencies of liquid coatings from jet impingement in railroad friction control applications, an experimental investigation into Newtonian and viscoelastic liquid jet impingement on moving surfaces is presented.Seven PEO-glycerine-water solutions and three commercial liquid friction modifiers were tested with a variety of jet speeds, jet diameters, surface speeds and surface roughnesses. The effects of these test conditions on jet impingement splash behaviours as well as jet and lamella geometries were studied. High-speed imaging was employed to visualize the interaction between the impinging jet and the moving surface.Experiments on the effect of modest surface roughness revealed that, while jet and surface speed were both important factors, splash was more likely to occur on surfaces with lower roughness levels. By analyzing experimental results for Newtonian liquids, a relation between lamella geometry and test conditions were found, which can be used to predict lamella dimensions. Three types of non-Newtonian behaviours were observed at high surface speed and low jet speed: jet necking, jet bending and jet stretching.

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Transient Jet Impaction on a High Speed Moving Surface (2015)

In the railroad industry liquid friction modifiers are applied on the rail track in the form of a liquid jet in order to reduce the friction and fuel consumption. In this application, the transfer efficiency of the liquid on the rail track is very important. To maximize the transfer efficiency, Newtonian and non-Newtonian transient liquid jet impingement on a dry moving surface was studied. Five different water glycerin solutions with widely varying shear viscosities were used as Newtonian test liquids to isolate the effect of shear viscosity from other fluid properties. Furthermore, the effect of surface roughness on the impaction was investigated using four different roughness heights. The effects of jet velocity and surface speed were also studied. High speed imaging was performed to visualize the interaction between the jet and the moving surface. For surface roughness heights between 0.02 μm and 0.64 μm, it was found that as the roughness increases, the jet becomes more prone to splash. It was also shown that increased jet and surface speeds trigger the splash. The transient jet characteristics were also investigated for Newtonian liquids at different nozzle back pressures. It was found that at higher Reynolds and Weber numbers the transient jet breaks up downstream of the nozzle; However, it was shown that the Weber number has the dominant role in jet break-up compared to the Reynolds number. A numerical study was also undertaken to determine the drag force exerted on the plunger of the solenoid valve in the nozzle. The simulation results were in reasonable (16% on average) agreement with experiment.

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Micro-PIV measurement of flow through forming fabrics (2014)

This thesis describes an experimental investigation of the flow field upstream of forming fabrics that are typically used in the paper making process. Micro Particle Image Velocimetry was used to measure the velocity distribution upstream of a forming fabric. The velocity upstream of two different types of forming fabrics, namely Monoflex D60TM and IntegraTM, was studied. As expected, the experiments show the existence of a highly variable drainage velocity field upstream of both fabrics. The drainage velocity over the holes can be several times greater than the drainage velocity above the fabric filaments. Since fines and filler tend to follow fluid streamlines, one would therefore expect substantially higher fines and filler concentrations in the holes between the filaments as compared over fabric knuckles. The decay in drainage velocity variations can be represented by the equation Aexp(-Bz/D)+C, where A and B are constant and C is the uncertainty in the experimental setup. D and z represent the fabric’s filament diameter and distance above the fabric surface.It is expected that the response of pulp fibers to the velocity variations caused by the fabric’s weave structure is strongly correlated to their length. The fibers with a length greater than 1.5 mm experience a weighted-average velocity field along their length that is approximately uniform. The deposition of short fibers with length
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Design of an optical uroflowmeter and assessing bladder pressure through video analysis of the male urine stream (2013)

Voiding dysfunction, such as benign prostatic hyperplasia and impaired detrusor contractility, affects more than half of men over the age of 50. Uroflowmetry provides quantitative information of flow dysfunction by measuring the flow rate and total volume of urine expelled by the body. The majority of existing clinical uroflowmeters determine flow rate using a scale to measure increasing mass of urine expelled with time; however, they are expensive and typically found only in specialists’ offices, making it difficult for patients to receive testing. An opportunity therefore exists to develop a much more affordable device which would allow flow rate testing to become a part of routine care and to be conducted in a wider variety of environments such as General Practitioners’ offices and home monitoring. The high demand for digital cameras, particularly due to their extensive use in mobile devices, has resulted in their accelerated advancement and cost reduction. Therefore, a device based on this technology is investigated. In addition to the development of this device, a study was conducted to investigate if information regarding bladder pressure may be obtained by analyzing digital images of the urine stream. Voiding dysfunction may result in abnormally high bladder pressure, caused by urinary obstruction, or low bladder pressure which may be caused by reduced detrusor contractility. The clinical implications and treatment for these two cases are very different; however, they present with similar low flow rate voiding patterns and cannot currently be distinguished non-invasively. It was postulated that increased inertia and turbulence may exist in high pressure flows, and may be identifiable in the digital images of the urine stream.

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Hydrodynamic interaction between cylinders at moderate Reynolds numbers (2013)

The hydrodynamic interaction between two cylinders perpendicular to the freestream, in a tandem arrangement was studied for moderate Reynolds numbers (1≤Re≤40). The influence of multiple geometric variables was considered: separation distances between the cylinders, ellipticity of the cylinders, the cylinder aspect ratio, and the angular inclination between the cylinders. In the first part of this study, a numerical investigation of the two-dimensional steady flow past cylinders was carried out. The characteristic length, D, in all simulations was taken to be twice the major axis of the cylinder cross-section, (i.e. equal to the diameter for cylinders of circular cross-section). The two-dimensional flow was studied for separations up to 50D. Four different ellipticities were studied. The drags experienced by front and rear cylinders were compared with that experienced by a single cylinder of the same cross-section. The second part of the study consisted of the steady three-dimensional flow analysis for parallel cylinders in tandem for separations ranging from 2D to 20D and cylinder lengths up to 20D. In the third part of this thesis, a steady flow analysis was done for two circular cylinders in tandem with lengths equal to 5D but with the cylinder axes in different orientations relative to the plane normal to the flow. This angular separation between the cylinders produces a hydrodynamic moment, which is dependent on the geometry and the flow Reynolds number.The fourth and final part of this work is the study of the unsteady three-dimensional flow that would result from the hydrodynamic moment discussed in relation to the third part of the thesis. The thesis closes with some remarks on the implications of these findings to papermaking and recommendations for future work.

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An Experimental Study of Liquid Jet Impingement on a Moving Surface: The Effects of Surrounding Air Pressure and Fluid Properties (2012)

The impingement of a high-speed liquid jet on a moving surface and the resulting deposition or splash is important in a variety of technical and industrial processes. Of particular interest is the coating of the top-of-rail surface, in the rail road industry, with a thin film of viscoelastic liquid friction modifier, by liquid jet impingement, to control friction and reduce wear at the wheel-rail interface, thereby reducing fuel consumption and maintenance costs. For effective operation it is required that the fluid deposited by the jet adhere to the surface after impingement. An experimental investigation into the effect of surrounding air pressure and fluid properties on liquid jet impingement on a moving surface was performed. The study was carried out with Newtonian liquids impacting smooth, dry surfaces. A variety of ambient air pressures, jet speeds, surface speeds, surface tensions, and liquid viscosities were studied. The interaction between the impinging jet and the moving surface was analysed through high-speed imaging. It was observed that, as is the case for Newtonian droplet impact, the surrounding air pressure plays a crucial role in the splashing behaviour of jet impingement. There exists a threshold pressure below which splash does not occur. It is proposed that for certain impingement conditions lamella detachment from the surface occurs due to aerodynamic forces acting on the leading edge of the lamella, which destabilizes the balance between surface tension and fluid pressure forces. It was observed that both the Reynolds number and Weber number were salient to the occurrence of lamella detachment, with lamella detachment having a non-linear dependence on the Reynolds number. Lamella detachment was prone to occur for intermediate Reynolds numbers as the Weber number was increased, bounded by regions of deposition at higher and lower Reynolds numbers.

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An experimental study of the surface distribution of filler material in paper (2012)

A series of experiments were conducted to observe the effect of different pulp suspension and formation characteristics on the variation in filler concentration on the surface of paper. Hand sheet samples were formed in a laboratory apparatus. The surface distribution of two types of filler material was investigated: Precipitated Calcium Carbonate (CaCO₃) and Kaolin Clay (Al₂Si₂O₅(OH)₄). The effect of retention aids, dewatering rate, and forming fabric geometry on filler distribution was tested.The analysis was focused on the variation in surface filler concentrations on the scale of individual strands of the forming fabric. The procedure involved locating areas of interest in the samples, particularly the area of paper formed over knuckles, threads, and openings in the fabric, at which point the sample was analysed with Energy Dispersive X-Ray Spectroscopy and image analysis techniques to determine relative filler concentrations.In samples formed by gravity and vacuum drainage, Kaolin displayed a significantly greater variation in local surface filler concentration than PCC, though the difference was reduced under vacuum drainage conditions. This effect is attributed to the electrostatic attraction between PCC and pulp fibres in contrast with the repulsion felt by Kaolin filler. The attraction resists the distributing forces of the flow at low drainage velocities but the bonds are broken by large shear forces. The distribution on the top side of the paper was comparable between the filler types, due to the more uniform flow field at a distance from the forming fabric. Vacuum drainage increased the spatial variation of both fillers by a similar amount. It was found that under vacuum drainage, retention aids did not improve filler uniformity on the wire side. However, on the top side of the paper, a moderate reduction in spatial variation was observed. Additionally, on the wire side of samples made with gravity drainage, it was found that the addition of retention aids produced a significant improvement in the uniformity of the filler material. Finally, it was found that a finer forming fabric improved the uniformity of filler distribution.

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An Experimental Study on Jet Impingement on a Very High Speed Moving Surface (2012)

Motivated by the need to improve transfer efficiencies of liquid coatings from jet impingement, an experimental investigation into jet impingement on very high speed moving surfaces is presented. Seven different Newtonian liquids with widely varying shear viscosities were made to impinge on a surface which could be made to move at speeds up to 350km/hr. Tests for the Newtonian liquids were done with several modified surfaces to study the effects of roughness and surface inconsistencies. Nozzle sizes and impingement angles were varied to interrogate their effects on the interaction of the impacting jet and moving surface while high speed photography was employed to capture these interactions. Spread radii and spread widths were measured for viscous fluids which deposited.While it was observed that stable jets of fluids with sufficiently high viscosities almost always deposited, tests with water indicate that the effects of the impingement angle as well as jet diameter significantly alter the locations of boundaries between deposition, spatter and lamella lift-off. Impingement angles that result in jet velocities with large components of velocity parallel to the surface velocity are prone to deposit. Jets of smaller diameters are also prone to deposit. It was observed that both the jet velocity and surface velocity are important determining factors in the likelihood of deposition.The deposition of viscous fluids demonstrated that it is possible to observe transitions from deposition to lift-off and vice versa through mechanisms that trigger random fluctuations in the lamella. The track distance covered before a transition from lift-off to deposition occurs is shown to be a Poisson Process.

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Newtonian and Elastic Liquid Jet Interaction with a Moving Surface (2011)

In the railroad industry a friction modifying agent may be applied to the rail or to the wheel in the form of a liquid jet. In this mode of application the interaction between the high speed liquid jet and a fast moving surface is important. Seven different Newtonian liquids with widely varying shear viscosities along with twelve different solutions of polyethylenoxide (PEO) and water with varying relaxation times were tested to isolate the effect of viscosity and elasticity from other fluid properties. Tests for the Newtonian liquids were done with five surfaces having different roughness heights to investigate the effects of surface roughness. High speed video imaging was employed to scrutinize the interaction between the impacting jet and the moving surface. For both Newtonian and Elastic liquids and all surfaces, decreasing the Reynolds number reduced the incidence of splash and consequently enhanced the transfer efficiency. At the elevated Weber numbers of the testing, the Weber number had a much smaller impact on splash than did the Reynolds number. The ratio of the surface velocity to the jet velocity has only a small effect on the splash, whereas increasing the roughness-height-to-jet-diameter ratio substantially decreased the splash threshold. Moreover, the Deborah number was also salient to the splash of elastic liquids.

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PIV measurements of flow through forming fabrics (2011)

Three-dimensional velocity fields in the single phase approach flow to a multiple layer woven forming fabric were measured using Particle Image Velocimetry (PIV). The measurements were conducted on a scale model of a forming fabric in a water/glycerin flow loop. Each strand on the paper side of the model forming fabric had a filament diameter around 15.4mm, and the loop test section was 310mm squared, permitting the measurement of detailed velocity distributions over multiple strands of the fabric. The flow speed in the loop test section were varied to achieve screen Reynolds numbers (Res), calculated based on paper side filament diameter (d), between 15 and 65. PIV measurements showed that the normalized ZD velocity deviation decreases from 19.7% at a plane 0.25d upstream from the forming fabric to 4.2% at a plane 1.5d upstream. The normalized CMD velocity deviation decreases from 15.3% at a plane 0.25d upstream from the forming fabric to 1.9% at a plane 1.5d upstream. The normalized MD velocity deviation decreases from 14.5% at a plane 0.25d upstream from the forming fabric to 2.3% at a plane 1.5d upstream. The highest ZD velocity is about 3.3 times higher than the lowest ZD velocity at a plane 0.25d above the fabric. This ratio decreases to 1.2 at a plane 1.5d above the fabric. These findings show that the flow non-uniformity caused by the fabric weave is restrained to a short distance above the fabric. However, even this non-uniformity is not particularly felt by fibers, whose length scale results in an averaging of the local velocity field. CFD simulations of the same flow were consistent with the PIV measurements.

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The role of suction boxes on forming section retention and filler migration (2010)

An apparatus was constructed to observe fibre mat formation under applied vacuum pressure comparable to that experienced in a suction box. The main focus of study was to determine the effects of system parameters on overall retention, filler distribution, and filler migration by analysing samples through weighing, ashing and EDX analysis. It was found that increasing suction pressure slightly decreased the overall retention, although the effect was greater at higher filler loadings. The forming fabric selection was statistically significant in determining the overall retention, and the significance of forming fabric selection grows with increasing filler loading. The most important factor in determining overall retention was the presence of retention aids. Measurement of the instantaneous permeability of the forming fabric and fibre mat during the forming process showed differences in the permeability curves between forming fabrics, particularly during the initial forming process. The permeability variations are correlated with differences in retention. Tests performed under gravity drainage, to provide a correlation between fabric properties and overall retention results, showed that air permeability had the highest correlation.Sheet splitting and ashing hand sheets formed using cationic PCC filler showed that applying a vacuum during the drainage process decreased the average filler content. The filler was preferentially removed from the wire side of the sheet. Similar tests performed with anionic filler showed that filler charge affects the distribution in a hand sheet. Anionic filler also showed little change in distribution when vacuum was applied during forming. Cationic and anionic filler have different retention mechanisms; attachment and filtration, respectively. Applied vacuum was found to affect the filler distribution of particles retained by attachment with the highest changes at the wire side. Applied vacuum was found to have only a small affect on particles retained by filtration. The reason for both is the compaction of the fibre mat, which occurs to the greatest extent at the wire side. The compaction reduces the size of openings in the mat which will further trap large particles retained by filtration but increase the drag on small particles, possibly exceeding the attractive forces responsible for attachment to the pulp fibres.

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