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Train sanders are ubiquitous in remediating low wheel–rail adhesion. Sanders operate by taking sand stored in a hopper, pneumatically conveying it through a nozzle, then spraying it into the wheel–rail interface. In this research, the wheel–rail–sander system was simulated experimentally in a laboratory. The system was optically accessible, and Particle Tracking Velocimetry was used to observe the trajectory of sand particles approaching the nip. The percentage of sand conveyed through the nozzle that makes it to the wheel–rail nip – the deposition efficiency – was measured gravimetrically. The maximum efficiency was found to be 91% for 1.15 mm mean diameter silica sand with a proprietary coating, and the minimum efficiency was 59% for uncoated aluminum oxide with a 0.91 mm mean diameter, both at a simulated train speed of 18 km/h. Irregular particles were found to be less efficient when compared to spherical particles with a similar size and composition. Increasing the size of silica sand from 0.18 mm to 1.05 mm in diameter slightly decreased the sanding efficiency from 67% to 60%. There was no statistically significant dependence of the efficiency on the particle coefficient of restitution. The single parameter most closely correlated with the deposition efficiency is the expansion of the particle-laden jet downstream of the nozzle. Larger, round particles typically had the smallest jet expansion and the highest efficiency, whereas rough particles with large diameters were found to have a large jet expansion and lowest efficiency. Finally, the effect of train speed on deposition efficiency was studied. The deposition efficiency was found to be very low at low train speeds and asymptotically approaches a fixed value at higher speeds. A simple physical model is proposed that explains the low efficiency at low speeds.

Experiments are conducted to explore the rolling of a cylinder over a pool of viscous fluid. The speed, width and loading of the cylinder are varied along with the initial depth and length of the viscous pool. Depending on the conditions, the cylinder will either ride on a lubrication film or remain in solid contact with the underlying substrate. For the former situation, a lubrication theory is presented that describes the pressure underneath the cylinder and the thickness of the film. The theory approximates the flow by the one-dimensional Reynolds equation with the addition of one term, with an adjustable parameter, to account for the flux of fluid to the cylinder sides. Once this parameter is calibrated against experiment, the theory predicts peak lubrication pressures, gap sizes and film thicknesses to within approximately ten per cent. For lubricated rolling, the film splits evenly between the cylinder and substrate downstream of the nip. 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.

Locomotive sanders are used to optimize the traction between the train wheels and the 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 study, pneumatic conveying of sand through the wheel–rail nip is numerically modeled through coupled computational fluid dynamics and discrete element method simulations. The gas phase, discrete phase, and coupled two-phase flows are separately validated against the literature, and the parameters affecting the deposition of sand into the nip are analyzed to determine their impact 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 (e.g. particle bouncing) are found to have a negligible effect on the deposition. In the absence of crosswinds, it is recommended to employ particles with a smaller Stokes number to enhance the sander efficiency. A larger airflow rate through the nozzle is also recommended. Crosswinds strongly and adversely affect sander efficiency. The effects of crosswinds can be mitigated by reducing the nip–nozzle distance and using coarser particles.

Flaring in oil and gas production is the controlled burning of unwanted exhaust gases to enhance safety. To improve flare combustion, gas flares are equipped with air nozzles that introduce extra oxygen and improve mixing in the combustion zone. These nozzles are operated in the subsonic, sonic, or supersonic regimes. In this paper, we are concerned with turbulence modeling of the jet flow exiting from a particular convergent–divergent nozzle used in flare systems. That nozzle has convergent and divergent sections that are connected via a throat section with a finite length and constant diameter. The Realizable k – ε and SST k – ω models are used to study the compressible flow within the nozzle. The velocity profiles, turbulent kinetic energy, Mach number profiles, and entrainment rate coefficients predicted by both turbulence models are compared for nozzle pressure ratios in the range 1.18 ≤ NPR ≤ 1.78. It is shown that both turbulence models predict nearly identical flow evolution along the nozzle. When the flow becomes supersonic, the shock surface, and consequently nozzle outlet velocity profiles, predicted by the SST k – ω model deviates slightly from the other model. The differences, however, become negligible a couple of diameters downstream of the nozzle outlet.

The manufacturing of low-density tissue paper involves a key process called creping, which consists of pressing and bonding a wet web onto a drying cylinder rotating at a high speed, and scraping it off subsequently. Creping is understood as a periodic debonding and buckling process which creates a series of micro-folds in the paper. Despite the fact that fibers in the web undergo significant plastic deformation during creping, previous models treat the web as a single thin elastic layer. In this paper we apply a particle dynamics model to investigate the effects of plasticity on creping. A bilinear elastoplastic material model with associated kinematic hardening rule is used to describe the constitutive behavior of the web and a discrete cohesive zone model is implemented for the interfacial delamination. Inclusion of the plasticity of the web leads to significant decrease in creping force and wavelength. A virtual tensile test is performed to predict the stretch and stiffness of the simulated tissue paper. It is found that the stretch increases and the stiffness decreases as the ratio between the creping amplitude and the wavelength increases, thus leading to a higher softness. The simulated tensile stress-strain curve shows significant nonlinearity and qualitatively agrees with experiments. Finally, we explore the “explosive bulk” regime by modeling the web as three individual layers connected by inter-layer bonds. A phase diagram for the creping regimes is constructed. Our simulations indicate that the “explosive bulk” is more likely to occur when the interfacial fracture energy is high and the cohesion of the web is weak.

A custom experimental apparatus is designed to perform through air drying under well-controlled drying conditions such as air temperature and mass-flowrate. Using a novel optical measurement technique, the spatial distribution of moisture content in paper during through air drying is quantified as a function of time. The technique is capable of measuring the moisture content distribution with high spatiotemporal resolution while air flows through a paper mat sitting on a permeable dryer fabric. Four commercially available fabrics with different structural design and properties are used in the investigations. The effect of the fabrics’ structural properties, which are characterized using optical coherence tomography (OCT), is studied under various drying conditions. 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. However, at low rates of drying (i.e., low air temperature and flowrate), no correlation between d...

Existing measurement techniques have prevented extensive investigations of the effect of dryer fabric structure on contact drying of paper. Using a novel optical measurement method, the moisture content (MC) of paper can be accurately quantified at high spatial and temporal resolution while it is sandwiched between the heater surface and the dryer fabric. To study the paper drying process, 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 fabrics manufactured by weaving synthetic filaments are used in the investigations. The 3D structure of the fabrics is characterized using optical coherence tomography (OCT). The fabrics are used in the experiments to investigate the effects of the filament structure and paper/fabric contact on the drying process. It is shown the fabric structure affects the drying rate and the drying time. Fabrics that have a relatively large drying rat...

Centrifugal air classifiers are used to separate particles as small as 3 microns from a mixed-size dust. In this paper, the flow in a high-speed classifier is simulated. The 3-d air-phase Reynolds-averaged Navier–Stokes equations are solved in the classifier with two different turbulence closure models. The Discrete Phase Model, which neglects inter-particle interactions, is utilized to track particles in the airflow. The model also permits one to calculate particulate concentration contours in the classifier. We find that particles of diameter near the classifier cut-point are dramatically concentrated (by factors in excess of 100) in locations near the outer blade radius. We speculate that this high concentration makes particle–particle interactions much more important than expected based on the feed concentration, which could in turn reduce the acceptance of the smallest particles.

Enthalpy exchangers using water vapor perm-selective membranes are used in building ventilation systems due to their small footprint, simplicity, reduced contaminant crossover, and relatively high efficiency. Moisture permeation properties of the membrane media that vary with operating air humidity and temperature lead to significant changes in the performance of an enthalpy exchanger and thus the whole ventilation system, impacting building energy efficiency. Evaluation of the actual energy savings potential of such energy recovery devices in building ventilation systems requires models that account for this variable membrane performance. A theoretical model is developed for current generation asymmetric composite membranes used in enthalpy exchangers. This model predicts the membrane permeability as a function of local values of air humidity and temperature, based on a limited number of kinetic water vapor sorption tests of the membrane material. The membrane model is coupled with a finite-difference model of the conjugate heat and mass transfer in full cross-flow enthalpy exchanger cores. The model predictions are validated against experimental data of a commercial-scale enthalpy exchanger. The model is used to predict the influence of outdoor air parameters (temperature, humidity) on an enthalpy exchanger and the predictions are compared against a baseline case that assumes constant membrane permeability. Such assumption can result in deviations in effectiveness predictions by up to 15%. Depending on the mode of operation, outdoor air relative humidity can increase or decrease the effectiveness of enthalpy exchangers by up to 12%. In contrast, outdoor air temperature appears to have only a minimal influence on effectiveness parameters.

Membrane-based Energy Recovery Ventilators (ERV) have become an important part of modern ventilation systems for commercial and residential buildings due to their high sensible and latent effectiveness. Using ERVs in winter conditions, however, can result in condensation and frost formation. Whereas frost formation requires extremely low temperatures, condensation can occur even in mild winter weather conditions. In this study, a widely used ERV is experimentally tested under various indoor and outdoor operating conditions. Short time tests are used to determine the onset of condensation while long time tests are used to investigate the effect of channel blockage due to condensation on pressure drop and effectiveness of the ERV. The presence of condensation is inferred from visual observation of water in the exchanger, investigation of the sensible and latent effectiveness, and measurements of pressure drop over the exchanger. It is shown that condensation increases the sensible effectiveness of the supply side and decreases the sensible effectiveness of the exhaust side. Additionally, the latent effectiveness of both air streams increases when condensation occurs, although the increase in exhaust side latent effectiveness is more significant. Increasing the relative humidity and temperature of the indoor air increases the possibility of condensation and its rate, while increasing flowrate only increases the rate of condensation and does not affect its onset. Finally, the accumulation of water in the channels significantly increases the pressure drop in the exhaust side while it does not significantly impact the effectiveness.

The impact of air-side particulate fouling on the performance of membrane-based, fixed-plate energy recovery ventilators (ERVs) is investigated for both fine and coarse (0.3–10 μm) as well as ultrafine (∼0.1 μm) aerosols. Two residential size cross-flow ERV exchanger cores were fouled with ISO A3 medium test dust. It was found that coarse dust loading, equivalent to that of a few years of exposure in a heavily polluted environment, has minimal impact on the performance of ERV exchanger cores. In both cases, the sensible and latent effectiveness were actually slightly enhanced due to boundary layer thinning and additional turbulence potentially caused by the dust layer. Heavy dust loadings, in the absence of appropriate filtration upstream, may result in a fan energy penalty (∼50%) due to the added pressure drop across the exchanger cores. Samples of three different membrane transport media, extracted from commercial HVAC ERV exchanger cores, were loaded with graphite and NaCl aerosol nanoparticles. Accelerated loading experiments were conducted in a laboratory apparatus to simulate several years of fouling in the field. Initial and post-loading water vapor permeance through the membrane samples were experimentally determined for each loading to quantify the effects of fouling. The impact of relative humidity on the performance of loaded membranes was also studied by exposing membranes loaded with particles in dry air to an elevated RH of 75%, leading to surface condensation. The experiments show that the deposition of particles in dry air can only affect the membrane when the fouling is severe enough to form a cake layer on the membrane surface comparable to the thickness of the membrane. In the case of membranes loaded with hygroscopic salt particles, surface condensation at high RH values can lead to vapor permeance reductions of up to 15% well before the cake layer formation phase of fouling, whilst no permeance reduction was observed for membranes loaded with non-hygroscopic graphite particles. This indicates a net porosity reduction in the microporous substrate layer of exposed salt-loaded samples. A pore-narrowing process of the substrate layer, due to the mobilization of salt particles in aqueous form, is a potential explanation for these observations.

The impingement of high speed jets on a moving surface was studied. The jet fluids were dilute suspensions of neutrally buoyant particles in water–glycerin solutions. At these low particle concentrations, the suspensions have Newtonian fluid viscosity. A variety of jet and surface velocities, solution properties, nozzle diameters, mean particle sizes, and volume fractions were studied. For each case the splash-deposition threshold was quantified. It was observed that for jets with very small particles, addition of solids to the jet enhances deposition and postpones splash relative to a particle-free water–glycerin solution with the same viscosity. In contrast, jets with larger particles in suspension were more prone to splash than single phase jets of the same viscosity. It is speculated that the change in character of the splash response for the jets with larger particles in suspension occurs when the particle diameter is comparable to the lamella thickness. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4673–4684, 2017

A viscoelastic solid sheet fed from a certain height towards a rigid horizontal plane folds on itself provided that there is no slip. This phenomenon commonly occurs in the manufacturing process of textile and paper products. In this paper we apply a particle dynamics model to investigate this phenomenon. At a low feeding velocity and low viscosity, the inertial effect and the viscous dissipation within the sheet are negligible, and our model successfully reproduces the existing quasistatic results in the gravitational regime. As the feeding velocity and the viscosity of the sheet increase, the folding process changes significantly. The length of the folds decrease and the "rolling back" motion of the sheet vanishes. In the inertial regime, a scaling law between the fold length and the feeding velocity is derived by balancing the kinetic energy and the elastic bending energy involved in folding, which is verified by the simulation. It is found that above a critical feeding velocity, the folding morphology transforms from line contact into point contact with the sheet exhibiting a lemniscate-like pattern. Finally, a phase diagram for the folding morphology is constructed. The results presented in this work may offer some insights into the high-speed manufacturing of paper and fabric sheets.

Experiments are performed for a rigid, high-aspect-ratio, rectangular channel with a portion of one wall replaced by a flexible membrane (a “2D” Starling resistor). The fluid is air, which is driven by a pressure drop up to 300 Pa, producing Reynolds numbers up to 22,000. The experiments include pressure measurements at 6 locations along the channel, 1 velocity measurement, and high speed video of the membrane which is analyzed to extract the membrane motion. The primary variables considered are membrane tension, inlet pressure, and area of the side-wall gap. Steady and unsteady behaviors are observed for the 3 membrane tensions considered. The unsteady behaviors are categorized as “traveling”, “mode 2”, or “complex” oscillations, which may be recognized by the spectral characteristics of their pressure signal. Hysteresis is clearly observed depending on how the inlet pressure is adjusted. The side-wall gap, which permits air leakage around the membrane, is an important factor, and is characterized as a function of membrane tension and inlet pressure.

A method for extracting solid boundary motion from dynamic CT images of a human oropharyngeal swallow is presented. The data-set has high spatial resolution () but low temporal resolution (10 Hz). The low temporal resolution results in motion artefacts (i.e. blurring, ghosting) due to the fast moving solid structures. Automated segmentation and registration methods were not successful, so a tool for manual 3D deformable registration was created as a plug-in for the open-source modelling software, Blender. The tool gives users a high level of control to sculpt a mesh to match 3D volumetric image data. The resulting series of meshes, each corresponding to an instance in time, can be used in a fluid simulation using a technique such as smoothed-particle hydrodynamics.

In this article, measurements of full-scale freight train underbody aerodynamics relevant to top-of-rail spraying are presented. The velocity near the wheel was measured using hot wire anemometers mounted on the train. The pressure was measured using transducers mounted adjacent to the track. Velocity scaled linearly with locomotive speed and pressure scaled linearly with dynamic pressure, implying negligible Reynolds number effects. The mean velocity near the wheels was less than half of the locomotive speed when the vehicle moved at or greater than the ambient wind speed. The velocity upwind of the wheel was 30% greater than downwind of the wheel. These mean velocities are consistent with computational fluid dynamics simulations of the flow field in the vicinity of the wheel. Turbulence intensity levels were measured to be 0.08–0.16. The pressure at the track depends on the configuration of the leading car; the maximum pressure drop was 65% greater when the hopper car preceded the locomotive com...

Composite membranes combining a structural microporous substrate with a dense selective layer are used in various water vapor transport applications. The impact of exposure to aerosols on the water vapor permeance is investigated to develop an understanding of the potential for air pollution to degrade the membrane performance. Samples of commercial membranes were loaded with hygroscopic NaCl and non-hygroscopic graphite nanoparticles. Permeance measurements showed that the deposition of both particle types under dry loading conditions (RH 75%) and the associated surface condensation, the membrane permeance reduced by up to 16%. This permeance reduction is shown to be caused by pore narrowing, which results in increased resistance of the microporous substrate. SEM analysis of the fouled membrane surfaces confirmed a reduction in the average pore diameter of degraded samples, proportional to the fouling degree. The reversibility of the fouled membrane permeance, achieved through membrane cleaning, implies that re-crystallization of salt ions, entrained onto the edges of the substrate pores in an aqueous form, is a potential explanation for the permeance changes observed.

The manufacturing of low-density paper such as tissue and towel typically involves a key operation called creping. In this process, the wet web is continuously pressed onto the hot surface of a rotating cylinder sprayed with adhesive chemicals, dried in place, and then scraped off by a doctor blade. The scraping process produces periodic microfolds in the web, which enhance the bulk, softness, and absorbency of the final tissue products. Various parameters affect the creping process and finding the optimal combination is currently limited to costly full-scale experiments. In this paper, we apply a one-dimensional (1D) particle dynamics model to systematically study creping. The web is modeled as a series of discrete particles connected by viscoelastic elements. A mixed-mode discrete cohesive zone model (CZM) is embedded to describe the failure of the adhesive layer. Self-contact of the web is incorporated in the model using a penalty method. Our simulation results delineate three typical stages during the formation of a microfold: interfacial delamination, web buckling, and post-buckling deformation. The effects of key control parameters on creping are then studied. The creping angle and the web thickness are found to have the highest impact on creping. An analytical solution for the maximum creping force applied by the blade is derived and is found to be consistent with the simulation. The proposed model is shown to be able to capture the mechanism of crepe formation in the creping process and may provide useful insights into the manufacturing of tissue paper.

The key characteristics of an air filter—flow resistance and filtration efficiency—are strongly affected by captured particles. The impact of exposing loaded heating, ventilating, and air conditioning air filters to a relative humidity (RH) other than that experienced during loading is investigated to develop an understanding of the role of RH throughout filter operation. Flat sheets of commercial filter media were loaded with hygroscopic, non-hygroscopic, or a mixture of particles in a laboratory apparatus. When filters loaded with hygroscopic particles in dry air were exposed to an elevated RH of 40%, the flow resistance reduced by up to 47%, depending on the filter being tested. Investigation of filter efficiency before and after changes in RH in the same samples shows reductions of up to 11 percentage points in the 130-nm size range. Further increasing RH causes additional drops in flow resistance and efficiency whereas reverting back to a lower humidity does not change the filter characteristics. The...

Exposure to airborne particles is a serious health concern worldwide and indoor air quality is a critical factor influencing exposure. This work investigates the impact of modified ventilation and filtration system designs to inform building designers, operators, and policy makers of relative effectiveness and costs. Indoor aerosol dynamics, filter cost, and epidemiological models were combined to compare size-resolved indoor particle concentrations, operation costs, and monetized health benefits to occupants within an office building. System airflow and filter efficiency were modified to compare the relative economic implications. Comparisons were made for a number of cities to examine the impact of variation in local air quality, electricity prices, and economic conditions. The operation cost of filtration systems was found to vary by a factor of 3 between cities. The monetized health benefits of filter installations outweigh the operation costs by up to a factor of 10. In the majority of scenarios investigated the net benefits of improved filtration were greatest for the highest efficiency filters. Adding or increasing recirculated and return air in the system provides a net financial benefit due to (indirect) societal health benefits outweighing (direct) operational costs for small increases in airflow but has diminishing returns for large increases. Though system changes are economically beneficial from a societal viewpoint, the costs and benefits are borne by disparate parties and policy changes may be required to ensure optimum design and operation.

Computer simulation of liquid bolus flow is used to test the assumption that a slip boundary condition approximates a healthy swallow due to the presence of saliva lubricating the bolus. Six dynamic, 320-row area detector CT (ADCT) sequences of normal subjects swallowing thin, nectar, and honey-thick liquids are used in this work. The aerodigestive tract is segmented from the images in order to create a dynamic 3D geometry, which is subsequently used to drive a Smoothed Particle Hydrodynamics (SPH) fluid simulation of the bolus. The results show that the no-slip simulation, approximating no-lubrication, provides a closer match to the ADCT bolus images than the slip simulation, particularly in the oral phase. This finding suggests that the role of saliva in swallowing liquid boluses is not to lubricate the aerodigestive tract, and that there is another reason for its importance in normal swallowing of liquids.

In the flow through porous media such as screens the structure of the screen affects the upstream flow field. This is relevant for filtration and deposition processes where the local filtrate deposition rate depends on the upstream flow field, while deposition also alters this flow field over time. Here, we investigate the flow through forming fabrics that retain pulp fibers during the papermaking process, while the liquid phase passes through. The associated drainage velocity through the fabric has a significant impact on the quality of the finished product. Microparticle image velocimetry (micro-PIV) was used to measure the drainage velocity distribution upstream of two different fabrics. To make measurements at the scale of the forming fabric filaments, an experimental micro-PIV procedure was developed to permit velocity measurements several millimeters into the fluid stream with a depth of correlation of $$28\,\upmu \hbox {m}$$ and an in-plane resolution of $$40 \,\upmu \hbox {m} \times 40 \,\upmu \hbox {m}$$ . For the single phase flow of water, the experiments show the existence of a highly variable drainage velocity field upstream of both fabrics. The normalized standard deviation (NSD) of the velocity fields decays exponentially with distance upstream of the fabric. The decay constant is on the order of one filament diameter at moderate Reynolds numbers $$(Re=52-140)$$ . At a constant freestream velocity, the deposition of a small number of wood fibers onto a fabric results in a higher NSD than that of the bare fabric. This is believed to be due to partial obstruction of some holes in the fabric, which leads to higher velocities through unobstructed holes. Once about 5 g per square meter of fiber has been deposited onto the fabric, the velocity field above the fabric with adhering fiber mat becomes uncorrelated with the velocity field through the bare fabric.

A three-dimensional (3D) computer simulation of swallowing is presented. The soft structures (i.e. pharyngeal wall, soft palate and tongue) are simulated using finite element models. Bony structures (e.g. mandible, hard palate and hyoid) are simulated as rigid bodies. A fluid bolus is simulated using smoothed particle hydrodynamics (SPH). A Newtonian viscosity model is validated by comparing a 3D SPH simulation of Hagen–Poiseuille flow with theoretical results. A previously unreported source of error is reported and discussed. In the swallowing simulation, fluid boundaries are determined by the rigid and deformable surfaces, and the coupling is in one direction only. Movement of solid boundaries was determined in previous work for a deformable solid bolus. Two swallowing simulations are presented with different bolus viscosities in order to demonstrate that SPH can be used to simulate and track the liquid phase of a bolus during swallow. We find that SPH robustly handles moving boundary conditions as well...

This paper describes a feasibility study investigating an inexpensive novel technique to measure urine flow rate using image processing techniques. The majority of existing clinical uroflowmeters determine urine 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 in 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 was investigated and found to have comparable accuracy to currently used clinical devices.

A series of experiments were conducted on handsheets to investigate small-scale variations in filler concentration on the surface of paper. 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. Local filler concentration was found to be strongly correlated with the relative flow velocity during formation. In samples formed by gravity and vacuum drainage, kaolin displayed a significantly greater variation in local concentration than precipitated calcium carbonate, though the difference was reduced under vacuum drainage conditions. The distribution on the top side of the paper was comparable between the filler types, independent of drainage velocity. 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, the addition of retention aids produced a significant improvement in the uniformity of the filler material. These filler distribution trends are believed to be related to variable filler retention as a function of filler type, drainage velocity, and chemical retention aids. Additionally, samples made with an industry forming fabric showed the same distribution trends and an improvement in the uniformity of the filler material.

The three-dimensional velocity field in the single phase approach flow to a multiple layer woven forming fabric was measured using PIV. The measurements were conducted on a scaled-up 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 ( d) of 1 5 mm, and the flow loop test section was 3 1 0 mm squared, permitting the measurement of detailed velocity distributions over multiple strands of the fabric. The flow speed in the loop test section was varied to achieve screen Reynolds numbers between 12 and 6 5 . PIV measurements showed that when the distance t o the paper side of the fabric changes from 0.25d to 1 . 5d, the normalized ZD, CMD and MD velocity deviation decreases from 1 9 .7% to 4 .2%, 1 5 . 3 % to 1 .9% and 1 4 . 5 % t o 2 . 3 %, respectively; the ratio between maximum and minimum ZD velocity decreases from 3 .3 to 1 .2 . These findings indicate that the flow non-uniformity caused by the fabric weave is confined to a short distance above the fabric. CFD simulations of the same flow were consistent with the PIV measurements.

During sheet forming, the structure of the forming fabric leaves wire marks on the pulp mat. Paper nonuniformity caused by the wire mark can lead to ink nonuniformity in printing. We investigated wire mark numerically through simulations of the interaction of individual fibers with a forming fabric. In the simulations, the flow field through the forming fabric was taken to be that of single-phase water flow without disturbance of fibers. A particle level simulation method was applied to simulate the motion of fibers in the flow through a single layer sine-wave fabric. A hundred fibers of random initial distribution were placed into the flow above the fabric. Those fibers were advected onto the fabric, forming a fiber mat. The surface roughness of the resulting fiber mat was then calculated. The results show that during the initial formation, topographic wire mark is caused partially by fiber bending and partially by the geometry of the fabric. For the specific fibers and sinusoidal forming fabric considered, more than 50% of topographic wire mark is the result of geometry, with the remainder attributed to fiber bending. Fabrics with different geometries (e.g., different filament pitches or a nonsinusoidal geometry) will have different relative influences from geometry and fiber bending.

A model has been developed to predict the energy efficiency and annual operation cost for filters installed in an HVAC air handling system using filter data from standard ASHRAE 52.2-2007 filter tests. Thirty filters from six manufacturers were investigated to determine the most energy efficient and cost effective filtration solutions for an airport installation in Vancouver, Canada. A comparison of the output of the proposed model with the ‘kep’ and Wattage methods was performed to highlight the possible differences in filter choice that would be made using alternative approaches. The outcomes have been shown to differ due to data not incorporated in the older models such as filtration efficiency and particulate concentration. The sensitivity of filter cost to model parameters was also studied. It was found that the concentration of particles in the air stream and the cost of electricity had the largest effect on annual cost of operation. Increasing the concentration of particles in the air stream increases the cost of operating the filter and causes the installation of a prefilter upstream of the primary filter to be more economically attractive. Increasing electricity cost also increases the operation cost but has the reverse effect on attractiveness of prefilter installations.

In the railroad industry a friction-modifying non-Newtonian liquid, showing elastic behavior, may be applied to the rail in the form of a liquid jet. The interaction of this elastic liquid jet and the moving surface—specifically whether it splashes or adheres without splash—is important in this industrial application. Twelve different elastic liquids with widely varying relaxation times were tested to isolate the effect of elasticity from other fluid properties. Using high-speed imaging, the interaction between the impinging jet and the moving surface could be captured and analyzed. Although similar to Newtonian jets, for which the Reynolds number plays a major role, the Deborah number was also salient to the splash of elastic liquids. At the elevated Weber numbers of the testing, the Weber number had a much smaller impact on splash than did the Reynolds or Deborah numbers. The ratio of the surface velocity to the jet velocity has only a small effect on the splash. © 2012 American Institute of Chemical Engineers AIChE J, 2012

In the railroad industry a friction modifying agent may be applied to the rail or 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 were tested to isolate the effect of viscosity from other fluid properties. Tests were also done on five surfaces of 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 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 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.

In a companion article [1] , we described computer simulations of the flow around 2 two-dimensional, tandem circular cylinders in a flow for 1 ⩽ Re ⩽ 20 . In this article we adopt a similar approach to characterize the flow around side-by-side cylinders with surface-to-surface separation/diameter in the range 0.1 s / D At low Reynolds numbers, 1 ⩽ Re ⩽ 5 , for all gap spacings, the flow contains no regions of flow separation. At higher Re, four distinct flow behaviors were observed. For very small gap spacings, e.g. 0.1 s / D s / D s / D ≈ 1 separation regions form only on the inside portions of the cylinders. For larger gap spacings s / D > 1 the flow reverts to something similar to that around an isolated cylinder in the flow, i.e. two attached vortices on the rear side of each cylinder. In general, the drag coefficient increases as the gap spacing increases. At higher Reynolds number it is known that the cylinder lift coefficients decrease monotonically with gap spacing. In contrast, at these lower Reynolds number the lift coefficient curves rise to a maximum for 0.3 s / D s / D .

The Bernoulli equation is arguably the most commonly used equation in fluid mechanics. For the incompressible, inviscid flow along a streamline, the Bernoulli equation states that the total head of the fluid (the sum of the pressure head, velocity head, and elevation head) is constant. Neglecting elevation changes, the Bernoulli equation therefore limits the maximum pressure coefficient in a flow to 1, which occurs at stagnation points in the flow. Normally, the action of viscosity causes the total head in a fluid to decrease in the streamwise direction, which means the stagnation-point pressure coefficient is less than 1. However, at low to moderate Reynolds numbers, where viscous forces are most significant, stagnation-point pressures exceed 1. This counterintuitive result is explained by reference to the shear work term in the steady-flow energy equation.

In the forming section of a papermachine, a water suspension of pulp fibers is drained through a forming fabric. One canonical test case that incorporates some key features of this process is that which studies the interaction of a single fiber with a cylinder. This article concerns numerical simulations of this interaction. Even the seemingly simple flow of a fiber near a cylinder involves consideration of a number of variables including: the fiber length, diameter, and stiffness; the fluid velocity, density and viscosity; the fiber initial orientation and position; and the frictional properties of the fiber/cylinder interface. There is a range of dimensionless groups for which the fiber can hang up on the cylinder, whereas for other values of the dimensionless groups the fiber slides off the cylinder. These results provide fundamental insight into the linting process in papermaking, and suggest potential conditions which may encourage linting in a papermachine. The results may also be useful in understanding other physical phenomena, such as vegetation entanglement in storm drains, hair clogging in sink stoppers and inhalation of fibers in the respiratory tract.

Health care facility ventilation design greatly affects disease transmission by aerosols. The desire to control infection in hospitals and at the same time to reduce their carbon footprint motivates the use of unconventional solutions for building design and associated control measures. This paper considers indoor sources and types of infectious aerosols, and pathogen viability and infectivity behaviors in response to environmental conditions. Aerosol dispersion, heat and mass transfer, deposition in the respiratory tract, and infection mechanisms are discussed, with an emphasis on experimental and modeling approaches. Key building design parameters are described that include types of ventilation systems (mixing, displacement, natural and hybrid), air exchange rate, temperature and relative humidity, air flow distribution structure, occupancy, engineered disinfection of air (filtration and UV radiation), and architectural programming (source and activity management) for health care facilities. The paper describes major findings and suggests future research needs in methods for ventilation design of health care facilities to prevent airborne infection risk.

This study compares the citations characteristics of researchers in engineering disciplines with other major scientific disciplines, and investigates variations in citing patterns within subdisciplines in the field of engineering. Utilizing citations statistics including Hirsch’s (Proc Natl Acad Sci USA 102(46):16569–16572, 2005) h-index value, we find that significant differences in citing characteristics exist between engineering disciplines and other scientific fields. Our findings also reveal statistical differences in citing characteristics between subdisciplines found within the same engineering discipline.

The flow around two-dimensional cylinders at moderate Reynolds numbers has been much studied, both for cylinders perpendicular to the flow and for cylinders yawed to the flow. In contrast, yawed finite aspect ratio cylinders have received little attention. In this article we describe computer simulations of cylinders with aspect ratios 2 ⩽ L/D ⩽ 20 yawed at angles 0° ⩽ α ⩽ 90° relative to a free stream. The simulations were carried out for Reynolds numbers in the range 1 ⩽ Re ⩽ 40. The simulations show that the Independence Principle [Zdravkovich MM. Flow around circular cylinders, vol. 2: applications. New York: Oxford University Press; 2003 [1] ] is not accurate for α ⩽ 45°. We have also found that for all aspect ratios, the ratio of the lift to drag force reaches a maximum for 40°

An experimental investigation of a model forming fabric was conducted. The forming fabric was simplified and represented by a bank of two rows of cylinders. Particle image velocimetry (PIV), pressure drop, and hydrogen bubble visualization were used to evaluate the upstream and gross flow patterns for various diameter ratios and cylinder spacings at a Reynolds number of 65. It was found that for a row separation of 0.75 times the upstream cylinder diameter, the upstream flow matched that for a single row of cylinders. Further, it was found that when the pressure drop through the bank of cylinders was equal to the sum of the individual rows’ pressure drops, the upstream flow converged to that of a single row.