Measurement Of Terminal Velocity Research Articles

Terminal Velocity Determinations for Switchgrass Nodes and Internodes

HighlightsA vertical wind tunnel was fabricated to aerodynamically suspend switchgrass particles to measure terminal velocity.Overall terminal velocity estimates for node and internode were 8.04 and 5.68 m s-1, respectively.Terminal velocity prediction equation for spherical particles (Mohsenin, 1970) produced values almost identical to experimental values unlike an equation for infinite-length cylindrical particles.Hollow switchgrass particle behavior was complex with particle bouncing, rolling, tumbling, and other dynamic behaviors during aerodynamic equilibrium. Abstract. Terminal velocity is a fundamental aerodynamic property often used to separate plant anatomical components. A vertical wind tunnel was fabricated to investigate whether terminal velocities of switchgrass stem internodes and nodes were distinctly different. Wind tunnel features included a clear observation section for suspended particles and fine adjustment of airflow. Each sample terminal velocity was measured with 45 anemometer readings from nine locations and five repeated measures. The experiment evaluated two sample moisture contents (52% and 15% wet basis, hereafter referred to as w.b.), three particle lengths (0.64, 1.27, and 2.54 cm), node versus internode, and 12 replications. The 6,480 anemometer readings provided significant differences between factors and interactions. The greatest magnitude in mean terminal velocity difference was 4.55 m s-1 (i.e. 9.62 to 5.07) that resulted in a velocity ratio of 190% [(9.62/5.07) x 100]. The least magnitude of mean terminal velocity difference, while significant, was 0.36 m s-1 (i.e. 6.59 to 6.23). This offered a limited difference and may indicate that separations may need to be confined within groups of moisture category and/or particle length. Terminal velocity measurements were most similar to those calculated using the Mohsenin (1970) spherical particle equation yielding a mean (6.86 vs. 6.91 m s-1), standard deviation (1.41 vs. 1.42 m s-1), minimum (4.65 vs. 4.69 m s-1), and maximum (9.95 vs. 10.03 m s-1) for measurement and spherical particle equation, respectively. Keywords: Anatomical component, Biomass property, Physical experiment, Separation, Sorting, Switchgrass, Vertical wind tunnel.

Experiments on the separation of sphere clusters in hypersonic flow

In this work, we develop a new methodology for hypersonic multi-body free-flight experimentation and conduct several tests to explore the aerodynamic separation of equal-sized spherical fragments, which approximates the atmospheric disruption of meteoroids. A novel suspension design enabled by 3D printing is introduced, allowing for rapid, reliable release of clustered spheres into hypersonic flow, and high-speed stereoscopic imagery is employed to visualize the aerodynamically separating spheres. A new data-reduction technique based on synthetic image fitting, along with previous edge-detection and photogrammetric reconstruction methods, is used to track sphere motions; these motions also anchor a novel self-calibration procedure for the camera apparatus. To probe the separation characteristics of disrupted meteoroids with increasing fragment population, clusters of 4, 11, and 36 equal-sized spheres are subjected to Mach 6 flow. Strong dependence of trajectories on subcluster interactions is discerned for both 4 and 11 spheres, with two-body lifting pairs identified as critical arrangements capable of producing outlying fragments, whereas the initial stage of mutual repulsion is observed to exert greater influence as the cluster population is increased. Finally, terminal lateral velocity measurements are compared with other studies to synthesize a coherent picture of separation trends for equal-sized bodies.

ANALYSIS OF LIQUID VISCOSITY VALUE USING FALLING BALL METHOD USING DIGITAL IMAGE TECHNOLOGY BASED ON LONG EXPOSURE FEATURES

Physics is the science that studies natural phenomena which observation is one of the most important aspect. Observations were made to study the physical phenomena and, if necessary, measurements can be made using appropriate, easily accessible as well as sophisticated devices. In this study, observation and measurement of a straight motion in a viscometer tube device has been developed. The device is also able to measure viscosity of the liquid (indirectly) using the falling ball method by means of Long Exposure technique. The viscosity of a liquid is essentialy related to drag force that caused by friction between the liquid molecules, which are able to resist fluid flow. Long Exposure is a technique of image acquisition which can preserve information about traces of objects moving at a certain time that might not be able to be captured with the naked eye. The falling ball method is based on a measurement of terminal velocity of the falling ball in a viscous liquid. In the experiments, lightmeter is a solid ball with varying sizes coated with phosphorus paint which was released from the surface of the liquid (glycerin and honey) inside a cylindrical tube. A camera with long exposure feature is placed in front of a perforated disk that serves as a chopper, which are essentially slits for the camera to capture the trajectory of the ball and convert the continuous trace into discrete traces. Using a simple digital image processing and digital image analysis techniques, the traces of the trajectory of the ball can be analyzed and thus we can obtain the data of the position for each time interval, thus the speed of the ball can be observed and the type of the motion can be analyzed (accelerated and motion with constant velocity). The calculated liquid viscosity is 0.7885 Pa.s viscosity with error 6.55% for glycerin, and as for honey the viscosity is 3.9162 Pa.s with precision of 99.98%. It can be concluded that these devices can be used to observe the phenomenon of straight motion with constant velocity and accelerated motion in viscosity tube, determines the value of the viscosity of a liquid with a good accuracy and precision

Effect on bubble dynamics during pool boiling heat transfer in a novel aqueous binary mixture of surfactants

Temperature near the heating region changes with the water boiling curve when the heat flux applied. In this study, experiments were carried out by maintaining a cylindrical subcutaneous hypodermic needle as a single active nucleation site. By controlling heat supplied to the site, a single bubble was formed in the saturated water. The boiling phenomenon was recorded. The surfactants used were sodium dodecyl sulfate (SDS) and centrimonium bromide (CTAB). Aqueous binary mixture SDS-CTAB was prepared on a volume percent basis. The effect was measured by studying a single bubble. The vapor bubble resulting from the nucleation site was observed. Bubble parameters, without and with a surfactant, were plotted in two heat fluxes concerning the excess temperature. It is found that, compared with saturated water, the average measurements of bubble detachment diameters and terminal velocities decreased, but the bubble departure frequency increased. On the other side of analysis, with increasing excess needle temperature of site, at 601 kW/m2, the detachment diameter decreased, departure frequency increased, rising velocity was increased and at 950 kW/m2, the detachment diameter increased, departure frequency increased, rising velocity decreased.

A video camera recording method for measuring terminal velocity of seed dispersal by wind

An accurate and convenient method is essential for measuring the terminal velocity of seeds dispersed by wind. Systematic and random errors produced by existing methods lower the accuracy and convenience in determining seed terminal velocity. In this study, a video camera was used to record the falling process of forty-one species of wind-borne seed with eight appendage structures and seven aerodynamic behaviors in a settling tower at a speed of 50 frames per second (fps). The videos were analyzed by Quick Time Player to determine seed acceleration height, acceleration time, and terminal velocity. The results showed that acceleration height and time, terminal velocity, and the difference between terminal velocity and descent velocity (DTD) increased with wing loading. Compared with dropping methods, the camera recording method eliminated the effect of acceleration and corrected seed terminal velocity. Based on wing loading, release heights were determined for accurate measurement of terminal velocity of different seeds. This method, due to its inexpensive equipment, high accuracy, easy observation and operation, can be applied to measure the terminal velocity of wind dispersed seeds, and provides a promising method in exploring the dispersal process of seeds.

Partitioning intraspecific variation in seed dispersal potential using a low‐cost method for rapid estimation of samara terminal velocity

Abstract Seed or samara terminal velocity is a key trait affecting the dispersal potential of wind‐dispersed plants. However, this trait is often represented in dispersal models by a single mean value per species. This is despite considerable variation in dispersal traits within species and individuals that may have implications for both phenotypic selection and rates of spread. Methodological constraints may have acted as a barrier for robust assessments of intraspecific variation in seed terminal velocity. To quantify intraspecific variation in wind dispersal traits, we develop a low‐cost, time‐efficient method to measure the terminal velocity of a large number of samaras. We made three separate terminal velocity measurements for each of 750 Pinus radiata samaras, allowing partitioning of variation among individual cones, trees and source populations. We use the mechanistic WALD model to assess the potential influence of observed variation in samara terminal velocity on predicted dispersal kernels under a variety of realistic conditions. We demonstrate a twofold range in samara terminal velocity within P. radiata, with the highest variation occurring within individual cones, and the lowest among cones within individual trees. We identify a potential influence of source population on terminal velocity. Our modelling results demonstrate that this within‐species variation is sufficient to affect the shape of the predicted dispersal kernels, particularly the kernel tails and therefore the likelihood of long‐distance dispersal events. The effect of samara terminal velocity on dispersal is especially pronounced under environmental conditions that enhance seed dispersal. Our findings illustrate the scale of within‐species variation in a key dispersal trait, and the likely effect of this variation on dispersal distance. We suggest that the high level of variation observed within individual cones of P. radiata is likely to reduce the potential for phenotypic selection, and may either be indicative of a “bet‐hedging” strategy, or simply the result of the constraints of cone morphology on samara development. To obtain accurate dispersal models for wind‐dispersed species we highlight the necessity of capturing this variation for inclusion in future modelling approaches, and describe a device that can achieve such measurements easily and at low cost.

In situ terminal settling velocity measurements at Stromboli volcano: Input from physical characterization of ash

Ash particle terminal settling velocity is an important parameter to measure in order to constrain the internal dynamics and dispersion of volcanic ash plumes and clouds that emplace ash fall deposits from which source eruption conditions are often inferred. Whereas the total Particle Size Distribution (PSD) is the main parameter to constrain terminal velocities, many studies have empirically highlighted the need to consider shape descriptors such as the sphericity to refine ash settling velocity as a function of size. During radar remote sensing measurements of weak volcanic plumes erupted from Stromboli volcano in 2015, an optical disdrometer was used to measure the size and settling velocities of falling ash particles over time, while six ash fallout samples were collected at different distances from the vent. We focus on the implications of the physical parameters of ash for settling velocity measurements and modeling. Two-dimensional sizes and shapes are automatically characterized for a large number of ash particles using an optical morpho-grainsizer MORPHOLOGI G3. Manually sieved ash samples show sorted, relatively coarse PSDs spanning a few microns to 2000 μm with modal values between 180 and 355 μm. Although negligible in mass, a population of fine particles below 100 μm form a distinct PSD with a mode around 5–20 μm. All size distributions are offset compared to the indicated sieve limits. Accordingly, we use the diagonal of the upper mesh sizes as the upper sieve limit. Morphologically, particles show decreasing average form factors with increasing circle-equivalent diameter, the latter being equal to 0.92 times the average size between the length and intermediate axes of ash particles. Average particle densities measured by water pycnometry are 2755 ± 50 kg m−3 and increase slightly from 2645 to 2811 kg m−3 with decreasing particle size. The measured settling velocities under laboratory conditions with no wind, <3.6 m s−1, are in agreement with the field velocities expected for particles with sizes <460 μm. The Ganser (1993) empirical model for particle settling velocity is the most consistent with our disdrometer settling velocity results. Converting disdrometer detected size into circle equivalent diameter shows similar PSDs between disdrometer measurements and G3 analyses. This validates volcanological applications of the disdrometer to monitor volcanic ash sizes and settling velocities in real-time with ideal field conditions. We discuss ideal conditions and the measurement limitations. In addition to providing sedimentation rates in-situ, calculated reflectivities can be compared with radar reflectivity measurements inside ash plumes to infer first-order ash plume concentrations. Detailed PSDs and shape parameters may be used to further refine radar-derived mass loading retrievals of the ash plumes.

Particle classification and drag coefficients of irregularly-shaped combustion residues with various size and shape

In a vast number of industrial applications, particle-laden flows consist of irregularly-shaped particles with various sizes and shapes and thus, the drag coefficient is strongly affected and different for each particle. The key issue is to incorporate these characteristics within numerical calculations. Therefore, a sample-set of irregularly-shaped combustion residues or rather clinker flakes, with sizes between 50μm and 250μm was experimentally and numerically investigated. Particle geometry, terminal velocity measurements and drag analysis were carried out within the present work. Areflected-light microscope and an optical particle analyzer were used for geometry analysis. Terminal velocities were measured in a water filled glass column with a commercially available digital camera with a recording rate of 1000 frames per second and a frame-by-frame tracking method. At first a simple particle classification method based on this geometrical analysis and terminal velocity measurements in a static fluid was introduced. As a result, several particle groups were defined based on the obtained data. As a second step, this data were used as input parameters for two simple drag models from literature. The required particle shape parameters were determined by velocity recalculations and data fitting. Furthermore, the applicability of these drag models in combination with the experimentally determined particle shape descriptors was evaluated within a simple test rig, where freely falling particles are exposed to a lateral compressed airflow. The particles would be deflected and settle at different positions at the bottom of the test rig. Numerical calculations of the test rig were performed using a commercial Computational Fluid Dynamics (CFD) code and a numerically efficient Euler-Lagrangian approach in order to predict the accurate motion of particles. The particle mass dispersion at the bottom of the test rig was compared to numerical results. It was shown that the used drag models in combination with the experimentally determined particle shape descriptors improved the prediction of particle drag coefficients and trajectories significantly without an increase of computational cost and time.

Accurate Radar Measurements of Drag Coefficients in Free Flight

Undergraduate lab design balances several factors: 1) simple experiments connected with learning objectives, 2) experiments sufficiently accurate for comparisons between theory and measurements without gaps when students ascribe discrepancies to confounding factors (imperfect simplifying assumptions, measurement uncertainties, and “human error”), and 3) experiments capturing student attention to ensure due diligence in execution and analysis. Drag coefficient measurements are a particular challenge, though there has been some success using accurate measurements of terminal velocities. Video shows promise in several areas of kinematics, but the number of trials in a reasonable time is limited, and analysis techniques to determine drag coefficients often include numerical integration of differential equations. Here we demonstrate a technique with potential to measure drag coefficients to near 1% accuracy using an affordable 2.4 GHz Doppler radar system and round plastic pellets from an Airsoft launcher.

Aerodynamic properties of sesame (cv.N-8) as affected by moisture content of seed

The aerodynamic properties of crop grains influence the selection of the design and operational parameters of equipment. These properties are crop variety specific and moisture dependent. Measurement of terminal velocity is important to determine other aerodynamic properties. A terminal velocity measuring apparatus with vertical tapering rectangular air duct was developed which can measure velocity from 0 to 15 m/s. The sesame (Sesamum indicum Linn.) seeds of variety N-8 were dipped in water to obtain test samples of moisture contents 9.50, 13.46, 18.89, 24.17 and 28.99 per cent. The terminal velocity measured with the newly developed apparatus was found increased from 3.05 to 5.25 m/s with corresponding increase in moisture contents from 9.50 to 28.99 per cent (w.b.), respectively. In other aerodynamic properties, the values of drag co-efficient were found decreased from 2.9 to 0.6 and Reynolds number increased from 3939.9 to 11043.6 with corresponding increase in moisture contents from 9.50 to 28.99 per cent (w.b.), respectively. Simple linear regression equations were fitted to the obtained data to predict the aerodynamic properties of sesame seeds.

Expansion properties of alginate beads as cell carrier in the fluidized bed bioartificial liver

Liquid fluidization offers the advantage of homogeneous and controllable expansion of suspended particles with limited pressure drop and favorable heat and mass transfer conditions. Bioreactors can exploit such potential and fluidized-bed-based biomedical devices acting as bioartificial liver have proved an effective alternative to other solutions. In such a systems, alginate beads hosting individual or agglomerated hepatic cells are fluidized by a perfusion medium, with the bioreactor performance significantly affected by the hydrodynamics and mass transfer. In the present work, the intrinsic and fluidization properties of alginate beads are carefully analyzed using two rigs at different scales. Appropriate alginate beads were prepared by the technique of alginate drop gelation in calcium chloride. The beads were characterized in terms of size distribution and density, obtaining a Sauter mean diameter D=813μm and density ρ=1020kg/m3. The latter value is very close to usual perfusion fluids, requiring careful evaluation also of the liquid properties. Expansion properties were evaluated for free alginate beads (i.e. without hepatic cells) using appropriate saline solutions as fluidization medium. Bed expansion tests over a wide range of voidage values have been conducted in a 1-cm diameter column used for perfusion during in vitro experiments as well as in a 10-cm diameter column close to human size bioreactor at ambient (20°C) conditions. Expansion data, terminal velocity measurements and velocity-voidage plots are reported and elaborated on in terms of Richardson-Zaki parameters.

Particle terminal settling velocities in non‐Newtonian viscoplastic fluids

Accurate prediction of the settling velocity of a single particle in a quiescent, non‐Newtonian fluid is often required for analysis of fluid‐particle systems, e.g. the design and operation of slurry pipelines and solid‐liquid separation processes. Wilson et al. presented a direct method that was able to provide reasonable predictions of the terminal settling velocity of a sphere in a fluid with a yield stress. This method is somewhat limited in its applicability: if the fluid yield stress is greater than the calculated reference shear stress, the correlation cannot produce a prediction of terminal settling velocity. Measurements of terminal fall velocities of precision spheres in quiescent Kaolinite‐water suspensions were collected in the present study. Kaolinite volume concentrations were 10.6–21.7 % (0.106–0.217 L/L) resulting in suspension yield stresses of 1.3–30 Pa. Both Casson and Bingham models were satisfactory for modelling the clay‐water mixture rheology. An analogy of the Wilson‐Thomas analysis for the pipe flow of non‐Newtonian fluids was used to develop a new method for predicting terminal settling velocity of a sphere in a viscoplastic fluid. The new method does not have the limitations of the Wilson et al. method, and also provides more accurate predictions. The experimental results obtained here show that further research is needed to better characterize particle behaviour at low shear Reynolds numbers (Re* &lt; 10).

Measurements of Terminal Velocities of Cirrus Clouds in the Upper Trosphere

Cirrus clouds are composed of ice crystals condensed from humidity due to low temperature condition in the upper atmosphere. The microphysics of cirrus clouds including sizes and shapes of ice particles are not well understood but are important in climate modeling. Ice crystal will fall under gravitational sedimentation to reach terminal velocities which depend on the size, mass, and ice habit. We studied here the terminal velocity of cirrus clouds by using lidar observations at Chungli (25N, 121E). The terminal velocities for a few cases of stable cirrus clouds are measured to determine the ice particle sizes and processes in the upper atmosphere.

The distribution function of the Galaxy's dark halo

Starting from the hypothesis that the Galaxy's dark halo responded adiabatically to the infall of baryons, we have constructed a self-consistent dynamical model of the Galaxy that satisfies a large number of observations, including measurements of gas terminal velocities and masers, the kinematics of 180 000 giant stars from the RAVE (RAdial Velocity Experiment) survey and star-count data from the Sloan Digital Sky Survey. The stellar disc and the dark halo are both specified by distribution functions of the action integrals. The model is obtained by extending the work of Piffl et al. from the construction of a single model to a systematic search of model space. Whereas the model of Piffl et al. violated constraints on the terminal-velocity curve, our model respects these constraints by adopting a long scalelength Rd = 3.66 kpc for the thin and thick discs. The model is, however, inconsistent with the measured optical depth for microlensing of bulge stars because it attributes too large a fraction of the density at R ≲ 3 kpc to dark matter rather than stars. Moreover, it now seems likely that the thick disc's scalelength is significantly shorter than the model implies. Shortening this scalelength would cause the constraints from the rotation curve to be violated anew. We conclude that we can now rule out adiabatic compression of our Galaxy's dark halo.

Particle characterization of polydisperse quartz filtration sand

In this paper, different methods for particle characterization were applied to 16 polydisperse fractions of quartz filtration sand obtained by sieving, with sieve diameters in the interval dm=0.359 to 2.415. For each fraction, volume diameter was measured and projected diameter and 2D shape factor were obtained using the scanned image of the projection of a large number of particles. The correlations between the volume diameter, projected diameter and 2D shape factor with sieve diameter were proposed. All of the correlations show linear dependence between the variables.The sphericity was determined for the fractions from packed-bed pressure drop measurements; from terminal velocity measurements using different correlations for the calculation of CD, direct correlations for Ut and from direct empirical correlations. The sphericities obtained using different methods and correlations gave very different results. Both the sphericity and the 2D shape factor were shown to decrease with increase in particle sieve diameter.

Shipment and storage effects on the terminal velocity of seeds

AbstractMechanistic models of seed dispersal by wind include terminal velocity as the main seed characteristic that influences the dispersal process and hence the resulting dispersal kernels and spread rates. Accurate measurement of the terminal velocity of seeds is therefore pivotal. However, compression during shipment through the post or during storage between collection in the field and terminal velocity measurements in the lab may affect these measurements. To evaluate the effects of shipment and storage on terminal velocity measurements, capitula of Carduus nutans, an invasive thistle species from Eurasia, were stored for 1–5 years and subjected to three different packing treatments. Seeds from capitula were then assessed for terminal velocity values, plume area, seed mass, wing loading, number of filaments per pappus, qualitative assessments of pappus damage, and number of intact dispersal units per capitulum. Compression significantly increased seed terminal velocity. However, storage duration for 1–5 years did not cause a significant increase or decrease in any of the response variables. The compression treatment was validated by shipment of seeds from New Zealand to the United States. When capitula that are to be used for terminal velocity measurements are stored or shipped, they should be packaged in incompressible containers to avoid damage to the fragile dispersal structures. Studies using capitula that were originally collected and stored for other purposes, such as transcontinental demographic studies, should rescale observed terminal velocity values to take into account possible damage.

Terminal velocity and drag reduction measurements on superhydrophobic spheres

Super water-repellent surfaces occur naturally on plants and aquatic insects and are created in the laboratory by combining micro- or nanoscale surface topographic features with hydrophobic surface chemistry. When such types of water-repellent surfaces are submerged they can retain a film of air (a plastron). In this work, we report measurements of the terminal velocity of solid acrylic spheres with various surface treatments settling under the action of gravity in water. We observed increases in terminal velocity corresponding to drag reduction of between 5% and 15% for superhydrophobic surfaces that carry plastrons.

Terminal settling velocity measurements of volcanic ash during the 2002–2003 Etna eruption by an X‐band microwave rain gauge disdrometer

This is the first report in the scientific literature of direct measurement of the terminal settling velocity of volcanic particles during an eruption. Field measurements using a continuous wave X‐band disdrometer were carried out at Mt. Etna on 18 and 19 December 2002, when the explosive activity produced a 4 km high volcanic plume. These data allow the estimation of the intensity of the fallout and the measurement of the terminal settling velocities of the volcanic particles in real‐time. The main results are: (1) the tested instrument detected coherent falling volcanic particles from 0.2 to 1 mm diameter; (2) measured terminal settling velocities were in agreement with both experimental and theoretical methods; (3) however, the measured velocities were clustered around few discrete values, rather than a range of velocities as would be expected if the particles were falling simultaneously and discretely. This new methodology has many new applications for local hazard mitigation and improved understanding of fallout processes.

Um reoviscosímetro de queda de esferas de baixo custo para fluidos alimentares.

The falling ball viscosimeter (Hoppler) was modified to measure the rheological properties of non-Newtonian food fluids. The theory that formed the basis in developing this rheoviscosimeter was the analysis of slow falling of rigid spheres in the vicinity of non-Newtonian fluids. An electromagnetic device with automatic chronometry has permited the determination of the corresponding shear stress and the shear rate through the terminal velocity measurements, including non transparent fluids. The falling ball rheoviscosimeter demonstrated precision when tested with a Newtonian product (glycerol) and gave flow constants not significantly different from those obtained using rotoviscosimeters for the evaluation of a non-Newtonian product (carrageenan). The rheological parameters (K, n) of carageenan, in this work, demonstrated agreement when compared with results obtained with different rheoviscosimeters. Although the modified Hoppler viscosimeter as reported here does not encompass as wide a range of shear rates as some of the more expensive instruments, its range is sufficiently large to include most food fluids in respect to the stimulations associated with the sensory evaluation of viscosity.

Sizing of microdrops

Several techniques for determining the size of small fluid microdrops with diameters ranging from 5 to 30 μm have been developed and evaluated using an automated variation on the Millikan oil drop experiment. The average diameter of a large sample of monodisperse fluid drops was determined by measuring their terminal velocity in air, or if charged, their motion under the influence of an electric field, as well as by measurement of the magnitude of their Brownian motion. The diameter of individual drops was determined optically, by direct observation using an imaging system based on a charge-coupled-device camera. The technique used to analyze the image data is based on a best-fit technique taking the point spread function of the lens into account, and yields results accurate to 1% (based on a single image) without the need for any calibration. By combining this technique with terminal velocity measurements, the density of the fluid can be determined to similar accuracy.