Visualizing near-surface concentration fluctuations using laser-induced fluorescence

A method for observing near-surface fluctuations in pH caused by a water–air flux of carbon dioxide under conditions of ambient atmospheric carbon dioxide levels is developed and tested. Peaks in fluorescence intensity measured as a function of pH and turbulence are shown to be consistent with predictions from a chemical kinetics model of CO₂ exchange. The square root of the frequency of the pH fluctuations scale linearly with independently measured bulk air–water gas transfer velocities in agreement with surface divergence models for air–water gas transfer. These data indicate that the method proposed here is tracking changes in near-surface CO₂ concentrations. This laser-induced fluorescence method can be used to study the air–water exchange of CO₂ in wind-wave tunnels without the need for elevated CO₂ concentrations in the gas phase.     

In situ force-balance tensiometry

 Although a fundamental physical parameter, surface tension is difficult to measure. Common tensiometry inaccuracy comes from failure to control air–liquid–solid contact conditions, or account for liquid meniscus geometry and buoyancy corrections. This paper describes an in situ tensiometry technique, based on withdrawal of a thin-walled tube from the liquid interface, that enforces a known air–liquid–solid contact condition. This technique can be pursued at any level of experimental hygiene. Experimental results for filtered tap water, an alcohol–water solution, and a surfactant–water solution show that results repeatable to three significant digits are obtained with modest effort for a variety of geometrical parameters. Received: 7 October 1997/Accepted: 23 April 1998     

A Phase-Partitioning Model for CO<Subscript>2</Subscript>–Brine Mixtures at Elevated Temperatures and Pressures: Application to CO<Subscript>2</Subscript>-Enhanced Geothermal Systems

Correlations are presented to compute the mutual solubilities of CO₂ and chloride brines at temperatures 12–300°C, pressures 1–600 bar (0.1–60 MPa), and salinities 0–6 m NaCl. The formulation is computationally efficient and primarily intended for numerical simulations of CO₂-water flow in carbon sequestration and geothermal studies. The phase-partitioning model relies on experimental data from literature for phase partitioning between CO₂ and NaCl brines, and extends the previously published correlations to higher temperatures. The model relies on activity coefficients for the H₂O-rich (aqueous) phase and fugacity coefficients for the CO₂-rich phase. Activity coefficients are treated using a Margules expression for CO₂ in pure water, and a Pitzer expression for salting-out effects. Fugacity coefficients are computed using a modified Redlich–Kwong equation of state and mixing rules that incorporate asymmetric binary interaction parameters. Parameters for the calculation of activity and fugacity coefficients were fitted to published solubility data over the P–T range of interest. In doing so, mutual solubilities and gas-phase volumetric data are typically reproduced within the scatter of the available data. An example of multiphase flow simulation implementing the mutual solubility model is presented for the case of a hypothetical, enhanced geothermal system where CO₂ is used as the heat extraction fluid. In this simulation, dry supercritical CO₂ at 20°C is injected into a 200°C hot-water reservoir. Results show that the injected CO₂ displaces the formation water relatively quickly, but that the produced CO₂ contains significant water for long periods of time. The amount of water in the CO₂ could have implications for reactivity with reservoir rocks and engineered materials.     

An experimental study of a water droplet impinging on a liquid surface

An experimental study is presented for water droplet impingement on a liquid surface. The impaction process was recorded using a high-speed digital camera at 1,000 frames/s. The initial droplet diameter was fixed at 3.1 mm ± 0.1 mm, and all experiments were performed in atmospheric air. The impact velocity was varied from 0.36 m/s to 2.2 m/s thus varying the impact Weber number from 5.5 to 206. The impacted liquid surface consisted of two fluids, namely water and methoxy-nonafluorobutane, C₄F₉OCH₃ (HFE7100). The depth of the water and HFE7100 pool was varied from 2 mm to 25 mm. The collision dynamics of water in the HFE7100 pool was observed to be drastically different from that observed for the water droplet impingement on a water pool. The critical impact Weber number for jet breakup was found to be independent of liquid depth. Water–HFE7100 impact resulted in no jet breakup over the range of velocities studied. Therefore, no critical impact Weber number can be defined for water–HFE7100 impact. Received: 27 June 2001/Accepted: 29 November 2001     

Effect of salt on boiling heat transfer of ammonia-water mixture

Nucleate pool boiling heat transfer coefficients were determined experimentally for NH₃–H₂O, NH₃–H₂O–LiNO₃ and NH₃–H₂O–LiBr mixtures. Both the salts were effective in increasing the heat transfer coefficient of NH₃–H₂O mixture. A concentration of 10 mass% of the salts in water, produced the greatest enhancement in heat transfer coefficient at all the range of pressure, heat flux and ammonia concentration studied in this investigation. The experiments indicated that ammonia concentration also has the impact on the augmentation of heat transfer coefficient in NH₃–H₂O binary mixture by the addition of salts. For the solution of ammonia mass fraction 0.30, high concentration of LiBr gives the highest heat transfer coefficient, for ammonia mass fraction of 0.25, high concentration of LiNO₃ gives the maximum heat transfer coefficient, for ammonia mass fraction of 0.15, both the salts are equally effective in increasing the heat transfer coefficient.     

Optimal nonlinear observers for chaotic synchronization with message embedded

This paper presents an optimal nonlinear observer for synchronizing the transmitter-receiver pair with guaranteed optimal performance. In the proposed scheme, a generalized nonlinear state-space observer via uniform matrix transformations is constructed to estimate the transmitter state and the information signal, simultaneously. A nonlinear optimal design approach is used to synchronize chaotic systems. Solving the Hamilton–Jacobi–Bellman (H–J–B) equations we can obtain a linear optimal feedback scheme for piecewise-linear chaotic systems. Moreover, a robust scheme derived from the H _∞ optimization theory improves the synchronization performance of general nonlinear chaotic systems by suppressing the influence of their high order residual terms. Finally, two numerical simulation examples are illustrated by the chaotic Chua’s circuit system and the Lorenz chaotic system to demonstrate the effectiveness of our scheme.     

Type of reflection of a near-wall shock wave in the process of diffraction from a square channel

The results of an experimental and numerical investigation of the process of diffraction of shock waves from a square channel at a ninety-degree convex corner are presented for various incident shock wave Mach numbers M₀ (1.4<M₀<7). The type of reflection of the near-wall fragment of the diffracting shock wave from the wall and the wave velocity are determined as functions of M₀, direction, and time. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 145–151, January–February, 2000. The work was carried out with partial support from the Russian Foundation for Basic Research (project No. 96-02-16170a).     

Turbulent time and length scale measurements in high-velocity open channel flows

In high-velocity open channel flows, the measurements of air–water flow properties are complicated by the strong interactions between the flow turbulence and the entrained air. In the present study, an advanced signal processing of traditional single- and dual-tip conductivity probe signals is developed to provide further details on the air–water turbulent level, time and length scales. The technique is applied to turbulent open channel flows on a stepped chute conducted in a large-size facility with flow Reynolds numbers ranging from 3.8E+5 to 7.1E+5. The air water flow properties presented some basic characteristics that were qualitatively and quantitatively similar to previous skimming flow studies. Some self-similar relationships were observed systematically at both macroscopic and microscopic levels. These included the distributions of void fraction, bubble count rate, interfacial velocity and turbulence level at a macroscopic scale, and the auto- and cross-correlation functions at the microscopic level. New correlation analyses yielded a characterisation of the large eddies advecting the bubbles. Basic results included the integral turbulent length and time scales. The turbulent length scales characterised some measure of the size of large vortical structures advecting air bubbles in the skimming flows, and the data were closely related to the characteristic air–water depth Y ₉₀. In the spray region, present results highlighted the existence of an upper spray region for C > 0.95–0.97 in which the distributions of droplet chord sizes and integral advection scales presented some marked differences with the rest of the flow.     

Investigation of flow mechanism of a robotic fish swimming by using flow visualization synchronized with hydrodynamic force measurement

When swimming in water by flapping its tail, a fish can overcome the drag from uniform flow and propel its body. The involved flow mechanism concerns 3-D and unsteady effects. This paper presents the investigation of the flow mechanism on the basis of a 3-D robotic fish model which has the typical geometry of body and tail with periodic flapping 2-freedom kinematical motion testing in the case of St = 0.78, Re = 6,600 and phase delay mode (φ = −75°), in which may have a greater or maximum propulsion (without consideration of the optimal efficiency). Using a special technique of dye visualization which can clearly show vortex sheet and vortices in detail and using the inner 3-component force balance and cable supporting system with the phase-lock technique, the 3-D flow structure visualized in the wake of fish and the hydrodynamic force measurement were synchronized and obtained. Under the mentioned flapping parameters, we found the key flow structure and its evolution, a pair of complex 3-D chain-shape vortex (S–H vortex-rings, S₁–H₁ and S₂–H₂, and their legs L₁ and L₂) flow structures, which attach the leading edge and the trailing edge, then shed, move downstream and outwards and distribute two anti-symmetric staggering arrays along with the wake of the fish model in different phase stages during the flapping period. It is different with in the case of St = 0.25–0.35. Its typical flow structure and evolution are described and the results prove that they are different from the viewpoints based on the investigation of 2-D cases. For precision of the dynamic force measurement, in this paper it was provided with the method and techniques by subtracting the inertial forces and the forces induced by buoyancy and gravity effect in water, etc. from original data measured. The evolution of the synchronized measuring forces directly matching with the flow structure was also described in this paper.     

On the Repeatability of Friction and Wear Tests for Polyimides in a Hertzian Line Contact

Tribological properties for polymers are mainly experimentally determined, while few standards are available and variation in data is often large. Polyimide is slid against steel on a cylinder-on-plate tribotester at 50–200 N and 0.3 m/s. There is a statistical variation of ±7% on dynamic friction, ±10% on static friction, ±8% on wear rates from weight loss and ±12% from wear rates from dimensional measurements, or even higher at high normal loads. Different parameters influencing statistical repeatability are discussed. Friction for polymers shows higher variation and wear rates show lower variation than steel/steel pairs due to visco-elastic deformation that has a contribution to friction but reduces stress concentrations. It is experimentally verified that the visco-elastic deformation of polymers in line contact is higher than calculated from theoretical models. The role of recoverable and permanent deformation is verified and there is a difference in deformation at 50–100 N and 150–200 N revealed from static loading tests, creep tests and wear measurements. The limit between running-in and steady-state coincides with the stabilization in contact pressures after 250 μm diameter reduction. Besides test rig design, a variation in counterface roughness seems the second most important influence.     

Rheological properties of binary associating polymers

Dynamics of associating polymer solutions above the reversible gelation point are studied. Each macromolecule consists of a soluble backbone (B) and a small fraction of specific strongly interacting groups (A or C stickers) attached to B. A mixture of B–A and B–C associating polymers with 1:1 stoichiometric ratio is considered. As a result of AC association, the polymers reversibly gelate above the overlap concentration. It is shown that (1) the network strands are linear complexes (double chains) of B–A and B–C; (2) “diffusion” of the network junction points is characterized by an apparent activation energy, which can be significantly higher than the energy of one AC bond; (3) most importantly, the randomness of sticker distribution along the chain can significantly slow down the network relaxation leading to a markedly non-Maxwellian viscoelastic behavior. The theory elucidates the most essential features of rheological behavior of polysaccharide associating systems (with A = adamantyl moiety, C = β-cyclodextrin, B = either chitosan or hyaluronan) including similar behavior of G ^′ and G ^″ in a wide frequency range, strong temperature dependence of the characteristic frequency ω _x , and an extremely strong effect of added free stickers (fC) on the dynamics. This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006.     

Influence of disturbances generated by the nozzle boundary layer on the heat exchange on the cylindrical nose of a body in a hypersonic flow

The heat transfer to a cylindrical surface whose generators are perpendicular to the freestream direction is investigated. Experiments were carried out in a short-duration wind tunnel at Mach numbers M=6 and 16. At M=6, the Reynolds number based on the cylinder diameter was varied on the range from 2.2·10⁴ to 0.95·10⁶ for the purpose of studying the effect of acoustic disturbances generated by the nozzle boundary layer on the heat exchange. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 125–131, January–February, 1999. The study was financially supported by ONERA (France). The authors wish to thank V. N. Gusev, S. M. Boldyrev, S. N. Krutii, and R. A. Kazanskii from TsAGI and J. Délery and B. Chanetz from ONERA for their assistance with the investigation.     

Microstructure and viscoelasticity in thermotropic copolyesters: the influence of monomer concentration

This research investigates the influence of monomer composition on the thermal transitions, mi crostructure, and viscoelastic properties of thermotro pic liquid crystalline polymers (LCPs) based on 1, 4-hydroxy-benzoic acid (B) and 2,6-hydroxy-naphthoic acid (N). Compositions B–N of 1:1, 1:3, 3:1, and 2:1 mol% were studied. The solid-to-nematic transition T _s→n was greatly influenced by the monomer composition, ranging from 230 to 280 °C. However, the decomposition temperature T _dec was independent of composition, all the materials degrading at T _dec = 509 °C. Polarized optical microscopy showed a threaded texture in the nematic phase. Fiber X-ray diffraction showed aperiodic meridional maxima for all LCPs, the number of maxima depended on composition. B–N 3:1 and 1:3 mol% favor the orthorhombic crystallographic phase whereas the 1:1 and 2:1 mol% crystallized in a pseudohexagonal phase. Dynamic time sweeps showed that the nematic phases are stable at the temperatures studied. Strain sweeps showed the existence of a linear viscoelastic (LVE) regime. The LVE properties ranged from predominantly viscous (G^′ < G^″) for the 1:1 mol% composition to predominantly elastic (G^′ > G^″) and with a well-defined rubber-like regime for the 1:3 mol% composition, resembling the rheology of flexible polymer melts. The persistence length q appears to be the parameter driving the rheological behavior.

Gas flow activated in an electron-beam plasma

Probe measurements of electron temperature and density, electron energy distribution functions, and plasma potential in a free gas jet activated in an electron-beam plasma and in a planar reactor are presented. The measurements are performed by single, double, and triple electrostatic probes in jets of helium-argon and helium-argon-monosilane gas mixtures. The latter mixture is used to deposit films of microcrystalline and epitaxial silicon. Microcrystalline silicon films of higher quality are obtained in a dense (n_e ≈ 10¹⁷ m⁻³) and cold (T_e ≈ 1.0–0.5 eV) plasma with a low potential (U_sp ≈ 10 V), whereas the growth of monocrystalline silicon films requires a hotter plasma (T_e ≈ 3–5 eV) with a potential U_sp ≈ 15 V. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 3–10, January–February, 2007.     

Steady Flow of a Navier–Stokes Liquid Past an Elastic Body

We perform a mathematical analysis of the steady flow of a viscous liquid, L{\mathcal{L}} , past a three-dimensional elastic body, B{\mathcal{B}} . We assume that L{\mathcal{L}} fills the whole space exterior to B{\mathcal{B}} , and that its motion is governed by the Navier–Stokes equations corresponding to non-zero velocity at infinity, v _∞. As for B{\mathcal{B}} , we suppose that it is a St. Venant–Kirchhoff material, held in equilibrium either by keeping an interior portion of it attached to a rigid body or by means of appropriate control body force and surface traction. We treat the problem as a coupled steady state fluid-structure problem with the surface of B{\mathcal{B}} as a free boundary. Our main goal is to show existence and uniqueness for the coupled system liquid-body, for sufficiently small |v _∞|. This goal is reached by a fixed point approach based upon a suitable reformulation of the Navier–Stokes equation in the reference configuration, along with appropriate a priori estimates of solutions to the corresponding Oseen linearization and to the elasticity equations.     

Transport properties in mixtures involving carbon dioxide at low and moderate density: test of several intermolecular potential energies and comparison with experiment

It is the purpose of this paper to extract unlike intermolecular potential energies of five carbon dioxide-based binary gas mixtures including CO₂–He, CO₂–Ne, CO₂–Ar, CO₂–Kr, and CO₂–Xe from viscosity data and compare the calculated potentials with other models potential energy reported in literature. Then, dilute transport properties consisting of viscosity, diffusion coefficient, thermal diffusion factor, and thermal conductivity of aforementioned mixtures are calculated from the calculated potential energies and compared with literature data. Rather accurate correlations for the viscosity coefficient of afore-cited mixtures embracing the temperature range 200 K < T < 3273.15 K is reproduced from the present unlike intermolecular potentials energy. Our estimated accuracies for the viscosity are to within ±2%. In addition, the calculated potential energies are used to present smooth correlations for other transport properties. The accuracies of the binary diffusion coefficients are of the order of ±3%. Finally, the unlike interaction energy and the calculated low density viscosity have been employed to calculate high density viscosities using Vesovic–Wakeham method.     

Inverse problem of fracture mechanics for a disk fitted onto a rotating shaft

A plane problem of fracture mechanics for a circular disk fitted onto a rotating shaft is considered. The disk is assumed to be fitted tightly onto the shaft, and there are N randomly located straight-line cracks of length 2l_k (k = 1, 2, ..., N) near the inner surface of the disk. The interference between the disk and the rotating shaft, providing minimization of fracture parameters (stress intensity factor) of the disk, is theoretically studied on the basis of the minimax criterion. A closed system of algebraic equations is constructed, which allows the problem of optimal design to be solved. A simplified method of minimization of disk fracture parameters is considered. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 201–209, July–August, 2009.     

Elastic properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–NiAl: a modified version of Hashin–Shtrikman bounds

The modified nonlinear relations for the estimation of elastic constants of Al₂O₃–NiAl composite material are developed. The concept of microstructure and interconnectivity of phases at the interface is used. Hashin–Shtrikman relations are described in their actual form and modified version of Hashin–Shtrikman relations for bulk and shear moduli are discussed. These relations for elastic and mechanical properties are applied mainly for Al₂O₃–NiAl composite material. Theoretical predictions using modified relations are compared with Hashin–Shtrikman bounds and experimental results of elastic properties for Al₂O₃–NiAl matrix-inclusion-based composite. It is found that the predicted values of elastic and mechanical properties using modified relations are quite close to the experimental results.     

Water Vapor Diffusion Through Soil as Affected by Temperature and Aggregate Size

Water vapor diffusion through the soil is an important part in the total water flux in the unsaturated zone of arid or semiarid regions and has several significant agricultural and engineering applications because soil moisture contents near the surface are relatively low. Water vapor diffusing through dry soil is absorbed for both long and short terms. Long-term absorption allows more water to enter than exit the soil, as reflected in the concentration gradient. Short-term absorption leads to an apparent reduction in the diffusion rate, as reflected in the diffusion coefficient. This investigation studied the effects of soil temperature and porosity on the isothermal diffusion of water vapor through soil. The diffusion model consisted of 25.4 cm × 8.9 cm × 20.3 cm Plexiglas box divided into two compartments by a partition holding a soil reservoir. Water vapor moved from a container suspended by a spring in one compartment, through the porous medium in the center of the model, to calcium chloride in a container suspended by a spring in the other compartment. The porous materials consisted of aggregates of varying size (2–2.8, 1–2, and 0.5–1 mm) of a Fayatte silty clay loam (a fine-silty, mixed mesic Typic Hapludalf). The flow rates of water vapor were measured at temperatures of 10, 20, 30, and 40°C. Warmer temperatures increased the rate of diffusion through dry soil while reduced the amount of water absorbed by that soil. Reducing porosity slowed the rate of diffusion and increased the amount of water absorbed. The dry soil in this study absorbed from 1/8 to 2/3 of the diffusing water. Maximum absorption rates occurred with the most compact soil samples at the highest temperature, though the maximum absorption as a percentage of the diffusing water was in the compact samples at the lowest temperature. The diffusivity equation D/D ₀ = [(S – 0.1)/0.9]² fit the D/D ₀ values obtained from these data if a coefficient of 1/3 or 1/3.5 is added to correct for the time delays caused by temporary sorption of the diffusing water vapor. The data, influenced by the interaction of water vapor and soil materials, represent a diffusion rate lower than the diffusion rate that would have resulted without this interaction. Mention of trade names, proprietary products, or specific equipment is intended for reader information only and does not constitute a guarantee or warranty by the USDA-ARS nor does it imply approval of the product named to the exclusion of other products. An erratum to this article can be found at     

The complex deformation of metals along a plane curvilinear astroid-type trajectory

The constitutive relations of the complanarity hypothesis are used to construct an image of the process of loading of 9×2 steel for a plane deformation.astroid-type trajectory, which is realized in the plain Э₁-Э₃ of the deviator subspace of Il'yushin's deformation. The laws governing changes in the scalar and vector properties of the material are considered. The computed results are compared with experimental data obtained on a CH-DC computer-aided system. State Technical University, Tver', Russia. Translated from Prikladnaya Mekhanika, Vol. 36, No. 7, pp. 130–136, July,2000.