Increasing Rotation Rate Research Articles

Boundary layers in rotating weakly turbulent Rayleigh–Bénard convection

The effect of rotation on the boundary layers (BLs) in a Rayleigh–Bénard system at a relatively low Rayleigh number, i.e., Ra=4×107, is studied for different Pr by direct numerical simulations and the results are compared with laminar BL theory. In this regime, we find a smooth onset of the heat transfer enhancement as function of increasing rotation rate. We study this regime in detail and introduce a model based on the Grossmann–Lohse theory to describe the heat transfer enhancement as function of the rotation rate for this relatively low Ra number regime and weak background rotation Ro≳1. The smooth onset of heat transfer enhancement observed here is in contrast to the sharp onset observed at larger Ra≳108 by Stevens et al. [Phys. Rev. Lett. 103, 024503 (2009)], although only a small shift in the Ra-Ro-Pr phase space is involved.

Investigation of the effect of impeller rotation rate, powder flow rate, and cohesion on powder flow behavior in a continuous blender using PEPT

In this paper, we examine the movement of particles within a continuous powder mixer using PEPT (Positron Emission Particle Tracking). The benefit of the approach is that the particle movement along the vessel can be measured non-invasively. The effect of impeller rotation rate, powder flow rate, and powder cohesion on the particle trajectory, dispersive axial transport coefficient, and residence time is examined. Increase in the impeller rotation rate decreased the residence time, increased the axial dispersion coefficient, and resulted in longer total path length. Effect of flow rate was different at two different rotation rates. At lower rotation rate, increase in flow rate increased the residence time, decreased the axial dispersion, and resulted in longer total path length. At higher rotation rate, increase in flow rate decreased the residence time, increased the total path length and showed a complex dependence on the axial dispersion coefficient. Increasing cohesion (measured using the flow index, dilation, and the Hausner ratio) did not affect the axial dispersion coefficient significantly, but had significant effects on the total particle path length traveled and the residence time. These results, relevant to pharmaceutical powders, provide better physical understanding of the influence of operating parameters on the flow behavior in the continuous mixer. In addition, one of the main obstacles of modeling continuous mixing of particles is to know the appropriate values for the modeling parameters as well as validate modeling approaches. One example is the dispersion coefficient which leads to an analytical solution for the axial dispersion model of a continuous blending process.

Energy cascade processes in rotating stratified turbulence with application to the atmospheric mesoscale

Numerical experiments of rotating stratified turbulence are conducted in order to investigate the mesoscale energy cascade process in the free atmosphere. We examine the downscale energy cascade process originated by energy injection at large scales. The energy spectrum created by this injection follows a power law, and its slope depends on planetary rotation rate and static stability. While the spectral slope tends to be steeper with increased static stability in cases without planetary rotation, it becomes insensitive to the planetary rotation rate and static stability and converges to the range from −1.9 to −2.1 in cases with an increased rotation rate. The roles of geostrophic and gravity modes in the cascade processes are discussed. It is shown that nonlinear interactions between geostrophic and gravity modes play a crucial role in the downscale energy cascades. In particular, the effect of the planetary rotation mainly influences the triad interaction composed of one geostrophic and two gravity modes in the energy cascade process. Energy flux to smaller scales is intensified by this type of triad interaction with increased planetary rotation rate.

Mass Transfer of Protons during Electrodeposition of Cobalt in Chloride Electrolytes

In acid cobalt chloride electrolytes, the electrodeposition of cobalt and the evolution of hydrogen take place simultaneously. On a rotating platinum disk electrode, the current efficiency for cobalt deposition was calculated based on the anodic charge needed for stripping of the cobalt deposits divided by the total cathodic charge. The results showed a decrease in current efficiency with increasing rotation rate. From the partial current density for hydrogen evolution, the diffusion coefficient for protons was calculated. The derived diffusion coefficients varied with overpotential and pH but were always 1 order of magnitude lower compared to what was expected from literature values. This was attributed to water drag when transporting cobalt ions toward the electrode. The variations in the calculated diffusion coefficients were explained by the change in the transfer number when the proton concentration was changed and in the potential gradient when the potential was varied.

Serotonin prolongs survival of encapsulated pond snail embryos exposed to long-term anoxia

Embryos of the pond snail, Helisoma trivolvis, develop bilateral serotonergic neurons that innervate ciliary bands and stimulate cilia-driven rotation. This behaviour is postulated to increase oxygen availability during hypoxia by mixing the capsular fluid. We hypothesised that the stimulation of ciliary-driven rotation by serotonin (5-HT) enhances the survival of embryos during prolonged hypoxia. Embryo rotation and survival were monitored in different levels of oxygen for 24-48 h while in the presence or absence of 5-HT (100 micromol l(-1)) or a 5-HT antagonist (50 micromol l(-1)). Long-term hypoxia caused delayed embryonic development that appeared morphologically normal. Hypoxia also induced a transient increase in rotation rate in embryos exposed to artificial pond water (APW) or 5-HT that lasted around 3 h. 5-HT-treated embryos had an elevated rotation rate over embryos in APW throughout the long-term exposure to hypoxia. Long-term anoxia also induced a transient increase in rotation rate in embryos exposed to APW or 5-HT. Rotation ceased in embryos exposed to APW by 13 h but persisted in 5-HT-treated embryos for up to 40 h. Fifty percent mortality was reached at 9 h of anoxia in embryos in APW and at 24 h in 5-HT-treated embryos. The 5-HT antagonist mianserin partially inhibited the 5-HT enhancement of rotation but not the prolongation of survival in anoxia. The ability of 5-HT to prolong survival in anoxia reveals a 5-HT-activated metabolic pathway that liberates an alternative energy source.

Atmospheric Dynamics of Earth‐Like Tidally Locked Aquaplanets

We present simulations of atmospheres of Earth‐like aquaplanets that are tidally locked to their star, that is, planets whose orbital period is equal to the rotation period about their spin axis, so that one side always faces the star and the other side is always dark. Such simulations are of interest in the study of tidally locked terrestrial exoplanets and as illustrations of how planetary rotation and the insolation distribution shape climate. As extreme cases illustrating the effects of slow and rapid rotation, we consider planets with rotation periods equal to one current Earth year and one current Earth day. The dynamics responsible for the surface climate (e.g., winds, temperature, precipitation) and the general circulation of the atmosphere are discussed in light of existing theories of atmospheric circulations. For example, as expected from the increasing importance of Coriolis accelerations relative to inertial accelerations as the rotation rate increases, the winds are approximately isotropic and divergent at leading order in the slowly rotating atmosphere but are predominantly zonal and rotational in the rapidly rotating atmosphere. Free‐atmospheric horizontal temperature variations in the slowly rotating atmosphere are generally weaker than in the rapidly rotating atmosphere. Interestingly, the surface temperature on the night side of the planets does not fall below ∼240 K in either the rapidly or slowly rotating atmosphere; that is, heat transport from the day side to the night side of the planets efficiently reduces temperature contrasts in either case. Rotational waves and eddies shape the distribution of winds, temperature, and precipitation in the rapidly rotating atmosphere; in the slowly rotating atmosphere, these distributions are controlled by simpler divergent circulations. Both the slowly and rapidly rotating atmospheres exhibit equatorial superrotation. Systematic variation of the planetary rotation rate shows that the equatorial superrotation varies non‐monotonically with rotation rate, whereas the surface temperature contrast between the day side and the night side does not vary strongly with changes in rotation rate.

New insights into the mechanism of nitrite reduction on a platinum electrode

This paper reinvestigates the mechanism of HNO 2 and NO 2 - reduction on polycrystalline platinum as a function of electrolyte pH and reactant concentration. Intermediates and/or reaction products were detected by means of various (combined) techniques: RRDE (for NH 2OH detection), OLEMS (for volatile products) and FTIRS. In acidic media, HNO 2 is depleted due to homogeneous-phase reactions (accelerated by stirring) that generate NO: the latter species, which readily forms an adlayer on Pt, is reduced in a first wave to N 2O, while HNO 2 is reduced in a following diffusion-limited wave to mainly NH 2OH. The two waves display different reaction orders. Loss of HNO 2 (as NO) in the blanketing Ar stream hampered an accurate quantitative evaluation of the product distribution. When the pH is increased, NO 2 - is reduced in a single peak with a much lower current density than in the previous case. In RDE experiments, the peak was found to decrease with increasing rotation rates. The presence of a sluggishly reduced intermediate (NH 2OH) has been proposed. A general mechanistic scheme, including NO, HNO 2 and NO 2 - , is discussed.

Activating and deactivating mass transport effects in methanol and formic acid oxidation on platinum electrodes

Transient increases in rotation rate at an RDE increase the methanol oxidation current, even though in slower experiments the current decreases with increasing rotation rate as usually reported. Methanol oxidation on smooth polycrystalline platinum rotating disk electrodes in sulfuric acid electrolyte was studied by RDE voltammetry and hydrodynamic impedance spectroscopy combined with cyclic voltammetry. A positive low-frequency real part in the hydrodynamic admittance spectra for the main oxidation peak was used to predict that a transient increase in rotation rate would increase the current, as was observed. In contrast, slow scan rate voltammograms showed a decrease in current with increasing rotation rate. The transient current increase was explained by enhanced production of soluble intermediates, while increased production of adsorbed CO poisoning explained the slower inhibition. Comparative experiments for formic acid oxidation showed increasing current with rotation rate in both hydrodynamic admittance spectra and slow-scan voltammograms.

G0500-6-6 準剛体回転流を用いた単段分級方式における高流量化に伴う精度変化の実験的考察([G0500-6]流体工学部門一般講演(6))

In a single-stage classification system using an almost rigidly flow in which small feed-powder particles suspended in a liquid medium with a low mass-concentration are accurately classified into fine and coarse products by the difference in centrifugal force and fluid drag acting on each particle due to the particle-size difference, with the aim of considering the change in accuracy with increasing flow-rate, we have conducted classification experiments, keeping the centrifugal-effect parameter constant to hold the cut size constant. With increasing Rossby number (flow rate) by decreasing Ekman number (by increasing rotation rate), the cut size scarcely changes and the classification accuracy is more improved. This is due to decreasing Ekman number. With increasing Rossby number further, however, the accuracy decreases drastically. Corresponding to this fact, the flow state of the classification field changes definitely.

Functional and Structural Changes Induced By cTNT-Related FHC Mutations in TNT1 Alter Actomyosin Binding Interactions

Familial Hypertrophic Cardiomyopathy (FHC) is a primary disease of the cardiac sarcomere. Many FHC mutations in hcTnT are found within the TNT1 domain, with a mutational hotpot at residues 160-163. These residues fall within a highly charged region (158-RREEEENRR-166), which may create a flexible hinge necessary for function, the structure and function of which is affected by FHC mutations. We are investigating the effects of these hotspot mutations using in vitro motility (IVM) assays, SDSL-EPR, and transgenic mouse models. IVM data indicate that mutations Δ160E and E163R disrupt actin binding to heavy meromyosin under standard assay conditions. By reducing the ionic strength of the motility solutions, thin filament binding and sliding are restored suggesting that mutations in this region cause disease by disrupting the weak electrostatic interactions between the thin filament and myosin necessary for crossbridge formation. CW-EPR spectra show an increase in spin label isotropic rotational rate at hcTnT residue 153 (upstream of the putative hinge region) between Troponin ternary complexes containing Δ160E verses WT hcTnT, suggesting an increase in flexibility due to backbone changes induced by the mutation. We are expanding our SDSL-EPR experiments with additional cysteine substitutions superimposed onto 160-163 mutant proteins to provide further data regarding secondary structural changes imposed by these mutations. These results correspond with our Δ160E mouse model showing dose dependant myofilament disarray. Preliminary observations of an E163R model suggest that this mutant is less severely affected, tolerating a higher transgene dose. The structural and functional changes observed in vitro may contribute to the structural impairment seen in vivo. By correlating our IVM and SDSL-EPR findings with in vivo data generated from the Δ160E and E163R models, a mechanism of disease for these hotspot mutations can be determined.

Exploring thePcycvs.Protrelation with flux transport dynamo models of solar-like stars

Aims: To understand stellar magnetism and to test the validity of the Babcock-Leighton flux transport mean field dynamo models with stellar activity observations Methods: 2-D mean field dynamo models at various rotation rates are computed with the STELEM code to study the sensitivity of the activity cycle period and butterfly diagram to parameter changes and are compared to observational data. The novelty is that these 2-D mean field dynamo models incorporate scaling laws deduced from 3-D hydrodynamical simulations for the influence of rotation rate on the amplitude and profile of the meridional circulation. These models make also use of observational scaling laws for the variation of differential rotation with rotation rate. Results: We find that Babcock-Leighton flux transport dynamo models are able to reproduce the change in topology of the magnetic field (i.e. toward being more toroidal with increasing rotation rate) but seem to have difficulty reproducing the cycle period vs activity period correlation observed in solar-like stars if a monolithic single cell meridional flow is assumed. It may however be possible to recover the $P_{cyc}$ vs $P_{rot}$ relation with more complex meridional flows, if the profile changes in a particular assumed manner with rotation rate. Conclusions: The Babcock-Leighton flux transport dynamo model based on single cell meridional circulation does not reproduce the $P_{cyc}$ vs $P_{rot}$ relation unless the amplitude of the meridional circulation is assumed to increase with rotation rate which seems to be in contradiction with recent results obtained with 3-D global simulations.

Nd:YVO 4 crystal growth by Czochralski technique with a submerged plate

This paper is to investigate the growth of Nd:YVO 4 (yttrium vanadate) crystal by the modified Czochralski technique with a submerged plate. Numerical studies are performed to examine melt convection and heat transfer during Nd:YVO 4 growth. The attention is paid to study the effects of initial elevation of the submerged plate, crystal diameter, and melt level on melt inclusions. It is found that the increase in crystal rotation rate and crystal diameter, and the decrease in melt level will increase the axial temperature gradient at the edge and in the center of the crystal, and change the interface shape from convex to flat. The experiments are also carried out to confirm the feasibility of the proposed new technique for controlling melt inclusions in Nd:YVO 4 crystal growth.

Experimental investigation of transition to laminar mixing of a homogeneous viscous liquid in a tilted-rotating tank

Abstract A tilted and partially filled rotating tank is investigated experimentally at O(1) Reynolds and small ( ⪡ 1 ) capillary numbers, to study the mixing of a viscous homogeneous fluid. Of particular interest is the transition from a previously studied low Reynolds number flow regime [Ward, T., Metchik, A., 2007. Viscous fluid mixing in a titled tank by periodic shear. Chemical Engineering Science 62, 6274–6284], that exhibited two large vortices, to the laminar flow regime which results in additional vortex generation. In the laminar Reynolds number limit O(1) the two primary vortices generated by the liquid rotation axis can interact with the bottom wall, generating two secondary counter-rotating vortices, via a cascade that is qualitatively similar to the well known Moffatt [1964. Viscous and resistive eddies near a sharp corner. Journal of Fluid Mechanics 18, 1–18] vortices in Stokes flow. While the secondary vortices aid in transporting material from the walls to the bulk, they also intensify in magnitude with increasing rotation rate leading to finite sized unmixed regions via the appearance of KAM-like surfaces [Alvarez-Hernandez, M.M., Shinbrot, T., Zalc, J., Muzzio, F.J., 2002. Practical chaotic mixing. Chemical Engineering Science 57, 3749–3753]. This suggests that there may be an optimal tilt angle, for a given speed, with which to achieve the maximum mixed cross sectional area within a minimum amount of elapsed time. Experiments are performed using a 90% glycerol, 10% water mixture at two volume portions with angles ranging between 25 ∘ and 65 ∘ measured from the horizontal. Laser fluorescence is used to illuminate the vortices via experimental Poincare mapping [Fountain, G.O., Khakhar, D.V., Ottino, J.M., 1998. Visualization of three dimensional chaos. Science 281, 683–686], and the resulting images are analyzed to determine the mixed cross sectional area versus elapsed time.

Effect of tool rotation rate on microstructure and mechanical properties of friction stir welded copper

Defect free copper welds were achieved by friction stir welding (FSW) carried out at a constant welding speed of 100 mm min−1. The influence of tool rotation rate on microstructure, mechanical properties and fracture location was investigated. As the tool rotation rate increased, the grains of nugget zone grew significantly, the thermomechanically affected zone became indistinct and the grain size increased, but the effect of tool rotation rate on the grain size of heat affected zone was limited. Both ultimate tensile strength (UTS) and elongation increased first and then decreased with increasing rotation rate and the UTS achieved a highest value of 282 MPa at the rotation rate of 400 rev min−1 together with the welding speed of 100 mm min−1, which was on the level of the base metal. The fracture occurred at the cavity defect on the advancing side of the joint when the FSW was performed at a low tool rotation rate, while it occurred on the retreating side when the tool rotation rate was relatively high.

Influence of turbulent flow on the corrosion of Al‐Zn‐Mg galvanic anode in artificial seawater media

AbstractThe effect of hydrodynamics on the corrosion of Al(14 wt%)‐Zn(8 wt%)‐Mg alloy in artificial seawater media at room temperature was studied in a rotating cylinder electrode (RCE) system under turbulent flow conditions. Five different rotation rates were studied: 100, 1000, 3000, 5000, and 7000 rpm. The corrosion rates were measured by electrochemical impedance spectroscopy (EIS). For the system studied, the steady‐state corrosion potential increased with increase in rotation rate. The effect of increasing the rotation rate is to increase the availability of oxygen at the surface, which in turn will polarize the corrosion reaction in the more noble direction. The corrosion rate also increases with increase in RCE rotation rate. This reflects the fact that the rate of corrosion is controlled, at least in part, by the rate of mass transfer. In this case, the effect of increase in the rotation rate on the corrosion rate is to increase the interfacial concentration of the reactant (oxygen).

Dynamo generated toroidal magnetic fields in rapidly rotating stars

Aims. Results presented in the recent observational paper by Petit et al. (2008, MNRAS, 388, 80) suggest that, for solar-like stars, the large-scale surface toroidal fields become strong for rotational periods less than about 12 d. We discuss this observation in the context of stellar dynamo theory, as a manifestation of a bifurcation in dynamo regimes occurring around this rotation period. Methods. Working in the context of mean field theory, we first consider two options for such a bifurcation for a given stellar rotation law: (a) a bifurcation resulting in a sudden increase of the near-surface toroidal field, with all other details of the model being kept unaltered; (b) a new type of surface boundary condition at the stellar surface, forced by internal reorganization of magnetic field with increasing rotation rate, which causes a more-or-less abrupt increase in large-scale surface toroidal field. Results. Neither of these options seem to provide anything like the reported behaviour of surface toroidal field for plausible choices of parameters, although we cannot conclusively eliminate a possible role for the latter mechanism. We conclude that any such bifurcation most plausibly is associated with some reorganization in the stellar hydrodynamics as the stellar rotation rate increases. The simplest suggestion, i.e. a transition from a solar-like rotation law (with spoke-like angular velocity contours through the bulk of the convection zone) to a law with quasi-cylindrical isorotation contours as thought to be appropriate to rapidly rotating stars, seems to reproduce the observed phenomenology reasonably well. Conclusions. While we appreciate the manifold uncertainties in the available theory and observations, we thus suggest that the bifurcation deduced by Petit et al. (2008) is an observational manifestation of the transition between solar-like and quasi-cylindrical rotation laws, occuring near a rotational period of 12 d.

Wake structure of a transversely rotating sphere at moderate Reynolds numbers

The uniform flow past a sphere undergoing steady rotation about an axis transverse to the free stream flow was investigated numerically. The objective was to reveal the effect of sphere rotation on the characteristics of the vortical wake structure and on the forces exerted on the sphere. This was achieved by solving the time-dependent, incompressible Navier–Stokes equations, using an accurate Fourier–Chebyshev spectral collocation method. Reynolds numbers Re of 100, 250 and 300 were considered, which for a stationary sphere cover the axisymmetric steady, non-axisymmetric steady and vortex shedding regimes. The study identified wake transitions that occur over the range of non-dimensional rotational speeds Ω* = 0 to 1.00, where Ω* is the maximum velocity on the sphere surface normalized by the free stream velocity. At Re = 100, sphere rotation triggers a transition to a steady double-threaded structure. At Re = 250, the wake undergoes a transition to vortex shedding for Ω* ≥ 0.08. With an increasing rotation rate, the recirculating region is progressively reduced until a further transition to a steady double-threaded wake structure for Ω* ≥ 0.30. At Re = 300, wake shedding is suppressed for Ω* ≥ 0.50 via the same mechanism found at Re = 250. For Ω* ≥ 0.80, the wake undergoes a further transition to vortex shedding, through what appears to be a shear layer instability of the Kelvin–Helmholtz type.

Structural and Functional Characterization of cTnT in Familial Hypertrophic Cardiomyopathy

Familial Hypertrophic Cardiomyopathy (FHC) is a primary disease of the cardiac sarcomere. Many disease-causing mutations in the thin filament protein cTnT are found within the TNT1 region. Residues 160-163 represent a mutational hotspot within a highly charged region (158-RREEEENRR-166). In this region, this highly alpha helical domain may unwind to create a flexible hinge that is necessary for function, the structure and dynamics of which may be affected by FHC mutations. We are investigating the structure and function of this region using in vitro motility (IVM) assays and SDSL-EPR. The purpose of our IVM experiments is two-fold: to functionally analyze our spin labeled proteins and to gain insight into the function of TNT1 in the presence of cysteine substitutions and FHC mutations. Preliminary IVM data shows a progressive increase in the severity of the functional effects of cysteine substitution and spin labeling across the putative hinge region (153<168<172), suggesting that this region is dynamically important and may be making critical interactions with other components of the sarcomere. Preliminary CW-EPR spectra show an increase in isotropic rotational rate at residue 153 (upstream of the putative hinge region) between cTnT alone and in the troponin ternary complex, suggesting that there is a decrease in alpha helical character at this residue in the ternary complex. Introduction of Δ160E further increases the isotropic rotational rate, suggesting an increase in flexibility due to backbone changes induced by the mutation. To further investigate structural and functional changes caused by FHC mutations within the putative hinge region, we will continue to expand our IVM functional analyses with additional cysteine substitutions, as well as FHC mutations at residues 160 and 163. Double label SDSL-EPR are currently underway that will provide secondary and tertiary structural information.

The Influence of Platinum Surface Morphology on the Electrooxidation of Methanol in Alkaline Solutions

In this work we compare methanol oxidation characteristics in pH 0 and pH 14 electrolytes, and examine the effect of methanol concentration and platinum surface condition (e.g. H-UPD, OH adsorption, Pt oxidation/reduction, planar, nanoporous) on the oxidation current. We observe that in rotating disc electrode (RDE) experiments the oxidation currents on smooth platinum decrease with increasing rotation rate. We show that this decrease is associated with increasing the rate at which oxidation intermediates are swept into the bulk electrolyte before being fully oxidized. To increase the dwell time of intermediates a platinum electrode with 3 nm length scale surface porosity was synthesized by dealloying a Pt-Cu alloy. We then perform the same RDE experiments and show that in this case the methanol oxidation current increases with increasing convection. We attribute this behavior to the trapping of reaction intermediates that otherwise were swept away on the polished sample.

Rotational Hydrodynamic Diffusion System To Study Mass Transport Across Boundaries

The design and operation of a new mass transport technique is presented. Rotational hydrodynamic diffusion system (RHDS) is a method that can be adapted for analytical laboratory analysis as well as industrial-scale separation and purification. Although RHDS is not an electrochemical technique, its concept is derived from hydrodynamic rotating disk electrode voltammetry. A diffusion advantage gained using the RHDS is higher flux of probe molecules across the boundary (e.g., membrane or porous media) with increased rotation rate compared to the static two-half-cell (THC) method. The separation concept of RHDS differs from pressurized, agitated, electrodialysis, and reversed osmosis systems in design and theory. The detection mechanism of the RHDS opens the possibility to study mass transport properties of a large variety of molecules using different types of ultrathin membranes. Therefore, the RHDS is a potential alternative to classical mass transport detection methods such as THC, impedance spectroscopy, and cyclic and rotating disk electrode voltammetry. Theoretical analysis on the rotational hydrodynamic flux is derived and compared to experimental flux measured using HCl, KCl, KNO 3, Ni(NO 3) 2, LiCl, camphor sulfonic acid, and K 3Fe(CN) 6 ionic solutions. Values of effective diffusion coefficients of salts across Nucleopore membranes of thickness 6.0 and 10 mum with pore size 0.1 and 0.2 mum, respectively, are presented and discussed.