Rotating-drum experiments for particle-laden flows: a new view

Shear in the annular space between drums is a well-known model for particle-laden flows. When this technique was introduced by Bagnold, it was assumed that the shear rate and particle concentration were uniform within the annular space. It is now known that this is not generally the case, in part because the distribution of particles in the annulus is influenced by hydrodynamic lift, which is discussed in the paper. The shear stress attributable to solids is also found to be influenced by different boundary conditions, and all these factors affect the usefulness of drum experiments for predicting other flow configurations.The author is happy to have the opportunity to thank M.Sc student Yan Su and summer students Susan Pfister, Anna-Marie Psaila and Alice Blair for their hard work in the experimental program that led to this paper. Acknowledgement is also due to the National Science and Engineering Research Council of Canada for financial support.     

Geophysical granular and particle-laden flows: review of the field

An introduction is given to the title theme, in general, and the specific topics treated in detail in the articles of this theme issue of the Philosophical Transactions. They fit into the following broader subjects: (i) dense, dry and wet granular flows as avalanche and debris flow events, (ii) air-borne particle-laden turbulent flows in air over a granular base as exemplified in gravity currents, aeolian transport of sand, dust and snow and (iii) transport of a granular mass on a two-dimensional surface in ripple formations of estuaries and rivers and the motion of sea ice.     

Hyperbolic systems of conservation laws in gravity-driven,particle-laden thin-film flows

Our study focuses on gravity-driven, particle-laden flows that are pertinent to a wide range of industrial and geophysical settings in which transport of suspensions occurs. In the present study we employ a previously derived model by Murisic et al. (Physica D, 240, 2011) that uses the lubrication approximation to describe particle-laden films on an incline. The model consists of a coupled system of hyperbolic conservation laws for the interface position and the particle concentration. While it has been shown that the model compares well quantitatively with experiments, it lacks analysis. The objectives of this paper focus on the study of the Riemann problem for this system of conservation laws and how the results relate to experiments. We investigate the governing system analytically and numerically; the equations exhibit rich mathematical structures, including double-shock wave solutions, rarefaction waves, and singular shocks.     

Micro-mechanical analysis and modelling of granular materials loaded at constant volume

The present paper is devoted to the analysis and the modelling of the local phenomena, which are observed in a two-dimensional granular media loaded at constant volume. A micro-mechanical approach is followed here combined with a computer simulation method. Local phenomena observed during test are used to provide some necessary elements to build realistic models. The importance of the induced anisotropy during the test is especially shown, as well as its necessary link to the dilatancy. To illustrate the study a model based on a micro-mechanical approach is validated.     

Shear-thinning and constant viscosity predictions for rotating sphere flows

The steady motion of a rotating sphere is analysed through two contrasting viscoelastic models, a constant viscosity (FENE-CR) model and a shear-thinning (LPTT) model. Giesekus (Rheol. Acta 9:30–38, 1970) presented an intriguing rotating viscoelastic flow, which to date has not been completely explained. In order to investigate this flow, sets of parameters have been explored to analyse the significant differences introduced with the proposed models, while the momentum-continuity-stress equations are solved through a hybrid finite-element/finite volume numerical scheme. Solutions are discussed for first, sphere angular velocity increase (\(\varOmega\)), and second, through material velocity-scale increase (\(\alpha\)). Numerical predictions for different solvent-ratios (\(\beta\)) show significant differences as the sphere angular velocity increases. It is demonstrated that an emerging equatorial anticlockwise vortex emerges in a specific range of \(\varOmega\). As such, this solution matches closely with the Giesekus experimental findings. Additionally, inside the emerging inertial vortex, a contrasting positive second normal stress-difference (\(N_{2} ( \dot{\gamma} ) = \tau_{rr} - \tau_{\theta\theta}\)) region is found compared against the negative \(N_{2}\)-enveloping layer.     

Molar heat capacity at constant volume for air from 67 to 300 K at pressures to 35 MPa

Measurements of the molar heat capacity at constant volumeC _v for air were conducted with an adiabatic calorimeter. Temperatures ranged from 67 to 300 K, and pressures ranged up to 35 MPa. Measurements were conducted at 17 densities which ranged from gas to highly compressed liquid states. In total, 227C _v values were obtained. The air sample was prepared gravimetrically from research purity gases resulting in a mole fraction composition of 0.78112 N₂ + 0.20966 O₂ + 0.00922 Ar. The primary sources of uncertainty are the estimated temperature rise and the estimated quantity of substance in the calorimeter. Overall, the uncertainty (± 2) of theC _v values is estimated to be less than ± 2% for the gas and ±0.5% for the liquid.Nomenclature C _v Molar heat capacity at constant volume, J · mol^–1 K^–1 - C _v ⁰ Molar heat capacity in the ideal-gas state, J · mol^–1 · K^–1 - V _bomb Volume of the calorimeter containing sample, cm³ - P Pressure, MPa - P Pressure rise during a heating interval, MPa - T Temperature, K - T ₁,T ₂ Temperature at start and end of heating interval, K - T Temperature rise during a heating interval, K - Q Calorimetric heat energy input to bomb and sample, J - Q ₀ Calorimetric heat energy input to empty bomb, J - N Moles of substance in the calorimeter, mol - Fluid density, mol · dm^–3     

定容法测量小孔流导的方法研究

规则小孔的流导可以通过计算得到，但对于非规则小孔，若要准确得到小孔流导的大小，就必须通过实验测量得到。文章论述了定容法测量小孔流导的方法，进行了测量不确定度的评定，得到了整个校准范围内小孔流导随进气压力变化的拟合曲线和方程，小孔流导的测量不确定度为1．1％。     

Corrections to facilitate planar imaging of particle concentration in particle-laden flows using Mie scattering. Part 2: diverging laser sheets

Part 1 describes a model to account for the effect of particles on laser sheet attenuation in flows where particles are heterogeneously distributed and where particles are small compared with the imaged volume. Here we extend the model to account for the effect of a strongly diverging light sheet, which is desirable when investigating many turbulent flows, e.g., in two-phase combustion problems. A calibration constant, C(kappa), is derived to account for the attenuation of the incident laser sheet due to extinction of the laser beam through a seeded medium. This is shown to be effective in correcting both the effect of in-plane laser sheet attenuation and out-of-plane signal trapping due to particles in a jet flow heavily seeded with 5 g/s of 25-40 microm spherical particles. In the uncorrected case, attenuation causes up to 15% error in the mean concentration and 35% error on the rms fluctuations. Selecting an appropriate C(kappa) was found to remove the error in the mean concentration and reduce error on the rms fluctuation by half. Methods to estimate or measure an appropriate value of C(kappa) are also presented.     

Corrections to facilitate planar imaging of particle concentration in particle-laden flows using Mie scattering, part 1: collimated laser sheets

Planar nephelometry is a laser-based technique of imaging the light scattered from particles to provide information about the local number density of these particles. In many seeded flows of practical interest, such as pulverized coal flames, particle loadings are sufficiently high for the incident laser beam to be severely attenuated. Measurements in these flows are therefore difficult, and limited data are available under these conditions. Laser attenuation experiments were conducted in suspensions of spherical particles in water at various concentrations. This is used to formulate a calibration for the effects of diffuse scattering and laser sheet extinction. A model for the distribution of light through a heavily seeded, light-scattering medium is also developed and is compared with experimental results. It is demonstrated that the scattered signal may be considered proportional to the local particle concentration multiplied by the incident laser power. The incident laser power varies as a function of the attenuation by obscurement. This correction for planar nephelometry images thus extends the technique to provide pseudoquantitative data for instantaneous particle concentration measurements.     

Corrosion cracking of metals at constant stress and constant strain rate

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 1, pp. 31–38, January–February, 1989.     

Thermodynamic model of creep at constant stress and constant strain rate

A thermodynamic model has been developed that describes the entire creep process, including primary, secondary, and tertiary creep, and failure for both constant stress (CS) tests ($\text{σ =}\text{const.}$) and constant strain rate (CSR) tests ($\text{? =}\text{const.}$), in the form of a unified constitutive equation and unified failure criteria. Deformation and failure are considered as a single thermoactivated process in which the dominant role belongs to the change of entropy. Failure occurs when the entropy change is zero. At that moment, the strain rates in CS tests reach the minima and stress in CSR tests reaches the maximum (peak) values. Families of creep (? vs t) and stress-strain (σ vs ?) curves, obtained from uniaxial compression CS and CSR tests of frozen soil, respectively (both presented in dimensionless coordinates), are plotted as straight lines and are superposed, confirming the unity of the deformation and failure process and the validity of the model. A method is developed for determining the parameters of the model, so that creep deformation and the stress-strain relationship of ductile materials such as soils can be predicted based upon information obtained from either type of test.     

Self-similarity of the Crack Front in Stress Corrosion Fracture

In this letter, a new method was proposed to visualize the crack front in stress corrosion fracture of high strength steel. The fractal characteristic of the crack front was analyzed by measuring its fractal dimension and roughness exponent at the same time. The experimental results show that the irregularity of the crack front was partly self-affine.     

Change of state as a bubble rises in a liquid of constant volume

Summary A liquid-filled container of constant volume is considered. A bubble of a perfect gas is allowed to rise from the bottom of the container to the top. Based on common assumptions, i.e. neglecting temperature changes and considering the liquid as incompressible, one obtains the unlikely result that, irrespective of the bubble’s size, the pressure in the bubble remains unchanged, while the pressure in the liquid increases by an amount equal to the hydrostatic pressure difference between the bottom and the top of the container. To resolve this paradox, the change of state of the thermodynamic system, consisting of a slightly compressible liquid, a bubble of a perfect gas, and the interface between them is determined on the basis of the energy balance. Solutions for the changes of pressure, temperature and bubble volume are given in closed form. Estimates of the orders of magnitude of non-dimensional parameters lead to conditions for neglecting surface tension and/or the temperature change of the liquid. Results of general nature, as well as for the particular case of an air bubble in water, are shown in diagrams, and several limiting cases, including the limiting case of constant pressure in the bubble, are discussed. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday     

定容压差式泄漏检测机的使用和校准

采用已校准的标准漏孔调校泄漏检测机时，由于所在地区处于不同的海拔高度造成在不同大气压的情况下使用，使不同地区的检测结果有较大的差异，给检测结果合格与否的判定带来一定困难。本文通过分析提出了一种补偿计算方法，可使泄漏检测机作为检定装置使用时的状态与被校准时所处的状态达到统一，有效提高了检测的准确率。     

Temperature distribution in laminar flows at large shear stresses

The energy equation is solved for the case of laminar flow of a compressible Newtonian liquid with allowance for heat of friction. Theoretical temperature profiles are presented for flow in channels with constant and linearly varying capillary wall temperatures. The theoretical values of the mean temperature are in good agreement with the experimental results.     

Low-friction flows of liquid at nanopatterned interfaces

With the important development of microfluidic systems, miniaturization of flow devices has become a real challenge. Microchannels, however, are characterized by a large surface-to-volume ratio, so that surface properties strongly affect flow resistance in submicrometre devices. We present here results showing that the concerted effect of wetting properties and surface roughness may considerably reduce friction of the fluid past the boundaries. The slippage of the fluid at the channel boundaries is shown to be greatly increased by using surfaces that are patterned on the nanometre scale. This effect occurs in the regime where the surface pattern is partially dewetted, in the spirit of the 'superhydrophobic' effects that have been discovered at macroscopic scales. Our results show for the first time that, in contrast to common belief, surface friction may be reduced by surface roughness. They also open the possibility of a controlled realization of the 'nanobubbles' that have long been suspected to play a role in interfacial slippage.