▪ Abstract We review the fluid mechanics and rheology of dense suspensions, emphasizing investigations of microstructure and total stress. “Dense” or “highly concentrated” suspensions are those in which the average particle separation distance is less than the particle radius. For these suspensions, multiple-body interactions as well as two-body lubrication play a significant role and the rheology is non-Newtonian. We include investigations of multimodal suspensions, but not those of suspensions with dominant nonhydrodynamic interactions. We consider results from both physical experiments and computer simulations and explore scaling theories and the development of constitutive equations.

Fluid mechanics and rheology of dense suspensions

Sea salt aerosol (SSA) exerts a major influence over a broad reach of geophysics. It is important to the physics and chemistry of the marine atmosphere and to marine geochemistry and biogeochemistry generally. It affects visibility, remote sensing, atmospheric chemistry, and air quality. Sea salt aerosol particles interact with other atmospheric gaseous and aerosol constituents by acting as sinks for condensable gases and suppressing new particle formation, thus influencing the size distribution of these other aerosols and more broadly influencing the geochemical cycles of substances with which they interact. As the key aerosol constituent over much of Earth's surface at present, and all the more so in pre-industrial times, SSA is central to description of Earth's aerosol burden.

Sea Salt Aerosol Production: Mechanisms, Methods, Measurements, and Models - A Critical Review

▪ Abstract Filament-stretching rheometers are devices for measuring the extensional viscosity of moderately viscous non-Newtonian fluids such as polymer solutions. In these devices, a cylindrical liquid bridge is initially formed between two circular end-plates. The plates are then moved apart in a prescribed manner such that the fluid sample is subjected to a strong extensional deformation. Asymptotic analysis and numerical computation show that the resulting kinematics closely approximate those of an ideal homogeneous uniaxial elongation. The evolution in the tensile stress (measured mechanically) and the molecular conformation (measured optically) can be followed as functions of the rate of stretching and the total strain imposed. The resulting rheological measurements are a sensitive discriminant of molecularly based constitutive equations proposed for complex fluids. The dynamical response of the elongating filament is also coupled to the extensional rheology of the polymeric test fluid, and this can...

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Filament-stretching rheometry of complex fluids

The total stress of a concentrated suspension of noncolloidal spheres in a Newtonian fluid was characterized by independent measurements in viscometric flows. Using a suspension balance formulation, the normal stress in the vorticity direction (Σ33) for a suspension undergoing simple shear was extracted from Acrivos et al.’s [Int. J. Multiphase Flow 19, 797 (1993)] resuspension data in a Couette device. Employing a new correlation for the relative viscosity μr which obeys the Einstein relation in the dilute limit while diverging at random close packing, it was found that Σ33/τ (where τ is the magnitude of the shear stress) was a strong function of the solid volume fraction φ, scaling as φ3e2.34φ. The relative viscosity, measured in a parallel plate viscometer, was in good agreement with the proposed correlation, while the normal stress differences N1 and N2 for concentrated suspensions (φ=0.30–0.55) were characterized using parallel plate and cone-and-plate geometries, as well as laser profilometry measur...

The characterization of the total stress of concentrated suspensions of noncolloidal spheres in Newtonian fluids

Mixing and mass transfer in tall bubble columns

Coalescence of gas bubbles in aqueous solutions of inorganic electrolytes

A new apparatus is presented which allows the determination of the viscosity of suspensions of high density particles in low viscosity media. Results obtained on suspensions of low density particles compare well with those obtained on a Weissenberg Rheogoniometer equipped with a cone-and-plate and a bob-and-cup. Also, a very interesting observation is that the Eilers equation, conveniently modified to take into account the shape of the particles by means of the intrinsic viscosity, can well correlate all the data.

Shear viscosity of settling suspensions

Extensional flow behaviour of polymer solutions

Drag reduction data for five concentrations of a water-soluble polymer and three tube diameters are presented. The data are correlated by a single curve relating two dimensionless parameters; these have been obtained from a phenomenological analysis of the mechanism of drag reduction.

Luigi Nicodemo

Papers

Coalescence of gas bubbles in aqueous solutions of inorganic electrolytes

Shear viscosity of settling suspensions

Extensional flow behaviour of polymer solutions

A phenomenological interpretation and correlation of drag reduction

Velocity distributions and normal stresses in viscoelastic turbulent pipe flow