Daniel De Kee

Transport processes in bubbles, drops and particles

1. Constitutive Moedling of Bubbly Liquids K.R. Rajagopal and L. Tao 2. Analytical Expressions E.E. Michaelides 3. Electrokinetic- and Thermocapillary-Flow-Driven Aggregation of Particles and Bubbles on Surfaces P.J. Slides, J.L. Anderson, H. Kasumi, S.A.Guelcher, and Y.E. Solomentsev 4. Recent Developments in the Bubble Velocity Jump Discontinuity D. Rodrigue and D. DeKee 5. Cavitation and Bubble Dynamics P.R.Williams 6. Foam Darinage, Coasrening and Evaporation S.A.Magrabi and B.Z. Dlugogorski 7. Interphase Mass and Heat Transfer in Gas-Fluidized Beds J.R.Grace 8. Progress in an Industrial Application of Fluidized Beds: Advances in the Sand Coremaking Process S.I.Bakhtiyarov, R.A.Overfelt and D.A. Siginer 9. Sedimentation and Fluidization of Solid Particles in LiquidsR. Di Felice 10. Determination of the Constitutive Relationship for Filer Cakes in Cake Filtration Using the Analogy between Filtration and Diffusion B.V. Ramarao, C. Tien and C.N. Styadev 11.Tracer Dispersion in Fluid Motion through a Porous Medium J.P. du Plessis 12. Flows of Concentrated Granular Mixtures P. Coussot 13. Wall Effects on Spheres Falling Axially in Cylindrical Tubes R.P. Chhabra 14. Steady and Transient Motion of Spherical Liquids G.H. McKinlye 15. Particle Deposition in Membrane Systems V. Chen and D.E. Wiley 16. Rheological Properties of Concentrated Suspensions P.J. Carreau and F. Cotton

A slotted plate device for measuring static yield stress

A slotted-plate device was constructed with a balance and a linear-motion platform to directly measure static yield stresses of suspensions by moving the plate in the suspension in a similar mode as is done in the well-known Wilhelmy-plate technique for measuring surface tension. Wall effects associated with the original plate yield-stress instrument [De Kee et al. (1980)] were minimized by opening a series of slots on the plates. Yield-stress experiments were conducted on both high-concentration (40, 50, 60, and 70 wt % TiO2) and low-concentration (2, 3, and 5 wt % bentonite) aqueous suspensions. The new setup avoids the disadvantages of the vane instrument, possible secondary flow between the blades as well as a nonuniform stress distribution along a virtual cylindrical surface. Yield stress values of TiO2 suspensions were compared with the values obtained via a variety of other methods, including indirect extrapolation from steady-shear data, vane creep testing, and vane stress-ramp measurements using ...

PLA/clay/wood nanocomposites: nanoclay effects on mechanical and thermal properties

Poly(lactic acid) (PLA)/clay/wood nanocomposites were prepared by melt extrusion of PLA, nanoclay, and wood flour (WF). The clay particles exhibit an intercalated structure in the PLA matrix and the addition of WF slightly increases the spacing in the galleries of the intercalated structure. The intercalated clay particles and WF in the PLA matrix restrict the motion of the PLA molecules and crystals. The tensile and flexural moduli of PLA/clay/wood nanocomposites with 30 wt% WF, respectively, increase from 3.75 to 7.08 GPa and from 3.83 to 6.01 GPa compared to neat PLA by adding up to 5 wt% nanoclay. Voids around clay particles, observed via scanning electron microscopy are associated with the negative effect of the clay particles on the interfacial adhesion between the WF and the PLA matrix. Clay particles improve the thermal decomposition temperature (T d) of PLA/clay/wood nanocomposites by about 10°C compared to that of PLA/wood composites. The effects of clay particles on other thermal properties such as glass transition temperature (Tg), melting temperature (Tm), and linear thermal expansion are also discussed in this article.

Bubble velocities : further developments on the jump discontinuity

Abstract The motion of a gas bubble in a non-Newtonian fluid has been further examined in order to determine the conditions for the possible existence of a discontinuity in the bubble velocity-bubble volume log–log plot. It has been proposed in the past that this phenomenon was the result of a sudden change in the hydrodynamics of the moving bubble, resulting in a transition from a Stroke to a Hadamard regime. Furthermore, this abrupt transition was only qualitatively attributed to the elasticity of the fluid. Using our data as well as those of Leal et al., we demonstrate here that the discontinuity results as a balance between elastic and Marangoni instabilities, providing another major difference between Newtonian and non-Newtonian hydrodynamics.

The slow motion of a single gas bubble in a non-Newtonian fluid containing surfactants

Abstract The drag force experienced by bubbles, rising freely in an inelastic shear-thinning fluid is calculated. In particular, the effect of contaminants is considered when the continuous phase can be represented by the power-law or the three parameter Carreau models. Two cases are examined in order to take into account the effect of surfactants: (a) interfacial mass transfer is taken into account via a perturbation around the thermodynamic equilibrium values using Gibbs elasticity, (b) a continuous distribution of impurities over the whole interface (uniform retardation) leading to Marangoni stresses. The relations obtained are based on perturbation methods around the Newtonian solution. The drag force can be evaluated via the rheological model parameters, the physical properties of the system and the concentration of impurities in the fluid. The presence of contamination was found to increase the drag resulting in a decrease of the rise velocity. Inversely, the effect of shear thinning is to decrease the drag, thus leading to a balance between both effects.

Modeling diffusion through geomembranes

A phenomenological model that incorporates swelling is adopted and used to solve the one-dimensional sorption problem. The model predictions are in good agreement with experimental data, involving the transport of dichloromethane, trichloroethylene, and benzene through high-density polyethylene and poly(vinyl chloride ) geomembranes. The theoretical curves predict weight-gain and flux-time profiles, including the case where the flux goes through a maximum.

Network constitutive equation with internal viscosity: application to stress jump prediction

A stress jump, defined as the instantaneous gain or loss of stress on startup or cessation of a deformation, has been predicted by various models and has relatively recently been experimentally observed. In this paper, the internal viscosity idea is incorporated into the transient network model. Via appropriate approximations, we obtain a closed constitutive equation where the total stress equals the sum of an elastic contribution and a viscous contribution. As the latter is rate dependent, the model predicts a stress jump and we consider data on shear flow in this contribution. We successfully compare the model predictions with the stress jump measurements of Liang and Mackay [C.H. Liang, M.E. Mackay, J. Rheol. 37 (1993) 149]. The model yields good quantitative predictions of the steady, transient and dynamic material functions.

Effect of temperature and elongation on the liquid diffusion and permeation characteristics of natural rubber, nitrile rubber, and bromobutyl rubber

The diffusive properties of acetone, dichloromethane, and toluene in natural, nitrile, and bromobutyl rubber membranes at temperatures between 273 and 313 K and uniaxial elongations between 0 and 40% were investigated. As the temperature and elongation increase, the steady state flux increases, and the breakthrough time decreases. An increase in temperature leads to an increase in permeability, and small extensions do not cause significant changes in the diffusive properties.

Influence of external stress on the barrier properties of rubbers

The effect of an external stress on the barrier properties of natural, bromobutyl, and nitrile rubber were studied using a modified ASTM permeation method. Stress-induced changes such as a decrease in the breakthrough time with mechanical elongation was observed. Upon application of a small mechanical deformation, little change was observed in terms of steady-state permeation flux. On the other hand, a stress-enhanced diffusion was observed for most of the solvent/rubber pairs studied.

Thermal Dependence of Young’s Modulus of Wood/Polymer/Clay Nanocomposites

The dependence of Young’s modulus on temperature and clay content of polyethylene/clay nanocomposites (PCN) and wood/polymer/clay nanocomposites (WPCN) is investigated. It is found that the moduli of PCN and WPCN vary linearly with temperature within 25 and 80°C. The addition of nanoclay in the presence of a maleic anhydride grafted polyethylene (MAPE) compatibilizer blend results in an increase of the modulus and strength of the composites. The Young’s moduli of the PCN and WPCN decrease linearly with increase in temperature.