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PJ Stiles

Publications and source records attributed to PJ Stiles.

13 recordsLinked to original sources
PubMed1999

Convective Sedimentation of Colloidal Particles in a Bowl.

A physical model, which regards a colloidal dispersion as a single fluid continuum, is used to investigate cellular convection accompanying gravitational sedimentation in a hemispherical bowl with a thin cylindrical shaft along its vertical axis of symmetry. We have adapted the stream-function-vorticity form of the Navier-Stokes equations to describe momentum conservation in axially symmetric containers. These hydrodynamic equations have been coupled to the mass balance equation for binary hydrodynamic diffusion in the presence of a vertical gravitational field. Using finite-element software we have solved the equations governing coupled diffusive and hydrodynamic flow. A rapidly intensifying horizontal toroidal vortex develops around the axis of the bowl. This vortex is characterized by downward barycentric flow along the curved surface of the bowl and upward flow in the vicinity of its axis. We find that after a short period of time this large-scale cellular convection associated with the curved boundary of the bowl greatly enhances the rate of sedimentation. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Spontaneous Thermal Convection in the Vicinity of Electrolyte/Water Interfaces.

We present theoretical evidence for transient roll-cell convection induced in the vicinity of freshly prepared electrolyte/water interfaces. The mechanism relies on a hitherto unrecognized type of double-diffusive convection. Electrolyte diffusion down the strong concentration gradient at the interface produces local heating just below the interface as the electrolyte becomes more dilute. If the concentration gradient at the interface is sufficiently large, temperature gradients on the order of one Kelvin per centimeter can be induced by this mechanism. We assume the horizontal electrolyte/water interface is contained in a long prism with a square vertical cross section and that the electrolyte solution is denser than the supernatant water layer. Provided that the sidewalls of the prism are thermally conducting, convection commences at the junction of the interface (at half the height of the square section) and these walls. In each vertical semi-cross-section, two roll cells evolve at the interface and the lower cell rapidly gains intensity at the expense of the counter-rotating upper cell. After a short period of time the lower cell migrates diagonally downward to lie just beneath the interface and the associated region of local heating. Although the fluid velocities associated with this roll cell initially increase with time, they do not appear to be sufficiently strong to distort the vertical stratification of the electrolyte's concentration profile. In a cylindrical annulus standing on its circular base the dominant roll cell takes the form of a toroidal vortex resembling a Taylor vortex. Copyright 1999 Academic Press.

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