E. J. Shaughnessy

Dynamics of electro-wetting droplet transport

A model is formulated to describe the dynamics of electro-wetting-induced transport of liquid droplets. The velocity of droplet transport as a function of actuation voltage is derived. The operating parameters include the viscosity of the droplet and the medium through which it actuates, contact-line friction, system geometry, and surface tension. Numerical coefficients are extracted from experimental data to represent the effect of operating parameters on electro-wetting dynamics. The power dissipation of droplet transport is analyzed which reveals the key limiting factors for device operation as well the effect of scaling on device power requirements. # 2002 Published by Elsevier Science B.V.

TURBULENCE GENERATION BY ELECTRIC BODY FORCES.

The effect of an electric body force on vorticity production and turbulence generation in a gas is investigated by examination of the governing electrohydrodynamic equations. The theoretical concepts are illustrated by hot-film anemometer measurements of the electrically induced turbulence in a large scale electrostatic precipitator. The results indicate dramatic increases in turbulence and diffusivity due to the corona discharge and suggest that turbulence control in this application requires a modification in electrode geometry.

Laser light-scattering measurements of particle concentration in a turbulent jet

A laser light-scattering technique has been used to study the relative particle concentration field in a round turbulent air jet. Measurements were made in the far field of a smoke-marked turbulent jet exhausting into a secondary air stream. Radial distributions of mean particle concentration, concentration fluctuation intensity and intermittency were measured at several streamwise locations. Concentration fluctuation power spectra and the micro- and integral scales of the concentration fluctuations were measured on the jet axis. The effects of ambiguity noise and noise due to optical path attenuation on the performance of the laser light-scattering system are discussed.

Thermoconvective Motion of Low Prandtl Number Fluids Within a Horizontal Cylindrical Annulus

Steady natural convection in very low Prandtl number fluids is investigated using a double perturbation expansion in powers of the Grashof and Prandtl numbers. The fluid is contained in a horizontal cylindrical annulus, the walls of which either are held at constant temperature or support a constant heat flux. In both cases the evolution of the flow for increasing Grashof number is of interest. It is found that the basic flow pattern consists of one eddy. For both boundary conditions the center of this eddy falls into the lower half of the annulus as the Grashof number increases. Such behavior is directly opposite to experimental results obtained in fluids of higher Prandtl number.

The Fluid Mechanics of Electrostatic Precipitators

The role of the electric body force in the generation of secondary flows and turbulence in precipitators is poorly understood at present, despite the fact that these disturbances are thought to be detrimental to precipitator performance. This paper undertakes a fundamental analysis of the problem using the Navier-Stokes and reduced Maxwell equations. It is shown that the rotational component of the current density causes vorticity production in the gas, and is therefore the source of secondary flows and turbulence. When the current density is irrotational, the electric body force causes a change in the pressure distribution but has no effect on the velocity field. Since the current density distribution is determined by the electrode geometry alone, the electrodes should be designed to minimize the rotational component of the current density and thus reduce gas flow disturbances.

Microscale pressure fluctuations in a mature deciduous forest

Static pressure fluctuations in the microscale range were measured in a mature deciduous forest. Pressure measurements were taken at the ground and above the canopy, and mean profile data of windspeed were collected from above the canopy to near the forest floor. Time series, spectra, and cross-correlations were calculated under different canopy conditions, and relationships between surface pressure fluctuations and mean windspeeds were determined. High-frequency pressure fluctuations that occur over aerodynamically smoother surfaces do not occur at the forest floor. These surface fluctuations are advected by the wind above the canopy, not that within the trunk space. The shapes of the pressure spectra are affected by changes in windspeed. Comparisons of spectra above and below the canopy also show some effect of the canopy itself on the shape of the pressure spectra.

A technical problem in the calculation of laminar flow near irregular surfaces described by sampled geometric data

The numerical simulation of fluid flow and transport near biological surfaces must take into account the natural irregularity of these surfaces if the influence of the surface geometry on the near-wall flow field is to be modeled. If the geometric description of a biological surface has a limited resolution, what impact will this have on the accuracy of a computational simulation of the near-wall flow field? It is important to emphasize here that the problem arises from the limited number of data points describing the geometry and not from any limit on the number of mesh points in any subsequent calculation. In this note we show that if every point in a geometric data set describing an axisymmetric model of a diseased coronary artery is taken as a mesh point, then a well converged and otherwise accurately calculated wall shear stress distribution contains a degree of uncertainty which is attributable wholly to the limited resolution of the original geometric model. The approach taken is to repeat the numerical calculation on a reduced resolution version of the original geometric data set, comparing the wall shear stress distribution with that obtained originally. We conclude that accurate computational modeling and simulation of transport processes near irregular biological surfaces will be highly dependent on the availability of well-resolved geometric data describing the surface under study.

Thermal convection in rotating spherical annuli—1. Forced convection

Abstract The steady forced convection of a viscous fluid contained between two concentric spheres which are maintained at different temperatures and rotate about a common axis with different angular velocities is considered. Approximate solutions to the governing equations are obtained in terms of a regular perturbation solution valid for small Reynolds numbers and a modified Galerkin solution for moderate Reynolds numbers. The resulting flow pattern, temperature distribution, and heat-transfer characteristics are presented for the various cases considered. The theoretical heat-transfer results for small and moderate Reynolds number flows within a spherical annulus with a stationary outer sphere are compared with previous experimental results for the large Reynolds number flow situation. The difference between conduction, Stokes flow, and boundary-layer convection is shown.

The deconvolution of Doppler-broadened positron annihilation measurements using fast Fourier transforms and power spectral analysis

Abstract A deconvolution procedure which corrects Doppler-broadened positron annihilation spectra for instrument resolution is described. The method employs fast Fourier transforms, is model independent, and does not require iteration. The mathematical difficulties associated with the incorrectly posed first order Fredholm integral equation are overcome by using power spectral analysis to select a limited number of low frequency Fourier coefficients. The FFT/power spectrum method is then demonstrated for an irradiated high purity single crystal sapphire sample.

Electrohydrodynamic Pressure of the Point-to-Plane Corona Discharge

In this article we discuss the electrohydrodynamics of the point-to-plane discharge, which is geometrically somewhat simpler than the wire-plate electrode arrangement