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## Full-Text Articles in Mechanical Engineering

The Effect Of Streamwise Vortices On The Frost Growth Rate In Developing Laminar Channel Flows, Brian Storey, Anthony Jacobi

#### The Effect Of Streamwise Vortices On The Frost Growth Rate In Developing Laminar Channel Flows, Brian Storey, Anthony Jacobi

*Brian Storey*

An experimental study is presented to assess the influence of streamwise vortices on frost growth in a steady, developing, laminar channel flow. Using a simple model and scale analysis, frost growth rate (ablimation) data are normalized with respect to temperature, humidity and time. Measurements from baseline experiments in a rectangular channel are found to be accurately correlated using the proposed scaling relation. Upon introducing streamwise vortices in the channel flow, frost growth still follows the scaling relation, but local growth rates were observed to increase by more than 7% in regions where the streamwise vortices induce a surface-normal flow toward ...

Electrohydrodynamic Instabilities In Microchannels With Time Periodic Forcing, David Boy, Brian D. Storey

#### Electrohydrodynamic Instabilities In Microchannels With Time Periodic Forcing, David Boy, Brian D. Storey

*Brian Storey*

In microfluidic applications it has been observed that flows with spatial gradients in electrical conductivity are unstable under the application of sufficiently strong electric fields. These electrohydrodynamic instabilities can drive a nonlinear flow despite the low Reynolds number. Such flows hold promise as a simple mechanism for mixing fluids. In this work, the effect of a time periodic electric field on the instability is explored. The case where an electric field is applied across a diffuse interface of two fluids with varying electrical conductivity is considered. Frequency-dependent behavior is found only in the regime where the instability growth rates are ...

Electrokinetic Instabilities In Thin Microchannels, Brian D. Storey, Burt S. Tilley, Hao Lin, Juan G. Santiago

#### Electrokinetic Instabilities In Thin Microchannels, Brian D. Storey, Burt S. Tilley, Hao Lin, Juan G. Santiago

*Brian Storey*

An important class of electrokinetic, microfluidic devices aims to pump and control electrolyte working liquids that have spatial gradients in conductivity. These high-gradient flows can become unstable under the application of a sufficiently strong electric field. In many of these designs, flow channels are thin in the direction orthogonal to the main flow and the conductivity gradient. Viscous stresses due to the presence of these walls introduce a stabilizing force that plays a major role in determining the overall instability. A thin channel model for fluid flow is developed and shown to provide good agreement with a complete three-dimensional model ...

Bistability In A Simple Fluid Network Due To Viscosity Contrast, John Geddes, Brian Storey, David Gardner, Russell Carr

#### Bistability In A Simple Fluid Network Due To Viscosity Contrast, John Geddes, Brian Storey, David Gardner, Russell Carr

*Brian Storey*

We study the existence of multiple equilibrium states in a simple fluid network using Newtonian fluids and laminar flow. We demonstrate theoretically the presence of hysteresis and bistability, and we confirm these predictions in an experiment using two miscible fluids of different viscosity—sucrose solution and water. Possible applications include blood flow, microfluidics, and other network flows governed by similar principles.

A Depth-Averaged Electrokinetic Flow Model For Shallow Microchannels, Hao Lin, Brian D. Storey, Juan G. Santiago

#### A Depth-Averaged Electrokinetic Flow Model For Shallow Microchannels, Hao Lin, Brian D. Storey, Juan G. Santiago

*Brian Storey*

Electrokinetic flows with heterogeneous conductivity configuration occur widely in microfluidic applications such as sample stacking and multidimensional assays. Electromechanical coupling in these flows may lead to complex flow phenomena, such as sample dispersion due to electro-osmotic velocity mismatch, and electrokinetic instability (EKI). In this work we develop a generalized electrokinetic model suitable for the study of microchannel flows with conductivity gradients and shallow-channel geometry. An asymptotic analysis is performed with the channel depth-to-width ratio as a smallness parameter, and the three-dimensional equations are reduced to a set of depth-averaged equations governing in-plane flow dynamics. The momentum equation uses a Darcy ...

Instability Of Electro-Osmotic Channel Flow With Streamwise Conductivity Gradients, Jose Santos, Brian D. Storey

#### Instability Of Electro-Osmotic Channel Flow With Streamwise Conductivity Gradients, Jose Santos, Brian D. Storey

*Brian Storey*

This work considers the stability of an electro-osmotic microchannel flow with streamwise electrical conductivity gradients, a configuration common in microfluidic applications such as field amplified sample stacking. Previous work on such flows has focused on how streamwise conductivity gradients set a nonuniform electro-osmotic velocity which results in dispersion of the conductivity field. However, it has been known for many years that electric fields can couple with conductivity gradients to generate unstable flows. This work demonstrates that at high electric fields such an electrohydrodynamic instability arises in this configuration and the basic mechanisms are explored through numerical simulations. The instability is ...

Argon Rectification And The Cause Of Light Emission In Single-Bubble Sonoluminescence, Brian D. Storey, Andrew J. Szeri

#### Argon Rectification And The Cause Of Light Emission In Single-Bubble Sonoluminescence, Brian D. Storey, Andrew J. Szeri

*Brian Storey*

In single-bubble sonoluminescence, repeated brief flashes of light are produced in a gas bubble strongly driven by a periodic acoustic field. A startling hypothesis has been made by Lohse and co-workers [Phys. Rev. Lett. 78, 1359 (1997)] that the non-noble gases in an air bubble undergo chemical reaction into soluble products, leaving only argon. In the present work, this dissociation hypothesis is supported by simulations, although the associated temperatures of about 7000 K seem too low for bremsstrahlung, which has been proposed as the dominant light emission mechanism. This suggests that emission from water vapor and its reaction products, heretofore ...

Steric Effects On Ac Electro-Osmosis In Dilute Electrolytes, Brian D. Storey, Lee Edwards, Mustafa Sabri Kilic, Martin Z. Bazant

#### Steric Effects On Ac Electro-Osmosis In Dilute Electrolytes, Brian D. Storey, Lee Edwards, Mustafa Sabri Kilic, Martin Z. Bazant

*Brian Storey*

The current theory of alternating-current electro-osmosis (ACEO) is unable to explain the experimentally observed flow reversal of planar ACEO pumps at high frequency (above the peak, typically 10–100 kHz), low salt concentration (1–1000 μM), and moderate voltage (2–6 V), even taking into account Faradaic surface reactions, nonlinear double-layer capacitance, and bulk electrothermal flows. We attribute this failure to the breakdown of the classical Poisson-Boltzmann model of the diffuse double layer, which assumes a dilute solution of pointlike ions. In spite of low bulk salt concentration, the large voltage induced across the double layer leads to crowding of ...

Inertially Driven Inhomogeneities In Violently Collapsing Bubbles: The Validity Of The Rayleigh-Plesset Equation, Hao Lin, Brian D. Storey, Andrew J. Szeri

#### Inertially Driven Inhomogeneities In Violently Collapsing Bubbles: The Validity Of The Rayleigh-Plesset Equation, Hao Lin, Brian D. Storey, Andrew J. Szeri

*Brian Storey*

When a bubble collapses mildly the interior pressure field is spatially uniform; this is an assumption often made to close the Rayleigh-Plesset equation of bubble dynamics. The present work is a study of the self-consistency of this assumption, particularly in the case of violent collapses. To begin, an approximation is developed for a spatially non-uniform pressure field, which in a violent collapse is inertially driven. Comparisons of this approximation show good agreement with direct numerical solutions of the compressible Navier-Stokes equations with heat and mass transfer. With knowledge of the departures from pressure uniformity in strongly forced bubbles, one is ...

Rayleigh-Taylor Instability Of Violently Collapsing Bubbles, Hao Lin, Brian D. Storey, Andrew J. Szeri

#### Rayleigh-Taylor Instability Of Violently Collapsing Bubbles, Hao Lin, Brian D. Storey, Andrew J. Szeri

*Brian Storey*

In a classical paper Plesset has determined conditions under which a bubble changing in volume maintains a spherical shape. The stability analysis was further developed by Prosperetti to include the effects of liquid viscosity on the evolving shape modes. In the present work the theory is further modified to include the changing density of the bubble contents. The latter is found to be important in violent collapses where the densities of the gas and vapor within a bubble may approach densities of the liquid outside. This exerts a stabilizing influence on the Rayleigh–Taylor mechanism of shape instability of spherical ...

Shape Stability Of Sonoluminescence Bubbles: Comparison Of Theory To Experiments, Brian Storey

#### Shape Stability Of Sonoluminescence Bubbles: Comparison Of Theory To Experiments, Brian Storey

*Brian Storey*

Single bubble sonoluminescence (SBSL) is the brief flash of light emitted from a single, stable, acoustically forced bubble. In experiments, the maximum pressure amplitude with which a bubble may be forced is limited by considerations of spherical stability. The traditional linear stability analysis predicts a threshold for SBSL at a much lower pressure amplitude than experimental observations. This work shows that if one constructs an accurate model of the radial dynamics, the traditional linear stability analysis predicts a boundary that is in excellent agreement with experimental data.

Bulk Electroconvective Instability At High Péclet Numbers, Brian D. Storey, Boris Zaltzman, Isaak Rubinstein

#### Bulk Electroconvective Instability At High Péclet Numbers, Brian D. Storey, Boris Zaltzman, Isaak Rubinstein

*Brian Storey*

Bulk electroconvection pertains to flow induced by the action of a mean electric field upon the residual space charge in the macroscopic regions of a locally quasielectroneutral strong electrolyte. For a long time, controversy has existed in the literature as to whether quiescent electric conduction from such an electrolyte into a uniform charge-selective solid, such as a metal electrode or ion exchange membrane, is stable with respect to bulk electroconvection. While it was recently claimed that bulk electroconvective instability could not occur, this claim pertained to an aqueous, low-molecular-weight electrolyte characterized by an order-unity electroconvection Péclet number. In this paper ...

Field-Amplified Sample Stacking And Focusing In Nanofluidic Channels, Jess M. Sustarich, Brian D. Storey, Sumita Pennathur

#### Field-Amplified Sample Stacking And Focusing In Nanofluidic Channels, Jess M. Sustarich, Brian D. Storey, Sumita Pennathur

*Brian Storey*

Nanofluidic technology is gaining popularity for bioanalytical applications due to advances in both nanofabrication and design. One major obstacle in the widespread adoption of such technology for bioanalytical systems is efficient detection of samples due to the inherently low analyte concentrations present in such systems. This problem is exacerbated by the push for electronic detection, which requires an even higher sensor-local sample concentration than optical detection. This paper explores one of the most common preconcentration techniques, field-amplified sample stacking, in nanofluidic systems in efforts to alleviate this obstacle. Holding the ratio of background electrolyte concentrations constant, the parameters of channel ...

Argon Rectification And The Cause Of Light Emission In Single-Bubble Sonoluminescence, Brian D. Storey, Andrew J. Szeri

*Brian Storey*

In single-bubble sonoluminescence, repeated brief flashes of light are produced in a gas bubble strongly driven by a periodic acoustic field. A startling hypothesis has been made by Lohse and co-workers [Phys. Rev. Lett. 78, 1359 (1997)] that the non-noble gases in an air bubble undergo chemical reaction into soluble products, leaving only argon. In the present work, this dissociation hypothesis is supported by simulations, although the associated temperatures of about 7000 K seem too low for bremsstrahlung, which has been proposed as the dominant light emission mechanism. This suggests that emission from water vapor and its reaction products, heretofore ...

Shape Stability Of Sonoluminescence Bubbles: Comparison Of Theory To Experiments, Brian D. Storey

#### Shape Stability Of Sonoluminescence Bubbles: Comparison Of Theory To Experiments, Brian D. Storey

*Brian Storey*

Single bubble sonoluminescence (SBSL) is the brief flash of light emitted from a single, stable, acoustically forced bubble. In experiments, the maximum pressure amplitude with which a bubble may be forced is limited by considerations of spherical stability. The traditional linear stability analysis predicts a threshold for SBSL at a much lower pressure amplitude than experimental observations. This work shows that if one constructs an accurate model of the radial dynamics, the traditional linear stability analysis predicts a boundary that is in excellent agreement with experimental data.

Field-Amplified Sample Stacking And Focusing In Nanofluidic Channels, Jess M. Sustarich, Brian D. Storey, Sumita Pennathur

*Brian Storey*

Nanofluidic technology is gaining popularity for bioanalytical applications due to advances in both nanofabrication and design. One major obstacle in the widespread adoption of such technology for bioanalytical systems is efficient detection of samples due to the inherently low analyte concentrations present in such systems. This problem is exacerbated by the push for electronic detection, which requires an even higher sensor-local sample concentration than optical detection. This paper explores one of the most common preconcentration techniques, field-amplified sample stacking, in nanofluidic systems in efforts to alleviate this obstacle. Holding the ratio of background electrolyte concentrations constant, the parameters of channel ...

Instability Of Electrokinetic Microchannel Flows With Conductivity Gradients, Hao Lin, Brian D. Storey, Michael H. Oddy, Chuan-Hua Chen, Juan G. Santiago

#### Instability Of Electrokinetic Microchannel Flows With Conductivity Gradients, Hao Lin, Brian D. Storey, Michael H. Oddy, Chuan-Hua Chen, Juan G. Santiago

*Brian Storey*

Electrokinetic flow is leveraged in a variety of applications, and is a key enabler of on-chip electrophoresis systems. An important sub-class of electrokinetic devices aim to pump and control electrolyte working liquids with spatial gradients in conductivity. These high-gradient flows can become unstable under the application of a sufficiently strong electric field. In this work the instability physics is explored using theoretical and numerical analyses, as well as experimental observations. The flow in a long, rectangular-cross-section channel is considered. A conductivity gradient is assumed to be orthogonal to the main flow direction, and an electric field is applied in the ...

Radial Response Of Individual Bubbles Subjected To Shock Wave Lithotripsy Pulses In Vitro, Thomas J. Matula, Paul R. Hilmo, Brian D. Storey, Andrew J. Szeri

#### Radial Response Of Individual Bubbles Subjected To Shock Wave Lithotripsy Pulses In Vitro, Thomas J. Matula, Paul R. Hilmo, Brian D. Storey, Andrew J. Szeri

*Brian Storey*

Direct measurements of individual bubble oscillations in lithotripsy fields have been performed using light-scattering techniques. Studies were performed with bubble clouds in gassy water as well as single levitated bubbles in degassed water. There is direct evidence that the bubble survives the inertial collapse, rebounding several times before breaking up. Bubble dynamics calculations agree well with the observations, provided that vapor trapping (a reduction in condensation during bubble collapse) is included. Furthermore, the afterbounces are dominated by vapor diffusion, not gas diffusion. Vapor trapping is important in limiting the collapse strength of bubbles, and in sonochemical activity. © 2010 American Institute ...

Heat And Mass Transfer During The Violent Collapse Of Nonshperical Bubbles, Andrew Szeri, Brian Storey, Antony Pearson, John Blake

#### Heat And Mass Transfer During The Violent Collapse Of Nonshperical Bubbles, Andrew Szeri, Brian Storey, Antony Pearson, John Blake

*Brian Storey*

The very high speed of collapse of cavitation bubbles is responsible for a number of phenomena of interest in science and engineering: Luminescence, sonochemistry, cavitation damage, ultrasonic cleaning, etc. Strongly forced bubbles may collapse with such violence that the relatively slow processes of diffusion of the heat of compression and of excess vapor to the bubble wall are obviated. This leads to an approximately adiabatic system with nearly constant mass during the final stages of extreme collapses, accompanied by the evolution of sharp thermal and compositional boundary layers on either side of the interface. It is shown that the boundary ...

Rayleigh-Taylor Instability Of Violently Collapsing Bubbles, Hao Lin, Brian D. Storey, Andrew J. Szeri

*Brian Storey*

In a classical paper Plesset has determined conditions under which a bubble changing in volume maintains a spherical shape. The stability analysis was further developed by Prosperetti to include the effects of liquid viscosity on the evolving shape modes. In the present work the theory is further modified to include the changing density of the bubble contents. The latter is found to be important in violent collapses where the densities of the gas and vapor within a bubble may approach densities of the liquid outside. This exerts a stabilizing influence on the Rayleigh–Taylor mechanism of shape instability of spherical ...

Electrohydrodynamic Instabilities In Microchannels With Time Periodic Forcing, David A. Boy, Brian D. Storey

#### Electrohydrodynamic Instabilities In Microchannels With Time Periodic Forcing, David A. Boy, Brian D. Storey

*Brian Storey*

In microfluidic applications it has been observed that flows with spatial gradients in electrical conductivity are unstable under the application of sufficiently strong electric fields. These electrohydrodynamic instabilities can drive a nonlinear flow despite the low Reynolds number. Such flows hold promise as a simple mechanism for mixing fluids. In this work, the effect of a time periodic electric field on the instability is explored. The case where an electric field is applied across a diffuse interface of two fluids with varying electrical conductivity is considered. Frequency-dependent behavior is found only in the regime where the instability growth rates are ...

Bistability In A Simple Fluid Network Due To Viscosity Contrast, John B. Geddes, Brian D. Storey, David Gardner, Russell T. Carr

#### Bistability In A Simple Fluid Network Due To Viscosity Contrast, John B. Geddes, Brian D. Storey, David Gardner, Russell T. Carr

*Brian Storey*

We study the existence of multiple equilibrium states in a simple fluid network using Newtonian fluids and laminar flow. We demonstrate theoretically the presence of hysteresis and bistability, and we confirm these predictions in an experiment using two miscible fluids of different viscosity—sucrose solution and water. Possible applications include blood flow, microfluidics, and other network flows governed by similar principles.

Bulk Electroconvective Instability At High Péclet Numbers, Brian D. Storey, Boris Zaltzman, Isaak Rubinstein

*Brian Storey*

Bulk electroconvection pertains to flow induced by the action of a mean electric field upon the residual space charge in the macroscopic regions of a locally quasielectroneutral strong electrolyte. For a long time, controversy has existed in the literature as to whether quiescent electric conduction from such an electrolyte into a uniform charge-selective solid, such as a metal electrode or ion exchange membrane, is stable with respect to bulk electroconvection. While it was recently claimed that bulk electroconvective instability could not occur, this claim pertained to an aqueous, low-molecular-weight electrolyte characterized by an order-unity electroconvection Péclet number. In this paper ...

Instability Of Electro-Osmotic Channel Flow With Streamwise Conductivity Gradients, J. Jobim Santos, Brian D. Storey

#### Instability Of Electro-Osmotic Channel Flow With Streamwise Conductivity Gradients, J. Jobim Santos, Brian D. Storey

*Brian Storey*

This work considers the stability of an electro-osmotic microchannel flow with streamwise electrical conductivity gradients, a configuration common in microfluidic applications such as field amplified sample stacking. Previous work on such flows has focused on how streamwise conductivity gradients set a nonuniform electro-osmotic velocity which results in dispersion of the conductivity field. However, it has been known for many years that electric fields can couple with conductivity gradients to generate unstable flows. This work demonstrates that at high electric fields such an electrohydrodynamic instability arises in this configuration and the basic mechanisms are explored through numerical simulations. The instability is ...

Steric Effects On Ac Electro-Osmosis In Dilute Electrolytes, Brian D. Storey, Lee R. Edwards, Mustafa Sabri Kilic, Martin Z. Bazant

#### Steric Effects On Ac Electro-Osmosis In Dilute Electrolytes, Brian D. Storey, Lee R. Edwards, Mustafa Sabri Kilic, Martin Z. Bazant

*Brian Storey*

The current theory of alternating-current electro-osmosis (ACEO) is unable to explain the experimentally observed flow reversal of planar ACEO pumps at high frequency (above the peak, typically 10–100 kHz), low salt concentration (1–1000 μM), and moderate voltage (2–6 V), even taking into account Faradaic surface reactions, nonlinear double-layer capacitance, and bulk electrothermal flows. We attribute this failure to the breakdown of the classical Poisson-Boltzmann model of the diffuse double layer, which assumes a dilute solution of pointlike ions. In spite of low bulk salt concentration, the large voltage induced across the double layer leads to crowding of ...

A Depth-Averaged Electrokinetic Flow Model For Shallow Microchannels, Hao Lin, Brian D. Storey, Juan G. Santiago

*Brian Storey*

Electrokinetic flows with heterogeneous conductivity configuration occur widely in microfluidic applications such as sample stacking and multidimensional assays. Electromechanical coupling in these flows may lead to complex flow phenomena, such as sample dispersion due to electro-osmotic velocity mismatch, and electrokinetic instability (EKI). In this work we develop a generalized electrokinetic model suitable for the study of microchannel flows with conductivity gradients and shallow-channel geometry. An asymptotic analysis is performed with the channel depth-to-width ratio as a smallness parameter, and the three-dimensional equations are reduced to a set of depth-averaged equations governing in-plane flow dynamics. The momentum equation uses a Darcy ...