Single-bubble water boiling on small heater under Earth's and low gravity
NPJ microgravity, 2018
Today's trends for enhancing boiling heat transfer in terrestrial and space applications focu... more Today's trends for enhancing boiling heat transfer in terrestrial and space applications focus on removal of bubbles to prevent formation of a vapor layer over the surface at high overheat. In contrast, this paper presents a new boiling regime that employs a vapor-air bubble residing on a small heater for minutes and driving cold water over the surface to provide high heat flux. Single-bubble boiling of water was investigated under normal gravity and low gravity in parabolic flights. Experiments demonstrated a negligible effect of gravity level on the rate of heat transfer from the heater. Due to self-adjustment of the bubble size, the heat flux provided by boiling rose linearly up with increasing heater temperature and was not affected by a gradually rising water temperature. The fast response and stable operation of single-bubble boiling over a broad range of temperatures pave the way for development of new devices to control heat transfer by forming surface domains with disti...
TRANSDUCERS '03. 12th International Conference on Solid-State Sensors, Actuators and Microsystems. Digest of Technical Papers (Cat. No.03TH8664), 2000
An experimental and theoretical study is described concerning the dielectric motion of particles ... more An experimental and theoretical study is described concerning the dielectric motion of particles in a suspension subject to high-gradient AC electric fields. The experiments were performed on very dilute suspensions of polystyrene latex heads in DI water.
Fast drying of nano-drug particle laden strip-films formed using water-soluble biocompatible poly... more Fast drying of nano-drug particle laden strip-films formed using water-soluble biocompatible polymers via forced convection is investigated in order to form films having uniform drug distribution and fast dissolution. Films were produced by casting and drying a mixture of poorly water soluble griseofulvin (GF) nanosuspensions produced via media milling with aqueous hydroxypropyl methylcellulose (HPMC E15LV) solutions containing glycerin as a plasticizer. The effects of convective drying parameters, temperature and air velocity, and film-precursor viscosity on film properties were investigated. Two major drying regimes, a constant rate period as a function of the drying conditions, followed by a single slower falling rate period, were observed. Films dried in an hour or less without any irreversible aggregation of GF nanoparticles with low residual water content. Near-infrared chemical imaging (NIR-CI) and the content uniformity analysis indicated a better drug particle distribution when higher viscosity film-precursors were used. Powder X-ray diffraction showed that the GF in the films retained crystallinity and the polymorphic form. USP IV dissolution tests showed immediate release (∼20 min) of GF. Overall, the films fabricated from polymer-based suspensions at higher viscosity dried at different conditions exhibited similar mechanical properties, improved drug content uniformity, and achieved fast drug dissolution.
Experiments in both microgravity (aboard the NASA research aircraft KC-135) and ground-based envi... more Experiments in both microgravity (aboard the NASA research aircraft KC-135) and ground-based environments were conducted in a clinostat (a channel slowly rotated around its horizontal axis to simulate weightlessness) in which a dilute suspension of heavy, positively polarized ...
The velocity fluctuations present in macroscopically homogeneous suspensions of neutrally buoyant... more The velocity fluctuations present in macroscopically homogeneous suspensions of neutrally buoyant, non-Brownian spheres undergoing simple shear flow, and their dependence on the microstructure developed by the suspensions, are investigated in the limit of vanishingly small Reynolds numbers using Stokesian dynamics simulations. We show that, in the dilute limit, the standard deviation of the velocity fluctuations is proportional to the volume fraction, in both the transverse and the flow directions, and that a theoretical prediction, which considers only for the hydrodynamic interactions between isolated pairs of spheres, is in good agreement with the numerical results at low concentrations. We also simulate the velocity fluctuations that would result from a random hard-sphere distribution of spheres in simple shear flow, and thereby investigate the effects of the microstructure on the velocity fluctuations. Analogous results are discussed for the fluctuations in the angular velocity of the suspended spheres. In addition, we present the probability density functions for all the linear and angular velocity components, and for three different concentrations, showing a transition from a Gaussian to an Exponential and finally to a Stretched Exponential functional form as the volume fraction is decreased. We also show that, although the pair distribution function recovers its fore-aft symmetry in dilute suspensions, it remains anisotropic and that this anisotropy can be accurately described by assuming the complete absence of any permanent doublets of spheres. We finally present a simple correction to the analysis of laser-Doppler velocimetry measurements.
Microfluidic Dielectrophoretic Gates for the Front-End Device of a Biodetection System
We present a novel micro-fluidic device for the front-end of a biodetection system to discriminat... more We present a novel micro-fluidic device for the front-end of a biodetection system to discriminate between biological and non-biological analytes. By combining AC dielectrophoresis along the flow streamlines and a field-induced phase-separation, the device utilizes "dielectrophoretic gating" to separate analytes suspended in a flowing fluid based on their intrinsic polarizability properties. The gates are integrated into batch fabricated self-sealed surface-micromachined fluid channels. We demonstrate that setting the gate to a moderate voltage in the radio frequency range removed bacteria cells from a mixture containing non-biological particles without the need for fluorescent labeling or antibody-antigen hybridization and present a model for the coupling of shear, dielectrophoresis, and phase separation. We see a potential use for the proposed technology for discriminating between biological and non-biological analytes that are captured in air samples.
Electrical Conductivity of Aqueous Solutions of Surfactants with Added Electrolytes
We analyze the electrical conductivity of aqueous solutions of sodium dodecyl sulphate (SDS) and ... more We analyze the electrical conductivity of aqueous solutions of sodium dodecyl sulphate (SDS) and lithium dodecyl sulfate (LDS) with added electrolytes as a function of the surfactant and electrolyte concentrations. A molecular thermodynamic model of surfactant aggregation in aqueous solutions was used to predict the micelle concentration, the average size and shape of aggregates, and the detailed size distribution of aggregates. Based on these characteristics, the electrical conductivity of a solution was then computed within the framework of the classical Onsager theory for a multicomponent electrolyte. Theoretical predictions were compared with experimental data. Measurements were carried out on a broadband dielectric spectrometer BDS-80, Novocontrol. Experiments cover a broad range of the surfactant and electrolyte concentrations, from above the critical micelle concentration (CMC) to infinite dilution. Deviation of theoretical predictions from experimental data provides insight ...
Macrokinetics of structural transformation during the gasless combustion of a titanium and carbon powder mixture
Combustion Explosion and Shock Waves
The presented results provide a phenomenological description of the structural evolution of the w... more The presented results provide a phenomenological description of the structural evolution of the wave of a Ti and C powder mixture combustion. They show that further progress in the understanding of the mechanisms of combustion and the structure formation is linked to the solution of two problems:1)What is the mechanism underlying the generation of carbide particles?2)Which kinetic laws and mechanisms govern the growth of carbide particles?
A cone-shaped meniscus of electrified fluids, often called a Taylor cone, is observed in rain dro... more A cone-shaped meniscus of electrified fluids, often called a Taylor cone, is observed in rain drops and lightning and employed in various physical instruments and experimental techniques, but the way it evolves from a rounded shape to a cone is a long-standing puzzle. Earth's gravity and microgravity measurements on the meniscus whose height is just shy of droplet ejection reveal that field-driven cusp evolution exhibits a universal self-similarity insensitive to the forcing field and scaled by the fluid surface tension and density. Our work paves the way for dynamic control of field-driven phenomena in fluids.
Rotation d'une suspension magnétorhéologique dans un champ magnétique constant. I. Equation du mouvement et conditions aux limites sur la surface libreRotation of a magnetorheological suspension in a permanent magnetic field. I. Equation of motion and boundary conditions on the free surface
Mouvement d'une particule, magnétiquement douce à symétrie axiale dans un écoulement hydrodynamique sous l'action d'un champ magnétique intense et tournantNotion of a soft magnetic axisymetrical particle in a hydrodynamical flow under high and rotating magnetic fiels
Processus de transfert convectif dans des fluides stables chimiquement et réactifs à structure interneOn convective transfer processes in chemically stable and reacting fluids with an internal structure
Single-bubble water boiling on small heater under Earth's and low gravity
NPJ microgravity, 2018
Today's trends for enhancing boiling heat transfer in terrestrial and space applications focu... more Today's trends for enhancing boiling heat transfer in terrestrial and space applications focus on removal of bubbles to prevent formation of a vapor layer over the surface at high overheat. In contrast, this paper presents a new boiling regime that employs a vapor-air bubble residing on a small heater for minutes and driving cold water over the surface to provide high heat flux. Single-bubble boiling of water was investigated under normal gravity and low gravity in parabolic flights. Experiments demonstrated a negligible effect of gravity level on the rate of heat transfer from the heater. Due to self-adjustment of the bubble size, the heat flux provided by boiling rose linearly up with increasing heater temperature and was not affected by a gradually rising water temperature. The fast response and stable operation of single-bubble boiling over a broad range of temperatures pave the way for development of new devices to control heat transfer by forming surface domains with disti...
TRANSDUCERS '03. 12th International Conference on Solid-State Sensors, Actuators and Microsystems. Digest of Technical Papers (Cat. No.03TH8664), 2000
An experimental and theoretical study is described concerning the dielectric motion of particles ... more An experimental and theoretical study is described concerning the dielectric motion of particles in a suspension subject to high-gradient AC electric fields. The experiments were performed on very dilute suspensions of polystyrene latex heads in DI water.
Fast drying of nano-drug particle laden strip-films formed using water-soluble biocompatible poly... more Fast drying of nano-drug particle laden strip-films formed using water-soluble biocompatible polymers via forced convection is investigated in order to form films having uniform drug distribution and fast dissolution. Films were produced by casting and drying a mixture of poorly water soluble griseofulvin (GF) nanosuspensions produced via media milling with aqueous hydroxypropyl methylcellulose (HPMC E15LV) solutions containing glycerin as a plasticizer. The effects of convective drying parameters, temperature and air velocity, and film-precursor viscosity on film properties were investigated. Two major drying regimes, a constant rate period as a function of the drying conditions, followed by a single slower falling rate period, were observed. Films dried in an hour or less without any irreversible aggregation of GF nanoparticles with low residual water content. Near-infrared chemical imaging (NIR-CI) and the content uniformity analysis indicated a better drug particle distribution when higher viscosity film-precursors were used. Powder X-ray diffraction showed that the GF in the films retained crystallinity and the polymorphic form. USP IV dissolution tests showed immediate release (∼20 min) of GF. Overall, the films fabricated from polymer-based suspensions at higher viscosity dried at different conditions exhibited similar mechanical properties, improved drug content uniformity, and achieved fast drug dissolution.
Experiments in both microgravity (aboard the NASA research aircraft KC-135) and ground-based envi... more Experiments in both microgravity (aboard the NASA research aircraft KC-135) and ground-based environments were conducted in a clinostat (a channel slowly rotated around its horizontal axis to simulate weightlessness) in which a dilute suspension of heavy, positively polarized ...
The velocity fluctuations present in macroscopically homogeneous suspensions of neutrally buoyant... more The velocity fluctuations present in macroscopically homogeneous suspensions of neutrally buoyant, non-Brownian spheres undergoing simple shear flow, and their dependence on the microstructure developed by the suspensions, are investigated in the limit of vanishingly small Reynolds numbers using Stokesian dynamics simulations. We show that, in the dilute limit, the standard deviation of the velocity fluctuations is proportional to the volume fraction, in both the transverse and the flow directions, and that a theoretical prediction, which considers only for the hydrodynamic interactions between isolated pairs of spheres, is in good agreement with the numerical results at low concentrations. We also simulate the velocity fluctuations that would result from a random hard-sphere distribution of spheres in simple shear flow, and thereby investigate the effects of the microstructure on the velocity fluctuations. Analogous results are discussed for the fluctuations in the angular velocity of the suspended spheres. In addition, we present the probability density functions for all the linear and angular velocity components, and for three different concentrations, showing a transition from a Gaussian to an Exponential and finally to a Stretched Exponential functional form as the volume fraction is decreased. We also show that, although the pair distribution function recovers its fore-aft symmetry in dilute suspensions, it remains anisotropic and that this anisotropy can be accurately described by assuming the complete absence of any permanent doublets of spheres. We finally present a simple correction to the analysis of laser-Doppler velocimetry measurements.
Microfluidic Dielectrophoretic Gates for the Front-End Device of a Biodetection System
We present a novel micro-fluidic device for the front-end of a biodetection system to discriminat... more We present a novel micro-fluidic device for the front-end of a biodetection system to discriminate between biological and non-biological analytes. By combining AC dielectrophoresis along the flow streamlines and a field-induced phase-separation, the device utilizes "dielectrophoretic gating" to separate analytes suspended in a flowing fluid based on their intrinsic polarizability properties. The gates are integrated into batch fabricated self-sealed surface-micromachined fluid channels. We demonstrate that setting the gate to a moderate voltage in the radio frequency range removed bacteria cells from a mixture containing non-biological particles without the need for fluorescent labeling or antibody-antigen hybridization and present a model for the coupling of shear, dielectrophoresis, and phase separation. We see a potential use for the proposed technology for discriminating between biological and non-biological analytes that are captured in air samples.
Electrical Conductivity of Aqueous Solutions of Surfactants with Added Electrolytes
We analyze the electrical conductivity of aqueous solutions of sodium dodecyl sulphate (SDS) and ... more We analyze the electrical conductivity of aqueous solutions of sodium dodecyl sulphate (SDS) and lithium dodecyl sulfate (LDS) with added electrolytes as a function of the surfactant and electrolyte concentrations. A molecular thermodynamic model of surfactant aggregation in aqueous solutions was used to predict the micelle concentration, the average size and shape of aggregates, and the detailed size distribution of aggregates. Based on these characteristics, the electrical conductivity of a solution was then computed within the framework of the classical Onsager theory for a multicomponent electrolyte. Theoretical predictions were compared with experimental data. Measurements were carried out on a broadband dielectric spectrometer BDS-80, Novocontrol. Experiments cover a broad range of the surfactant and electrolyte concentrations, from above the critical micelle concentration (CMC) to infinite dilution. Deviation of theoretical predictions from experimental data provides insight ...
Macrokinetics of structural transformation during the gasless combustion of a titanium and carbon powder mixture
Combustion Explosion and Shock Waves
The presented results provide a phenomenological description of the structural evolution of the w... more The presented results provide a phenomenological description of the structural evolution of the wave of a Ti and C powder mixture combustion. They show that further progress in the understanding of the mechanisms of combustion and the structure formation is linked to the solution of two problems:1)What is the mechanism underlying the generation of carbide particles?2)Which kinetic laws and mechanisms govern the growth of carbide particles?
A cone-shaped meniscus of electrified fluids, often called a Taylor cone, is observed in rain dro... more A cone-shaped meniscus of electrified fluids, often called a Taylor cone, is observed in rain drops and lightning and employed in various physical instruments and experimental techniques, but the way it evolves from a rounded shape to a cone is a long-standing puzzle. Earth's gravity and microgravity measurements on the meniscus whose height is just shy of droplet ejection reveal that field-driven cusp evolution exhibits a universal self-similarity insensitive to the forcing field and scaled by the fluid surface tension and density. Our work paves the way for dynamic control of field-driven phenomena in fluids.
Rotation d'une suspension magnétorhéologique dans un champ magnétique constant. I. Equation du mouvement et conditions aux limites sur la surface libreRotation of a magnetorheological suspension in a permanent magnetic field. I. Equation of motion and boundary conditions on the free surface
Mouvement d'une particule, magnétiquement douce à symétrie axiale dans un écoulement hydrodynamique sous l'action d'un champ magnétique intense et tournantNotion of a soft magnetic axisymetrical particle in a hydrodynamical flow under high and rotating magnetic fiels
Processus de transfert convectif dans des fluides stables chimiquement et réactifs à structure interneOn convective transfer processes in chemically stable and reacting fluids with an internal structure
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Papers by Boris Khusid