Power Consumption And Granular Flow In A Vibro-Fluidized Stirred Granular Bed
This work examines the behavior of a deep granular bed subject to simultaneous vertical vibration and stirring. The power necessary to stir a 5.6 cm diameter and 20 cm deep granular bed of 150 micron glass beads using a 4-blade vane impeller was measured over a wide range of forcing conditions. Impeller rotation rates from 0 – 1000 rpms and vibration accelerations in the range 0 ≤ Γ = ω2a/g ≤ 4.0 were explored. Both the power required for stirring and vibration were recorded. Sharp changes in vane power draw indicate flow transitions from dense granular flow to vibro-fluidized flow at a critical acceleration (Γc ). The total power profile (vane plus vibration power) demonstrates a minimum just above the critical acceleration. Progressive increases or decreases n both vane speed and Γ independently show hysteresis as the flow bifurcates between two primary states of dense granular flow and loose-packed, vibrofluidized behavior. These observations are compared to those found in fluidized systems and flows generated in high-shear granulators. Finally, preliminary results of direct density measurements using a localized capacity probe will be discussed. These observations are compared to those found in fluidized systems and flows generated in high-shear granulators.
Consumption And Granular Flow In A Vibro-Fluidized Stirred Granular Bed
This work examines the behavior of a deep granular bed subject to simultaneous vertical vibration and stirring. The power necessary to stir a 5.6 cm diameter and 20 cm deep granular bed of 150 micron glass beads using a 4-blade vane impeller was measured over a wide range of forcing conditions. Impeller rotation rates from 0 – 1000 rpms and vibration accelerations in the range 0 < gamma < 4.0 were explored. Both the power required for stirring and vibration were recorded. Sharp changes in vane power draw indicate flow transitions from dense granular flow to vibro-fluidized flow at a critical acceleration. The total power profile (vane plus vibration power) demonstrates a minimum just above the critical acceleration. Progressive increases or decreases n both vane speed and gamma independently show hysteresis as the flow bifurcates between two primary states of dense granular flow and loose-packed, vibrofluidized behavior. These observations are compared to those found in fluidized systems and flows generated in high-shear granulators.
Rapid Convective Deposition Of Microsphere Monolayers For Fabrication Of Microlens Arrays
Micron-sized microspheres were deposited into thin films via rapid convective deposition using a similar method to that studied by Prevo and Velev, Langmuir, 2003. By varying deposition rate and contact angle, the optimal operating ranges in which 2D closed-pack of silica existed were obtained. Using a confocal laser scanning microscope, dynamic self-assembly of colloidal particles under capillary force during solvent evaporation was revealed. The resulting microstructure is controlled by varying the macroscale parameters and interaction between substrate and colloidal particles played an important role in formation of ordered crystalline arrays. Using the same technique, stacked layers of 1 micron silica monolayer on top of 1.1 micron polystyrene monolayers and subsequent melting of the polystyrene to partially wet the silica microspheres were deposited on GaN layer. This process was implemented on the top p-GaN layer of InGaN quantum wells light emitting diode (LEDs) device structure, resulting in the formation of a microlens array for enhancing its light extraction efficiency. This approach led to ~230% increase of the LEDs output power.
Shear-induced migration of suspensions in 3D microfluidic geometries
We investigated shear-induced migration of 1 micron Brownian particles in 1D, 2D, 3D steady microfluidic flows generated in straight, herringbone, and staggered herringbone channels respectively. The transverse flows induced by recessed herringbone structures in the top of the channels interplay with particle migration to the low shear regions of the pressure-driven flow. Using high-speed confocal laser scanning microscopy, we were able to image directly flowing particles inside the channels. Moreover, we located the 3D positions for each particle and obtained 2D concentration and 2D velocity profiles to better understand of the effects from the underlying flow topology, colloidal hydrodynamics, and Reynolds and Pclet number on particle migration.
Deposition of microsphere monolayers for microlens arrays
Colloidal silica microspheres of 0.5 and 1 micron were deposited into thin films on a glass substrate via a rapid convective deposition method. By varying deposition rate and contact angle, the optimal operating ranges in which 2D closed-pack of silica existed were obtained. Using a confocal laser scanning microscope, dynamic self assembly of colloidal particles under capillary force during solvent evaporation was revealed. In addition, interaction between substrate and colloidal particles played an important role in formation of ordered crystalline arrays. The interaction was altered by varying pH (2-11) and salt concentration of either substrate rinsing solution or colloidal suspension. Using the same technique, stacked layers of 1 micron silica monolayer on top of 1.1 micron polystyrene monolayers and subsequent melting of the polystyrene to partially wet the silica microspheres were deposited on GaN layer. This process was implemented on the top p-GaN layer of InGaN quantum wells light emitting diode (LEDs) device structure, resulting in the formation of a microlens array for enhancing its light extraction efficiency. This approach led to ~230% increase of the LEDs output power.