George G. Chase

Improved scale-up strategies of bioreactors

Effective scale-up is essential for successful bioprocessing. While it is desirable to keep as many operating parameters constant as possible during the scale-up, the number of constant parameters realizable is limited by the degrees of freedom in designing the large-scale operation. Scale-up of aerobic fermentations is often carried out on the basis of a constant oxygen transfer coefficient, kLa, to ensure the same oxygen supply rate to support normal growth and metabolism of the desired high cell populations. In this paper, it is proposed to replace the scale-up criterion of constant kL by a more direct and meaningful criterion of equal oxygen transfer rate at a predetermined value of dissolved oxygen concentration. This can be achieved by using different oxygen partial pressures in the influent gas streams for different scales of operation. One more degree of freedom, i.e., gas-phase oxygen partial pressure, is thus added to the process of scale-up. Accordingly, one more operating factor can be maintained constant during scale-up. It can be used to regulate the power consumption in large-scale fermentors for economical considerations or to describe the fluid mixing more precisely. Examples are given to show that the results of optimization achieved in the bench-scale study can be translated to the production-scale fermentor more successfully with only a small change in the gas-phase oxygen partial pressure employed in the bench-scale operation.

Electrical, structural, and chemical properties of semiconducting metal oxide nanofiber yarns

The electrical, structural, and chemical properties of twisted yarns of metal-oxide nanofibers, fabricated using a modified electrospinning technique, are investigated in this report. In particular, synthesized zinc oxide and nickel oxide yarns having diameters in the range of 4–40μm and lengths up to 10cm were characterized, whose constituent nanofibers had average diameters of 60–100nm. These yarns have one macroscopic dimension for handling while retaining some of the properties of nanofibers.

Separation of Water‐in‐Oil Emulsions Using Glass Fiber Media Augmented with Polymer Nanofibers

Water‐in‐oil emulsion separations are important to the petrochemical industry for product quality, safety, environmental, and economic reasons. Glass fiber filter media are often used to remove water droplets out of water‐in‐oil emulsions. The experimental results in this work show that 1% by mass of polyamide nanofibers with diameters of about 150 nm added to conventional micron‐sized glass fiber filter media improves the separation efficiency of the filter media from 71 to 84%. The addition of similar amounts of micron‐sized polyamide fibers to the glass fiber media do not improve filter capture efficiency.

A preliminary examination of zeta potential and deep bed filtration activity

Over the past 20 years, researchers have attempted to develop a general correlation for predicting filtration activity within a deep bed filter, with limited success. The zeta potential had been used previously in filtration work to explain the observed macroscopic behavior through complex, theoretical analyses. This work demonstrates a possible novel use of the zeta potential as a predictive tool, broadening the application by using it as a qualitative macroscopic device. Through examination of the zeta potential difference between the media and the particles, this method provides a preliminary indicator of the filter performance without requiring complicated models and excessive experimentation. Results of zeta potential measurements for Berea sandstone, kaolinite clay, halloysite clay and illite clay are presented. These measurements are then used to plan and conduct proof-of-concept filtration experiments on the sandstone media with indigenous kaolinite clay and injected illite clay.

Electrospinning Route for the Fabrication of P-n Junction Using Nanofiber Yarns

Electrospinning is a simple, versatile, and cost effective method for generating nanoscale fibers, wires, and tubes. Nanowires and nanotubes could be important building blocks for nanoscale electronics, optoelectronics, and sensors as they can function as miniaturized devices as well as electrical interconnects. We report on a simple method to fabricate free standing ceramic nanofiber heterostructures, which exhibit rectifying behavior of a p-n junction.Electrospinning is a simple, versatile, and cost effective method for generating nanoscale fibers, wires, and tubes. Nanowires and nanotubes could be important building blocks for nanoscale electronics, optoelectronics, and sensors as they can function as miniaturized devices as well as electrical interconnects. We report on a simple method to fabricate free standing ceramic nanofiber heterostructures, which exhibit rectifying behavior of a p-n junction.

A Versatile Microparticle-Based Immunoaggregation Assay for Macromolecular Biomarker Detection and Quantification

The rapid, sensitive and low-cost detection of macromolecular biomarkers is critical in clinical diagnostics, environmental monitoring, research, etc. Conventional assay methods usually require bulky, expensive and designated instruments and relative long assay time. For hospitals and laboratories that lack immediate access to analytical instruments, fast and low-cost assay methods for the detection of macromolecular biomarkers are urgently needed. In this work, we developed a versatile microparticle (MP)-based immunoaggregation method for the detection and quantification of macromolecular biomarkers. Antibodies (Abs) were firstly conjugated to MP through streptavidin-biotin interaction; the addition of macromolecular biomarkers caused the aggregation of Ab-MPs, which were subsequently detected by an optical microscope or optical particle sizer. The invisible nanometer-scale macromolecular biomarkers caused detectable change of micrometer-scale particle size distributions. Goat anti-rabbit immunoglobulin and human ferritin were used as model biomarkers to demonstrate MP-based immunoaggregation assay in PBS and 10% FBS to mimic real biomarker assay in the complex medium. It was found that both the number ratio and the volume ratio of Ab-MP aggregates caused by biomarker to all particles were directly correlated to the biomarker concentration. In addition, we found that the detection range could be tuned by adjusting the Ab-MP concentration. We envision that this novel MP-based immunoaggregation assay can be combined with multiple detection methods to detect and quantify macromolecular biomarkers at the nanogram per milliliter level.

Incompressible Cake Filtration of a Yield Stress Fluid

Filtration of Non-Newtonian fluid occurs frequently in industry. A correlation is developed by introducing the Yield Stress model in place of the Newtonian model used in the Ergun equation. The resulting model has three parameters that are functions of the geometry and roughness of the particle surfaces. Two of the parameters can be deduced in the limit as the yield stress becomes negligible and the model reduces to the Ergun equation for Newtonian fluids. The third model parameter is determined from experimental data. The correlation relates a defined friction factor to the dimensionless Reynolds and Hedstrom numbers that can be used to predict pressure drop for flow of a yield stress fluid through a packed bed of spherical particles. This model is applied to predict incompressible cake filtration performance of a yield stress fluid. Modeling results show that for a constant pressure filtration the cake growth rate and filtrate flow rate for the incompressible filter cake are similar to that for a Newtonian fluid, until the flow rate decreases to the level that the shear stress is not sufficient to maintain the flow. At this point the friction factor increases more rapidly than that for the Newtonian fluid, and the flow rate and cake growth rates decrease rapidly. For a given material and pressure drop the transition between Newtonian-like flow and the yield stress flow can be predicted as a function of cake height.

Contact Angles of Drops on Curved Superhydrophobic Surfaces

Superhydrophobic surfaces have contact angles that exceed 150 degrees and are known to reduce surface fouling, protect surfaces, and improve liquid-liquid separations. Electrospun sub-micron fiber mats can perform as superhydrophobic surfaces. Superhydrophobic behavior is typically measured on planar surfaces, whereas applications may require curved surfaces. This paper discuses the measurement of water contact angles of fiber mats formed on cylindrical surfaces to create superhydrophobic behavior on curved surfaces. Equations are derived that relate the radius of curvature of spherical and cylindrical surfaces and drop size to the observed contact angle on the curved surfaces. Calculations from the equations agree well with experimental observations on spherical surfaces reported in literature and on cylindrical surfaces created in our lab.

Performance of B-E-glass fiber media in coalescence filtration

Abstract Compressed air is used in a variety of applications. For many applications, the air must be cleaned and filtered to remove contaminants. Among all the contaminants, oil mist and other liquid aerosols often pose the greatest challenge. In practice, nonwoven glass fiber media effectively remove these oil droplets. To preserve the structural stability of these coalescing media, a binder that holds the fibers together is employed. Most of the organic binders (acrylic or epoxy) have to be applied with an organic solvent. The use of a solvent not only poses a health problem, but also increases processing costs in the form of solvent disposal and recovery costs. This paper describes a use of a novel combination of B and E glass fibers that eliminates the organic binder and the solvent. Comparisons are made between this B–E-glass media and the traditional media with an acrylic binder. The results indicate that the B–E-glass media performs significantly better than the media with the organic binders both in terms of capture efficiency and quality factor.

Erbia-modified electrospun titania nanofibres for selective infrared emitters

Tetraisopropyl titanate (TPT) was mixed with a solution of polyvinylpyrrolidone (PVP) and the solution electrospun into nanofibres. Thermal annealing at 900 °C was used to pyrolyse the PVP, leaving nanofibres of rutile-phase titania. Erbium (III) oxide particles were also added into the solution before electrospinning, and selectively modified the near-infrared optical properties of the titania nanofibres as verified by both absorption and emission spectra. We thereby demonstrate the production of high-temperature optically functionalized nanostructures that can be used in a thermophotovoltaic energy conversion system.