Richard R. Wheeler

Complex permittivities and dielectric relaxation of granular activated carbons at microwave frequencies between 0.2 and 26 GHz

Carbonaceous materials are amenable to microwave heating to varying degrees. The primary indicator of susceptibility is the complex permittivity (e*), of which the real component correlates with polarization and the imaginary term represents dielectric loss. For a given material, the complex permittivity is dependent upon both frequency and temperature. Here we report the complex permittivities of three activated carbons of diverse origin over the frequency range from 0.2 to 26 GHz. Dielectric polarization-relaxation phenomena for these materials are also characterized. Measurements were made using a coaxial dielectric probe and vector network analyzer based system across the temperature region between 22 and 190 8C.  2003 Elsevier Science Ltd. All rights reserved.

Enzymatic Determination of Ethanol Using ‘Reagentless’ Electrocatalyzed Luminol Chemiluminescence

Abstract Flow analysis methodology is presented for the determination of aqueous ethanol in concentrations between 3–340 μM. Alcohol oxidase catalyzes the production of hydrogen peroxide which is detected by luminol chemiluminescence. Adjustment of the pH to alkaline conditions and addition of the luminophore are implemented using in-line flow-through beds containing crystalline media. The requirement for a homogeneous catalyst is eliminated by electrochemical initiation of luminescence. Traditional laboratory reagents are replaced by packed beds containing immobilized enzyme, solid phase basification media, and crystalline luminol. The methodology is suitable for application in both continuous flow and flow injection analysis configurations.

Porous cobalt spheres for high temperature gradient magnetically assisted fluidized beds.

Porous metallic cobalt spheres have been prepared as high temperature capable media for employment in gradient magnetically assisted fluidization and filtration technologies. Cobalt impregnated alginate beads are first formed by extrusion of an aqueous suspension of Co3O4 into a Co(II) chloride solution. The organic polymer is thermally decomposed yielding cobalt oxide spheres, followed by reduction to the metallic state, and densification. Cobalt beads have been produced with porosities ranging between 10 and 50%, depending upon sintering conditions. The product media have been characterized by scanning electron microscopy (SEM), nitrogen adsorption porosimetry, and vibrating sample magnetometry.

“Reagentless” Flow Analysis Determination of Hydrogen Peroxide by Electrocatalyzed Luminol Chemiluminescence

Flow analysis methodology is presented for the determination of micromolar levels of aqueous hydrogen peroxide by luminol chemiluminescence. Adjustment of the pH to alkaline conditions and addition of the luminophore are implemented using in-line flow-through beds containing crystalline media. The requirement for a homogeneous catalyst is eliminated by electrochemical initiation of luminescence. Traditional laboratory reagents are replaced by packed beds containing solid phase basification media, and crystalline luminol. The methodology is suitable for application in both continuous flow and flow injection analysis configurations.

Regenerable Microbial Check Valve: Life Cycle Tests Results

Life cycle regeneration testing of the Microbial Check Valve (MCV) that is used on the Shuttle Orbiter to provide microbial control of potable water is currently in progress. Four beds are being challenged with simulated reclaimed waters and repeatedly regenerated. Preliminary results indicate that contaminant systems exhibit unique regeneration periodicities. Cyclic throughput diminishes with increasing cumulative flow. It is considered to be feasible to design a regenerable MCV system which will function without human intervention and with minimal resupply penalty for the 30 year life of the Space Station.

Miniature microwave powered steam sterilization chamber

A small device for the rapid ultrahigh temperature sterilization of surfaces is described. Microwave power generated by a 2.45 GHz magnetron is delivered via coaxial cable to a silicon carbide block housed within the chamber. Small quantities of water or aqueous hydrogen peroxide are introduced into the chamber. Upon application of power, the liquid flashes to vapor and superheats producing temperatures to 300 °C. The hot vapor permeates the enclosed space and contacts all exposed surfaces. Complete microbial kill of >10 6 colony forming units of the spore forming thermophile, Bacillus stearothermophilus, has been demonstrated using a variety of temperatures and exposure times in both steady state and thermal pulse modes of operation.

Brine Dewatering Using Ultrasonic Nebulization

Recovery of water from brine is a critical element of water loop closure for future extended manned space missions where water resupply logistics become increasingly prohibitive beyond low earth orbit (LEO). In these situations, brines will be derived from pooled wastewater in which the primary water recovery system recovers greater than 90% of the original water while the remaining water is retained in a contaminant laden brine. In this paper, the use of ultrasonic nebulization to recover water from brine is described. This novel method utilizes ultrasonic energy to eject micron-sized droplets of brine from the air-liquid interface forming a mist that is readily dried under a partial vacuum at moderate temperature. For brine originating from urine and other metabolic byproducts, low drying temperatures prevent decomposition of thermally sensitive contaminants. Ultrasonic nebulizer advantages include mist creation without nozzles that can become plugged, minimal power requirements, and simple and compact design. Once generated, the mist is transferred to a drying chamber where rapid drying occurs at low temperature due to the small droplet size and vacuum conditions. Following capture of the dried brine aerosol by a regenerable filtration method, water vapor is condensed and recovered. Significant findings from this program presented in this paper include: 1) water recoveries of greater than 95% were demonstrated for the Ultrasonic Brine Dewatering System (UBDS); 2) mist generation depends directly on the sweep gas flow rate, which impacts dryer, filtration, and condenser designs; 3) mist and brine compositions are identical, allowing long-term nebulization without the formation of precipitates; 4) particle removal feasibility was demonstrated; 5) microgravity compatibility is feasible when an ultrasonically transparent, open wicking material is present at the liquid-gas interface, and; 6) dried brine particles retained less than 5% moisture. These findings demonstrate the potential for continued advancement of the UBDS technology.

Development and Testing of a Microwave Powered Regenerable Air Purification Technology Demonstrator

Dielectric heating via microwave irradiation of contaminant laden sorbents offers distinct advantages in comparison to conventional thermal regeneration techniques. High temperatures may be achieved very rapidly because electromagnetic energy is absorbed directly by the sorbent material. A Technology Demonstrator, incorporating efficient rectangular waveguide based sorbent cartridge designs and effective microwave transmission systems was designed, fabricated and tested. Importantly, the performance of the Molecular Sieve 13X Waveguide Cartridge for the removal of water vapor, the Molecular Sieve 5A Waveguide Cartridge for the removal of CO2, and the Activated Carbon Waveguide Cartridge for removal of volatile organics from air, were each validated by successive sorption/ microwave desorption cycles.

Dissolved Oxygen Determination by Electrocatalysed Chemiluminescence with In-line Solid Phase Media

Dissolved elemental oxygen is determined in a flowing aqueous stream using glucose oxidase to catalyse the reaction between D-glucose and O2 to produce hydrogen peroxide. The levels of the resulting H2O2 are detected and quantified by luminol chemiluminescence using in-line solid phase media for pH adjustment of the reagent stream and for controlled release of the luminophore. The reaction is initiated by electrochemical catalysis. By the use of excess D-glucose in the reagent flow stream, the intensity of chemiluminescence is rendered proportional only to fluctuations in the dissolved O2 concentration. The methodology provides a means for the detection of aqueous O2 in the range 0-10 mg/L.

A Microwave-Powered Sterilizable Interface for Aseptic Access to Bioreactors That Are Vulnerable to Microbial Contamination

Novel methods and apparatus that employ the rapid heating characteristics of microwave irradiation to facilitate the aseptic transfer of nutrients, products, and other materials between microbially sensitive systems and the external environment are described. The microwave‐sterilizable access port (MSAP) consists of a 600‐W magnetron emitting at a frequency of 2.45 GHz, a sterilization chamber with inlet and outlet flow lines, and a specimen transfer interface. Energy is routed to the sterilization chamber via a coaxial transmission line where small quantities of water couple strongly with the incident radiation to produce a superheated vapor phase. The efficiency of energy transfer is enhanced through the use of microwave susceptors within the sterilization chamber. Mating surfaces are thermally sterilized through direct contact with the hot gas. Efficacy has been demonstrated using the thermophile Bacillus stearothermophilus.