Industrial Multi-Plug Conveying Analysis

Single-plug conveying systems have the advantage of being easy to handle and highly controllable. In industry, however, multi-plug conveying systems are the most common choice due to their high transporting capacity. In order to study a multi-plug industrial conveying system, the system parameters were varied along with the materials being conveyed. The responses obtained were compared to the single-plug laboratory system, noting differences and similarities. The pneumatic conveying system at an industrial facility consisted of a 0.01 m Schedule 10 aluminum pipe, approximately 100 m long. To measure the pressure at different points along the system, a total of seven transducers were installed, four air transducers and three flush transducers. This study also used a high-speed video camera to view the plugs as they passed through the transparent viewing port, providing more detailed information on the multi-plug conveying process. Three materials were tested at different superficial air velocities and solid mass flows. In each experiment all transducers took data with a sample rate of 1,000 Hz, giving a highly detailed overview of the conveying process. The analysis included plug velocity and plug size with respect to the superficial air velocity. The Mi model for plug-flow pressure drops was found to yield agreement with the data within ±25%. For this type of industrial operation, this agreement is considered acceptable. The visual observations recorded with the camera showed that there were conditions of stable plug formation as well as varying degrees of plug stability and integrity depending on the operational conditions.     

Gas–Liquid Oxygen Mass-transfer; from Fundamentals to Applications in Hydrometallurgical Systems

Oxygen gas is used as a reactant in many hydrometallurgical processes. However, oxygen is sparingly soluble in aqueous electrolyte solutions, and the driving force for its masstransfer from the gas to the aqueous phase is also very low. Hence, the mass-transfer of oxygen depends significantly on the interfacial area between the gas and the liquid phase, which in turn depends on the mixing conditions inside the reactor. A change in the solution composition or the presence of solids can further alter the rate of oxygen masstransfer. All such phenomena related to the gas-liquid oxygen mass-transfer in hydrometallurgical unit operations are critically reviewed in the present article – from the basic thermodynamics and kinetics of oxygen dissolution in aqueous solutions to the most recent advances in oxygen mass-transfer systems.     

Gas-Liquid Oxygen Mass-transfer; from Fundamentals to Applications in Hydrometallurgical Systems

Abstract

Oxygen gas is used as a reactant in many hydrometallurgical processes. However, oxygen is sparingly soluble in aqueous electrolyte solutions, and the driving force for its mass-transfer from the gas to the aqueous phase is also very low. Hence, the mass-transfer of oxygen depends significantly on the interfacial area between the gas and the liquid phase, which in turn depends on the mixing conditions inside the reactor. A change in the solution composition or the presence of solids can further alter the rate of oxygen mass-transfer. All such phenomena related to the gas-liquid oxygen mass-transfer in hydro-metallurgical unit operations are critically reviewed in the present article - from the basic thermodynamics and kinetics of oxygen dissolution in aqueous solutions to the most recent advances in oxygen mass-transfer systems.     

Stress in Leached Phase-Separated Glass

When a phase-separated glass is leached, stresses develop because of release of thermal stresses, creation of surface area, ion exchange, and hydration. Analyses are presented for the thermal stresses, including the portion that develops on cooling from the heat-treatment temperature to the setting temperature of the less viscous phase. During leaching, the interfacial energy of the residual phase increases, so that phase tends to contract. A more important effect is the contraction caused by removal of alkali and B₂O₃ from the residual phase during leaching. The extent of removal of B₂O₂ decreases with heat-treatment time, t_H , because the scale of the microstructure increases as t^1/3_H. The change in residual B₂O₂ content with t_H is shown to be consistent with diffusion-controlled ion exchange. The dependence of stress on t_H in partially leached glasses, measured by Drexhage and Gupta, results principally from the change in extent of ion exchange; the reduction in surface area with increasing t_H also has a significant effect on the stresses.     

Effect of Antioxidants on Malonaldehyde Production and Fatty Acid Composition in Pieces of Bovine Muscle and Adipose Tissue Stored Fresh and Frozen

TBA-reactive material was produced in pieces of bovine semitendinosus muscle and adipose tissue during storage at 2° 2°C and ?10° 2°C. The process was faster in muscle than in adipose tissue and the total content, higher at 2°C than at ?10°C. The effect of sprying butylated hydroxytoluene and a citric acid-EDTA-ascorbic acid mixture on the production of malonaldehyde was studied. Declines in both saturated and unsaturated fatty acid proportions of the polar lipids without increases in the content of free fatty acids suggests that enzymes involved in lipid catabolism remain active at low temperatures. Whereas lipid breakdown was unaffected, malonaldehyde production was inhibited by sprying antioxidants in early stages of the slaughtering process.     

Characterization of Hot-Pressed Cement Pastes

Very-high-strength cement pastes (compressive strengths ∼100,000 psi) were prepared using hot-pressing techniques at temperatures up to 250°C. The results of characterization studies summarized include X-ray diffraction, DTA, ir spectra, and microstructural investigations. Much less Ca(OH)₂ is formed than in normally hydrated pastes. Some well- crystallized hydroxyl-containing hydrates, C₅S₂H, C₃SH_1.5, C₃AH₆, and C₄A₃H₃, as well as poorly crystalline CSH, are formed. The structure of the CSH, as revealed by ir absorption studies, does not appear to be very different from that in low- temperature hydrated cement pastes. Microstructures are extremely dense and, in some cases, the sulfate-containing phase concentrates along original grain boundaries.     

Playtime

Three installation projects take tropes such as the labyrinth, the lumberjack culture and the neighbor's fence, and turn them into spaces of gathering and play.     

A Stock/Flow Model Of Defining Racially Integrated Neighborhoods

ABSTRACT: This article discusses the appropriate measurement of neighborhood racial integration and proposes a new operational definition. A neighborhood is integrated if currently (1) its stock of households may be classified as “mixed” (no single group comprises more than 75% of the neighborhood's population), and (2) the flow of households into and out of this stock is such that it will be so classified for a decade in the future. The article mathematically develops stability boundaries that researchers and policy makers can use to assess the degree to which contemporaneous flows of households into and out of mixed neighborhoods will render them integrated in the future.     

Conversion of CaO·Al2O3·10H2O to 3CaO·Al2O3·6H2O

The morphological changes accompanying the conversion of the hexagonal CaO·Al₂O₃·10H₂O phase to the cubic 3CaO·Al₂O₃·6H₂O phase were studied by scanning electron microscopy. The hydration and conversion reactions were monitored by X-ray diffraction analysis. From the micrographs, it was inferred that changes in the pore structure and the presence of large cubic crystals of questionable adhesive value were probably the principal factors responsible for the loss of strength in converted calcium aluminate cement pastes.     

Infrared-Transmitting Glasses in the System K2O-Sb2O3-Sb2S3

Glasses were discovered in the system K₂O-Sb₂O₃b₃ Raw materials used in the preparation of these glasses were potassium pyroantimonate, potassium hydroxide, potassium nitrate, antimony oxide, and antimony trisulfide. Details of the methods of preparing the glasses and the compositions investigated are given. A glass, prepared by melting a mixture of potassium pyroantimonate and antimony trisulfide in air, was investigated in some detail. It was found to have an average infrared transmission of 42% in the range 2 to 7 μ. The glass annealed at about 150°C. and softened at about 230°C. Its coefficient of linear thermal expansion, in the range 240° to 200°C., was 20 × 10⁻⁶ per °C. The glass had a specific gravity of 3.94, a modulus of elasticity of about 5 × 10⁶lb. per sq. in., a Knoop hardness of about 135, and was highly resistant to attack by atmospheric moisture.