Polydisperse granular flows in a bladed mixer: Experiments and simulations of cohesionless spheres

The flow and segregation of polydisperse, spherical particle mixtures in a bladed mixer was investigated using experimental and computational techniques. Discrete element simulations were able to reproduce the qualitative segregation profiles and surface velocities observed experimentally. For a binary system with a 2:1 size ratio, segregation by size occurs due to a sieving mechanism. Segregation in the binary system is fast, with a fully segregated system observed after just 5 revolutions. However, the numerical simulations showed that the extent of segregation in the bladed mixer can be reduced by introducing intermediate particle sizes in between the smallest and the largest particles. Addition of intermediate particle sizes increases convective and diffusive particle motion promoting a mixing mechanism that reduces segregation via the sieving mechanism. Void fraction within the bladed mixer increases as the degree of polydispersity is increased allowing the particles to move more freely throughout the particle bed. Higher void fractions also increase the ability of large particles to penetrate deeper into the particle bed. Normal and shear stresses are also affected by particle size distributions, with lower average values obtained for the system with the largest number of particle species. Differences in the amount of stress generated by each particle species were observed. However, the difference in stresses is reduced as the number of particle species in the system is increased.     

Supercooling of water droplets in jet aviation fuel

Ice formation in aircraft fuel systems is an ongoing problem with potentially disastrous consequences. Unfortunately, the icing of fuel systems is poorly understood. It is well known that at temperatures below 0 °C particles of H₂O suspended in fuel can exist as crystalline ice or metastable supercooled water. In this paper we show that micron sized water droplets immersed in Jet A-1 aviation fuel can exist in a metastable supercooled state to around −36 °C. In fact, the majority of droplets in our experiments froze homogeneously showing that the fuel itself did not catalyse ice formation. We suggest that H₂O particles will remain in a supercooled liquid state until they come into contact with a suitable solid surface in an aircraft’s fuel system or the temperature falls below the homogeneous freezing limit.     

ANALYSIS OF BATCH DRYING DATA USING SAS

An analysis technique is described which uses the nonlinear curve fitting capabilities of the Statistical Analysis System (SAS) to analyze batch drying data. The technique does not require any apriori assumptions about whether a constant rate period exists. Rather, the only assumptions necessary are the possible forms of the equations which can be used to describe the drying phenomenon. The program will then determine, based upon statistical techniques, where each equation should be used during the drying process in order to best describe the overall drying process. Two examples are given; the first analyzes the drying of. sand, a material having a constant rate period; the second analyzes the data describing the drying of French fried potato pieces.     

Ultraporous poly(lactic acid) scaffolds with improved mechanical performance using high‐pressure molding and salt leaching

A novel processing technique, i.e. high‐pressure compression molding/salt leaching, was developed to fabricate ultraporous poly(lactic acid) (PLA) scaffolds. The optimized composition was studied in relation to the porosity, pore morphology, thermal property, and mechanical performance of the PLA scaffolds. At a porogen (CaCO₃) content of 90 wt %, the scaffolds have an interconnected open pore structure and a porosity above 80%. It was truly interesting that the structural stability of high‐pressure molded scaffolds was remarkably improved based on the fact that its glass transition temperature (83.5°C) increased about 20°C, as compared to that of the conventional compression‐molded PLA (60°C), which is not far from physiological temperature (～37°C) at the risk of structural relaxation or physical aging. More importantly, the mechanical performance of PLA scaffolds was drastically enhanced under optimized processing conditions. At pressure and temperature of 1000 MPa and 190°C, the porous PLA scaffolds attained a storage modulus of 283.7 MPa, comparable to the high‐end value of trabecular bone (250 MPa) ever reported. In addition, our prepared PLA scaffolds showed excellent cellular compatibility and biocompatibility in vitro tests, further suggesting that the high‐pressure molded PLA scaffolds have high potential for bone tissue engineering applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3509–3520, 2013     

Propylen/Propan‐Trennung im Festbettadsorber und durch Membranpermeation

The metal‐organic framework Mg₂(dhtp) with the linker dihydroxyterephthalate is known as MOF‐74 or CPO‐27. Mg₂(dhtp) has been synthesized as powder to measure breakthrough curves in a fixed‐bed adsorber and adsorption isotherms, and as a supported thin membrane layer for permeation studies. The measurement of the breakthrough curves of the binary propylene/propane mixture shows that separation with the fixed bed adsorber is possible. Propylene shows a higher affinity to Mg₂(dhtp). Although the single gas propane flux is slightly higher than the one of propylene, the binary propane/propylene mixture is not separated.     

Disentangling the drivers of fertilising material inflows in organic farming

Organic farming systems are often nutrient-limited. Moreover, even if organic guidelines emphasize the reliance on ecological processes and recycling, the trend towards farm specialisation induces an increased reliance on off-farm fertilising materials in arable areas. There is, therefore, a need to better understand the drivers of nutrient inflows on organic farms. Our objectives were to assess the nitrogen (N,) phosphorus (P) and potassium (K) farm-gate inflows through fertilising materials, and the nutrient budget and use efficiency over a large range of organic farming systems. To do this, 56 interviews with organic farmers concerning their nutrient management for the years 2010 and 2011 were carried out in 2012 in three French agricultural districts distributed over a gradient of farming activity. The results showed that the farm-gate fertilising material inflows were strongly related to both the ratio of land under cereal and oilseed crops (proxy of nutrient ‘demand’) and the stocking rate (proxy of nutrient ‘supply’). However, other inflows (biological N fixation, feed use, fodders and straws) increased with the stocking rate, leading to low farm-gate N and K use efficiency (0.2 and 0.7, respectively) on livestock farms compared to arable, stockless farms (1.4 and 3.5, respectively). Such results helped to disentangle the drivers of nutrient use in organic farms compared to previous analyses based solely on farm production typology.     

Liquid Metal Marbles

Liquid metal marbles that are droplets of liquid metal encapsulated by micro‐ or nanoparticles are introduced. Droplets of galinstan liquid metal are coated with insulators (including Teflon and silica) and semiconductors (including WO₃, TiO_2, MoO₃, In₂O₃ and carbon nanotubes) by rolling over a powder bed and also by submerging in colloidal suspensions. It is shown that these marbles can be split and merged, can be suspended on water, and are even stable when moving under the force of gravity and impacting a flat solid surface. Furthermore, the marble coating can operate as an active electronic junction and the nanomaterial coated liquid metal marble can act as a highly sensitive electrochemical based heavy metal ion sensor. This new element thus represents a significant platform for the advancement of research into soft electronics.     

Production of ultra-thin porous metal paper by fibre space holder method

Abstract

The fibre space holder (FSH) method combines powder metallurgy and lost-foam casting with the aim of producing novel ultra-thin materials with micro-porous structures. A fabric, used as a spaceholder, is coated with metal powder (stainless steel, copper, nickel or titanium) in a water-soluble polymer binder. During sintering, the spaceholder is removed by a high temperature treatment to obtain the final porous metal sheet. This new material combines the advantages of fabric and porous metal. Its large specific surface area, minimum thickness of <30 μm, maximum porosity of >95% and strong liquid absorbency make it suitable for various application, in particular electrodes in hydrogen fuel cells and medical applications. The metal sheet can be further functionalised by coating with nanopowders.     

Physical Layer Development Framework for OsmocomBB

The open source GSM protocol stack of the OsmocomBB project offers a versatile development environment regarding the data link and network layer. There is no solution available for developing physical layer baseband algorithms in combination with the data link and network layer. In this paper, a baseband development framework architecture with a suitable interface to the protocol stack of OsmocomBB is presented. With the proposed framework, a complete GSM protocol stack can be run and baseband algorithms can be evaluated in a closed system. It closes the gap between physical layer signal processing implementations in Matlab and the upper layers of the OsmocomBB GSM protocol stack. An embedded version of the system has been realized with FPGA and PowerPC to enable real-time operation. The functionality of the system has been verified with a testbed comprising an OpenBTS base-station emulator, a receiver board with RF transceiver and our developed physical layer signal processing system.     

Experimental study on the mechanical properties and consolidation mechanism of microbial grouted backfill

Backfill mining technology is the practice of returning waste materials underground for both disposal and geotechnical stability, however, a challenge with current technologies is that they commonly require cement-based binders which have a relatively high environmental impact. Finding alternatives to cement-based binders can improve environmental performance and this paper proposes microbial grouted backfill (MGB) as a potential solution. In this paper, the effects of the cementation solution concentration (CSC), volume ratio of bacterial solution to cementation solution (VRBC), particle sizes of the aggregates, and the number of grouting batches on the mechanical properties of MGB are studied. The experimental results show that MGB strength increased, up to a peak value, as CSC was increased, before decreasing as CSC was increased further. The results also show that MGB strength increased, up to a peak value, as VRBC decreased, before decreasing as the VRBC was decreased further. The peak strength was achieved at a CSC of 2 mol/L and a VRBC of 1:9. The strength of the MGB also increased as the number of grouting batches increased. Graded MGB samples showed the highest UCS, 25.12 MPa, at particle sizes of 0.2 to 0.8 mm, while full (non-graded) MGB samples displayed mean UCS values ranging from 1.56 MPa when the maximum particle size was 0.2 mm, up to 13 MPa when the maximum particle size was 1.2 mm. MGB samples are consolidated by the calcium carbonate that is precipitated during microbial metabolism, and the strength of MGB increases linearly as calcium carbonate content increases. The calcium carbonate minerals produced in MGB materials are primarily calcite, with secondary amounts of vaterite.