Convective diffusion in a parallel plate duct with one catalytic wall—laminar flow—first order reaction: Part II: Experimental

The catalytic reaction rate of combustion of hydrogen in air on platinized alumina was measured in a flat rectangular flow reactor with one catalytic wall in laminar flow. Since the rate of reaction is very high, this measurement normally must be made in turbulent flow. However, with the aid of the measured concentration profiles and the analysis presented in Part I, it was possible to ascertain the reaction rate in the laminar flow regime. The rate constants compare well with literature values which were measured in the turbulent flow regime. Average Nusselt numbers for mass transfer calculated for the diffusionally limited cases were in good agreement with those obtained from Part I. A narrow rectangular channel (aspect ratio = 8:1) with 16-in. of one wall comprising the reactive section was constructed for this investigation. The channel has a long preheat section, an adiabatic section with multiple heaters, and thermocouples for maintaining isothermal conditions. Two micrometer mounted probes are inserted through the wall opposite the replaceable catalytic section. Concentrations are measured at the inlet, inside the reactive section, and at the outlet in a mixing chamber.     

DUAL-TEMPERATURE ION EXCHANGE FRACTIONATION

ABSTRACT

This paper reviews the results obtained by studying the dual-temperature ion-exchange fractionation (DTIXF) technique. The DTIXF is based on the use of different affinity at different temperatures of ion exchangers towards ions to be separated. This technique allows to design absolutely reagentless and, as a result, wasteless fractionation technology. The review considers the temperature dependencies of selectivity of commercially available ion-exchange (LX) resins towards components of ionic mixtures of different complexity starting from binary model systems up to naturally existing nonacomponent effluents. A novel approach for predicting the temperature sensitivity of a given LX system is presented and discussed. The same approach has been shown to be applicable for the design of IX resins with temperature-dependent selectivity. The paper also reports the results obtained in the practical application of DTIXF technique for concentration of magnesium from seawater and copper from acidic mine waters. The flowsheets of DTLXF processes are proposed and discussed.     

The electrical delivery of a sublimable II–VI compound by vapor transport in carbon nanotubes

Progress in the field of femtogram (10⁻¹⁵ g) mass delivery relies on finding dependable transport vehicles and uncomplicated methods to tailor the deposition of active substances. Here, current-conductive containers consisting of turbostratic carbon nanotubes were used to store a light-emitting ternary alloy and guide its delivery on demand. We found that the electrically-activated delivery process of this sublimable compound, performed inside a transmission electron microscope, was highly dependent on factors such as the substrate type and current injection mode. Furthermore, our observations suggest that the alleged “missing matter” problem is not solely due to surface migration. Besides extending the field of electrical delivery to the realm of functional materials, the extrusion and mass transport of a sublimable II–VI compound demonstrates that it is possible to guide vapor migration using a carbon nanotube support.     

Internal geometry evaluation of non-crimp 3D orthogonal woven carbon fabric composite

Measurements of the internal geometry of a carbon fiber non-crimp 3D orthogonal woven composite are presented, including: waviness of the yarns, cross sections of the yarns, dimensions of the yarn cross sections, and local fiber volume fraction. The measured waviness of warp and fill yarns are well below 0.1%, which shows that the fabric termed here “non-crimp” has nearly straight in-plane fibers as-produced, and this feature is maintained after going through all steps of fabric handling and composite manufacturing. The variability of dimensions of the yarns is in the range of 4–8% for warp and fill directions, while the variability of the yarn spacing is in the range of 3–4%. These variability parameters are lower than respective ranges of variability of the yarn waviness and the cross-sectional dimensions in typical carbon 2D weave and 3D interlock weave composites, which are also illustrated in this work for comparison.     

Reactor technology options for distributed hydrogen generation via ammonia decomposition: A review

Hydrogen (H₂) fuel obtained via thermo-catalytic ammonia (NH₃) decomposition is rapidly attracting considerable interest for portable and distributed power generation systems. Consequently, a variety of reactor technologies are being developed in view of the current lack of infrastructure to generate H₂ for proton exchange membrane (PEM) fuel cells. This paper provides an extensive review of the state-of-the-art reactor technology (also referred to as reactor infrastructure) for pure NH₃ decomposition. The review strategy is to survey the open literature and present reactor technology developments in a chronological order. The primary objective of this paper is to provide a condensed viewpoint and basis for future advances in reactor technology for generating H₂ via NH₃ decomposition. Also, this review highlights the prominent issues and prevailing challenges that are yet to be overcome for possible market entry and subsequent commercialization of various reactor technologies. To our knowledge, this work presents for the first time a review of reactor infrastructure for distributed H₂ generation via NH₃ decomposition. Despite commendable research and development progress, substantial effort is still required if commercialization of NH₃ decomposition reactor infrastructure is to be realized.     

Concept of Effective Strain Rate: Different Approaches

The term “effective strain rate” is frequently encountered in literature devoted to the ice-structure interaction problem. As a rule, it is defined as a ratio between indentation velocity and structure width, multiplied by a certain nondimensional factor (αV∕d). Usually this parameter is used to separate different interaction regimes or different types of ice behavior during the indentation process. The concept of an effective strain rate, (esr) seems to be quite useful because it allows the comparison of the results of experiments conducted at different scales if esr is properly defined. What is more, the correct definition of esr may help to apply the results obtained on the basis of small-scale laboratory tests to real ice-resistant structures. On the other hand, the overall concept of an effective strain rate definitely lacks a fundamental basis and there is no consensus on the value of the nondimensional factor α. The present paper discusses various approaches to the definition of esr and gives a few analytical expressions for esr derived for different indentation problems.     

Grain boundary motion and grain growth in zinc in a high magnetic field

The motion of grain boundaries in zinc bicrystals (99.995 %) driven by the “magnetic” driving force was measured. An in situ technique for observations and continuous recording the boundary migration was applied. Planar symmetrical and asymmetrical $ \left\langle {10\overline{1} 0} \right\rangle $ tilt grain boundaries with rotation angles in the range between 60° and 90° were studied. The boundary migration was measured in the temperature regime between 330 and 415 °C. The mobility of $ \left\langle {10\overline{1} 0} \right\rangle $ tilt boundaries in zinc and its temperature dependence were found to depend on the misorientation angle and the inclination of the boundary plane. An application of a magnetic field during the annealing of cold rolled (90 %) zinc–1.1 % aluminum alloy sheet specimens substantially affected the texture and microstructure evolution. This effect is attributed to the additional magnetic driving force for grain growth arising due to the magnetic anisotropy of zinc.     

Silicon multi-branch nanostructures for decent field emission and excellent electrical transport

We report on the synthesis, field electron emission and electric transport properties of a novel nanomaterial: ordered arrays of crystallized silicon multi-branch nanostructures. A decent field electron emission with relatively low turn-on field of 3.16 V μm?1 and high field-enhancement factor of 1252 was received for the silicon nanobranches. The relevancies between field-emission current-voltage characteristic, turn-on field, threshold field and sample-anode distance have been thoroughly analyzed. In addition, electrical transport measurements revealed a small electrical resistance of 0.51 MΩ for as-prepared silicon nanobranches. In contrast, by improving the silicon nanobranch-electrode contact, vacuum annealing dramatically reduced the electrical resistance, by a factor approaching two, while thermal oxidation resulted in a much higher resistance due to the amorphous oxide coating of the silicon nanobranches, both of the current versus voltage curves became more linear and symmetrical, and the transport stability was obviously improved.