MEASUREMENT AND CONTROL OF ELECTROSTATIC CHARGES ON PULVERIZED COAL IN A PNEUMATIC PIPELINE*

Pulverized coal particles flowing in a pneumatic pipeline are naturally charged to a detectable level due to collisions with pipe walls. Systematic charge measurements of Anthracite (AN) coals, Medium Volatile Bituminous (MVB) coals and Lignite A (LIGA) coals in a grounded copper pipe have been made with an upgraded charge measuring system. The net particle charges were found to be positive, although both negative and positive charges were detected in all experiments. Effects of air humidity and conveying velocity on particle charges were examined. The mean particle charge was found in the order of 10^-12 Coulomb and the charge-to-mass ratio in the order of 10^-5 C/kg. Charge elimination techniques by strict humidity control and by introducing neutralizing charge carriers, such as minus 1 μm activated charcoal fines, ammonia, and piezoelectric ionized gas were explored. Effective reduction of 70 % to 85 % of particle charges was achieved. A charge neutralization mechanism was proposed to interpretate the measured results.     

SIMULATION OF GASEOUS COMBUSTION AND HEAT TRANSFER IN A VORTEX COMBUSTOR

This article presents the numerical simulation of gaseous combustion and heat transfer in a novel vortex combustor (VC) recently developed for commercial heating applications. A new algebraic Reynolds stress model for strongly swirling turbulence, the eddy break up model for turbulent combustion, and the four-heat-flux model for thermal radiation were employed in the present calculations. Different thermal boundary conditions were specified on the combustor walls. The calculations were conducted on a 22-cm ID VC firing gaseous fuel at 58-, 41-, and 38-kW thermal inputs. Detailed effects of firing rate on the gas axial and tangential velocities, streamlines, temperature, species mass concentrations and wall heat removal are presented, from which the distinct features of the VC flow, combustion, and heat transfer are delineated.     

Is the compression of tapered micro- and nanopillar samples a legitimate technique for the identification of deformation mode change in metallic glasses?

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A NOVEL QUICK-CLOSING PROBE FOR MEASURING LOCAL PARTICULATE PHASE DENSITY IN GAS-PARTICLE SUSPENSIONS

An innovative quick-closing probe system was designed, built, and tested for measuring the local particulate phase density of gas-particle suspensions. Experiments with glass beads and powder coals were conducted in a horizontal channel with an aspect ratio of 11 to 1, and also in a 0·25 m I.D. bench-scale vortex chamber. Results of particle density distributions in these two systems indicated the ability of the probe to perform in highly turbulent, swirling, dilute and intermediate phase gas-particle suspension flows. The probe was connected with a microcomputer-assisted particle weighing system for data collection and reduction. Comparison of measured data by this probe with calculated results was assessed. Since this probe requires no calibration curve nor empirical equation, it serves as a primary standard for particle density measurements. The design features, working principle, component characteristics, overall performance, and test results are discussed in this paper.     

Microstructure of reactively sputtered oxide diffusion barriers

Molybdenum oxide (Mo_1-x O _x ) and ruthenium oxide (RuO₂) films were prepared by rf reactive sputtering of Mo or Ru targets in an O₂/Ar plasma. Both films exhibit metallic conductivities. The influence of the deposition parameters on the phase that forms and on the microstructure of Mo_1-x O _x and RuO₂ films is reported. A phase transformation is observed in Mo_1-x O _x films subjected to heat treatment. The diffusion barrier performance of Mo_1-x O _x and RuO₂ layers interposed between Al and Si is compared.     

Achieving the Upper Bound of Piezoelectric Response in Tunable,Wearable 3D Printed Nanocomposites

The trade‐off between processability and functional responses presents significant challenges for incorporating piezoelectric materials as potential 3D printable feedstock. Structural compliance and electromechanical coupling sensitivity have been tightly coupled: high piezoelectric responsiveness comes at the cost of low compliance. Here, the formulation and design strategy are presented for a class of a 3D printable, wearable piezoelectric nanocomposite that approaches the upper bound of piezoelectric charge constants while maintaining high compliance. An effective electromechanical interphase model is introduced to elucidate the effects of interfacial functionalization between the highly concentrated perovskite nanoparticulate inclusions (exceeding 74 wt%) and light‐sensitive monomer matrix, shedding light on the significant enhancement of piezoelectric coefficients. It is shown that, through theoretical calculation and experimental validations, maximizing the functionalization level approaches the theoretical upper bound of the piezoelectric constant d₃₃ at any given loading concentration. Based on these findings, their applicability is demonstrated by designing and 3D printing piezoelectric materials that simultaneously achieve high electromechanical sensitivity and structural functionality, as highly sensitive wearables that detect low pressure air (<50 Pa) coming from different directions, as well as wireless, self‐sensing sporting gloves for simultaneous impact absorption and punching force mapping.     

Examination of selected synthesis and room‐temperature storage parameters for wood adhesive‐type urea–formaldehyde resins by 13C‐NMR spectroscopy. V

The effects of posttreatments of particleboard adhesive‐type urea–formaldehyde resins were studied. The resins were synthesized with formaldehyde/first urea (F/U₁) mol ratios of 1.40, 1.60, 1.80, 2.10, and 2.40 and then the second urea was added to give a final formaldehyde/urea ratio of 1.15 in alkaline pH. The resins were posttreated at 60°C for up to 13.5 h and the 2.5‐h heat‐treated resin samples were stored at room temperature for up to 27 days. Resins sampled during the posttreatments were examined by ¹³C‐NMR and evaluated by bonding particleboards. In the posttreatments, hydroxymethyl groups on the polymeric resin components dissociated to formaldehyde and reacted with the second urea, and methylene and methylene–ether groups were formed from reactions involving the second urea. Methylene–diurea and urea groups bonded to UF polymers were identified. As a result, the viscosity of the resins initially decreased but later increased along with the cloudiness of the resins. Bond‐strength and formaldehyde‐emission values of particleboard varied with posttreatment variables as well as with the F/U₁ mol ratios used in the resin syntheses. The results would be useful in optimizing resin synthesis and handling parameters. Various reaction mechanisms were considered. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1896–1917, 2003     

Modification of a neural network utilizing hybrid filters for the compensation of thermal deformation in machine tools

This study proposes a modified method that combines feed-forward neural network (FNN) and hybrid filters to improve the accuracy and reduce computation times for the prediction of thermal deformation in a machine tool. The hybrid filter consists of the linear regression (LR), moving average (MA) and autoregression (AR). Their outputs serve as input of FNN, which are estimated by the static and dynamic relationships between the temperature distributions and thermal deformations. This modified method enables the propagation accuracy between input and output layers of a static FNN to be improved and the learning time to be reduced. Furthermore, the modified method is compared with other three ones, which are traditional ARMA, FNN, and FNN combined with LR by numerical analysis and practical experiments. In analysis, the error margins of various approaches are compared using a finite element model that is determined for the relationships between thermal deformation and temperature distribution. Also, practical experiments of these approaches for a grinding machine are realized to compare the deformation predications according to temperature measurements.     

Superplasticity and superplastic forming of aluminum metal-matrix composites

Superplasticity hos been observed in many aluminum metal-matrix composites at extremely high strain rates (approximately 0.1–1 S^?1). These materials generally exhibited a strain-rate sensitivity value of about 0.3 and a maximum elongation of about 300%. It is believed thot the presence ofa liquid phose, or in some cases a low-melting-point region, at the reinforcement/matrix interfaces is responsible for the phenomenon. This phenomenon is not observed in all reinforced composites, despite the fact thot they contain fine grain sizes. Thus, a fine matrix grain size is a necessary but insufficient condition for the high-strain-rate superplasticity.     

Assessing the interfacial strength of an amorphous–crystalline interface

In this study, an amorphous-ZrCu/crystalline-Zr nanolaminate (500 nm each layer) was initially synthesised using sputter deposition and then fabricated into micropillar samples using focused ion beam machining with the amorphous–crystalline (a–c) interfaces inclined 45° to the pillar axis. These pillars were subsequently tested in compression in order to study the response of a–c interfaces to the applied shear stress, and further compared with the one that tested with their a–c interfaces normal to the compressive direction. By combining the stress–strain behavior and electron microscopic observations of fracture mode, we were able to estimate the a–c interfacial strength. It was strong (～1.3 GPa), it could effectively transfer the load and it was capable of accommodating large shear strain, but it was not strong enough to suppress the interfacial sliding. Molecular statics simulations were also carried out to reveal the elastic–plastic behavior and, in particular, the deformation mode of the pillars. The computed results were in excellent agreement with the experimental observations.