On modeling the deformations and tool-workpiece interactions during machining metal matrix composites

Significance of application of metal matrix composites (MMCs) in various industries has already been demonstrated. In order to address the challenges faced during machining MMCs, development of novel modeling techniques for understanding the mechanics of the process is crucial. This paper presents a new approach towards finite element modeling of MMC machining process to facilitate the analysis of plastic deformations. Transient Lagrangian modeling is used with adaptive remeshing control in order to reduce the effects of mesh distortions on accurate estimation of plastic deformation during machining. The thorough understanding of MMC plastic deformations, which is achieved using the developed model, is an asset in analysis of MMC behavior during the process.     

Analysis of the hazards for the molten cuprous chloride pouring operation in an industrial hydrogen production facility

An analysis is reported of a design for a local exhaust ventilation system for the molten cuprous chloride pouring station in an industrial plant. Heat recovery from molten cuprous chloride is a key process within the copper–chlorine (Cu–Cl) cycle of thermochemical water splitting for hydrogen production. Because of particulate matter, dust, and vapors emitted by the molten salt, an effective and safe design is crucial. The design process involves calculating duct diameters to provide the desired duct air velocity through the system. The static pressure is evaluated so that the fan size can be determined. An adequate supply of makeup air must be provided to replace the air exhausted through the ventilation system. The economics of the ventilation system and ways to protect employee health, as well as minimize the costs associated with exhaust ventilation, are also described. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparison of molten salt heat recovery options in the Cu-Cl cycle of hydrogen production

This paper presents a comparative review of different options for recovering heat from molten CuCl in the Cu-Cl cycle of hydrogen production. Various technologies exist for recovering heat from the molten CuCl in the cycle, but each has its advantages and challenges. In this paper, different parameters such as heat transfer rate, additional materials in the cycle, energy efficiency, temperature retention, economics, material issues, and design feasibility are considered in the evaluation of methods. It is shown that casting/extrusion, atomization methods, with a separate vessel using water as a coolant and rotary/spinning atomization using air as a coolant, can be considered as the most efficient and reliable methods for heat recovery from molten CuCl.     

Pinch analysis for recycling thermal energy in the Cu–Cl cycle

Due to lower temperature requirements than other thermochemical cycles, the copper-chlorine (Cu–Cl) cycle is one of the most promising cycles for hydrogen production. The cycle consists of a number of endothermic and exothermic processes. The overall efficiency of the cycle can be improved by recovering as much heat as possible from the exothermic processes within the cycle and minimizing the net heat input to the cycle. In this paper, a pinch methodology is used to determine the minimum energy requirement for the overall Cu–Cl cycle, if heat recovery within the cycle is optimized. All heating and cooling flows (actual or potential) are presented as temperature-energy flow profiles and combined into composite curves for the entire cycle. Additional equipment and the overall thermal layout of the cycle are also investigated.     

Real-time PH-based interpolation algorithm for high speed CNC machining

Various methods for parametric interpolation of non-uniform rational B-spline (NURBS) curves have been proposed in the past. However, the errors caused by the approximate nature of the NURBS interpolator were rarely taken into account. This paper proposes an integrated look-ahead algorithm for parametric interpolation along NURBS curves. The algorithm interpolates the sharp corners on the curve with the Pythagorean-hodograph (PH) interpolation. This will minimize the geometric and interpolator approximation errors simultaneously. The algorithm consists of four different modules: a sharp corner detection module, a PH construction module, a feedrate planning module, and a dynamics module. Simulations are performed to show correctness of the proposed algorithm. Experiments on an X?CY table confirm that the developed method improves tracking and contour accuracies significantly compared to previously proposed algorithms.     

Analysis of two‐dimensional porous fins with variable thermal conductivity

Analysis of porous fins for their higher heat transfer in comparison with solid fins with identical volumes has attracted significant attention. In this paper, a two‐dimensional thermal analysis of a porous fin having variable thermal conductivity coefficient is performed using finite difference method. Heat transfer through porous media is simulated using passage velocity from Darcy's model. The thermal conductivity of the solid phase is considered as a linear function of temperature. It is found that the temperature profile of the fin is completely two‐dimensional even for high Rayleigh and Darcy numbers (Ra = 10³～10⁴, Da = 0.01), because the temperature changes significantly along the transverse axis especially for lower Rayleigh and Darcy numbers. Also, the effects of important nondimensional parameters such as Rayleigh and Darcy numbers, porosity, Nusselt, thermal conductivity, and aspect ratio on the temperature profile are investigated. The results demonstrate that the temperature distribution is strongly dependent on the Rayleigh and Darcy numbers.     

Evaluation of exposure to (ultra) high static magnetic fields during activities around human MRI scanners

Objective

To assess the individual exposure to the static magnetic field (SMF) and the motion-induced time-varying magnetic field (TVMF) generated by activities in an inhomogeneous SMF near high and ultra-high field magnetic resonance imaging (MRI) scanners. The study provides information on the level of exposure to high and ultra-high field MRI scanners during research activities.

Materials and methods

A three-axis Hall magnetometer was used to determine the SMF and TVMF around human 3- and 7-Tesla (T) MRI systems. The 7-T MRI scanner used in this study was passively shielded and the 3-T scanner was actively shielded and both were from the same manufacturer. The results were compared with the exposure restrictions given by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).

Results

The recorded exposure was highly variable between individuals, although they followed the same instructions for moving near the scanners. Maximum exposure values of B = 2057 mT and dB/dt = 4347 mT/s for the 3-T scanner and B = 2890 mT, dB/dt = 3900 mT/s for 7 T were recorded. No correlation was found between reporting the MRI-related sensory effects and exceeding the reference values.

Conclusions

According to the results of our single-center study with five subjects, violation of the ICNIRP restrictions for max B in MRI research environments was quite unlikely at 3 and 7 T. Occasions of exceeding the dB/dt limit at 3 and 7 T were almost similar (30% of 60 exposure scenarios) and highly variable among the individuals.

     

Ultrasound-assisted fluidized bed drying of paddy: Energy consumption and rice quality aspects

Several studies have been conducted on equipping conventional fluidized bed with some technologies to increase drying efficiency and its performance. The objective of this study was to investigate the influence of high-power ultrasound (HPU) on fluidized bed drying of paddy in terms of drying kinetics, grain quality (percentage of cracked kernels and bending strength of grain kernels), and specific energy consumption (SEC). To decrease the initial moisture content of paddy from 26.5?±?0.5% (kg/kg, d.b) to the final moisture content of 13?±?0.5% (kg/kg, d.b), the experiments were conducted in a factorial design at three levels of ultrasound power densities (11.1, 14.6, and 18.7?kW/m³), four levels of frequencies (20, 25, 28, and 30?kHz), and three levels of drying air temperatures (30, 40, and 50°C). Application of HPU in conjunction with conventional fluidized bed drying led in 23% decrease in drying time as well as improvement in grain quality, in terms of percentage of cracked kernels and bending strengths. In addition, SEC reduced approximately by 22%, as HPU applied at selected drying condition.