Ultrasonic wave field effects on hydrogen production by water electrolysis

In this paper, Electrochemical impedance spectroscopy (EIS) was used to examine polarization impedance phenomena in ultrasonic water electrolysis. The method has been used previously for electrochemical analysis of fuel cells, corrosion, electroplating, etc. However, the EIS method and curvilinear regression have never been used before to analyze the electrochemical reactions which take place during water electrolysis. This study found that when a 2?V potential was applied, the ultrasonic wave field improved activity impedances and concentration impedances and accelerated the rising of hydrogen bubbles during water electrolysis. Ultrasonic power, electrode gap, and electrolyte concentration were the key parameters that affected water electrolysis. At normal temperature, when the electrode gap was 2?mm, the potential 4?V, and electrolyte concentration 40 wt%, the difference in current density between electrolysis without ultrasonic power and electrolysis with ultrasonic power of 225?W was 240?mA/cm². Deducting the power needed for the ultrasonic wave showed an power savings of 3.5?kW and an economical power efficiency of 15%.     

Tool design in electrochemical machining considering the effect of thermal-fluid properties

The effect of thermal-fluid properties are considered in the numerical simulation of the tool shape for a given workpiece shape in electrochemical machining. An embedding method is used for this inverse problem. A bubbly two-phase, one-dimensional flow model and a one-phase, two-dimensional flow model are applied to predict the fluid field of the electrolyte, respectively. Results show that the void fraction is the most important factor in determining the electrolyte conductivity and the shape of the workpiece. The proper machining conditions and numerical parameters are important to obtain a good solution. The relative error can be reduced under 0.002.     

Electrical-discharge wire cutting of ADI and its effect on impact energies

This study built up a set of machining data for electrical-discharge wire cutting (EDWC) of austempered ductile iron (ADI). The treated ADIs with the optimum toughness and the superior strength and hardness were very difficult to machine by the traditional technique. The EDWC process was used to cut the specimens of ADI and the remelted layer and the heat affected zone of the cut surfaces were measured and observed. Optimum cutting conditions were suggested for ADIs with different nodular counts and/or with varying matrix structures. Experimental results showed that if ADIs are cut by EDWC, then the formation of microvoids due to the decarburization and vaporization of graphite nodules at the remelted layer greatly deteriorate the quality of the machined surface. A severe bubbling was observed during cutting. This bubbling in the pool of dielectric fluid markedly lowered the cutting feedrate of EDWC. A model was proposed to correlate the cutting feedrate with the thickness of the workpiece, the time of the discharge spark, the feedrate override of the table, nodule counts of irons and the per cent retained austenite of ADIs.     

Analysis and Study on Polarization during Water Electrolysis Hydrogen Production

During a time of high energy consumption, water electrolysis is currently one of the alternative energy sources. At low voltages and low concentrations where activation and concentration polarizations are most dominant, the polarization effects are most significant and the electrolysis is most inefficient. Whereas at high voltages and high concentrations, the activation and concentration polarizations will quickly diminish, producing better electrolysis results. We can see from the empirical data that when the electrode distance is 2 mm and the electrolyte is 30 wt% KOH, a shorter electrode distance with an appropriate actual electrolysis voltage will produce lower polarization impedance values and hence the best efficiency in electrolysis. This study used electrochemical impedance spectroscopy (EIS) to detect relevant data on resistance. Applying it in the field of water electrolysis can provide another method to detect and clarify the phenomenon of polarization and impedance.     

Experimental investigation on the influence of electrochemical micro-drilling by short pulsed voltage

In this work, a tungsten carbide (WC) pin 50?μm in diameter was used to drill throughout nickel plates of 200?μm in thickness by electrochemical micro-machining. A novel pulsed power generator was used to support pulses of nanosecond duration in drilling. The influences of working parameters, such as pulsed duration, applied voltage, pulse frequency, electrolyte concentration, tool feed rates, and hole depth, on the hole overcut and conicity are investigated. A high-quality micro-hole with 11.1-μm overcut was drilled on a nickel plate of 200?μm in thickness.     

Modelling deposit growth on tilted rotating cylindrical substrate in centrifugal spray deposition

Abstract

Centrifugal spray deposition (CSD) using a tilted rotating cylindrical substrate may offer considerable technical benefits over the conventional CSD process using a reciprocating substrate in producing ring preforms. A model has been developed to calculate the deposit growth rate as a function of the liquid volume flowrate, the substrate radius, the tilt angle, the position of the atomising disc, and the longitudinal position at the substrate. The deposit band length is determined by the substrate radius and tilt angle. The distribution of the deposit growth rate is symmetrical provided the atomising disc is positioned on the substrate axis or displaced along the direction perpendicular to the tilt plane. For a tilt angle of <50·46°, the deposit thickness uniformity can be improved by increasing the displacement. A tapered deposit with a controlled gradient can be obtained if the atomising disc is positioned offcentre on the tilt plane.     

Two-dimensional two-phase numerical model for tool design in electrochemical machining

Tool design in electrochemical machining is investigated including the effects of thermal-fluid properties of the electrolyte. A two-dimensional two-phase numerical model is used to predict the thermal-fluid field. Simulation indicates that, as the curvature of the electrode shape varies widely, the two-dimensional phenomenon of the flow is apparent and the two-dimensional model should be used during the numerical simulation. In addition, a higher electrolyte flow rate slightly reduces the two-dimensional effects. As the curvature of the electrode shape varies only slightly, one-dimensional analysis is accurate and capable of reducing the calculation time.     

Numerical simulation of metal powder die compaction with special consideration of cracking

Abstract

Powder die compaction is modelled using the finite element method and a phenomenological material model. The Drucker–Prager cap model is modified with the goal to describe the formation of cracks during powder transfer, compaction, unloading, and ejection of the parts from the die. This is achieved by considering the cohesive strength and the cohesion slope, which characterise the current strength of the powder compact in the Drucker–Prager model, as state dependent variables. Evolution equations are formulated for these variables, so that the strength increases by densification and decreases by forced shear deformation. Some of the parameters appearing in the evolution equations are determined from measured green strength values. An iron based powder (Distaloy AE) is used for the experiments. Examples are shown to demonstrate that the density distribution can be calculated accurately as compared with an experiment, that cracking can be modelled at least qualitatively correctly, and that the compaction of complex 3D parts can be simulated.     

Numerical simulation of electrochemical drilling

The purpose of the present paper is to describe the simulation of electrochemical drilling (ECD), which is generally affected by the electrical field and the flow field between two electrodes. A body-fitted transformation is applied to predict precisely the gradient of the electric potential field, and a bubbly-two-phase flow model is used to simulate the quasi-static electrochemical drilling process. The metal removal rate, determined by the variation of electric potential and the thermal-fluid properties, is then calculated. Numerical results agree well with experimental data. The void fraction is the most important factor in determining the electrolyte conductivity and the equilibrium shape of the workpiece. The overcut of the workpiece can be reduced by increasing the tool feed rate or decreasing the electrolyte flow flux. A bare bit type of tool, compared with coated tool and bare tool, can also diminish the overcut in ECD.