Simultaneous synthesis and consolidation of nanostructured TaSi2–Si3N4 composite by pulsed current activated combustion

Dense nanostructured 4TaSi₂–Si₃N₄ composite was synthesized by pulsed current activated combustion synthesis (PCACS) method within 3 min in one step from mechanically activated powders of TaN and Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense 4TaSi₂–Si₃N₄ composite with relative density of up to 98% was produced under simultaneous application of a 60 MPa pressure and the pulsed current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated.     

Multi-agent-based task assignment system for virtual enterprises

Manufacturing enterprises continuously have to cope with changing markets that are unpredictable and diverse, with increased global competition and with ever-changing customer demands. These requirements have led to the emergence of the virtual enterprise (VE). The creation of these enterprises, called as VEs, is becoming a growing trend as enterprises concentrate on their core competencies and economic benefit. An enterprise participating as a member of the VE should take initiative in involvement according to the internal production condition, which is changing dynamically with independent management sovereignty. However, most of researches have not considered these issues, that is the constituting enterprises have been regarded as one of the enterprises having their work stations distributed geographically. This paper proposes a multi-agent-based task assignment system for VEs, which attempts to address the selection of individually managed partners and the process of assigning tasks to them. A case example of assigning the tasks to partners is presented to illustrate and prove the proposed system's applicability.     

Thermal and electrochemical behaviour of C/LixCoO2 cell during safety test

Thermal and electrochemical processes in a 1000 mAh lithium-ion pouch cell with a graphite anode and a Li_xCoO₂ cathode during a safety test are examined. In overcharge tests, the forced current shifts the cell voltage to above 4.2 V. This causes a cell charged at the 1 C rate to lose cycleability and a cell charged at the 3 C rate to undergo explosion. In nail penetration and impact tests, a high discharge current passing through the cells gives rise to thermal runaway. These overcharge and high discharge currents promote joule heat within the cells and leads to decomposition and release of oxygen from the de-lithiated Li_xCoO₂ and combustion of carbonaceous materials. X-ray diffraction analysis reveals the presence of Co₃O₄ in the cathode material of a 4.5 V cell heated to 400 °C. The major cathode product formed after the combustion process cells abused by forced current is Co₃O₄ and by discharge current the products are LiCoO₂ and Co₃O₄. The formation of a trace quantity of CoO through the reduction of Co₃O₄ by virtue of the reducing power of the organic solvent is also discussed.     

Stress‐life prediction of 25°C polypropylene materials based on calibration of Zhurkov fatigue life model

In this study, to evaluate the chemical and mechanical properties of polypropylene (PP), activation‐energy and tensile tests were performed at room temperature (25°C) on pure PP and PP reinforced with glass fibre (GF). To improve the prediction accuracy of the fatigue life, three models based on the calibration of the Zhurkov model were proposed: a regression model, modified strain‐rate model and lethargy coefficient‐based model. Based on the experimental data analysis and statistical assessment results, we proposed a modified strain‐rate model that satisfies the dependency of the physical parameters and is congruent with the predicted fatigue life data. The experimental data and modified strain‐rate model were compared with the direct cyclic analysis results. The tendency of the frequency factor as a correction parameter in the modified strain‐rate model corresponded to the experimental activation energy and the increasing GF content.     

Magnetic field effect on mixed convection in a lid-driven square cavity filled with nanofluids

A numerical investigation of laminar mixed convection heat transfer in a lid-driven cavity filled with nanofluid under the influence of a magnetic field is executed. The left and right vertical walls of the cavity are insulated while the top and bottom horizontal walls are kept constant but different temperatures. The top wall is moving on its own plane at a constant speed while other walls are fixed. A uniform magnetic field is applied in the vertical direction normal to the moving wall. The governing differential equations are discretised by the control volume approach and the coupling between velocity and pressure is solved using the SIMPLE algorithm. The heat and mass transfer mechanisms and the flow characteristics inside the cavity depended strongly on the strength of the magnetic field. A comparison is also presented between the results obtained from the Maxwell and modified Maxwell models. The results show that the heat transfer is generally higher based on the modified Maxwell model.     

The analysis of adhesion force at the interface of gas diffusion layer and channel in polymer electrolyte membrane fuel cell

The adhesion force of water droplet on the gas diffusion layer (GDL) is modeled based on the droplet deformation. The deformed droplet is represented as an ovoid shape. The adhesion force is calculated based on it and verified by the surface tilting experiment. The model predicts the shape of deformed droplet and adhesion force within 30% error, whereas previous models predict adhesion force with error larger than 30%. The modified model is used to compare the adhesion force among 3 types of GDL having pore gradient. The comparison result is well matched with the water distribution in polymer electrolyte membrane fuel cell (PEMFC) and water detachment phenomena at the GDL. High adhesion force makes more water accumulation at the interface of GDL and gas supplying channel. This makes different boundary condition and changes the water distribution in PEMFC.     

An effective shape of floor splitter for reducing sub-surface vortices in pump sump

An experimental investigation on the effective shape of a floor splitter to reduce sub-surface vortices and cavitation which arise in the vicinity of the pump bells in pump sump is performed. A test model sump was designed based on the Froude number similitude for the recommended structure layout by HI-9.8 standard for pump intake design. To obtain an effective shape of the splitter as an anti-vortex device (AVD), three types of quadrilateral submerged bar with different shape and dimension in sectional area are considered. From the experimental results with and without the splitter attached on the floor under the bell mouth, it was confirmed that the installation of the AVD is very effective to reduce abnormal vortices including sub-surface vortices, pre-swirls and other undesirable hydraulic phenomena. Because of the splitter, sub-surface vortices under the bell mouth did not appear anymore and the swirl was dramatically weakened. The evaluation of AVD was made by the measurement of swirl angles indicating the strength of the vortices and pre-swirls. Splitters with square sections showed partly large swirl angles beyond the acceptable criteria of HI standard though a large square was more effective than a small one. Meanwhile, the splitter with trapezoidal section was showed swirl angle values of less than 5 degrees in all cases of pump operation. Among the three types of AVD, the trapezoidal splitter is the most effective one to suppress the vortices. It is very useful to reduce the occurrence of submerged vortices and to obtain stable inflow condition for designing a high performance pump sump.     

Effect of thermal non-equilibrium on transient hydromagnetic flow over a moving surface in a nanofluid saturated porous media

This work is made to study the effect of local thermal non-equilibrium (LTNE) on transient MHD laminar boundary layer flow of viscous, incompressible nanofluid over a vertical stretching plate embedded in a sparsely packed porous medium. The flow in the porous medium is governed by simple Darcy model. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. Three temperature model is used to represent the local thermal non-equilibrium among the particle, fluid, and solid-matrix phases. By applying similarity analysis, the governing partial differential equations are transformed into a set of time dependent nonlinear coupled ordinary differential equations and they are solved by Runge-Kutta Fehlberg Method along with shooting technique. Numerical results of the boundary layer flow characteristics for the fluid, particle and solid phases are obtained for various combinations of the physical parameters. It is found that the thermal non-equilibrium effects are strongest when the fluid/particle, fluid/solid Nield numbers and thermal capacity ratios are small. Moreover, the amount of heat transfer is maximum in nanoparticles than that of fluid and solid phases because of enhancement of thermal conductivity in nanofluids.     

Properties and rapid consolidation of nanostructured Al2O3-Al2SiO5 composites by high frequency induction heated sintering

The rapid sintering of nanostructured Al₂O₃ and Al₂O₃ to Al₂SiO₅ composites was investigated by a high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nanostructured Al₂O₃ and Al₂O₃ to Al₂SiO₅ composites were produced with simultaneous application of a 80 MPa pressure and induced output current of a total power capacity (15 kW) within 3 min. The sintering behavior, grain size and mechanical properties of Al₂O₃ and Al₂O₃ to Al₂SiO₅ composites were investigated.