Entropy Generation Due to Natural Convection in a Partially Open Cavity with a Thin Heat Source Subjected to a Nanofluid

This article presents a numerical study of natural convection cooling of a heat source mounted inside the cavity, with special attention being paid to entropy generation. The right vertical wall is partially open and is subjected to copper–water nanofluid at a constant low temperature and pressure, while the other boundaries are assumed to be adiabatic. The governing equations have been solved using the finite volume approach, using SIMPLE algorithm on the collocated arrangement. The study has been carried out for a Rayleigh number in the range 10³ < Ra < 10⁶, and for solid volume fraction 0 <? <0.05. In order to investigate the effect of the heat source and open boundary location, six different configurations are considered. The effects of Rayleigh numbers, heat source and open boundary locations on the streamlines, isotherms, local entropy generation, Nusselt number, and total entropy generation are investigated. The results indicate that when open boundary is located up, the fluid flow augments and hence the heat transfer and Nusselt number increase and total entropy generation decreases.     

Damage Assessment and Ductility Evaluation of Post Tensioned Beams with Hybrid FRP Tendons

The study presented in this article concentrated on investigating the ductility and characterization of damage in concrete beams post tensioned with hybrid carbon-glass fiber-reinforced polymer (HFRP) composites. The investigation included an approach for design of flexural members with HFRP tendons and characterization of damage, load deformation response, ultimate strength, and failure modes. Direct tensile tests of hybrid FRP rods in a previous study had indicated elastoplastic response, enhanced ductility, and increased strain capacity. In this context, the current study focused on design and fabrication of post tensioned beams using glass or steel rebars for partial prestressing. All the beams were tested in flexure under four-point bending configuration. Results of the study are presented in terms of ductility index and enhanced load-deflection response in comparison with the conventional FRP materials. Damage characterization involved evaluating the specific features of the acoustic emissions for detecting the elastoplastic transition in the hybrid tendons. The method involved use of a high-resolution fiber-optic interferometer for detection and separation of acoustic emissions. By using the time domain response, it was possible to spatially localize the damage at various stages of the loading. Spectral energy of the acoustic emissions facilitated separation of carbon and glass fiber fractures.     

Microstructural evolution of a commercial ultrafine alumina powder densified by different methods

The densification and grain growth of bodies made from a commercial ultrafine alumina powder was investigated. The primary powder was initially subjected to dry (uniaxial cold pressing) and wet shaping (slip casting), followed by conventional (CS)-, two step (TSS)-, and microwave (MS) sintering to explore the effect of each series of treatments on the densification and microstructural evolution of the specimens. It was demonstrated that a uniform microstructure with higher density would be obtained using the wet shaping method. In addition, microwave sintering was found to be more effective into the densification of the specimens and in yielding a finer grain structure. It is believed that the high heating rate and effective particle packing are responsible for the improvements in these properties. On this basis, it was also demonstrated that the fracture toughness of the samples increased significantly through the application of microwave sintering.     

Agitation of Herschel–Bulkley fluids with the Scaba–anchor coaxial mixers

The design of the coaxial mixers depends on many interrelated parameters including the geometry and dimensions of the mixing vessel, the location and type of the impellers, speed ratio, impeller diameter, rotation mode, and fluid rheology. No study has been reported in the literature regarding the mixing performance of the coaxial mixers in the agitation of yield-pseudoplastic fluids. Thus, the main objective of this study was to evaluate the performance of a Scaba–anchor coaxial mixer (a novel configuration) in the mixing of xanthan gum solutions (yield-pseudoplastic fluids). The Herschel–Bulkley model was used to describe the rheological behavior of the xanthan gum solutions. To develop new correlations for the generalized Reynolds and power numbers of the coaxial mixers employed in the agitation of this class of non-Newtonian fluids, we utilized numerous experimental and computational fluid dynamics (CFD) data. The new correlations were tested successfully at different operating conditions (e.g. speed ratio, fluid rheology, and operation mode).     

Pearlite determination in plain carbon steel by eddy current method

Eddy current method has been used for the evaluation of pearlitic microstructure in low to high plain carbon steels. Plain carbon steel samples were heat treated in a furnace. Half of these were slowly cooled in the furnace and half in the air. This resulted in different pearlitic microstructures in the samples. Eddy current readings for all the samples were recorded and studied. It was found that eddy current measurement can be used for obtaining reliable and quick detection of pearlitic percentage in plain carbon steels.     

Effect of dust-neutral collisions on the dust characteristics in a magnetized plasma sheath

The characteristics of dust in a plasma sheath are investigated in the presence of an external magnetic field and taking into account the dust-neutral collision force. The continuity and momentum equations of ions and dust particles are solved numerically with various magnitudes of collision force by using the fluid model. The numerical results have revealed that the collision force reduces the dust gyro radius, changes the positions of the extrema of the dust density and the velocity in the depth direction. It is shown that the collision force reduces the dust kinetic energy which has no fluctuation even in a strong external magnetic field.     

Optimization of hole-making operations: a tabu-search approach

This paper reports a tabu-search approach to minimize the total processing cost for hole-making operations. Four issues, namely, tool travel scheduling, tool switch scheduling, tool selection, and machining speed specification have been simultaneously addressed in this study. The total processing cost consists of tooling cost, machining cost, non-productive tool travelling cost, and tool switching cost. This problem has a structure similar to the Travelling Salesman Problem (TSP) and hence is NP-complete. In addition, the problem under consideration is more complex since the cost associated with each operation is both sequence-dependent and position-dependent. To provide an efficient solution procedure, a tabu search approach is used. To improve the search performance two new neighbourhood generation and move selection policies have been proposed and tested. The decisions on the above issues can be made simultaneously based on the output of the proposed algorithm. The results obtained from computational experiments show that the total processing cost can be significantly reduced within a reasonable search time. The effects of some search parameters and diversification strategies on the search performance have also been investigated.