Modelling of the mass flow distribution around an array of rectangular blocks in-line arranged and simulating the cross-section of a winding disc-type transformer

Experimental and numerical studies have both depicted the distribution of mass flow around an array of rectangular blocks due to buoyancy driven flows. The geometric configuration (array of rectangular blocks in-line arranged) simulates the cross-section of a disc-type transformer. It is a two-dimensional model. Transversal flows through horizontal channels (space between blocks) have been observed on an experimental set-up. Laser Doppler velocimeter is used to measure the velocity field. Numerical simulations of the flow in the same configuration have proved the influence of buoyancy forces, the pitch ratio and the asymmetric heating on the distribution of mass flow rate around the blocks.To have a better insight of this phenomenon, a physical model characterised by half heated blocks in-line arranged with alternating asymmetry of heat dissipation per block in the stream wise direction is used. It is meant to point out the conjugate effect of asymmetric heating and block spacing on the mass flow distribution around the blocks. The model establishes conditions to allow transversal flow and a correlation between the Rayleigh number and the maximum mass flow rate through horizontal channel. It is also possible to modify deliberately the heat dissipation rate asymmetry to get all the fluid streams through horizontal channels and this without any block-washers to direct the flow. A configuration is proposed to apply to power transformers.In short this study brings a major solution – cheap and non-intrusive (without physical bodies) – to the cooling of horizontal channels in a configuration featuring rectangular blocks in-line arranged.     

Non-intrusive reliability analysis of unsaturated embankment slopes accounting for spatial variabilities of soil hydraulic and shear strength parameters

Engineering with Computers - Recent developments on shear strength (Vf) of steel fiber-reinforced concrete beam (SFRCB) simulation have been shifted to the implementation of the computer aid...     

Thermal Performance Enhancement of Triplex Tube Latent Thermal Storage Using Fins-Nano-Phase Change Material Technique

Latent heat thermal energy storage (LHTES) systems using a phase change material (PCM) can reduce the heat-transfer rates during charging/discharging processes because of their inherently low thermal conductivity. In this study, heat-transfer enhancement using various configurations of longitudinal fins employing both a PCM and a nano-PCM in a large triplex-tube heat exchanger (TTHX) was numerically investigated via the Fluent 15 software. The results showed that the thermal conductivity of the pure PCM (0.2 W/m K) can be observably enhanced by dispersing 10% alumina (Al₂O₃) to 25%. Therefore, the melting time is reduced to 12%, 11%, and 17% for the internal, internal-external, and external fins, respectively, compared with the case of the PCM without nanoparticle. It is concluded that the model of external fins-nano-PCM embedded in a large TTHX is the most efficient model for achieving complete PCM melting in a short time (188 min), where improving the thermal performance to 14% and 11% compared with the TTHX with internal and internal-external fins-nano-PCM, respectively. The simulation results are validated and agree well with experimental results for the PCM and nano-PCM.     

Hybrid friction diffusion bonding of aluminium tube-to-tube-sheet connections in coil-wound heat exchangers

The present study presents and evaluates an application of a new solid-state bonding process, hybrid friction diffusion bonding (HFDB). HFDB is used to fabricate tube-to-tube-sheet connections for aluminium coil-wound heat exchangers. An industry-applicable process variant is developed, and its feasibility is demonstrated by gas leak tightness tests and tensile pull-out tests. The joints meet the requirements of industrial applications. Furthermore, the process is characterised by the thermal field development in the weld area and the applied process forces. The microstructure of the joint is investigated, and dynamic recrystallization is assumed to be the primary grain refinement mechanism in the thermo-mechanically affected zone.     

Corrosion of single layer thin film protective coatings on steel substrates for high level waste containers

Single-layer thin film coatings have been deposited on steel substrates and tested for their corrosion resistance. These coatings include TiN, ZrO₂, TiO₂, Al₂O₃, and MoS₂, and it is proposed that they will act as barriers to provide protection to the steel canisters that are part of the dry cask storage system for high level nuclear waste. Corrosion testing was completed using electrochemical potentiodynamic polarization techniques in aerated 1 M NaCl solution. Results show an exponential increase in corrosion rate with increasing temperature and an exponential decrease in the passive breakdown overpotential, which is directly related to the ability of a material to form and sustain a corrosion-inhibiting passive film in a given environment. Additionally, kinetic activation parameters have been experimentally determined for each material, leading to predictive equations for corrosion rates. The bare and coated samples corrode analogously, indicative of pores allowing the coating and substrate to corrode simultaneously. The samples were also placed in circulating salt brines of varying pH as a supplementary corrosion testing mechanism to explore their corrosivity over extended time. Negligible weight change was experienced by the bare and coated steel samples over a period of 5 months. Increasing the coating thickness and the number of layers may provide higher resistance to uniform and localized corrosion.     

Effect of process parameters on the macrostructure and defect formation in friction stir lap welding of AA5456 aluminum alloy

Friction stir welding could be considered as a suitable technique for joining of aluminum alloys due to the emerging of different problems in fusion welding of these alloys, especially in lap joint designs. For this purpose, it is necessary to optimize the process parameters while in this study, the combined effects of tool rotation and welding travel speed on the macrostructure and defect formation of friction stir lap welding of AA5456 was investigated. The rotating tool was plunged from the 5 mm-thick AA5456-H321 (top sheet) surface into the 2.5 mm-thick AA5456-O (bottom sheet) and lap joints were fabricated by rotational speeds of 300, 600, 800 and 1000 rpm and welding speeds of 15, 30, 60 and 100 mm min⁻¹. The effect of tool rotation and welding speed on the macrostructure, material flow and defect formation, i.e. hooking, kissing-bond and cavity, were studied by optical microscopy and scanning electron microscope. The results declared that hooking height decreased as the welding speed increased while kissing-bond was formed at higher welding speeds. Moreover, hooking region was extended as the tool rotational speed increased. However, at a high rotational speed, cavity was even created.     

Dual function of benzotriazole as copper alloy corrosion inhibitor and hydrochloric acid flow improver

The corrosion of copper-nickel alloy in hydrochloric acid has been investigated at different temperatures, benzotrizole concentrations and corrosive solution velocities. Weight loss technique has been used to evaluate the corrosion rate data. Results obtained have proved that benzotrizole has a dual effect by reducing both metal corrosion and flow losses. Maximum inhibition efficiency was 91.5%, while maximum drag reduction was 52.4%. Several mathematical equations are suggested successfully to represent the data with high correlation coefficients. Molecular dynamic simulations have been also performed to investigate the adsorption behavior of the inhibitor on the copper alloy surface. One of the novelties of the given work is the analogy between the corrosion process and fluid flow, as well as the investigation of the dual effect of benzotriazole on the corrosion process and the flow losses.     

Mathematical model for the prediction of cement compressive strength at the ages of 7 and 28 days within 24 hours

In this study 450 cement mortar cubes were cast from 50 different cement samples taken from 9 different cement factories, to develop a mathematical model that can predict Portland cement compressive strength at ages 7 and 28 days within 24 hours only. This is in order to save time and expense, that is lost in waiting for such a long period, and for quality control assurance for both produced cement (in cement factories), and concrete mixes in constructions. In addition, attention has been made on the right choice of variables of the cement itself (phase composition and fineness). In addition, an attempt has been made to use other variables that are believed to affect compressive strength of Portland cement as the minor oxides MgO, SO₃ and soundness. Other variables obtained from chemical analysis of the cement as LOI, IR, and LSF were also included in the model. The most important thing in this study is to get use of the concept of using early age strength to predict Portland cement strength at later ages for the first time. An attempt was made to combine both accelerated strength testing (as an early strength and UPV of cement mortar specimens), with the characteristics of the cement mentioned above, in predicting the compressive strength of cement. It was found that the accelerated strength yields good and high correlation with the compressive strength of cement, especially at the age of 28 days. In this work too, the importance of the ultrasonic pulse velocity (UPV) and mortar density were evident and the usefulness of using these variables in predicting the compressive strength of the cement was proved (because of fixing most of the factors affecting this property). Thus, it is possible to have good results that can be used in the prediction of compressive strength of cement. It was found that using each of the accelerated compressive strength f_acc, UPV and density of the mortar cubes yielded high correlation with the compressive strength than any of the other variables. Different combinations of variables were introduced into the model, in order to choose the variables that can significantly predict the cement compressive strength. In this work, it was possible to obtain a model that can predict the cement strength with standard errors of only 1.887 and 1.904 MPa and coefficients of correlation of 0.903 and 0.928, for cement strengths at 7 and 28 days respectively.     

Synthesis of Zirconia Nanoparticles in Distilled Water Solution by Laser Ablation Technique

Pulsed laser ablation in liquid （PLAL） has become an increasingly important technique for metals production and metal oxides nanoparticles （NPs） and others. This technique has its many advantages compared with other conventional techniques （physical and chemical）. This work was devoted for production of zirconia （ZrO2） nanoparticles via PLAL technique from a solid zirconium target immersed in a wet environment in order to study the effect of this environment on the optical properties and structure of ZrO2 nanoparticles. The solutions which used for this purpose is distilled water （D.W）. The produces NPs were characterized by mean of many tests such as UV-visible （UV-Vis.）, transmission electron microscope （TEM） and Z-Potential. The UV-Vis. A spectrum has atwavelength is 271 nm. The TEM test shows less than 10 nm average particle sizes with spherical and irregular shapes. Z-Potential test shows value about ＋56.1 mV which indicate for NPs stability with extremely low agglomeration solution.