This book focuses on the dissemination of information of permanent interest in mechanic applications and engineering technology. The considered applications are widely used in several industrial fields, particularly in those of automotive and aerospace aspects. Many features related to Mechanic processes are presented. The presented case studies and development approaches aim to provide the readers, such as engineers and PhD students, with basic and applied studies broadly related to Mechanic Applications and Engineering Technology.
In the first chapter, the twisted Darrieus turbine is suggested as an amelioration of the conventional Darrieus rotor by modifying it to have helical blades. This reform affords the twisted turbine’s better performances with regard to the conventional turbine. For this, a computational study of a twisted Darrieus rotor is conducted through the unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. Different grid sizes are investigated to assess the impact of grid generation on the computing findings. The validation of the computing method with antecedent tests is carried out to select the adequate grid size. The flow characteristics of the water around the twisted Darrieus rotor have been assessed and discussed.
In the second chapter, the purpose is to study the heat exchange which is directly related to factors such as Reynolds number, thermal properties of materials, geometric shapes and dimensions. A numerical study of the heat exchanges between cross-sections selected of a mini-channel cooler is carried out. Three different forms have been considered for cooling an electronic component using a nanofluid (CuO-water) as a cooling liquid with a 4% volume concentration of nanoparticles. The simulation is carried out using the ANSYS Fluent software. The Reynolds number (Re) is taken between 100 and 700, and the stream regime is assumed to be stationary. The results obtained for the three forms of mini-channels proposed show that the rise in the exchange surface between the CuO-water nanofluid and walls of the mini-channels leads to the increase in the heat exchange coefficient and to the amelioration of the maximum temperature of electronic components by increasing the value of the flow velocity. This is confirmed by the results of the third case. In contrast to the first case that does not contain ribs, and the second case, which contains two ribs inside the channel, these two cases provide insufficient heat exchange, and the maximum temperature of the electronic component remains high compared to the third case, which contains four ribs, the latter contributes to the increase in heat exchange inside the channel.
The complexity of orthodontic treatments requires archwires with specific biomechanical properties according to the different stages of therapy. Thanks to their wide elastic zone and low stiffness, superelastic NiTi alloy is used in the leveling and alignment phases. The friction that accompanies the beginning of treatment is a very complicated phenomenon, since in the presence of arch misalignments, the present normal force, which compresses the orthodontic archwire-bracket couple, is very dependent on the clinical situation. The third chapter aims to identify the friction responses and the degradation mechanisms of a superelastic NiTi orthodontic archwire as a function of the applied normal load. The latter represents the charges delivered by the archwire during its unloading, all through the first phases of treatment. Circular and rectangular samples with the most commonly used dimensions have been tested in a dry environment at room temperature. The results confirm that the wear of the NiTi alloy is amplified as a function of the normal force applied for the two tested archwire shapes. Indeed, the degradation regimes observed by scanning electron microscopy present a transition by increasing the load from a mainly adhesive regime to a more complex situation, in which wear by adhesion is accompanied by abrasive and delamination wear.
In the fourth chapter, the influence of the Reynolds number on the flow around a Savonius wind rotor is investigated. Particularly, various regimes defined by different Reynolds number values equal to Re = 98000, Re = 111000, Re = 124000 and Re = 137000 are considered. For this, an open wind tunnel is used to evaluate the global characteristics of the Savonius wind rotor. The overall performance evaluation of the rotor is focused on the power, the dynamic and the static torque coefficient evolution.
In the fifth chapter, Zn-Mn electrodeposition from additive-free chloride bath on steel is investigated. Several operating parameters, namely the Mn2 concentration, the current density and the stirring, are explored with regard to the Mn content in the Zn matrix. The Mn content depends on the applied current density and jumps from zero to a maximum of 11.4% under 140 mA/cm2. At high current density, Zn-Mn coatings are darker, more dendritic and with bad adhesion to the substrate. The dark appearance of Zn-Mn alloys is linked to oxy/hydroxide inclusions formed into the co-deposits.
In the sixth chapter, divalent europium-activated alpha-distrontium diphosphate (α-S2P2O7) phosphor powders are successfully prepared by a conventional solid-state reaction method under a reduced atmosphere. Synthesized samples are characterized by means of X-ray diffraction (XRD) patterns, nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy which signify the formation of a pure single phase of Sr2P2O7. The optical properties are studied in both the ultraviolet (UV) and vacuum ultraviolet (VUV) regions. The emission spectra are obtained by excitation at 131 or 320 nm, which presents a single intense blue-emitting band from 350 nm to 500 nm due to the 5d-4f transition of Eu2+, indicating that α-Sr2P2O7:Eu2+ phosphor powders are suitable for near-UV light-emitting-diode (LED) chips (360-400 nm). The influence of temperature on the luminescence intensity of α-Sr2P2O7:1%Eu2+ is investigated. The activation energy (Ea) for thermal quenching is reported. The phosphor shows excellent thermal stability on temperature quenching. The luminescence properties show that this host material has a highly promising blue-emitting phosphor for white-LED applications.
With the increasing development in the field of electronics, electronic devices have become smaller in size and more heat dissipating. This excessive heat leads to damage to the electronic components, and also their performance becomes bad. Therefore, the process of cooling them must be improved to increase their effectiveness in performance. For this purpose, a numerical study is performed in the seventh chapter to investigate the effect of different nanofluids on heat exchange in a silicon mini channel cooler for cooling electronic components. Three different types of nanofluids are considered (TiO2 -H2O, Ag-H2O, and SWCNT-H2O). In this study, the volumetric fraction of nanoparticles is taken to be 2%, the Reynolds number (Re) is varied between 100 and 700, and the flow regime is assumed to be stationary. The ANSYS Fluent 17.1 commercial software is used as a calculation tool to solve the governing equations, which depend on the finite volume method (FVM) in its solution. The relaxation of decreasing factors used in this study is 0.7 and 0.3 to maintain momentum and pressure, respectively. The residual values of the continuity equation and velocity components are in the range of 10-5 and 10-6, respectively, and the second-order upwind scheme has been used. The obtained results confirm that the maximum temperature of the electronic component decreases with the increase in the Reynolds number. The reduction in the temperature of the electronic component is more noticeable for the TiO2-water and SWCNT water nanofluid. Since the values of the coefficient of heat exchange between the channel walls and the nanofluid that contains the single-walled carbon nanotubes nanoparticles are the highest compared to the nanoparticles that do not contain carbon in their composition, therefore, this condition can be considered the best in heat transfer. Therefore, it is recommended that nanofluids containing nanoparticles SWCNT for cooling high-temperature electronic components should be used.
In the eighth chapter, a novel additive based on alkylphenol ethoxylate sulphite is investigated in Zn-Mn electrodeposition on steel from a chloride bath. Electrochemical study via cyclic voltammetry shows that the tested additive increases the over-potential of the Zn deposition, resulting from strong adsorption of molecules additives on the cathode surface. Thus, Mn-rich alloy containing 16.3% of Mn is successfully co-deposited. The morphology and crystallographic structure of Zn-Mn co-deposits are analyzed using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), respectively. SEM micrographs show that Zn-16.3% Mn alloy obtained in the presence of the tested additive displays hexagonal pyramid morphology. XRD analysis exhibited that Zn-16.3% Mn alloy is monophasic with hexagonal close-packed ε-Zn-Mn phase.
The purpose of the ninth chapter is to empower the scientific and technological community with the knowledge to identify and define key concepts of fire modeling and to develop the ability to apply the CFD (Computer Fluid Dynamics) tools to fire investigation and prevention using basic mathematical models. Combustion, thermal radiation, turbulence, fluid dynamics, and other physical and chemical processes all contribute to the complexity of fire processes. Flame shape, plume behavior, combustion product diffusion, and thermal radiation effects on neighboring objects can all be modeled with Large Eddy Simulation (LES) software. This paper uses many small and large-scale case studies under various boundary conditions to demonstrate the strength of the Fire Dynamics Simulator (FDS), an LES code, established by the National Institute of Standards and Technology (NIST).
Wind energy is renewable energy that does not require any fuel, does not create greenhouse gases, and does not produce toxic or radioactive waste. Wind power offers the possibility of reducing the operating costs of the electricity system. Vertical axis wind turbines (VAWT) of the Darrieus type, especially in small installations, are increasingly appreciated in current research on wind energy. H-shaped turbines may provide appealing spaces for new design strategies that seek to reduce the visual effect of the rotors and then boost their degree of integration in a variety of installation contexts. The main purpose of the tenth chapter is to define and critically evaluate the main design parameters of a 10 kW H-Darrieus vertical axis wind turbine that can be considered a candidate for rural and off-grid urban applications.
National School of Engineers of Sfax (ENIS)
Laboratory of Electro-Mechanic Systems (LASEM)
University of Sfax