[en] Solar chimney power plant (SCPP) is an interesting project to produce clean and sustainable energy. An efficient SCPP system requires a very high chimney, and thus the optimization of the chimney shape presents an important way to enhance the SCPP performance. The aim of this paper is to analyze the effect of the divergent chimney shape on the airflow behavior inside SCPP. A comparison between four chimney shapes is carried out using CFD method: two cylindrical chimneys with different diameters and two divergent chimneys with different shapes. Indeed, both parameters were studied: the ratio of the inlet and outlet diameter of the chimney and the shape of the chimney which both hyperboloid and conical. The SCPP prototype was tested numerically and experimentally to validate the present computational outcomes. The obtained results confirm that the divergence shape affects directly the efficiency of the SCPP system. Moreover, the hyperboloid chimney presents the efficient solution which produces an important power output with keeping the chimney height constant.

[en] ASTM Mar-M247 is one of the superalloys used to manufacture gas turbine blades in power stations. This paper studies the microstructure across welded joints of a turbine blade made of a high-strength material (Mar-M247 alloy) employing AWS ERNiCrMo-3 as a filler alloy. This process was carried out using gas tungsten arc welding (GTAW). The dendritic and interdendritic structures were observed in the fusion zone. The results also showed the presence of epitaxial growth at the interface between the weld metal and the base alloy without solidification cracks. Al and Co concentrations gradually decrease towards the weld metal zone during the solidification process, while Cr content increases towards the fusion zone. Vickers hardness revealed that the hardness in the heat-affected zone (HAZ) is higher than that of the base metal and the weld metal zone, the average in the HAZ is 340HV, while in the base metal and the fusion zone is 322HV, 284HV respectively. Coarse grains in the HAZ were found with an agglomeration of carbides at the grain boundaries due to the input heat of the welding process. (author)

[en] Solar chimney power plant (SCPP) is an attractive way to produce electricity in the high solar radiations zones. It consists of three main components: collector, chimney and turbine. The chimney is considered as the most expensive part of the SCPP. This is due to the requirement of important height to achieve suitable performance. In this paper, a new chimney design of hyperbolic shape is proposed. The design is optimized by analyzing the impact of the divergence radius of the chimney on the SCPP performance using a 2D computational fluid dynamics code. For this end, the ratio of the hyperbolic chimney radius over the chimney height was varied from 0 to 0.3. Computational results were validated against test data from a developed experimental prototype. The comparison of the proposed designs with a conventional solar chimney power plant shows a significant performance improvement. In fact, the increase in the divergence chimney radius has led to more advanced power output. Specially, a rise of 295% of the total system efficiency is found when the divergence radius is set to 15 m.

[en] The hydrodynamic and turbulence model have been simulated by our computational fluid dynamics (CFD) code in a mechanically stirred tank equipped by axial turbine. The effect of the modified attack angle of the blade on the flow prediction is studied. The Reynolds-averaged continuity and Navier-Stokes equations were solved. For the closure of the above equations, a turbulence model κ-ε has been employed. The numerical solution of these equations was achieved by a finite-volume method. The CFD predicted flow fields at different locations in the tank as well as the power number show reasonably good agreement with the measured data and with those calculated from published experimental correlations

[en] Highlights: • This paper covers data lack of double entry turbine operating under gasoline engine. • This work examines double entry turbines behavior under in- and out-phase admission. • A comparison between intake admission modes of double-entry turbines was made. • The outer limb has a low ability to swallow the flow compared to the inner limb. • The turbine operates with a less fluctuating efficiency with the out-phase admission. The engine boosting system is one of the advanced technologies for engine downsizing. It reduces polluting emissions for diesel and gasoline engines. Double entry turbine turbocharger technology, typically used in diesel engines pressure boosting, plays a key role in improving horsepower and reducing wave interference between cylinders. The present work attempts to contribute to the knowledge of the double-entry turbine behavior for gasoline engines by the means of a comparative study between in-phase and out-phase admission modes. The turbine is modeled under the entire range of the gasoline engine flow pulse frequency from 33.33 Hz up to 200 Hz. From the numerical results, it was revealed that the outer limb of the double-entry turbine has a lower ability to swallow flow from the engine exhaust manifold compared to the inner limb under the out-phase admission mode. In this condition, the turbine total-to-static efficiency is increased by 10% compared to the in-phase admission mode. The results revealed a significant reduction in the hysteresis loop area of the total-to-static efficiency up to 35% under the out-phase admission mode.

[en] Highlights: • A numerical simulation is developed for an industrial boiler. • The fluid flow and the heat transfer characteristics are analyzed and discussed. • The numerical model is validated by comparison between numerical results and industrial measurements. -- Abstract: This paper aimed to develop a computational fluid dynamics simulation for an industrial boiler. The industrial boiler is used for the sulfuric acid production. A numerical model is carried out using the commercial code “ANSYS-FLUENT”. The simulations are developed for the case of the industrial boiler and a new proposed design. A clear understanding of the combustion phenomenon and the fluid flow within the boiler is provided from the simulations. The local characteristics of the fluid flow and the heat transfer such as the temperature; the velocity magnitude and the density distributions are presented and analyzed. The comparison between the numerical results and the experimental data is performed and a good agreement is found.

[en] Highlights: • The turbulent flow inside a new solar air heater test bench was investigated. • The natural and the forced convection modes have been considered. • The good agreement confirms the validity of the numerical method. • The range of temperatures is very useful in many industrial and domestic applications. In this work, the turbulent flow was studied in a new SAH (solar air heater) test bench. Particularly, we have considered the natural and the forced convection modes. The used test bench is composed by two passages separated by an absorber and powered by a fan working in a delivery mode, placed in the inlet side the insulation, for the forced convection mode. On this system, a glass is hanging on the front side and an absorber is inserted inside. On the glass side, it is connected to the box prototype through a pipe. The hot air flow is routed towards the box prototype. Two circular holes, are located in the same face of the box prototype. The inlet hole allows the hot air supply. However, the outlet hole allows its escape into the ambient environment. By using the ANSYS Fluent 17.0 software, the Navier-Stokes equations coupled with the standard k-ω turbulence model were solved. The numerical results were compared with our experimental data, established in the second passage of the SAH test bench. The good agreement confirms the validity of the numerical method. The range of temperatures is very useful in many applications such as industrial and domestic applications.

[en] In this work, the structural, electronic and optical properties of fluoroperovskite ABF₃ (A = K, Na; B = Mg, Zn) were studied using two different approaches: the full-potential linearized augmented plane wave method and the pseudo-potential plane wave scheme in the frame of generalized gradient approximation features such as the lattice constant, bulk modulus and its pressure derivative are reported. The ground state properties of these compounds such as the equilibrium lattice constant and the bulk modulus are in good agreement with the experimental results. The first principles calculations were performed to study the electronic structures of ABF₃ (A = K, Na; B = Mg, Zn) compounds and the results indicated that these four compounds are indirect band gap insulators. The optical properties are analysed and the source of some peaks in the spectra is discussed. Besides, the dielectric function, refractive index and extinction coefficient for radiation up to 25 eV have also been reported and discussed. (author)

[en] Highlights: • Experimental characterization of a Banki turbine for pressure regulation. • Banki turbine was tested under both in-range and out-range flow condition modes. • Performance correlations were developed for fast assessment for various flap angles. • An efficiency gain of 76% was obtained with an embedded flap regulation device. • The system allowed an efficient recovery of wasted energy in water supply networks. Efficiency improvement of water distribution networks needs to be in place to guarantee a long life period under suitable operating conditions. Excessive pressure is among the well-known issues encountered in water distribution networks which can cause strength damages to the piping system. In order to overcome this drawback and to reach a suitable water pressure delivery, the present work suggests a novel pressure regulation system. This regulation system is consisting of a Banki turbine equipped with a mobile flap as a control device. The suggested pressure regulation system was experimentally and numerically investigated under in-range i.e. like actual water distribution networks and out-range flow conditions. A set of computational fluid dynamic simulations was carried out to study the performance and flow characteristics around the turbine with and without a mobile flap. The flow solution was obtained by solving the Reynolds-averaged Navier–Stokes equations. Different rotor–stator interface and turbulence models, and mesh sizes were investigated to select the most accurate configuration of the numerical method. The validation of the numerical method was performed with an assessment of the standard error with respect to experimental data. Based on the experimental results, three correlations estimating the net head, the torque and the efficiency for given flap angle and volumetric flow rate were presented. Results revealed that the suggested regulation system presents a good efficiency up to 76% to recover the wasted hydrodynamics energy in water distribution networks.

[en] Highlights: • This paper proposes a new deflector system around Helical Savonius rotor. • Six deflector system configurations had been studied numerically. • The deflector system affects the hydrodynamic characteristics of the flow. • The rotor power coefficient was found dependent on the deflection angle. • The power coefficient of the rotor reaches 0.14 using the optimal configuration. -- Abstract: The use of renewable energy sources has becoming a necessity to generate electricity. Helical Savonius rotors have been preferred for small-scale hydropower generation. Numerous studies were carried out to improve the performance of the Helical Savonius rotor which has not been fully explored. In this paper, an experimental study was carried out to evaluate the performance of a Helical Savonius water rotor in an irrigation channel. In order to enhance the performance of the studied water rotor, a new deflector system design was proposed. Different configurations of the proposed deflector system were tested numerically using the commercial software ANSYS FLUENT 17.0. Without a deflector system, the maximum power coefficient is found to be equal to 0.125 at tip-speed ratio of 0.7. Using the optimal configuration of the new deflector system, the maximum power coefficient reaches 0.14. The utilization of this new design system is predicted to contribute towards a more efficient use of flows in rivers and channels for electricity production in rural areas.