Journal of Material Sciences & Engineering

This work reviewed the mixed convective heat transfer in absorber tubes similar to that of a linear Fresnel solar collector. Studies on the experimental and numerical simulations on linear Fresnel solar thermal collectors were reviewed to establish the gaps in the literature for further studies that could improve the overall performance of a linear Fresnel solar collector. The solar heat flux impinges on the absorber tubes of a linear Fresnel solar collector, from underneath independent of the position of the sun. This resulted in a circumferential non-uniform heat flux distributions around the tube wall, contrary to previous studies which assumed uniform heat flux boundaries for convenience. A number of studies had investigated mixed convection heat transfer in horizontal circular tubes for uniform heat flux distribution boundary symmetrical to the direction of the gravitational field. Studies are lacking for linear Fresnel solar collectors due to non-uniform circumferential heating of the absorber tubes from underneath for weak turbulent or laminar flow conditions. Studies are also lacking in the literature for the case of asymmetrical non-uniform heat flux distributions boundary on the absorber tube when the incident solar radiation deviated from the zenith angle position due to the sun tracking system of the collector. The degree of asymmetry of the heat flux distribution boundary could have significant influence on the internal heat transfers characteristics of the absorber tubes.

Nowadays, the use of light weight and yet resistant materials has a special place in the construction industry. Lightweight concrete is one of the materials that have been widely used in the construction industry due to its light weight, easier transportation and reduced production costs. Recently, the huge and extensive developments in concrete technology have been able to make significant progress in the concrete production industry by using new methods. The use of bacteria is considered a new and effective strategy in the concrete manufacturing industry. In this study, the role of calcite deposits on the compressive strength of lightweight concrete is investigated, before and after heat treatment of 150, 300, 450, 600 degrees celsius. The results obtained after examining the samples that were processed for 28 days in water and water containing calcium chloride and urea showed that the compressive strength of all samples decreased after being exposed to saturated heat. In addition, the presence of bacteria in the samples before the application of heat caused an increase. There is a significant increase in the compressive strength, and after the application of heat, the compressive strength of samples containing bacteria has a lower decreasing trend than the samples without bacteria, which indicates the positive effect of bacteria on the compressive strength of concrete even after applying heat.

Supported by the progress of High Entropy Composites (HEAs) produced by ordinary cycles in different applications, the improvement of HEAs for 3D printing has been progressing quickly lately. 3D printing of HEAs leads to an extraordinary potential for assembling mathematically complex HEA items with positive exhibitions, in this way rousing their expanded appearance in modern applications. Thus, an exhaustive survey of the new accomplishments of 3D printing of HEAs is given, in the parts of their powder improvement, printing processes, microstructures, properties, and likely applications. It starts with the presentation of the essentials of 3D printing and HEAs, as well as the remarkable properties of 3D printed HEA items. The cycles for the improvement of HEA powders, including atomization and mechanical alloying, and the powder properties, are then introduced. From that point, average cycles for printing HEA items from powders, to be specific, coordinated energy affidavit, specific laser softening, and electron pillar liquefying, are talked about concerning the stages, gem highlights, mechanical properties, functionalities, and possible utilizations of these items (especially in the aviation, energy, shaping, and tooling enterprises). At last, points of view are framed to give direction to future exploration.

DTA thermal analysis indicated that the polyaniline powder had discernible moisture content. This phenomenon was in agreement with the TGA results. Moreover, in the first run of DTA thermal analysis, an exothermic peak at 150ºC-310ºC was found. This peak was due to the chain cross linking, resulting from a coupling of two neighboring -N=Q=N-groups to give two -NH-B-NH groups through a link of the N with its neighboring Quindío ring. Thus, on the basis of thermal profile of these materials, we can say that among all composite material, the PANI/PbS composite materials, cross-linking or oxidative reaction starts at higher temperature, which indicates that the thermal stability of PANI/PbS nanocomposites is higher.

Direct Current-Electro Magnetic Pumps (DC-EMPs) are passive with no moving parts for circulating liquid metals in industrial applications, nuclear reactors, and experimental test loops. The Equivalent Circuit Model (ECM) is easy to apply and has been widely used to evaluate the performance of DC-EMPs. It over predicts the pumping pressure and the pump characteristics due to the incorporated assumptions. teffective magnetic flux density. This work quantifies the effects of these assumptions on the ECM predictions for a mercury DC-EMP. Analyzed experimental measurements for this pump show the fringe resistance and the magnetic flux density are not constant but depend on those of the liquid flow rate and the input electrical current. Results show that the 2D Finite Element Method Magnetics (FEMM) software accurately predicts the obtained values of the fringe resistance and the magnetic field flux density from the reported measurements at zero flow for use in ECM. With these values and the measured wall electrical contact resistance, the ECM over predicts the measured characteristics of the mercury pump by only ~7%. Neglecting the wall electrical contact resistance causes the ECM to over predict the pumping pressure for the mercury DC-EMP at an input electrical 6,740 A by 0.2-1.4%, depending on the flow rate. Nonetheless, accounting for the dependences of the fringe resistance and the magnetic flux density on the input electrical current and the liquid flow rate is important to accurately predicting the performance of DC-EMP, which is not possible using the ECM.

Now that weight saving is mandatory, composite springs invented by SARDOU SA are the best choice for automotive suspensions, compared to steel. A Joint Venture called Sara was created in order to mass produce composite coils springs, with start of production in 2014 for AUDI. This has demonstrated that the viability of producing composite coil springs. This paper describes the benefits of composite ‘C’ springs and ‘S’ springs for high performance vehicle suspensions, spacecraft stage separation, and satellite orbital launching. Developing spacecraft stage separation for CNES (Centre National d’Etudes Spatiales) used the concept of ‘line of action’. Two springs are inclined in such a way that the resultant line of action cross at a virtual center well above the springs. This virtual center is above the top stage which provides stable and straight guidance. This spacecraft technology can be transferred to buildings by creating a ‘virtual center’ of pendulation positioned above the building center of gravity. This is achieved by using tilted composite springs oriented in such a way that their line of action converges creating this ‘virtual center’. Thanks to the ‘virtual center’ position, the building behaves as a pendulum, hanging from above. When an earthquake happens, the building will oscillate around its ‘virtual center’ and will go back safely to equilibrium after the tremor. ‘C’ springs, offering anti rust, anti-settlement, fail safe suspension with a virtual center is a must for long lasting protection of buildings against earthquakes.