Effect of the temperature gradient,growth rate,and the interflake spacing on the microhardness in the directionally solidified Al-Si eutectic alloy

An alloy of composition Al-12.6 wt.% Si was prepared using metals of 99.99% purity. Weighed amounts of aluminium and silicon were melted in the vacuum-melting furnace. This irregular eutectic alloys were directionally solidified upward with a constant growth rate V (8.3×10⁻³ mm/s) and different temperature gradients G (2.0–7.8 K/mm) and also with a constant temperature gradient G (7.8 K/mm) and different growth rates V (8.3–498.7×10 ⁻³mm/s) in the directional solidification furnace. The interflake spacings λ and microhardness H_V were measured from both transverse section and longitudinal section of the specimen. The variations of H_V with respect to G, V, and λ have been determined by using the linear regression analysis method. It has been shown that H_V increases with the increasing values of G and V. On the other hand H_V values decreases with the increasing λ values. The Hall-Petch type relationships obtained in this work have been compared with the previous works.     

Energy Conservation Opportunities in an Industrial Boiler System

In this study, an experimental study has been performed for a natural gas fueled boiler operating at 42,000-kPa pressure and 713.15-K temperature with a nominal capacity of 33.33 kg/s to find improvement in the boiler efficiency. Temperature, pressure, velocity, and gas emissions measurements have been made and energy, mass balances, and exergy analysis have been formed. Then, efficiency of boiler, potential energy saving options and saving quantities, investment costs, and payback period for normal operating conditions have been calculated. From the measured data, the boiler and exergetic efficiency were calculated as 88.28 and 36.7%, respectively. It is seen that the main efficiency losses are leakage of air in the rotary type air heaters, operation of the boiler at high excess air/fuel ratios, operation of the boiler under the rated load, surface thermal losses, and high flue gas temperatures. The largest part of the boiler efficiency losses is due to the air leakage in the rotary type air heater. Due to air leakages, the load of the induced-draft fan increases and prevents the boiler to reach its normal boiler capacity. It has been calculated that if air leakage in rotary type air heater is reduced to acceptable limits (10%) in practice, boiler steam production capacity will be increased by 34.2% from 24.44 to 32.8 kg/s. Implementation cost is required only for reducing air leakages in the rotary type air heater and surface thermal losses. The investment cost for reducing air leakage in the rotary type air heater to the acceptable limits (10%) is between $600,000 and $700,000. Under these circumstances, the payback period of this investment cost is about 15 months.     

Effects of Surface Roughness on the Performance of Tangential Inlet Cyclone Separators

This study is carried out to investigate the effects of surface roughness on the flow field and cyclone performance. The flow inside the cyclone separator is modeled as a three-dimensional turbulent continuous gas flow with solid particles as a discrete phase. The continuous gas flow is predicted by solving the governing equations by using the Reynolds Stress turbulence model, and the modeling of the particle motions is based on a Lagrangian approach. The results of the numerical simulations are compared with experimental data as well as with the results of mathematical models. Analysis of computed results shows that increase of relative roughness due to corrosion, wear, or accumulation of particles on the inner walls considerably influences the tangential velocity, cyclone separation efficiency, and cyclone pressure drop especially for high inlet velocities. Decreases in cyclone collection efficiency and pressure drop with the increase in surface roughness are found to be more pronounced for high values of relative roughness.     

Multicriteria renewable energy planning using an integrated fuzzy VIKOR & AHP methodology: The case of Istanbul

The purpose of this study is twofold: first, it is aimed at determining the best renewable energy alternative for Istanbul by using an integrated VIKOR-AHP methodology. Second, a selection among alternative energy production sites in this city is made using the same approach. In the proposed VIKOR-AHP methodology, the weights of the selection criteria are determined by pairwise comparison matrices of AHP. In energy decision making problems, the judgments of decision makers are usually vague. As it is relatively difficult for decision makers to provide exact values for the criteria, the evaluation data for the alternative energy policies should be expressed in linguistic terms. In order to model this kind of uncertainty in human preferences, fuzzy logic is applied very successfully. Thus, both classical VIKOR and classical AHP procedures are performed under fuzzy environment. The originality of the paper comes from the application of the proposed integrated VIKOR-AHP methodology to the selection of the best energy policy and production site. It is found that wind energy is the most appropriate renewable energy option and Çatalca district is the best area among the alternatives for establishing wind turbines in Istanbul.     

Analytical characterisation and production of wool wax from Akkaraman and Morkaraman sheep's wool

The analytical characterisation and production of wool wax from Akkaraman and Morkaraman sheep in the East Anatolien region of Turkey have been investigated. It was shown that the analytical characteristics of Akkaraman and Morkaraman wool waxes differ only slightly from other wool waxes. Therefore, from a quality point of view, wool waxes obtained from this work can be used for the same purposes as wool waxes produced from different varieties of sheep.     

A study on microstructure of porous TiNbZr alloy produced as biomaterial

In the present study, titanium‐based biomaterial (Ti‐10Nb‐10Zr) with different porosity was fabricated by sintering at different temperatures. The porosity of fabricated samples is close to natural bone; also the compression strengths of the samples are higher than that of natural bone. The phases named α and β are seen in the microstructure of samples fabricated, but α phase partially converts into β phase with increasing sintering temperature. Porosity decreases with increasing sintering temperature, and compressive strength increases with decreasing porosity. Elastic modules of fabricated samples are close to natural bone, so these materials don't cause wear of bone.     

The current–voltage characteristics of V2O5/n-Si Schottky diodes formed with different metals

In this work, we reported the effect of different metal contacts on performance of metal–oxide–semiconductor (MOS)-structured Schottky diodes formed with the vanadium pentoxide thin film (V₂O₅) interfacial layer. V₂O₅ thin films were deposited by radio frequency (RF) magnetron sputtering on n-type silicon (n-Si) and Corning glass (CG) substrates at room temperature. Then, the obtained films were annealed at 300 °C and 500 °C. The effects of annealing temperature on physical properties of the films were investigated by X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, atomic force microscopy, UV–Vis spectroscopy, and photoluminescence. The MOS-structured Al/V₂O₅/n-Si, Ti/V₂O₅/n-Si and Au/V₂O₅/n-Si Schottky barrier diodes (SBDs) performance was analyzed with I–V measurements at room temperature. The Schottky diodes were compared with each other according to three methods (Classic, Norde and Cheung). The experimental results indicated that the Schottky diode produced with Al contact had better performance than the others.

     

Single steel strut mechanical testing: challenges and future research directions

Open-cell stainless steel foams, composed of hollow struts, are excellent candidates for energy absorption and thermo-mechanical applications. The basic mechanical element responsible for the function of these foams is the single strut. However, testing and characterisation of single foam struts to predict the foam strength have stirred up a new debate about approaches to micro-tensile testing of such elements. In this paper, we present a protocol for in-situ micro-tensile testing of hollow steel struts using a custom-made grip system. The adapted grips make it possible to perform analysis of the deformation of multiple sintered struts. Here we present and discuss challenges encountered during such micro-tensile testing of hollow steel struts.     

A robust integrator algorithm with genetic based fuzzy controller feedback for direct vector control

The voltage model used for direct vector control has in the flux calculation process an open integration problem, which is generally solved with a feedback loop. In this paper, a new design method is developed for the feedback loop of the integrator. The method, as apart from standards in the literature, uses a fuzzy controller. Fuzzy controllers are knowledge-based systems that include fuzzy rules and fuzzy membership functions to incorporate human knowledge into their knowledge base. The determination of these rules and membership functions is one the key problems when designing fuzzy controllers, and is generally affected by subjective decisions. In this study, a fuzzy controller with rules and membership functions determined by genetic algorithms (GAs) in this study is designed and tested on various motors of different power ratings. The proposed method is simulated by using MATLAB/SIMULINK and implemented on an experimental system using a TMS320C31 digital signal processor.     

Study of RF Linearity in sub-50 nm MOSFETs Using Simulations

We investigate the linearity performance of dual-gate and fully-depleted silicon-on-insulator MOSFETs through use of 2D computer simulations, which take into account quantum mechanical considerations and non-equilibrium transport effects. We show that DG MOSFET is superior not only in terms of g _m /I _d characteristics, central to analog performance, but also in terms of linearity performance, by up to 5 dBm, in most operating conditions. Linearity figures of devices considered in this work range from ?10 to ?20 dBm, which answer the needs of mobile communication standards currently in use. We also observe that, when properly scaled, bulk MOSFETs display competitive analog performance and have third-order intercept figures very similar to SOI device. We can identify, through simulation experiments, that quantum mechanical effects have positive impact on linearity, while non-equilibrium conditions lower linearity performance. With increasing drain bias, we find that linearity saturates at a moderately low voltage (～1 V) in all devices.