Browsing by Subject "Mechanisms"

Now showing 1 - 3 of 3
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    Oxidative and thermal instability of biodiesel
    (2008) Arisoy K.
    The term biodiesel means the monoalkyl esters of long-chain fatty acids made from biolipids such as vegetable oils, animal fats, or algae. Chemical reactivity of biodiesel can be divided into oxidative and thermal instability. Many of the biolipids contain polyunsaturated fatty acid chains in that their double bonds have high chemical reactivity. The oxidative and thermal degradation occurs on the double bonds of unsaturated aliphatic carbons chains in biolipids. Oxidation of biodiesel results in the formation of hydroperoxides. The formation of the hydroperoxide follows a well-known peroxidation chain mechanism. The olefinic unsaturated fatty acid oxidation is a multi-step reaction process where primary products (conjugated diene hydroperoxides) decompose and chemically interact with each other to form numerous secondary oxidation products. The oxidative and thermal instability are determined by the amount and configuration of the olefinic unsaturation on the fatty acid chains. The viscosity of biodiesel increases with the increase of thermal degradation degree due to the trans-isomer formation on double bonds. The decomposition of biodiesel and its corresponding fatty acids linearly increases from 293 K to 625 K. The densities of biodiesel fuels decreased linearly with temperatures from 293 K to 575 K. The combustion heat of biodiesel partially decreases with the increase of thermal degradation degree.
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    Design and simulation of a lqg robust controller for an electrical power system
    (2008) Oǧuz Y.; Erdal H.; Taşkin S.
    LQG robust controller, electrical power system, modeling, Matlab/Simulink. This paper describes a LQG robust controller for the load frequency control of an electrical power system. The controller is used in order to achieve robust stability and good dynamic performance against the variation of power system parameters and its load. The application of the proposed LQG robust control scheme is implemented through the simulation of a single area power system model. The proposed robust controller for power systems stability is designed using Matlab/Simulink program. Simulation results confirm the performance of the proposed controller for the electrical power system.
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    Improved mechanical performance of three-dimensional woven glass/epoxy spacer composites with carbon nanotubes
    (SAGE Publications Ltd, 2021) Yildirim F.; Aydin M.; Avci A.
    Three-dimensional polymer composites offer various features and design options due to their hollow structure and lightweight. However, to exploit their advantages, it is a must to improve their structural features and mechanical performances including out-plane direction. Although introducing thermoplastic fillers between the plies or multilayered design addresses on this critical issue, the benefits offered by the nanoparticles with superior mechanical properties come a step forward as an another engineering solution. Based on this motivation, the goal of this study is to investigate the impact of multiwalled carbon nanotubes on the mechanical and thermomechanical performances of three-dimensional woven glass/epoxy spacer composites. Therefore, multiwalled carbon nanotubes at various content were introduced into epoxy matrix, and the multiwalled carbon nanotubes–epoxy mixture was infused to three-dimensional woven fabric with the vacuum-assisted resin transfer method. The obtained results indicated that the three-point bending strength and modulus were enhanced up to 25 and 80% for warp direction and enhanced up to 44 and 85% for weft direction with carbon nanotube addition, respectively. Tensile strength developed in the warp direction by 7%, while the strength value in the weft direction did not change. The tensile strain values for warp and weft directions enhanced up to 19 and 12% with carbon nanotube addition, respectively. In addition, thermomechanical analysis has revealed that the glass transition temperature and storage modulus were also improved. Particle dispersion detection with color measurement and scanning electron microscopy analyses revealed the effectiveness of the ultrasonic mixing on the dispersion of carbon nanotubes in the epoxy matrix. The consequences of carbon nanotube addition on microscale morphology were discussed based on the fracture morphologies to nanoscale and microscale toughening mechanisms in the existence of carbon nanotube reinforcement. © The Author(s) 2021.