Current Issue : July - September Volume : 2013 Issue Number : 3 Articles : 6 Articles
The pyrolytic characteristics and kinetics of new marginal soil energy plant Helianthus annuus stalk were investigated using\r\nthermogravimetric (TG)method from50 to 800�°Cinan inert argonatmosphere at different heatingrates of 5, 10,20and30�°Cmin-1.\r\nThe kinetic parameters of activation energy and pre-exponential factor were deduced by Popescu, Flynn-Wall-Ozawa (FWO), and\r\nKissinger-Akahira-Sunose (KAS) methods, respectively.The results showed that three stages appeared in the thermal degradation\r\nprocess.Theprimary devolatilization stage of H. annuus stalk can be described by the Avrami-Erofeev function (?? = 4).The average\r\nactivation energy of H. annuus stalk was only 142.9 kJmol-1. There were minor kinetic compensation effects between the preexponential\r\nfactor and the activation energy.Theresults suggest thatH. annuus stalk is suitable for pyrolysis, and more importantly,\r\nthe experimental results and kinetic parameters provided useful information for the design of pyrolytic processing system using H.\r\nannuus stalk as feedstock....
DC/DC converters are widely used in many industrial and electrical systems. As DC/DC converters are nonlinear and timevariant\r\nsystems, the application of linear control techniques for the control of these converters is not suitable. In this paper, a\r\nnew sliding mode controller is proposed as the indirect control method and compared to a simple direct control method in\r\norder to control a buck converter in photovoltaic applications. The solar arrays are dependent power sources with nonlinear\r\nvoltage-current characteristics under different environmental conditions (insolation and temperature). Fromthis point of view, the\r\nDC/DC converter is particularly suitable for the application of the sliding mode control in photovoltaic application, because of its\r\ncontrollable states. Simulations are performed inMatlab/Simulink software. The simulation results are presented for a step change\r\nin reference voltage and input voltage as well as step load variations.The simulations results of proposedmethod are compared with\r\nthe conventional PID controller. The results show the good performance of the proposed sliding mode controller. The proposed\r\nmethod can be used for the other DC/DC converter....
This paper presents an improved Walsh function IWF algorithms as an alternative approach for active and reactive powers\r\nmeasurement in linear and nonlinear, balanced and unbalanced sinusoidal three-phase load system. It takes advantage of Walsh\r\nfunction unified approach, simple algorithm and its intrinsic high level of accuracy as a result of coefficient characteristics and\r\nenergy behaviour representation. The developed algorithm was modeled on the Matlab Simulink software; different types of load,\r\nlinear and nonlinear, were also modeled based on practical voltage and current waveforms and tested with the proposed improved\r\nWalsh algorithms.TheIEEE standard 1459ââ?¬â??2000 which is based on fast Fourier transformFFT approach was used as benchmark for\r\nthe linear load system. The data obtained from laboratory experiment to determine power components in harmonic load systems\r\nusing Fluke 435 power quality analyzer PQA which complies with IEC/EN61010-1-2001 standard was modeled and used to validate\r\nthe improved algorithm for nonlinear load measurement. The results showed that the algorithm has the potential to effectively\r\nmeasure three-phase power components under different load conditions....
Solar dryers are imperative for the tropical and sub-Saharan African countries, which are faced with the duo challenges of\r\ninadequate electrical energy supply, which has severely limited the application of conventional refrigeration as a means of\r\npreservation of agricultural produce, and the need to make produce competitive in the international market. In this study, a costeffective\r\nnatural convection solar dryer was developed; the thermal and drying analyses were done and tested to obtain some\r\nperformance evaluation parameters for the system in order to examine its efficiency and effectiveness by drying some plantain\r\nfillets. The collector and system efficiencies are found to be 46.4% and 78.73%, respectively, while a percentage moisture removal\r\nof 77.5% was achieved at the 20th hour in order to give final moisture contents of 15.75% in the product, which still maintained its\r\nintegrity.With a cost of about $195.00, it has been affordable for the small- and medium-scale enterprises as well as for private use\r\nin domestic applications....
In this paper, a pitch controller for a variable-speed wind turbine to be used in the high wind speed region is derived. The pitch\r\nregulator parameters are determined using analytical expressions and are compared with numerical calculations. In order to derive\r\nthe pitch regulated wind turbine model, blade element momentum theory is utilized and reformulated analytically. Appropriate\r\nsimplifications are made and, finally, the analytically derived pitch regulated wind turbine model is tested under grid disturbances\r\nsuch as voltage dips and spinning reserve provision. From this work it was found that by linearizing the blade profiles, one can\r\nanalytically derive a fully functioned pitch regulator. In spite of all nonlinearities, a single pitch controller setting which is valid for\r\nthe whole operation region is shown to be sufficient. This system is tested under grid disturbances and it is proven that the system\r\nis capable of operating well during a 0% remaining voltage dip and also during the voltage recovery back to the rated voltage level.\r\nAccordingly, grid codes commonly referred to can be handled with this simply derived pitch regulator. Moreover, it is shown that\r\nthe derived system works well for a spinning reserve application using a 90% spinning reserve ability and still maintains a robust\r\nturbine control....
Thefluid flow and heat transfer in a porous medium have received considerable attention due to its importance inmany engineering\r\napplications. In this study numerical investigation of fluid flow and heat transfer over a hot solid block inside a square porous block\r\nlocated in a channel was carried out.Thelattice Boltzmann method with nine velocities, D2Q9, was used for numerical simulations.\r\nBrinkman-Forchheimer model was successfully used to simulate fluid flow in porous media. The effects of parameters such as\r\nporosity, Reynolds number on flow pattern, and heat transfer were studied. The different effects of mentioned parameters were\r\ndiscussed in the paper....
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