2,033 research outputs found
Efficiency Analysis of Combined Cogeneration Systems with Steam and Gas Turbines
No full textIncreasing demand of energy and adverse environmental impact of the use of fossil fuels emphasized the need of using renewable energy. At this stage, cogeneration has come into question. Cogeneration, also called combined heat and power, is a consecutive generation of electrical power and heat energy. It is an efficient and cost-effective means to save energy and reduce emissions of human origin. In this study, a combined cogeneration system has been investigated. This cogeneration system uses a combined gas/steam turbine and draws gap steam from the steam turbine for heat production. Thermodynamic analysis of the system has been done and effects of some design parameters on performance values have been examined
Three-dimensional CFD modeling of a steam ejector
No full textSteam ejectors are one of the key components of steam ejector refrigeration/heat pump systems. Steam ejector is required to compress low-pressure stream to a higher pressure. Steam ejectors have no moving part, a simple structure, low cost, reliability, easy installation, high vacuum performance, corrosion resistance, and no consumption of electrical energy. In this study, steam ejector design was modeled using finite volume techniques, and Mach number and pressure in constant cross-section have been compared with analytical data reported in the literature. In this work, numerical calculations were performed with ANSYS Fluent(ANSYS FLUENT Theory Guide, ANSYS, Inc. Release 17.2, 2016, Canonsburg, PA, USA), a computational fluid dynamic code. In the turbulent flow, heat transfer-based analyses were performed using energy equations
Energy and Exergy Analyses Applied to a CI Engine Fueled with Diesel and Natural Gas
No full textIn this study, energy and exergy analysis of a direct injection compression ignition engine converted into dual fuel systems using different composition of mixed fuel formed from natural gas and diesel were performed. Effects of parameters, such as composition of mixed fuel, engine load, and speed, on various energetic and exergetic performance parameters of the engine were evaluated and compared with each other. The irreversibilities of mixed fuel and diesel were comparable at high engine speed but at low engine speed the irreversibility of mixed fuel was higher than that of diesel fuel
Photovoltaic-thermal system for building application: a case study
No full textIn buildings today, there is also a need of thermal energy, besides electrical energy. Hot air and hot water are forms of thermal energy that can be used in buildings. PV/T systems help produce these shapes of energies with the use of solar power. In this study, the supply of the required energy in buildings produced by a PV/T system, using two working fluids - air and water - has been investigated. The studies were conducted on typical winter, spring, and summer days which had different atmospheric conditions. At the same time, the amount of electrical and thermal energy gained between the selected intervals on those days was also investigated. The results show that the energy obtained in three different ways from a PV/T module are well high. The produce of hot air can be used as a residential need in winter. The results also show that a great portion of the need to heat a typical office up to 59% and to provide 55% of hot water consumption for one person on a daily basis in only 1 h can be provided by such a PV/T module. Additionally, the energy which is gained from air is well high in summer and can be used for other purposes by way of optimization. On the other hand, the production of electrical energy and hot water can also be used for residential needs in all seasons
Power and Efficiency Analysis of Brayton Cycles with Internal Irreversibility
No full textIn this article, power and efficiency analysis of irreversible Brayton cycle, which is one of the well-known heat engine cycles by the undergraduates, are carried out based on alternative criteria. Power, power density, and efficient power optimizations are also realized and the thermal efficiencies of the cycle are determined at maximum power and efficiency outputs. The efficient power is relatively new criterion and defined as the multiplication of power by efficiency. Therefore, this criterion considers not only the power output but also the cycle efficiency. Maximizing the efficient power function gives a compromise between power and efficiency. The effects of the external irreversibilities on the performances are investigated for various cycle parameters
Near-Optimal Feedback Guidance for Low-Thrust Earth Orbit Transfers
No full textThis research proposes a near-optimal feedback guidance based on nonlinear control for low-thrust Earth orbit transfers. For the numerical simulations, two flight conditions are defined: (i) nominal conditions and (ii) nonnominal conditions that account for the orbit injection errors and the stochastic failures of the propulsion system. Condition (ii) is studied through an extensive Monte Carlo Analysis, to demonstrate the nonlinear feedback guidance’s numerical stability andconvergence properties. To illustrate the performance under both conditions, an orbit transfer from low Earth orbit to geostationary orbit is considered. Near-optimality of the feedback guidance comes from carefully selecting the nonlinear control gains. Comparison of the transfer with an existing study that uses optimal control reveals that orbit transfers based on feedback orbit control are very close to the optimal solution.Control & Simulatio
The effects of zoledronic acid treatment on depression and quality of life in women with postmenopausal osteoporosis: A clinical trial study
No full textBackground: Osteoporosis affects quality of life (QoL) and may lead to depression in women. The purpose of this study was to evaluate the effects of zoledronic acid (ZA) treatment on depression and QoL in women with postmenopausal osteoporosis (PO). Materials and Methods: A total of 88 newly diagnosed women with PO were included in this study. All patients were treated with once-yearly ZA (5 mg). A QoL questionnaire from the European Foundation for Osteoporosis and Beck Depression Inventory were given to patients at baseline and at 12 months. The results for baseline and post - 12th month were compared, and bone mineral density (BMD) levels were compared. Results: The consumption of once-yearly ZA (5 mg) treatment increases BMD at levels of lumbers 1–4 (P = 0.026), total Hip T score's P value is same as femoral neck (P: 0,033). ZA 5 mg treatment also improved QoL (P = 0.001) and reduced depression (P = 0.001). Conclusion: ZA treatment increases BMD levels and QoL while reducing depression. Once-yearly ZA (5 mg) may be considered for postmenopausal women as a first-line treatment
Cellular Immunity-Pathogen Interactions in Infectious Diseases
No full textAbubakar, Muhammad/0000-0002-0245-0254; ATMACA, HASAN TARIK/0000-0001-8379-4114
An Investigation on the Effect of the Total Efficiency of Water and Air Used Together as a Working Fluid in the Photovoltaic Thermal Systems
No full textThe temperature of a PV (photovoltaic) panel increases when it produces electricity but its electrical efficiency decreases when the temperature increases. In addition, the electrical efficiency of the PV panel is very limited. To increase the PV efficiency, the rest of the solar irradiance must be used, together with the temperature being kept at an optimum value. With this purpose, an experimental study was conducted. Firstly, two specific photovoltaic-thermal (PV/T) systems were designed. The first was the PV/T system which used only a water heat exchanger. The other one was the PV/T system that used a water and air heat exchanger. In the latter PV/T system, air passed through both the top of the PV panel and the bottom of it while water passed through only the bottom of the panel in a separate heat exchanger. In this way, the water and air absorbed the thermal energy of the panel by means of separate heat exchangers, simultaneously. In addition to the two systems mentioned above, an uncooled photovoltaic module was also designed in order to compare the systems. As a result, three different modules were designed. This study was conducted in a natural ambient environment and on days which had different climatic conditions. The thermal, electrical and overall efficiencies of each PV/T module were determined. The results were compared with the uncooled module electrical efficiency. The results showed that when water and air were used together, it was more efficient than single usage in a PV/T system. The thermal gain of the working fluids was also found to be fairly high and so, the gained energy could be used for different purposes. For example, hot air could be used in drying systems and air condition systems. Hot water could be used in hot water supply systems
CFD modeling of a diesel evaporator used in fuel cell systems
No full textDiesel evaporators are one of the key components of diesel fuel processing for fuel cells. Diesel evaporator is required to evaporate diesel fuel in diesel fueled fuel cell systems. In this study, diesel evaporator which is a spiral-tube heat exchanger via indirect heat supplied by hot nitrogen gas is modeled and the fractional distillation curve results of diesel fuel are compared to experimental data reported in literature. In this work, the ANSYS Fluent 14.0 Computational Fluid Dynamics (CFD) code is used to simulate the 3-dimensional, turbulent, two-phase, multi-component and reacting flow-field, developed in a diesel evaporator. (C) Copyright 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
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