Conditions For Maximum Efficiency Research Articles

Numerical and experimental evaluation of a centrifugal compressor

The present paper provides a comparative study in the development of a centrifugal compressor impeller designed for methane (CH4) and tested in similitude conditions, using air as working fluid. The rotor was designed in maximum efficiency conditions and will be part of compression equipment used for underground gas storage for inaccessible areas, experiencing difficulties in gas supply. Optimization of the geometrical shape of the impeller was made using CFD programs based on the finite volume method. Since the experimental tests have taken place at the similitude, the rotating speed had to be adapted to 14915 rpm, to compensate for the change in working fluid. Redundant pressure and temperature probes have been placed on each radial location in order to minimize experimental errors. For the CFD side, the established best practices were employed, using the k-omega SST model with a y+<1 along the walls, with a growth ratio of ~1.2:1. Overall, the global performances were in good agreement with each other

Optimization of electrocoagulation process and combination of anaerobic digestion for the treatment of pistachio processing wastewater

Abstract It is very challenging to treat raw pistachio processing wastewater (PPW) by one step process due to its high chemical oxygen demand (COD) and total phenols (TP). In this study, electrochemical (EC) process and anaerobic digestion are combined to improve treatment efficiency. Central composite design (CCD) was used in EC experimental design with three factors at three levels of the independent variables. Impact of current density (50─100 A/m2), electrode distance (2─6 cm), and reaction time (60─300 min) on the removal of COD and TP were systematically investigated. A maximum removal efficiency of 43.7 and 56.4% of COD and TP, respectively, was obtained with the current density of 100 A/m2, electrode distance of 6 cm, and reaction time of 293 min. Specific energy consumption (SEC) was measured as 7.80 kWh/kgCOD for the same experimental conditions. In order to achieve further treatment, a batch anaerobic reactor was combined with EC process to produce biogas. COD and TP removal efficiency were measured in the anaerobic reactors at appropriate time intervals (0, 10, 25, 30, 40, and 50th d) and biochemical methane potential (BMP) tests lasted up to 50 d. BMP enhancement of raw PPW was found as 35.7 and 16.5% for electrocoagulated PPW under maximum COD and TP removal efficiency condition (100 A/m2 current density, 6 cm electrode distance, and 293 min reaction time) and under cost driven approach condition (53 A/m2 current density, 2 cm electrode distance, and 182 min reaction time) compared to raw PPW. The results showed that pre-treated PPW with EC process had the highest COD and TP removal efficiencies and enhanced the biochemical methane production, by decreasing the concentration of total phenols in the PPW. Energy balance revealed that EC under cost driven approach condition combined with anaerobic digestion can be used as an energy positive process for the treatment of PPW.

Enhanced adsorption of methylene blue onto graphene oxide-doped XFe2O4 (X = Co, Mn, Ni) nanocomposites: kinetic, isothermal, thermodynamic and recyclability studies

The nanocomposites XFe2O4/GO with various metal sites (X = Co, Mn, and Ni) were successfully synthesized via the polymerized complex method. The XFe2O4/GO family was characterized using X-Ray diffraction analysis, scanning electron microscopy (SEM), and a vibrating sample magnetometer. We also investigated the effect of three fundamental parameters (initial concentration, dosage, and pH) on the removal of methylene blue using the response surface methodology. A high F value, very low P value ( 0.95) demonstrated a strong correlation between experimental and predicted values of the responses. The predicted optimal conditions for maximum removal efficiency were easily determined to adhere to the following trend for actual test experiments: MnFe2O4/GO (60.1%) < CoFe2O4/GO (80.3%) < NiFe2O4/GO (87.7%). Moreover, the adsorption behavior was well-described by the Langmuir isotherm and a pseudo-second-order kinetic model. The maximum capacity for adsorption of methylene blue onto XFe2O4/GO was found from 42.2 to 80.6 mg/g. Moreover, the XFe2O4/GO could be regenerated for several cycles without a considerable decrease in removal yield, suggesting that this highly promising XFe2O4/GO could be applied as an efficient and novel adsorbent.

An investigation on frequency characteristics of wireless power transfer systems with relay resonators

PurposeThis paper aims to analyze the frequency characteristics of wireless power transfer (WPT) systems with relay resonators in terms of the power delivered to the load and system efficiency. Based on the analytical results, system parameters can be optimized to achieve maximum power transfer and higher system efficiency.Design/methodology/approachBased on Kirchhoff’s voltage law equations, WPT systems with relay resonators are described by the coupled linear second-order differential equations. Splitting frequencies are estimated by using the matrix theory. In addition, critical coupling conditions are demonstrated based on discriminant analysis.FindingsIt was found that multi-maximum values exist for the power delivered to the load and total system efficiency owing to multiple eigenfrequencies of the system. Also, frequency conditions of maximum power transfer and system efficiency, as well as their critical coupling conditions, were quantitatively estimated.Research limitations/implicationsDuring our analytical process, we assume that quality factors of resonators in the system are high and the crossing coupling between resonators is negligible.Originality/valueIn previous works, the exact analysis of frequency characteristics is limited to WPT systems with two resonators. The appealing feature of this work lies in its ability to present a simplified analytical method with negligible approximation errors for WPT systems with relay resonators.

Refuse Derived Fuel (RDF) production and gasification in a pilot plant integrated with an Otto cycle ICE through Aspen plus™ modelling: Thermodynamic and economic viability

This work deals with the development of a Refuse Derived Fuel (RDF) gasification pilot plant using air as a gasification agent. A downdraft fixed bed reactor is integrated with an Otto cycle Internal Combustion Engine (ICE). Modelling was carried out using the Aspen Plus™ software to predict the ideal operational conditions for maximum efficiency. Thermodynamics package used in the simulation comprised the Non-Random Two-Liquid (NRTL) model and the Hayden-O'Connell (HOC) equation of state. As expected, the results indicated that the Equivalence Ratio (ER) has a direct influence over the gasification temperature and the composition of the Raw Produced Gas (RPG), and effects of ER over the Lower Heating Value (LHV) and Cold Gasification Efficiency (CGE) of the RPG are also discussed. A maximum CGE efficiency of 57–60% was reached for ER values between 0.25 and 0.3, also an average reactor temperature values in the range of 680–700°C, with a peak LHV of 5.8MJ/Nm3. RPG was burned in an ICE, reaching an electrical power of 50kWel. The economic assessment of the pilot plant implementation was also performed, showing the project is feasible, with power above 120kWel with an initial investment of approximately US$ 300,000.

Wavelength scaling of silicon laser ablation in picosecond regime

Single pulse laser ablation of silicon has been investigated at 343, 515, and 1030 nm using a laser pulse duration of 50 ps. In this large spectral range, ablation thresholds of silicon vary from 0.01 to 0.83 J/cm2, confirming a strong dependence on the wavelength. By solving the free-carrier density rate equation at threshold conditions, we show that band-to-band linear absorption dominates energy deposition at 343 and 515 nm, whereas at 1030 nm, the energy leading to ablation is primarily absorbed by the generated free-carriers. This allows us to determine the relevant criteria to derive a simple model predicting the wavelength dependence of the ablation threshold in this regime. We obtain an excellent agreement between experimental measurements and calculations by simply considering an averaged energy density required in the absorption depth for surface ablation and accounting for the laser-induced variations of the important thermophysical parameters. On the basis of this analysis, we discuss the optimal wavelength and fluence conditions for maximum removal rate, ablation efficiency, and accuracy. Despite the difference in mechanisms at the different wavelengths, we find that the maximal efficiency remains at around 7 times the ablation threshold fluence for all investigated wavelengths. This work provides guidelines for high-quality and efficient micromachining of silicon in the scarcely explored picosecond regime, while new picosecond sources offer numerous advantages for real throughput industrial applications.

Photocatalytic degradation of pefloxacin in water by modified nano-zinc oxide

Nanocrystalline La-doped ZnO powders were synthesized by homogeneous precipitation method and characterized by various sophisticated techniques such as XRD, UV–vis DRS and SEM. Experimental results show that the La-doped ZnO could make ZnO particle size decrease and make specific surface area large, so the photocatalytic activity of La-doped ZnO was increased compared with pure ZnO. The optimal conditions for maximum efficiency of pefloxacin degradation under 6h UV irradiation were found as 1g/L dosage of La-doped ZnO nanocomposite, pefloxacin concentration of 15mg/L, and pH = 7.0. Under optimal operating conditions, degradation efficiency was reached to 93%.

A Review of Optimal Conditions for Achieving Maximum Power Output and Maximum Efficiency for a Series–Series Resonant Inductive Link

This paper presents the conditions for achieving maximum power output and maximum efficiency in a series–series (SS) resonant inductive link. It has been shown that output power depends on the nature of supply: current source or voltage source, resulting in different values for the same resonant link setup. For both types of sources, conditions for maximum power transfer with respect to different parameters have been derived. Efficiency, on the other hand, is independent of the nature of supply; it depends only on circuit parameters. Conditions for maximum efficiency with respect to circuit parameters have also been derived. It has been shown that an SS resonant inductive link is best suited for current-sourced input, since a voltage-sourced link behaves poorly when deviated from ideal tuning conditions. Moreover, for a voltage-sourced link, there exists an optimum value of mutual inductance at which maximum power transfer occurs. However, for a current-sourced link, output power increases with increase in coupling coefficient. The modeling and analysis has been supported with detailed simulation and experimental results.

REMOVAL OF URANIUM FROM LIQUID WASTE BY NATURAL NILE MUD

This effort deals with uranium removal from liquid waste using Natural Nile Mud (NNM). Accordingly, cost effective and simple approach to remove uranium from liquid waste by NNM was reported. The effects of shaking time, pH, the initial uranium concentration, adsorbent temperature, adsorbent amount (dose) and effect of foreign ion (iron) on the adsorption of uranium ions from liquid waste were examined. According to the results, the optimum conditions for maximum adsorption efficiency of the NNM for uranium from the solution were obtained fitted with the Langmuir and the maximum adsorption capacity was about 61 mg/g NNM.

Optimal matching between a diesel engine and a PRHTS transmission

The power reflux hydraulic transmission system (PRHTS), which is a new continuously variable transmission system, is one solution to improve the fuel economy of construction vehicles. For the combination of the diesel engine and the torque converter the conventional matching method uses the diameter of a circle as the design variable. However, this method is not applicable for matching the diesel engine and PRHTS. Focusing on this issue, we proposed a new matching method, which uses the blade angles at the pump exit, stator exit, and stator entrance as the design variables. According to the matching requirements, seven performance evaluation indexes are defined—the initial energy degree, maximum efficiency condition and rated condition approach degree, maximum power condition and rated condition approach degree, economic zone tolerance degree, power output coefficient of the high-efficiency area, adaptive coefficient amplification factor, and fuel consumption coefficient. The weight of performance evaluation indexes is determined using a precedence chart and the objective function for optimal matching is obtained using a radar chart. The genetic algorithm is used to find the global optimum in the given design space during the optimization procedure.

A new process for the capture of CO2 and reduction of water salinity

The present work evaluates a new process for the capture of CO2 and the reduction of water salinity. It is based on the Solvay process without the use of ammonia and involves the reaction of CO2 with saline water such as reject brine in the presence of calcium hydroxide. The effects of operating parameters such as reaction temperature, water pH and reaction stoichiometry on CO2 capture efficiency and sodium removal were examined for both traditional and modified Solvay process. The optimum conditions for maximum CO2 capture efficiency and sodium removal were determined using response surface methodology and were found to be at temperature of 20°C and a pH of greater than 10 for both processes. At the optimum conditions, CO2 capture of 86% and 99% and sodium removal of 29% and 35% were achieved for the traditional Solvay and the Modified process, respectively. The water pH was found to be a key parameter in the effectiveness of the reaction process; higher pH leads to better process performance in both CO2 capture efficiency and sodium removal. The experimental results clearly illustrated that the Modified Solvay process is superior in terms of CO2 capture efficiency, sodium removal and energy consumption.

Analytical and Numerical Solutions of the Rotor Flow in Tesla Turbines

This paper summarises the numerical and theoretical studies of the incompressible, laminar airflow through a single flow passage of a blade-less radial turbine. Furthermore, it yields the numerical validation of the simplified theoretical model for incompressible rotor flows without the consideration of mechanical losses. It exposes the accuracy of the simplified, analytical performance prediction and flow field for a given geometry, which is based on an optimisation of performance by solving the simplified and incompressible Navier-Stokes-Equations in cylindrical coordinates. The influences of the dimensionless machine parameters on performance and efficiency are obtained from a theoretical analysis. The stream-lines of the bulk flow are derived by analytical means. The inflow conditions for maximum performance and efficiency are theoretically determined and later compared to laminar CFD. In order to quantify the error of the simplified theoretical analysis, different inflow conditions and their influences on shaft power and flow behavior are examined by means of CFD. The de-velopment of the axial velocity distribution at the inlet zone is compared to the one from the theoretical inflow assumption. The influences of Reynolds number and revolution speed on the velocity profiles are investigated. In addition to that, a compressible flow model is introduced. Numerical results are obtained and compared to the incompressible solution. More-over, compressibility effects on turbine performance are derived.

Energy efficiency of smart windows made of photonic crystal

Windows are one of the main sources of energy loss in buildings. Many types of smart windows have been developed to reduce energy consumption. However, these windows cannot control visible light and near-infrared (NIR) light independently. This study introduces a new photonic crystals glazing (PCG) system that can be dynamically controlled to achieve high reflection of NIR without affecting the transmittance of visible light. A case study was used to determine energy consumption (heating and cooling load) of the proposed PCG system. The performance of the PCG system was compared to the commercially available glazing systems and the optimum climatic conditions for maximum efficiency of the PCG system was determined. This study found that the PCG is the most energy efficient system for reducing heating and cooling loads compared to the existing glazing systems. Additionally, the study showed that the PCG system saves more energy in cold climates with high heating loads.

Waste heat recovery plant for exhaust ducts using thermoelectric generators

Alternative methods for electricity production are needed in view of the scarcity of natural sources resulting from population growth and the consequent demand for energy. The inefficient use of energy requires new recovery processes in order to increase the system's gains. The use of Seebeck modules (TEG) have been shown the novel output of power recovery using waste heat energy. This work proposes a recovery plant from waste heat starting from a geometry optimization of exhaust duct. The distance between each TEG and surface was varied lengthwise to flow, creating a thermally resistive air layer, and from a heuristic optimization process, good results about equalization on surface temperature were found by finite element analysis. The thermoelectric modules used were tested in real conditions and results compared with data sheet. Finally it is exposed an electrical arrangement for a 42 TEG MPPT power plant. The novel design shows a low surface temperature gradient that allows TEG work closely to maximum efficiency condition and distant of mechanical failure.

Microwave absorption properties of polypyrrole-SrFe12O19-TiO2-epoxy resin nanocomposites: Optimization using response surface methodology

At a few works are discussed about formation of heterogeneous composites with different distribution of particle shape and size that are used for electromagnetic absorption purposes. In this study a novel heterogeneous nanocpmposites is investigated. The nanocomposite has been successfully prepared based on epoxy resin including various nano-metal oxides (TiO2, SrFe12O19) and polypyrrole (PPy) by sol-gel and the solution chemistry method, respectively. The performance of prepared nanocomposite in absorption of microwave in X-band range was investigated and transmission line method by X-band waveguide straight was used to measure EM parameters of nanocomposites. The Response surface methodology (RSM) with central composite design (CCD) was utilized to study the effects of the wt.% TiO2 in SrFe12O19, wt.% Tio2-SrFe12O19 in PPy and wt.% TiO2-SrFe12O19-PPy in epoxy resin, on the microwave absorption properties with the absorber thickness of only 2mm. The proposed quadratic model was in accordance with the experimental results with correlation coefficient of 96.5%. The optimum condition for maximum microwave absorption efficiency were wt.% TiO2 in SrFe12O19 of 70, wt.% TiO2-SrFe12O19 in PPy of 10 and wt.% TiO2-SrFe12O19-PPy in epoxy of 25. The sample prepared in optimal conditions indicated reflection loss of −15dB corresponding to 97% absorption, at the range of 9.2–10.8GHz.

Performance analysis and optimization of irreversible Dual–Atkinson cycle engine (DACE) with heat transfer effects under maximum power and maximum power density conditions

This study presents an analysis considering the effects of heat transfer loss and internal irreversibility due to adiabatic compression and expansion processes on the performance of an irreversible Dual–Atkinson cycle engine (DACE) under non-dimensional maximum power (MP), non-dimensional maximum power density (MPD) and maximum thermal efficiency (MEF) conditions. The effects of the inlet temperature, combustion constant and heat transfer constant on the engine performance are investigated. The results could be used by engine designers to optimize the performance of the internal combustion engines (ICEs).

Obtaining alantolactone and isoalantolactone from Inula racemose Hook.f. by optimized supercritical fluid extraction

Inula racemose Hook.f. (I. racemosa) is a traditional herbal medicine with strong anti-fungal and anti-inflammation activity while alantolactone (AL) and isoalantolactone (IAL) are the major active compounds of this plant. The aim of this paper was obtaining AL and IAL from the radix of I. racemosa by supercritical fluid extraction (SFE) which was optimized by response surface methodology (RSM). Our results showed that, the optimal conditions for maximum extraction efficiency were as follows: pressure 20MPa, extraction temperature 50°C, carbon dioxide (CO2) flow rate of 17.0×10−5kg/s and extraction time of 40min. Subsequently, an efficient freezing method was developed for purification of AL and IAL in the crude extract obtained from SFE. After purification by freezing, the total content of the target compounds was greatly improved by 30.7%. The results demonstrate that SFE coupled with freezing would be a powerful technique for extraction and purification of AL and IAL from the radix of I. racemosa.

Comparative Exergoeconomic Analyses of Gas Turbine Steam Injection Cycles with and without Fogging Inlet Cooling

The results are reported of exergoeconomic analyses of a simple gas turbine cycle without a fogging system (SGT), a simple steam injection gas turbine cycle (STIG), and a steam injection gas turbine cycle with inlet fogging cooler (FSTIG). The results show that (1) a gas-turbine cycle with steam injection and simultaneous cooling has a higher power output than the other considered cycle; (2) at maximum energy efficiency conditions the gas turbine has the highest exergy efficiency of the cycle components and the lowest value of exergy efficiency is calculated for the fog cooler, where the mixing of air and water at greatly different temperatures causes the high exergy destruction; and (3) utilization of the fogging cooler in the steam injection cycle increases the exergy destruction in the combustion chamber. Furthermore, the simple gas turbine cycle is found to be more economic as its relative cost difference, total unit product cost, and exergoeconomic factors are less than those for the two other configurations. However, its efficiency and net power output are notably lower than for the gas turbine with steam injection and/or fog cooling. The total unit product cost is highest for the simple gas turbine with steam injection.

Performance assessment and optimization of a combined heat and power system based on compressed air energy storage system and humid air turbine cycle

Renewable energy based power sources have grown rapidly in the past few years owing to the dual constraint of climate change and pollution control. Compressed air energy storage (CAES), as a large-scale energy storage system (ESS) technology, has huge potential to manage the intermittent renewable energy based power sources effectively. However, the compression heat generated during charge and waste heat carried in turbine exhaust during discharge are not fully recuperated in current stage. A combined heat and power (CHP) system consisting of a CAES system and a humid air turbine (HAT) system is proposed to utilize the both types of heat energy. The proposed system can boost the power output, enhance performance and improve efficiency through a simultaneous supply of power and heat. The thermodynamic analysis shows that the expansion train power can be improved about 26% compared with the conventional CAES system. The parametric analysis reveals that the exergy efficiency increases with the turbine inlet temperature (TIT) of high pressure turbine (HPT) and inlet pressure of low pressure turbine (LPT), but decreases with the TIT of LPT, L/G ratio and dry air inlet temperature of saturator. Meanwhile, the system optimization is carried out via particle swarm optimization (PSO) to determine the maximum power and exergy efficiency conditions.

УТИЛИЗАЦИЯ ТЕПЛОТЫ ОТРАБОТАВШИХ ГАЗОВ ГАЗОТУРБИННОЙ УСТАНОВКИ С ПОМОЩЬЮ ДВИГАТЕЛЯ СТИРЛИНГА

The article researches a feasibility of real cycles of combined power plants including gas turbine engines and Stirling engines. The variant of construction concepts of such power plants has been considered. The analysis of thermodynamic cycles has been performed, the dependences to calculate their basic parameters has been founded. Based on the research results quantify the heat utilization degree of the combustion products of a gas turbine engine for the Stirling engine has been given. Stirling engine’s efficiency, power and combined power plant’s efficiency in general has been identified. The heat exchanger’s type and heat transfer agent has been proposed, the optimal parameters by conditions of maximum efficiency of the plant has been identified. Proposals for the application and the empowerment of such power plants as part of the vehicles has been offered.