改进型格尼襟翼对不同实度的垂直轴风力机气动性能的影响

为了提升垂直轴风力机获能效率,为风力机叶片加装格尼襟翼并对格尼襟翼进行改进,通过数值模拟研究了两种格尼襟翼对不同实度的垂直轴风力机气动性能的影响。研究发现：当尖速比为3.1、实度为0.250时,原始格尼襟翼可提升10.92%的风能利用系数,改进型格尼襟翼可提升17.92%。在不同实度,改进型格尼襟翼在高尖速比时可较好地提升气动性能,而原始格尼襟翼在低尖速比时可较好地提升气动性能。当实度增大时,由于叶片间尾迹影响加剧而导致风能利用系数下降,但载荷波动情况得到改善;当实度为0.416时,载荷波动最小。     

全向导叶作用下叶片实度对垂直轴风力机气动特性的影响

为研究全向导叶作用下不同实度对垂直轴风力机气动性能的影响,通过改变叶片数及弦长调整实度并分析其对全向导叶垂直轴风力机气动性能的作用。结果表明：全向导叶使垂直轴风力机周围流体提速效果显著,最大风能利用率和力矩系数较原始垂直轴风力机分别提高41.6%和25%;随实度增大时,全向导叶垂直轴风力机最佳尖速比降低;改变弦长时,风能利用率峰值随弦长增大呈现先增后减的趋势,且在小尖速比工况下,高实度全向导叶垂直轴风力机力矩系数较高,最大可达0.192;改变叶片数时,风能利用率峰值随叶片数增多而降低,且大尖速比下的低实度全向导叶垂直轴风力机力矩系数较大,但不同实度的全向导叶垂直轴风力机最大力矩系数相差较小。     

叶片最大厚度前部修型的垂直轴风力机气动性能

风力机叶片是使风能转化为机械能的原动机构,是风力机的重要部件,风力机风能利用系数的高低主要取决于其叶片的气动外形。保持直叶片垂直轴风力机使用的NACA0022翼型的对称性不变,改变其叶片最大厚度前部的形状,以期得到高风能利用系数的垂直轴风力机翼型。利用Fluent软件,采用k-ωSST湍流模型和SIMPLE算法,运用滑移网格技术,对由不同叶片构成的风力机进行数值计算。计算结果表明,当叶片最大厚度前部是长短轴比为3∶2的椭圆形状时,风力机的风能利用系数更高,而且处于高风能利用系数的尖速比范围更宽;在尖速比为1.72时,风能利用系数最高,为24.8%,此时的风能利用系数较基本翼型提高了28%。叶片修型提高风力机性能的物理机制是最大厚度点前移后的叶片在大攻角下的扰流流动分离强度减弱了。     

基于格尼襟翼的多机组垂直轴风力机性能增效研究

为探究格尼襟翼对垂直轴风力机气动性能的影响,结合TSST湍流模型对直线翼垂直轴风力机展开数值模拟研究.结果表明:低尖速比下,格尼襟翼可显著提升垂直轴风力机的气动性能,但在高尖速比下会降低气动性能;垂直轴风力机组间流体速度随尖速比的增大而增加,此高速流体可有效提升机组风能利用系数;因上游风力机组间流体加速作用,下游风力机...     

伸缩式斜柱对垂直轴风力机气动性能影响研究

为改善垂直轴风力机动态失速特性,提出一种可随风力机方位角变化而自动伸缩的斜柱结构翼型。以NACA0021翼型为研究对象,采用数值模拟方法,分析其对垂直轴风力机动态气动性能的影响。结果表明：伸缩式斜柱在作用方位角内可显著抑制流动分离并提高垂直轴风力机转矩,最大风能利用系数较原始翼型提高13.6%;同时,伸缩式斜柱可使最佳工况点向低尖速比偏移,提高整机运行过程中的稳定性。     

不同扩散体对建筑增强型垂直轴风力机气动性能的影响

为研究不同建筑扩散体对建筑增强型直线翼垂直轴风力机的气动性能与流场结构的影响,采用CFD数值模拟的方法,以NACA0021为叶片翼型的多叶片建筑增强型直线翼垂直轴风力机为对象,研究其在不同建筑扩散体及不同尖速比下的气动性能。结果表明:建筑增强型直线翼垂直轴风力机存在最佳尖速比;不同建筑扩散体对提高直线翼垂直轴风力机风能利用率影响较大,在所选取的8种建筑扩散体模型中,梯形建筑扩散体下的直线翼垂直轴风力机在尖速比为4.62时标准化风能利用率可达1.560 7,而A1翼型式建筑扩散体下的直线翼垂直轴风力机前后压差较小,风能难以利用。     

尾缘非定常射流襟翼对垂直轴风力机气动特性影响研究

为提升垂直轴风力机气动性能并改善其动态失速特性,将射流襟翼布置于翼型尾缘压力面,并提出5种射流控制策略,采用计算流体力学方法研究不同策略对垂直轴风力机气动性能影响,从而确定最佳控制策略。结果表明：在180°~360°相位角范围内施加射流控制可使风力机风能利用系数在最佳尖速比下提升31.31%,并有效抑制吸力面尾缘涡形成与发展,增大翼面两侧压差;射流越靠近尾缘,垂直轴风力机气动性能提升效果越好。     

主动式凹槽-襟翼对垂直轴风力机气动性能影响研究

为提高垂直轴风力机气动效率,提出在翼型尾缘布置凹槽-襟翼结构,并通过主动控制实现凹槽-襟翼结构随风轮相位角变化的机制。基于该控制机制,以NACA0021翼型为研究对象,采用CFD方法进行数值模拟,研究主动式凹槽-襟翼对垂直轴风力机气动性能的影响。结果表明:与静态凹槽-襟翼结构相比,主动式凹槽-襟翼能有效提高垂直轴风力机风能利用率,同时降低最佳尖速比风轮转速,有利于提高运行稳定性,增大低尖速比下启动力矩以及降低气动噪声;当尖速比大于最佳尖速比时,主动式凹槽-襟翼对风力机气动性能提升效果逐渐减弱。     

基于正交试验凹槽-襟翼垂直轴风力机数值研究

为改善垂直轴风力机气动特性,对凹槽-襟翼开展研究。以NACA0021翼型为研究对象,采用正交试验设计对格尼襟翼高度、格尼襟翼位置及凹槽直径等参数进行组合,通过数值计算对垂直轴风力机气动性能与流场结构进行研究,分析凹槽-襟翼流动控制机理及对垂直轴风力机的作用效果。结果表明：格尼襟翼高度是影响垂直轴气动性能的主要因素,且襟翼高度为1.75%c、位置为1.50c及凹槽直径为1.50%c时效果最佳;同时,凹槽-襟翼通过改变尾缘库塔条件以加速翼型吸力面流体流动,从而改善流动分离,增加翼型表面压差,提高垂直轴风力机气动性能;凹槽-襟翼在低尖速比时对垂直轴风力机作用效果较明显,当尖速比为2.33时,凹槽-襟翼垂直轴风力机平均风能利用系数较原始翼型最大可提高35.82%。     

导流式翼缝对直线翼垂直轴风力机气动性能的影响

为减小流体从吸力面流至压力面的速度损失,基于小间距翼缝有助于减小气动损失的设计原理,针对NACA0021翼型,提出双侧导流式、内导流式和外导流式3种新型翼缝形式。通过数值模拟方法,分析不同翼缝对垂直轴风力机气动性能和流场结构的影响,并将其性能参数与原始翼型和非圆弧翼缝翼型进行对比。结果表明:内导流式翼缝风力机气动性能优于原始风力机,最佳尖速比减小8.06%,改善了叶片周围和整机流场结构,增强了风力机运行稳定性;在低尖速比下,双侧导流式翼缝风力机气动性能较高,而高尖速比时气动性能低于原始风力机;下游区叶片迎风速度较低,外导流式翼缝对流动分离现象改善效果不明显,导致气动性能较差;非圆弧翼缝的间距过大使最大风能利用系数降低了15.5%,不适用于直线翼垂直轴风力机。     

A framework for stochastic estimation of electric vehicle charging behavior for risk assessment of distribution networks

Power systems are being transformed to enhance the sustainability. This paper contributes to the knowledge regarding the operational process of future power networks by developing a realistic and stochastic charging model of electric vehicles (EVs). Large-scale integration of EVs into residential distribution networks (RDNs) is an evolving issue of paramount significance for utility operators. Unbalanced voltages prevent effective and reliable operation of RDNs. Diversified EV loads require a stochastic approach to predict EVs charging demand, consequently, a probabilistic model is developed to account several realistic aspects comprising charging time, battery capacity, driving mileage, state-of-charge, traveling frequency, charging power, and time-of-use mechanism under peak and off-peak charging strategies. An attempt is made to examine risks associated with RDNs by applying a stochastic model of EVs charging pattern. The output of EV stochastic model obtained from Monte-Carlo simulations is utilized to evaluate the power quality parameters of RDNs. The equipment capability of RDNs must be evaluated to determine the potential overloads. Performance specifications of RDNs including voltage unbalance factor, voltage behavior, domestic transformer limits and feeder losses are assessed in context to EV charging scenarios with various charging power levels at different penetration levels. Moreover, the impact assessment of EVs on RDNs is found to majorly rely on the type and location of a power network.     

Effect of corrosion inhibitors on hydrogen uptake by Al from NaOH solution

Corrosion rate, hydrogen permeation rate (hydrogen uptake) and stress corrosion cracking of Al were studied in NaOH solutions, pure and with the addition of H₃BO₃, EDTA, KMnO₄ and As₂O₃. The presence of the studied species in electrolyte and the implantation of Al surface with B⁺ ions inhibited corrosion. Hydrogen uptake was found to be promoted or inhibited by means of studied species, depending on the method of their introduction into the base solution and on the applied polarization. The observed different influence of corrosion inhibitors on the hydrogen uptake was associated with the different chemical composition and structure (revealed by XPS analysis) of the surface films, formed on Al under the various conditions. Under similar polarization conditions, the presence of H₃BO₃ in the base solution similarly affected the hydrogen uptake by Al and the susceptibility to stress corrosion cracking of the metal.     

Development of hybrid photovoltaic-fuel cell system for stand-alone application

In this paper we present firstly the different hybrid systems with fuel cell. Then, the study is given with a hybrid fuel cell–photovoltaic generator. The role of this system is the production of electricity without interruption in remote areas. It consists generally of a photovoltaic generator (PV), an alkaline water electrolyzer, a storage gas tank, a proton exchange membrane fuel cell (PEMFC), and power conditioning units (PCU) to manage the system operation of the hybrid system. Different topologies are competing for an optimal design of the hybrid photovoltaic–electrolyzer–fuel cell system. The studied system is proposed. PV subsystem work as a primary source, converting solar irradiation into electricity that is given to a DC bus. The second working subsystem is the electrolyzer which produces hydrogen and oxygen from water as a result of an electrochemical process. When there is an excess of solar generation available, the electrolyzer is turned on to begin producing hydrogen which is sent to a storage tank. The produced hydrogen is used by the third working subsystem (the fuel cell stack) which produces electrical energy to supply the DC bus. The modelisation of the global system is given and the obtained results are presented and discussed.     

Energy management strategy of Supercapacitor/Fuel Cell energy storage devices for vehicle applications

This paper addresses the management of a Fuel Cell (FC) – Supercapacitor (SC) hybrid power source for Electric Vehicle (EV) applications. The FC presents the main energy source and it is sustained with SCs energy storages in order to increase the FC source lifespan by mitigating harmful current transients. For this aim, the reported work proposes a Grey Wolf Optimizer (GWO) for an efficient power management of the studied hybrid power system. The key idea of the proposed approach is to incorporate the benefit of the GWO in terms of fast optimization and convergence accuracy, in order to achieve efficient energy sources exploitation and provide the desired driving performances. Simulations and experimental results verify the validity of the proposed management algorithm.     

A methodology for the performance evaluation of an experimental desiccant cooling system

An experimental investigation was conducted in an open cycle desiccant cooling system (DCS) operating on the ventilation mode in the laboratory site [M. Yıldırım, An experimental investigation on heat and mass transfer in a desiccant cooling system, PhD thesis, Gaziantep University, Turkey (2002). [1]]. Although the operation of DCS is presumably affected by the design of primary components of rotary regenerator (RR) and desiccant wheel (DW) the methodology used in the analysis of experimental data is presented in this paper to set a different approach for the performance evaluation of similar systems.

The rotational speeds of RR and DW (N_RR and N_DW), air mass flow rate (m_a) in process and regeneration lines, and the regeneration temperature (T_R) were defined as operation parameters. Meanwhile coefficient of performance (COP) and cooling capacity (CC) of the system were called as the performance parameters. The system operation with a variety of experimental conditions resulted in an extensive data set covering the ranges of N_RR, N_DW, m_a and T_R as 5 rpm ≤ N_RR ≤ 20 rpm, 0.1 rpm ≤ N_DW ≤ 0.4 rpm, 0.05 kg/s ≤ m_a ≤ 0.139 kg/s and 60 °C ≤ T_R ≤ 90 °C, respectively. The interactive influence of the operation parameters was determined through the realization of the psychrometric cycle in deviation from an ideal cycle. A dimensional analysis based on a trial and error procedure was followed to determine the functional relationship of COP and CC.

The proposed correlations between COP and CC and the introduced system performance parameter (PP) were determined to be a sole function of m_a independent of N_RR, N_DW and T_R in their covered ranges.     

Designing and modelling of the asymptotic perturbed extremum seeking control scheme for tracking the global extreme

This paper presents the designing and modeling of the Asymptotic Perturbed Extremum Seeking Control (aPESC) scheme that is capable to locate and track the Global Extremes on the multimodal patterns. The multimodal patterns may appear on power generated by a photovoltaic (PV) array under Partial Shading Conditions (PSCs), but also on net power generated by a Fuel Cell (FC) system. The proposed aPESC scheme uses a scanning technique to determine the GMPP on different multimodal patterns based on two components of the searching signal: (1) the scanning signal locates the LMPP by sweeping the PV pattern based on a asymptotic dither modulated by the first harmonic of the PV power and controlled by the dither gain (k₂); (2) the tracking signal finds and tracks accurately the GMPP based on similar loop used in PESC schemes proposed in the literature that is controlled by the loop gain (k₁). These tuning parameters are designed based on the averaged model of this aPESC scheme. Also, the averaged scheme and local averaged loop of the aPESCH1 scheme are used to estimate the searching gradient and analyze the closed ESC loop stability. The design methodology is tested on generic multimodal patterns and then is validated considering a PV system and a FC system.     

In-situ hydrogen peroxide synthesis with environmental applications in bioelectrochemical systems: A state-of-the-art review

Hydrogen peroxide (H₂O₂) is a versatile, eco-friendly, strong oxidizing chemical with numerous industrial applications. It is found that bioelectrochemical system (BES) is a promising technology for H₂O₂ biosynthesis including microbial fuel cell (MFC) and microbial electrolysis cell (MEC), generally. Since first discovery of H₂O₂ production in BES in 2009, a growing community of researchers payed attention to on-site H₂O₂ production and environmental applications based on BESs. In this review, we discussed the state-of-the-art development, performance and environmental applications of H₂O₂-BES in detail. The H₂O₂-BES has been getting more and more energy-saving even turning “waste” into wealth completely without other energy input. Moreover, coupling the H₂O₂-BESs with Fenton and ultraviolet/visible light is extensively employed for environmental applications, ranging from dye decolorization, metal deposition, emerging contaminants, real wastewater and primary sludge treatment in lab-scale. However, the pilot- or industrial-scale applications of BESs are challenging enough in environmental remediation up to now.     

Characterisation tools development for PEM electrolysers

Electrochemical impedance spectroscopy (EIS), current interrupt (CI) and current mapping (CM) were investigated as in-situ characterisation tools for PEM electrolysers. A 25 cm² cell with titanium anode and carbon cathode plates were utilised in this study. A commercial MEA consisting of 1 mg IrO₂/cm² on the anode and 0.3 mg Pt/cm² on the cathode was used. The electrocatalyst was deposited on Nafion^® membranes. The electrochemical losses in a PEM electrolyser namely: activation, ohmic and mass transfer losses were identified using EIS and CI and both the advantages and disadvantages of the methods were discussed. The current distribution over the membrane electrode assembly (MEA) at different current densities was measured using the current mapping method. It is also shown that under the given experimental conditions the current density decreases along the serpentine flow field.     

Optimal placement of PMUs for the smart grid implementation in Indian power grid—A case study

Efficient utilization of energy resources is essential for a developing country like India. The concept of smart grid (SG) can provide a highly reliable power system with optimized utilization of available resources. The present Indian power grid requires revolutionary changes to meet the growing demands and to make the grid smarter and reliable. One of the important requirements for SG is the instantaneous monitoring of the voltage, current and power flows at all buses in the grid. The traditional monitoring system cannot satisfy this requirement since they are based on nonlinear power flow equations. Synchro-phasor-measurement devices like phasor measurement units (PMUs) can measure the phasor values of voltages at installed buses. Consequently, the currents passing through all branches connected to that bus can be computed. Since the voltage phasor values at the neighboring buses of a bus containing the PMU can be estimated using Ohm’s law, it is redundant to install PMUs at all the buses in a power grid for its complete observability. This paper proposes the optimal geographical locations for the PMUs in southern region Indian power grid for the implementation of SG, using Integer Linear Programming. The proposed optimal geographical locations for PMU placement can be a stepping stone for the implementation of SG in India.     

Miniaturized polymeric enzymatic biofuel cell with integrated microfluidic device and enhanced laser ablated bioelectrodes

The present work establishes a simple, customized, and economical laser-induced graphene (LIG) material produced using a CO₂ laser. The one-step LIG bioelectrodes have been further validated for Enzymatic Biofuel Cell (EBFC) application by integrating them into a microfluidic device, fabricated by the conventional soft-lithography on Polydimethylsiloxane (PDMS). This electrode and device manufacturing technology delivers a simple and quick fabrication method, which eliminates the necessity of any further amendment and post-processing. LIG electrodes were created at optimized CO₂ laser (5.1 W power and 0.625 cm s^?1 speed) irradiation which has been further modified by Multi-walled carbon nanotubes (CNT), called C-LIG electrodes, which offers improved performance and enzyme stability. In this novel study, CNT functionalized LIG electrodes have been incorporated into a microfluidic device for biofuel cell applications. LIG and C-LIG bioelectrodes have been integrated into a microfluidic device under the laminar fluid flow regime and the electrochemical and polarization study of the platform have been carried out. This C-LIG bioelectrodes integrated microfluidic device, without any metal catalyst, generated 2.2 μW/cm² power density with an optimized 200 μl/min flow rate which is 1.37 times higher than the LIG bioelectrodes. Such novel and simple EBFC platform is amenable to further improvement for generating even more power output by optimizing the LIG formation, alternate nano-functionalisation and mediator based electrochemical analysis.