Terms Of Power Density Research Articles

Effect of operating and design parameters on the performance of a microbial fuel cell with Lactobacillus pentosus

Abstract A microbial fuel cell (MFC) is a novel biotechnological system able to simultaneously produce renewable energy and perform wastewater treatment. The aim of this work was to study the effect of configurational parameters, such as membrane area, anode electrode size and cell design and operating conditions, such as flow rate and shear stress on the MFC performance toward its optimization. A synthetic wastewater based on a dairy industry effluent and pure culture of Lactobacillus pentosus was used. For each condition tested, the MFC performance was evaluated in terms of power density, chemical oxygen demand (COD) removal rate and the characteristics of the L. pentosus biofilm attached to the anode electrode (biomass amount, cell viability and total and extracellular proteins and polysaccharides). The maximum power density, 8.09 ± 1.52 mW m−2, was achieved with the lower flow rate tested (0.05 L h−1). For all the conditions tested the COD removal rates were between 56% and 61%. The different configurational and operating conditions tested influenced the energy production and the biofilm characteristics. However, the wastewater treatment efficiency was not considerably affected. L. pentosus proved to be capable of treating a dairy wastewater and produce electricity without the presence of a mediator. Further investigation needs to be done to improve the MFC overall performance.

Effect of Magnet Types on Performance of High-Speed Spoke Interior-Permanent-Magnet Machines Designed for Traction Applications

Interior permanent magnet (PM) machines are considered the state of the art for traction motors, particularly in light-duty hybrid and electrical vehicles. These motors usually use neodymium–iron–boron (NdFeB) PMs. These magnets include both light rare-earth materials such as neodymium (Nd) as well as heavy rare-earth materials such as dysprosium (Dy). The main purpose of Dy is to enhance the magnet coercivity to avoid demagnetization under both high temperatures as well as flux weakening. One of the key risks in terms of using these rare-earth magnets is the significant fluctuation/increase in their prices over the past few years. Applications that use large quantities of these magnets, such as traction motors and wind generators, are the most affected by these fluctuations. There has been an ongoing global effort to try to reduce or eliminate the use of rare-earth materials (particularly Dy which is the most expensive) without sacrificing too much performance. This paper will focus on advanced spoke designs targeting traction applications. The goal of this paper is to come up with new spoke designs using various grades of Dy-free magnets as well as ferrites targeting the same set of specifications. This paper will provide a detailed comparison between the various designs highlighting the key tradeoffs in terms of power density, efficiency, flux-weakening capability, and magnet susceptibility to demagnetization. Also, a prototype using ferrites has been built and tested, and the experimental results will be presented.

Dual-Oxide Nanostructures Electrodes for High Energy Density Asymmetric Supercapacitors

Electricity storage is necessary to address the intermittency problem from renewable energy resources such as wind and solar energy. Supercapacitors are energy storage devices which are complimentary batteries in terms of power density are attractive for many applications. Developing high energy density supercapacitor with high power density remains a challenge. Here, we present a strategy to fabricate the high energy density dual-oxide and reduced graphene oxide composites of dual-oxide asymmetric pseudocapacitors operating in an environment friendly aqueous neutral electrolyte. The 1D and 2D rGO/V2O5 nanostructures display superior electrochemical performance compared to the V2O5 nanostructure electrodes in aqueous electrolytes. Nanostructured MoO3 was used as an anode to fabricate the dual-oxide asymmetric supercapacitor. The asymmetric supercapacitor devices show a working voltage window of 1.6 V. The energy and power density values are, to our knowledge, higher than any that have been previously reported for asymmetric supercapacitors using V2O5 electrodes. Reference: D. H. Nagaraju, Qingxiao Wang, P. Beaujuge and H. N. Alshareef J. Mater. Chem. A , 2014, 2, 17146-17152.

Online Parameter Identification of Ultracapacitor Models Using the Extended Kalman Filter

Ultracapacitors (UCs) are the focus of increasing attention in electric vehicle and renewable energy system applications due to their excellent performance in terms of power density, efficiency, and lifespan. Modeling and parameterization of UCs play an important role in model-based regulation and management for a reliable and safe operation. In this paper, an equivalent circuit model template composed of a bulk capacitor, a second-order capacitance-resistance network, and a series resistance, is employed to represent the dynamics of UCs. The extended Kalman Filter is then used to recursively estimate the model parameters in the Dynamic Stress Test (DST) on a specially established test rig. The DST loading profile is able to emulate the practical power sinking and sourcing of UCs in electric vehicles. In order to examine the accuracy of the identified model, a Hybrid Pulse Power Characterization test is carried out. The validation result demonstrates that the recursively calibrated model can precisely delineate the dynamic voltage behavior of UCs under the discrepant loading condition, and the online identification approach is thus capable of extracting the model parameters in a credible and robust manner.

Bioelectro-catalytic valorization of dark fermentation effluents by acetate oxidizing bacteria in bioelectrochemical system (BES)

Abstract Biovalorization of dark fermentation effluent (DFE) in a microbial fuel cell (MFC) was studied using the biocatalyst enriched from farm manure. The MFC performance was evaluated in terms of power density, substrate degradation, energy conversion efficiency and shifts in system redox state with operation time and organic loading rate (OLR). Higher power density of 165 mW m −2 (12.5 W m −3 ) was observed at OLR I, which dropped to 86 mW m −2 at OLR II and 39 mW m −2 at OLR III. The substrate degradation was also higher at OLR I (72%) and diminished with increasing the OLR. The pH showed rapid drop and fluctuations initially when shifted to DFE but adapted over time. Higher coulombic efficiency was observed (48% at OLR I) contributing to a total energy conversion of 11%, which is higher compared to the available literature. However, the MFC performance declined at higher OLR with respect to all the performance indicators. DFE consisted of residual sugars from first stage process along with the volatile fatty acids (VFAs) and alcohols, which contributed for the generation of organic acids with their simultaneous consumption and led to VFA increment in spite of COD removal. Cyclic voltammograms along with the derived electro-kinetics supported the observed shifts.

Comparing Various PM Synchronous Generators: A Feasible Solution for High-Power, Off-Highway, Series Hybrid, Electric Traction Applications

Different disc-type axial flux permanent magnet (AFPM) generators are designed and compared in this article for a Caterpillar D7E track-type tractor (TTT) electric drive model. The design of several feasible generators with multiple stators and rotors are completed for the given electrical and mechanical specifications and compared with a conventional permanent magnet (PM) generator in terms of power density, torque density, loss distribution, efficiency, heat dissipation, volume, inertia, and weight. Electromagnetic, mechanical, and thermal analyses are also accomplished to finalize the designs. The results reveal the benefits of axial gap PM generators over radial gap generators for a hybrid electric traction application.

Modified graphite and graphene electrodes for high-performance lithium ion hybrid capacitors

Lithium ion capacitors (LICs) have recently received considerable attention as a new class of energy storage system because they possess the combined advantages of lithium ion batteries and supercapacitors. LICs typically consist of activated carbon cathodes and pre-lithiated graphite anodes. Despite the promising electrochemical performance, most LICs still hold room for further improvement in terms of power density, which is largely related to the limited (de)intercalation kinetics of graphite. In an attempt to address these limited kinetics, we have developed a simple treatment to modify the morphology and surface characteristics of graphite engaging hydrogen peroxide. The treatment increases the exposed edge planes and generates more stable solid-electrolyte-interphase layers, which facilitate substantially improved power and cycling performance of the graphite anodes. Especially when integrated with a urea-reduced graphene cathode, the modified graphite-based LIC exhibits significantly higher energy and power densities compared to those of the pristine graphite-based and other reported counterparts.

Process optimization of ultrasound-assisted curcumin nanoemulsions stabilized by OSA-modified starch

This study reports on the process optimization of ultrasound-assisted, food-grade oil-water nanoemulsions stabilized by modified starches. In this work, effects of major emulsification process variables including applied power in terms of power density and sonication time, and formulation parameters, that is, surfactant type and concentration, bioactive concentration and dispersed-phase volume fraction were investigated on the mean droplet diameter, polydispersity index and charge on the emulsion droplets. Emulsifying properties of octenyl succinic anhydride modified starches, that is, Purity Gum 2000, Hi-Cap 100 and Purity Gum Ultra, and the size stability of corresponding emulsion droplets during the 1 month storage period were also investigated. Results revealed that the smallest and more stable nanoemulsion droplets were obtained when coarse emulsions treated at 40% of applied power (power density: 1.36 W/mL) for 7 min, stabilized by 1.5% (w/v) Purity Gum Ultra. Optimum volume fraction of oil (medium chain triglycerides) and the concentration of bioactive compound (curcumin) dispersed were 0.05 and 6 mg/mL oil, respectively. These results indicated that the ultrasound-assisted emulsification could be successfully used for the preparation of starch-stabilized nanoemulsions at lower temperatures (40-45 °C) and reduced energy consumption.

Effect of Different Mediator Concentrations on Power Generation in MFC Using Ti-TiO<sub class="sub">2</sub> Electrode

In this study, performance of MFC using three different mediators was investigated in terms of power density and internal resistance. Methylene blue (MB), neutral red (NR) and 2-hydroxy-1,4-naphthoquinone (HNQ)mediators were used to increase power generation in MFC with the mediator concentrations of 50, 100, 200, 300 and 400 µM. The maximum power densities were recorded as 36, 31 and 18.7 mW/m2withthe mediators of MB, NR and HNQ corresponding optimal mediator concentrations of 300, 200 and 50 µM, respectively. Further, it was observed that internal resistance changed with mediator concentration.

Ultrasubwavelength Ferroelectric Leaky Wave Antenna in a Planar Substrate-Superstrate Configuration

The possibility of achieving directive fan-beam radiation with planar Fabry-Pérot cavity antennas constituted by an upper ferroelectric thin film and a lower ground plane having ultrasubwavelength thickness is studied by means of a simple transverse-equivalent-network approach and a cylindrical leakywave analysis, deriving simple design formulas. The performance of the proposed antenna is investigated in terms of power density radiated at broadside and directivity in the principal planes, pointing out the main limitations and tradeoffs associated with the reduced thickness.

Investigation of a proton-conducting SOFC with internal autothermal reforming of methane

Abstract This study presents a performance analysis of a proton-conducting SOFC (SOFC-H+) with internal reforming of methane. The autothermal reforming within the SOFC-H+ stack is considered to be a potential solution of the carbon formation problem facing in operation of internal steam reforming SOFC-H+. A one-dimensional, steady-state model of the SOFC-H+ coupled with a detailed electrochemical model is employed to investigate its performance in terms of power density and fuel cell efficiency. The simulation results show that when SOFC-H+ is operated under an autothermal reforming environment, the presence of carbon monoxide, which is a major cause of carbon formation, in the fuel cell stack decreases. Effect of key operating parameters, such as temperature, steam-to-carbon and oxygen-to-carbon feed ratios, current density and fuel utilization, on the SOFC-H+ performance in terms of electrical efficiencies and energy demand is also investigated. The results indicate that operating temperatures have strong influence on SOFC-H+ performance, carbon monoxide production and heat generation.

(Invited) Heterogeneous Integration of III-V Devices and Si CMOS on a Silicon Substrate

Standard Si CMOS and SiGe BiCMOS enable unparalleled integration density, yield, and functionality on a single chip. In addition to realization of high performance mixed signal circuits, such as data converters, there have been many impressive demonstrations of highly integrated RF chips, including full multi-element phased arrays at mm-wave frequencies. However, the performance is not ideal because silicon cannot compete with III-V technologies in terms of power density, efficiency, noise figure, dynamic range or linearity, and speed. Heterogeneously integrating III-V devices with the CMOS gives the designers state of art III-V performance combined with the integration density and functionality of silicon. We present the status of the direct growth/fabrication of InP HBT and GaN HEMT materials/devices on a silicon substrate containing high density Si CMOS. The integration process is similar to the SiGe BiCMOS process and can be considered a III-V BiCMOS process.

Motors/generators for traction/propulsion applications: A review

The growing interest in electrification has led to a growing interest in hybrid/electrical traction applications. Many hybrid/electrical vehicles have been commercially introduced. Various technologies for the traction motors/generators have been developed. The requirements for motors/generators for hybrid/electrical traction applications are very demanding in terms of power density, efficiency, and cost. This article will provide a comprehensive review of the state of the art highlighting the key global trends and tradeoff of various technologies. The article will also discuss future trends and potential areas of research. The article will cover light-duty vehicles (with more focus), medium- and heavy-duty vehicles, off-highway vehicles (OHVs), locomotives, and ship propulsion. The goal of the article is to serve as a comprehensive reference for engineers working in the traction/propulsion area.

Design of novel SPEEK-based proton exchange membranes by self-assembly method for fuel cells

Fuel cell represents a new energy conversion device, which promises to provide clean source of power. Fuel cell [particularly proton exchange membrane fuel cell and direct methanol fuel cell (DMFC)] is a promising candidate for transportation and portable power source applications. In DMFC, there is a problem of methanol crossover. In order to reduce such a problem, there has been an intensive research activity in the modification of Nafion. In the present investigation, self-assembled membranes were fabricated with sulfonated polyether ether ketone as the core part of the membrane. Aminated polysulfone and sulfonated polysulfone were used as the layers in order to prevent the crossover of methanol. The assembled membranes were characterized by ion exchange capacity, water and methanol absorption, and durability. The methanol permeability and selectivity ratio proved a strong influence on DMFC application. Scanning electron microscopy proved smooth surface, which established strong cohesive force for the polymer chains. Among the synthesized self-assembled membranes, the membrane with two bilayers was the best in terms of power density in DMFC. The membrane electrode assembly with two bilayers showed higher performance (~61.05 mW/cm2) than sulfonated poly(ether ether ketone) and Nafion in DMFC.

GaN HEMT Class ${\hbox{E}}^{2}$ Resonant Topologies for UHF DC/DC Power Conversion

In this paper, the design and performance of class E2 resonant topologies for dc/dc power conversion at UHFs are considered. Combining the use of RF gallium-nitride HEMT devices, both for the inverter and synchronous rectifier, with high-Q lumped-element terminating networks, peak efficiency values over 70% may be obtained. Control strategies based on carrier bursting, switching frequency modulation, or outphasing are also shown to be feasible. Taking advantage of their improved dynamic response, when compared to low-frequency more traditional switched-mode converters, a class E3 polar transmitter for the EDGE standard has been designed and tested at 770 MHz, offering an average global efficiency over 46% at 4.3 W of output power, through RF-based amplitude and phase constituting branches. Finally, the potential of such a high frequency of operation in terms of power density is explored, absorbing undesired coil parasitics for the original LC series interconnecting network in a 1-GHz design methodology.

Moving towards high-power, high-frequency and low-resistance CNT supercapacitors by tuning the CNT length, axial deformation and contact resistance

In this paper it is shown that the electrochemical behaviour of vertically aligned multi-walled carbon nanotube (VANT) supercapacitors is influenced by the VANTs’ length (electrode thickness), by their axial compression and by their interface with the current collector. It is found that the VANTs, which can be interpreted as a dense array of nanochannels, have an active area available to ions that is strongly affected by the electrode’s thickness and compressional state. Consequently, the tested thinner electrodes, compressed electrodes or a combination of the two were found to be characterized by a significant improvement in terms of power density (up to 1246%), knee frequency (58 822% working up to 10 kHz), equivalent series resistance (ESR, up to 67%) and capacitance (up to 21%) when compared with thicker and/or uncompressed electrodes. These values are significantly higher than those reported in the literature where long VANTs with no control on compression are typically used. It is also shown that the ESR can be reduced not only by using shorter and compressed VANTs that have a higher conductance or by improving the electrode/collector electrical contact by changing the contact morphology at the nanoscale through compression, but also by depositing a thin platinum layer on the VANT tips in contact with the current collector (73% ESR decrease).

Power Density of a Bare Electrodynamic Tether Generator

The maximum performance of bare electrodynamic tethers as power generating systems under OML-theory is analyzed. Results show that best performance in terms of power density is achieved by designing the tether in such a way to increase ohmic impedance with respect to plasma contact impedance, hence favoring longer and thinner tethers. In such condition the corresponding optimal value of the load impedance is seen to approach the ohmic impedance of the conducting tether. At the other extreme, when plasma contact impedance dominates (which is not optimal but can be relevant for some applications) optimum power generation is found by matching the load impedance with an effective tether-plasma contact impedance whose expression is derived.

A New Topology of Low Speed Doubly Salient Brushless DC Generator for Wind Power Generation

The unit machine of the traditional doubly salient electro-magnetic generator (DSEG) has a 6/4-pole structure, so it must have a large number of stator poles when used as a low speed wind turbine generator. The matching relationship between the stator pole number and the rotor pole number of a multi-poles-rotor DSEG is deduced, and a new 3N/4N-pole DSEG is proposed. The magnetostatic field distribution, excitation inductance characteristic, as well as output characteristic of the DSEG is investigated by 2-D and 3-D finite element analysis. Comparisons between the two different structures are presented in terms of power density, voltage ripple and efficiency. A low speed 24/32-pole prototype machine is developed, and the experimental results are given to verify the validity of the simulation analysis and the reasonable structure of 3N/4N-pole DSEG.

COMPARACIÓN ENTRE LAS DOS TECNOLOGÍAS LÍDERES EN EL ALMACENAMIENTO DE ENERGÍA EN VEHÍCULOS ELÉCTRICOS: BATERÍAS Y PILAS DE COMBUSTIBLE

There are currently two technologies that dominate the current trends of electric vehicles: fuel cell and battery. Both options generate electricity to drive electric motors, eliminate pollution and improve vehicle efficiency. Fuel cells derive their energy from hydrogen stored in the vehicle, while the batteries get the energy from grid. The two forms of electricity generation have advantages and disadvantages in terms of power density and energy density, dynamic response, refueling time, autonomy and the possibility of regenerative braking, infrastructure for recharging.The electric vehicle configuration will consist of a series of blocks that must give the system a performance similar to the conventional configuration in the same terms of speed, acceleration, time of refueling and comfort.This paper develops the analysis of current technology in the propulsion system of electric vehicles for further optimal sizing of components and systems that make the same fundamental, a study of the most appropriate for the use of either technology .

Evaluation of Power Density for Three Phase Double-Sided Axial Flux Slotted PM Generator

There are two topologies for slotted double-sided axial flux permanent magnet generator (AFPG). Choosing an AFPG with high power density is an important parameter in applications. Hence, power density Evaluation between double-sided AFPM generators topologies is necessary. In this paper, the sizing equations of axial flux slotted one-stator-two-rotor (TORUS) and two-stator-one-rotor (AFIR) type PM generators is presented and comparison of the TORUS and AFIR topologies in terms of power density is illustrated. Finally a high power double-sided AFPG is introduced in the paper.