Generated Power Density Research Articles

Experimental and CFD studies on using coil wire insert in a proton exchange membrane fuel cell

In this paper a study on the role of wire coils inserted in the oxygen supply channels of a proton exchange membrane fuel cell (PEMFC) is reported. Different power densities have been obtained at different oxygen flow rates with and without insert. The experimental results clearly reveal that inserting a wire coil can increase the generated power density up to 41% in some layouts. The CFD modeling is carried out to explain and to analyze the observed results. The generated circumferential flow close to the gas diffusion layer (GDL) is found to be the main reason for the obtained experimental results.

Rechargeable Direct Carbon Solid Oxide Fuel Cells with a Gadolinium-doped Ceria (GDC) Anode and a La0.15Sr0.85MnO3/GDC Anode

Rechargeable direct carbon solid oxide fuel cells (RDCFCs) with oxide anodes were developed. An RDCFC directly uses solid carbon fuel deposited on the anode surface through pyrolysis of hydrocarbon fuel. High power density and stable power generation of RDCFCs with Ni cermets have been reported previously although Ni is known as a long-term degradation factor. In this research, two oxide anodes, namely, LSM/GDC and GDC, were applied and their electrochemical profiles investigated. With scandia-stabilized-zirconia electrolyte, the maximum power density of an RDCFC with a 65-µm-thick LSM/GDC anode reached 131 mW/cm2 and that of an RDCFC with a 65µm-thick GDC anode reached 95 mW/cm2. Effective anode thickness of the GDC anode for electrochemical reaction was more than 65µm, which was much thicker than that previously reported for a Ni/GDC anode (<12 µm).

Experimentally and numerically investigating cell performance and localized characteristics for a high-temperature proton exchange membrane fuel cell

This paper is to experimentally and numerically investigate the cell performance and the localized characteristics associated with a high-temperature proton exchange membrane fuel cell (PEMFC). Three experiments are carried out in order to study the performance of the PEMFC with different operating conditions and to validate the numerical simulation model. The model proposed herein is a three-dimensional (3-D) computational fluid dynamics (CFD) non-isothermal model that essentially consists of thermal–hydraulic equations and electrochemical model. The performance curves of the PEMFC predicted by the present model agree with the experimental measured data. In addition, both the experiments and the predictions precisely demonstrate the enhanced effects of inlet gas temperature and system pressure on the PEMFC performance. Based on the simulation results, the localized characteristics within a PEMFC can be reasonably captured. These parameters include the fuel gas distribution, liquid water saturation distribution, membrane conductivity distribution, temperature variation, and current density distribution etc. As the PEMFC is operated at the higher current density, the fuel gas would be insufficiently supplied to the catalyst layer, consequently causing the decline in the generation of power density. This phenomenon is so called mass transfer limitation, which can be precisely simulated by the present CFD model.

Development of a High Speed HTS Generator for Airborne Applications

General Electric, under contract with the Air Force Research Labs (AFRL), has successfully developed and tested a high speed, multimegawatt superconducting generator. The generator was built to demonstrate high temperature superconducting (HTS) generator technology for application in a high power density Multimegawatt Electric Power System (MEPS) for the Air Force. The demonstration tested the generator under load conditions up to 1.3 MW at over 10,000 rpm. The new MEPS generator achieved 97% efficiency including cryocooler losses. All test results indicate that the generator has a significant margin over the test points and that its performance is consistent with program specifications. This demonstration is the first successful full-load test of a superconducting generator for the Air Force. In this paper we describe the development of the generator and present some key test results used to validate the design. Extrapolation to a higher power density generator is also discussed.

Simulated Behavior of the 100-GHz Reentrant Linear Magnetron

The simulated behavior of a 100-GHz reentrant linear magnetron operated at a beam voltage of 2 kV is investigated using a two-dimensional particle-in-cell MAGIC code. The dimensions of the ten-vane reentrant resonator are selected to give a -mode resonance at 100 GHz, showing mode separation with the adjacent -1 mode of 0.2 %. The electron distribution and the time variation of the electric energy in each vane reveal that the -mode oscillation is dominant when the injected current density is several times higher than the start oscillation current, although the -1 mode is excited near the start oscillation current. With variation of the injected current density from 40 A/cm2 to 60 A/cm2, the generated power density is increased from 0.32 W/mm2 to 0.54 W/mm2 for an external magnetic eld of 0.78 T.

Heating in an Alternating Magnetic Field due to Non-Equilibrium Magnetization

Heating of a magnetizable body in an alternating magnetic field near the Curie point due to non-equilibrium magnetizing is theoretically investigated. The body is of a spherical shape and surrounded by a non-magnetizable unbounded medium. The heat generation power density is regarded as a piecewise linear function with a fracture at the Curie point. The steady temperature distribution within the body and outside it is found.

Non-Equilibrium Magnetization of a Dilute Suspension of Magnetic Particles

A suspension of magnetic particles in a viscous liquid magnetized in an alternating uniform magnetic field is theoretically studied. The suspension is regarded as so dilute that interaction of a single particle with the applied magnetic field can be considered without taking into account the influence of other particles. The complex magnetic susceptibility of the suspension is found as a function of the frequency of the applied magnetic field. The heat generation power density averaged over the period of the oscillations is calculated.

Exoelectrogenic bacteria that power microbial fuel cells

There has been an increase in recent years in the number of reports of microorganisms that can generate electrical current in microbial fuel cells. Although many new strains have been identified, few strains individually produce power densities as high as strains from mixed communities. Enriched anodic biofilms have generated power densities as high as 6.9 W per m(2) (projected anode area), and therefore are approaching theoretical limits. To understand bacterial versatility in mechanisms used for current generation, this Progress article explores the underlying reasons for exocellular electron transfer, including cellular respiration and possible cell-cell communication.

Direct thermal-to-electric energy conversion material consisting of environmentally-benign Mg2Si synthesized using waste Si sludge and recycled Mg alloy

AbstractIn order to perturb global warming and realize a sustainable global energy system, enhancements in the energy efficiency are required. One of the reliable technologies to reduce the greenhouse gas emissions and the consumption of fossil fuel that is attracting attention is thermoelectric technology, which can directly convert heat into electricity and consequently increase the energy conversion efficiency of power generation by combustion. Magnesium silicide (Mg2Si) has been identified as a promising advanced thermoelectric material operating in the temperature range from 500 to 800 K. Compared with other thermoelectric materials that operate in the same conversion temperature range, such as PbTe, TAGS (Ge-Te-Ag-Sb) and CoSb3, Mg2Si shows promising aspects, such as the abundance of its constituent elements in the earth’s crust and the non-toxicity of its processing by-products, resulting in freedom from care regarding prospective extended restriction on hazardous substances.Here we have tried to introduce reusing of industrial waste of Si sludge as a source material for Mg2Si, because the current product inversion rate of Si for semiconductor LSI devices remains at 25 to 30 %, while most of the remainder is disposed of as a waste; this is mainly discharged as sludge from grinding and polishing processes. It is possible that the reuse of this waste Si could be effective in both reducing the cost of source Si and in the reduction of industrial waste. On the other hand, recycled materials of standard lightweight magnesium alloys based on the Mg-Al-Zn-Mn system, such as AZ91 or AM50, were also introduced as a Mg source for Mg2Si synthesis. The concept of this work is a production of wasted heat recovery device using environmentally-benign Mg2Si by means of industrial waste or less pure recycled sources.The efficiency of a thermoelectric device is characterized by the dimensionless figure of merit, ZT=S2σT/κ, of its constituent thermoelectric material, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. As a target for practical use, ZT value exceed unity, which gives about 10 % conversion efficiencies, is expected. So far, we succeeded to obtain the Mg2Si with ZT=1.08 using rather pure Si (99.999% : solar grade) and Mg (99.95%) sources. In this article, we report multifarious fabrication processes in order to realize ZT value as high as unity and the detailed thermoelectric properties concerning Mg2Si initiated from reused Si sludge and the recycled Mg-alloy sources. In conjunction, we will also discuss the practical output-power characteristics of the samples with the formation of Ni electrodes by monobloc sintering. A tentative generated power density from the wasted heat at 773 K was ˜2 KW/m2.

Toward high output-power nanogenerator

In this paper, the factors that determine the power output of a piezoelectric nanowire (NW) nanogenerator (NG) have been analyzed. The output current is the sum of those contributed by all of the NWs while the output voltage is determined by the voltage generated by a single NW, the capacitance of the NW array and the system, and the contact resistance. By growing uniform ZnO NWs with diameters of ∼100nm and lengths of ∼5μm, the output current density and output voltage of the NG was improved to ∼8.3μA∕cm2 and 10mV, respectively, which are 20–30 times higher than that we previously reported. A power generation density of ∼83nW∕cm2 is achieved by using a single layer NW NG.

K 2NiF 4 type La 2 − xSr xCo 0.8Ni 0.2O 4 + δ as the cathodes for solid oxide fuel cells

K 2NiF 4 structured La 2Co 0.8Ni 0.2O 4 + δ is an oxygen overstoichiometric oxide with high oxygen diffusion and oxygen surface exchange coefficients at temperature range 450–800 °C. In this work, composites consisting of La 2 − x Sr x Co 0.8Ni 0.2O 4 + δ (LSCN, x = 0, 0.4, 0.8, 1.2, 1.6) and Ce 0.9Gd 0.1O 1.95 (GDC) have been investigated as the cathodes for low-and-intermediate temperature solid oxide fuel cells (SOFCs). AC impedance spectroscopy on symmetric cells indicated that among the series of LSCN–GDC composites, La 1.2Sr 0.8Co 0.8Ni 0.2O 4 + δ -based electrode had the lowest interfacial polarization resistance, which was 1.36 Ω cm 2 at 600 °C when the electrode was not activated. Significant activation effect was observed with a single cell when current treatment was performed at 200 mA cm − 2 within 30 min. The single cell with La 1.2Sr 0.8Co 0.8Ni 0.2O 4 + δ –GDC as the cathode generated power density up to 350 mW cm − 2 at 600 °C. In addition, the performance was pretty stable when a constant output voltage of 0.5 V was set for 36 h. These results suggest that La 2 − x Sr x Co 0.8Ni 0.2O 4 + δ could be promising materials as the cathodes for SOFCs that operated at low-and-intermediate temperatures.

CANDU reactor as minor actinide/thorium burner with uniform power density in the fuel bundle

A CANDU reactor fueled with a mixed fuel made of thoria (ThO 2) and nuclear waste actinides has been investigated. The mixed fuel composition has been varied in radial direction to achieve a uniform power distribution and fuel burn-up in the fuel bundle. The best fuel compositions with respect to power flattening as well as long term reactivity have been found by mixing thoria with 14% minor actinides in form of MAO 2 in the central fuel bundle and with a radially decreasing MAO 2 content at discrete levels down to 2% at the periphery. Furthermore, as an alternative fuel composition, 5% UO 2 has been added to the mixed fuel for the sake of a higher degree of nuclear safeguarding through denaturing the 233U component with 238U. The temporal variation of the criticality k ∞ and the burn-up values of the reactor have been calculated for a period of 10 years, operated at full power. The criticality starts at time zero near to k ∞ = ∼1.24 for both fuel compositions. A sharp decrease of the criticality has been observed during the first year as a consequence of rapid plutonium burnout in the actinide fuel. The criticality becomes quasi-constant after the 2nd year after sufficient 233U is accumulated and remains close to k ∞,end = ∼1.06 over ∼10 years. Quasi-uniform power generation density has been realized in the fuel bundle throughout the reactor operation. Very high burn-up could be achieved with the same fuel material (up to 200,000 MW D/MT), provided that the fuel rod claddings would be replaced periodically. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically.

Erratum: Polymeric materials for fuel cells: concise review of recent studies

AbstractPolym. Adv. Technol. 2007. DOI: 10.1002/pat.935The following changes should be recognised:On page 3 of the article 'The size of the hydrophilic clusters increased when they absorbed water. Subsequent ion exchange reaction with [Pt(NH3)4]Cl2 followed by reduction with 1‐pentanol at 125°C for 2 hr yielded Pt particles uniformly dispersed on SiO2‐PEM.On page 8 of the article 'The relation between the crossovers of methanol and its concentration in the anode compartment of DMFC's equipped with Nafion membranes was explored and its effect on the efficiency and power density generation was investigated.73–75Errors will be rectified prior to print publication.

Electricity generation with simultaneous wastewater treatment by a microbial fuel cell (MFC) with Cu and Cu–Au electrodes

AbstractBackground: A microbial fuel cell (MFC) consisting of anaerobic and aerobic chambers separated by a salt‐agar slab was used for electricity generation with simultaneous wastewater treatment where copper and gold covered copper wires were used as anode and cathode, respectively. The electrons produced from degradation of carbohydrates in anaerobic chamber traveled through the copper wire generating electricity and the protons were transferred from cathode to anode through the salt‐agar slab. Variation of the current intensity (mA) and the electrical power (mW) were investigated as function of the surface area of anode and also the chemical oxygen demand (COD) content of the synthetic wastewater.Results: The generated power density (mW m−2) increased with increasing surface area of the electrodes and also with the COD content of the wastewater. Both the current intensity (mA) and the power generated (mW) increased with time and reached maximum levels at the end of batch operation. More than 80% COD removal was achieved in the aerobic chamber with an electricity generation of 2.9 mW m−2 when the initial COD content was 6000 mg l−1.Conclusion: The MFC configuration and the use of Cu and Cu‐Au electrodes instead of graphite were proven to be effective for electricity generation with simultaneous wastewater treatment. The electrical current (0.24 mA) and power (2.9 mW m−2) obtained in our microbial fuel cell are comparable with the literature studies utilizing salt bridge. The microbial fuel cell developed in this study can be improved further to yield higher power generations by modifications. Copyright © 2007 Society of Chemical Industry

Optimization of Heat Sink–Limited Thermoelectric Generators

Many recent advances in thermoelectrics have focused on the nanoscale engineering of materials for higher figure of merit (Z). A thermoelectric generator using these thin-film materials can present new challenges due to its inherently large temperature gradient, but also correspondingly larger generated power if the heat can be managed. In such cases performance is expected to be limited as much by the heat sink as by intrinsic material properties. New criteria for optimizing the generated power density of devices in this regime are discussed here The effects of future material improvements on performance are studied, with the surprising result that optimizing material Z is not the best strategy for optimizing efficiency or power in this regime. The theory is tested with a numerical solution of the Onsager relations. This work was supported by the ONR.

Review of high power density superconducting generators: Present state and prospects for incorporating YBCO windings

This work focuses on the development of high power density generators for airborne applications by bridging the chasm between generator and high temperature superconducting (HTS) wire developmental efforts. Benefits of HTS power generation include improved efficiency, thermal management reduction, improved power handling, reduced life cycle costs, and size and weight reduction. Superconducting generator development from the 1970s is outlined, and the basic types of ac synchronous generators are described. The benefits of HTS conductors in general and HTS coated conductors in particular are discussed. Critical issues for the employment of HTS coated conductors are then considered and recommendations made for enhancements to the HTS coated conductor for implementation in the more advanced superconducting power generators.

Partial discharge, dissipation factor, and corona aspects for high voltage electric generator stator bars and windings

High voltage stator windings in modern electric generators are subject to high electrical, mechanical, and thermal stress. Operation of these machines in both air and high pressure hydrogen results in different considerations. Operation in the air environment does not offer the dielectric advantages of operating in high-pressure hydrogen. The two major design factors that are significant for the design of high voltage stator bars to be operated in air, are corona activity and PD activity. These of course are closely related. With the movement to increasing the power density of generators, which means operation at higher voltages and higher insulation stress levels, it has become more critical to be sure the design constraints are met in the stator bar design to minimize both partial discharge activity and corona activity involving the stator bars. The stator bar insulation system must be designed for minimum partial discharge activity and ideally is corona free at the stator winding operating stress levels, and at the operating conditions (temperature and pressure) the generator is subject to. This paper will present the findings associated with the development work in designing, testing and implementing a PD reduced and corona free design.

A new technique for boosting efficiency of silicon solar cells

A new type of photovoltaic system with higher generation power density has been studied in detail. The feature of the system is a V-shaped module (VSM) with two tilted monocrystalline solar cells. Compared to solar cells in a flat orientation, the VSM enhances external quantum efficiency and leads to an increase of 31% in power conversion efficiency. Due to the VSM technique, short-circuit current density was raised from 24.94 to 33.7 mA/cm2, but both fill factor and open-circuit voltage were approximately unchanged. For the VSM similar results (about 30% increase) were obtained for solar cells fabricated by using mono-crystalline silicon wafers with only conventional background impurities.

The behavior of palladium catalysts in direct formic acid fuel cells

Previous work has considered the behavior of platinum based catalysts in direct methanol and Direct Formic Acid Fuel Cells (DFAFCs). In this paper, we explore the behavior of palladium-based anode catalyst for DFAFCs. The palladium catalysts produce significant performance enhancements. DFAFCs operated with dry air and zero back-pressure can generate power densities of 255∼230 mW cm −2 at relatively high voltages of 0.40∼0.50 V in a concentration range of formic acid from 3.0 to 15.0 M at a room temperature of 20 °C, which are not quite different from a hydrogen–air polymer exchange membrane (PEM) fuel cell with power density of 320 mW cm −2 obtained under the comparable conditions, and much higher than a direct methanol fuel cell (DMFC) with power density of 50 mW cm −2. The stability of the membrane electrode assembly (MEA) with palladium catalyst has also been evaluated. There is some decay in performance over several hours. However, the performance loss of DFAFCs can be fully recovered by applying a positive potential at the fuel cell anode after short-term life test. These results demonstrate that DFAFCs with palladium anode catalyst have exceptional properties for portable power applications.

Direct oxidation of jet fuels and Pennsylvania crude oil in a solid oxide fuel cell

Abstract A Cu-ceria solid oxide fuel cell (SOFC) is shown to generate electric power using jet fuels and Pennsylvania crude oil through direct oxidation of the fuels. The liquid fuels contained up to 910 ppm of sulfur and were injected into the anode compartment either with or without N2 dilution. The performance of the fuel cell was stable over 30 h for jet fuels and Pennsylvania crude oil without N2 dilution whereas N2 dilution prolonged the stable power generation up to 100 h for jet fuel and up to 80 h for Pennsylvania crude oil. The generated power density was about 0.1 W cm−2 for both fuels.