Electric Power Density Research Articles

Power Density and Efficiency of Thermophotovoltaic Energy Conversion Using a Photonic-Crystal Emitter and a <formula formulatype="inline"><tex>$\hbox{2}$</tex> </formula>-D Metal-Grid Filter

Three-dimensional metallic photonic crystals have been suggested to be ideal candidates for thermal emitters in thermophotovoltaic energy conversion systems due to their high emission power in the allowed passband and also their emission suppression in the long-wavelength tail. In this paper, calculations were performed to compare a photonic-crystal emitter and a blackbody emitter in the thermodynamic limit of the maximum power density and efficiency that are achievable with an ideal photovoltaic cell. Additionally, realistic-source and GaSb photovoltaic-cell optical characteristics and a novel metal-grid filter are incorporated into the calculations. With an ideal antireflection coating, the measured photonic-crystal radiation was found to give a source electrical power density of 7.77 W/cm2 and a system efficiency of 47.58% with an effective source temperature of 1535 K.

A New Atmospheric Pressure Microwave Plasma Source (APMPS)

An atmospheric pressure microwave plasma source (APMPS) that can generate a large volume of plasma at an atmospheric pressure has been developed at Tsinghua University. This paper presents the design of this APMPS, the theoretical consideration of microwave plasma ignition and the simulation results, including the distributions of the electric field and power density inside the cavity as well as the accuracy of the simulation results. In addition, a method of producing an atmospheric pressure microwave plasma and some relevant observations of the plasma are also provided. It is expected that this research would be useful for further developing atmospheric pressure microwave plasma sources and expanding the scope of their applications.

FDTD Analysis of Magnetized Ferrite Sphere

In this paper, based on the medium characteristics of ferrite and Maxwell's Equation, the distribution of electric field and power density of the ferrite sphere in the free space are calculated by using the FDTD method. Furthermore, different cases such as: a ferrite-coated dielectric sphere and a dielectric sphere, are calculated. The stability of the results in electric field is compared in different time steps. According to the calculated results of the isolation and insertion loss of ferrite sphere, the analytical validity is verified by comparing the results in references.

Development of a New-Generation RoHS IGBT Module Structure for Power Management

This paper describes the design considerations for a high electric power density IGBT module structure mounted with smaller, new-generation chips. We have investigated heat flow depending on the copper foil thickness of an alumina based direct-copper-bonding (DCB) substrate, junction temperature rise in relation to the chip arrangement, electromagnetic noise dominated by the cupper circuit pattern, and lead-free solder layer stress as affected by the coefficient of thermal expansion (CTE) of DCB.Low thermal resistance was obtained by using a 0.6 mm thick copper DCB substrate; consequently the CTE of the DCB increased to 16 ppm/K, which is nearly equal to that of the Cu base as a heat sink. The thick copper DCB substrate can lower the junction temperature of a small chip with a high electric power density and can improve the thermal cycling capability of the DCB substrate mounted with a lead-free solder on the Cu base. Moreover the thick copper circuit effectively reduces the electromagnetic noise generated on the DCB substrate. Thus we have successfully realized a high electric power density IGBT module structure.

Redox Stable Electrodes for Hydrogen Producing Solid Oxide Electrolyzer

This report focuses on a study which measured the electrical conductivity of LSCrM, LSCr and LSM as a function of oxygen activity and temperature to evaluate the chemical and mechanical stability of the materials as an electrode in a solid oxide fuel-fed electrolyzer cell (SOFEC). The LSCrM symmetrical cell was fabricated using La0.75Sr0.25Cr0.5Mn0.5O3 (LSCrM) powder and evaluated using electrical conductivity, impedance spectroscopy, current density and power density as a function of temperature. During the evaluation, symmetrical cell tests and fuel cell tests were performed as a function of temperature. Silver (Ag) and platinum (Pt) were also used to compare the cell performance with and without precious metal as a current collector. Although the OCV was in the same level (about 1.2 V) in dry 10%H2-90%N2 with both Ag and Pt collectors, the current density and power density of the cell was increased more than 20 times when Pt was used as a current collector.

Selection of appropriate fuel processor for biogas-fuelled SOFC system

The performance of biogas-fed solid oxide fuel cell (SOFC) systems utilizing different reforming agents (steam, air and combined air/steam) has been investigated via thermodynamic analysis to determine the most suitable feed. The boundary of carbon formation was first calculated to specify the minimum amount of each reforming agent necessary to avoid carbon formation. The SOFC performance (electrical efficiency and power density) was determined at different biogas compositions and reforming agent:biogas ratios. The SOFC performance is better when the methane content in the biogas is higher. Steam is considered to be the most suitable reforming agent in this study as the steam-fed SOFC offers much higher power density than the air-fed SOFC although its electrical efficiency is slightly lower. When steam is added in the air-fed SOFC as in the case of the co-fed SOFC, the power density can be improved but the electrical efficiency becomes lower compared with the case of the air-fed SOFC. Finally, in order to improve the electrical efficiency of the steam-fed SOFC, the biogas split option was proposed. It was found that a higher electrical efficiency can be achieved. In addition, although the power density is lowered by this operation, the value is still higher than the case of the air-fed SOFC.

Thermodynamic assessment of solid oxide fuel cell system integrated with bioethanol purification unit

A solid oxide fuel cell system integrated with a distillation column (SOFC–DIS) has been proposed in this article. The integrated SOFC system consists of a distillation column, an EtOH/H 2O heater, an air heater, an anode preheater, a reformer, an SOFC stack and an afterburner. Bioethanol with 5 mol% ethanol was purified in a distillation column to obtain a desired concentration necessary for SOFC operation. The SOFC stack was operated under isothermal conditions. The heat generated from the stack and the afterburner was supplied to the reformer and three heaters. The net remaining heat from the SOFC system ( Q SOFC,Net) was then provided to the reboiler of the distillation column. The effects of fuel utilization and operating voltage on the net energy ( Q Net), which equals Q SOFC,Net minus the distillation energy ( Q D), were examined. It was found that the system could become more energy sufficient when operating at lower fuel utilization or lower voltage but at the expense of less electricity produced. Moreover, it was found that there were some operating conditions, which yielded Q Net of zero. At this point, the integrated system provides the maximum electrical power without requiring an additional heat source. The effects of ethanol concentration and ethanol recovery on the electrical performance at zero Q Net for different fuel utilizations were investigated. With the appropriate operating conditions (e.g. C EtOH = 41%, U f = 80% and EtOH recovery = 80%), the overall electrical efficiency and power density are 33.3% (LHV) and 0.32 W cm −2, respectively.

RF electric field penetration and power deposition into nonequilibrium planar-type inductively coupled plasmas

The RF electric field penetration and the power deposition into planar-type inductively coupled plasmas in low-pressure discharges have been studied by means of a self-consistent model which consists of Maxwell equations combined with the kinetic equation of electrons. The Maxwell equations are solved based on the expansion of the Fourier–Bessel series for determining the RF electric field. Numerical results show the influence of a non-Maxwellian electron energy distribution on the RF electric field penetration and the power deposition for different coil currents. Moreover, the two-dimensional spatial profiles of RF electric field and power density are also shown for different numbers of RF coil turns.

ASSESSMENT OF COMPLEX EMF EXPOSURE SITUATIONS INCLUDING INHOMOGENEOUS FIELD DISTRIBUTION

Assessment of exposure to time varying electric and magnetic fields is difficult when the fields are non-uniform or very localized. Restriction of the local spatial peak value below the reference level may be too restrictive. Additional problems arise when the fields are not sinusoidal. The objective of this review is to present practical measurement procedures for realistic and not too conservative exposure assessment for verification of compliance with the exposure guidelines of ICNIRP. In most exposure situations above 10 MHz the electric field (E) is more important than the magnetic field (B). At frequencies above 500 MHz the equivalent electric field power density averaged over the body is the most relevant indicator of exposure. Assessment of specific absorption rate (SAR) is not needed when the spatial peak value does not exceed by 6 dB the average value. Below 50 MHz down to 50 Hz, the electric field induces currents flowing along the limbs and torso. The current is roughly directly proportional to the electric field strength averaged over the body. A convenient way to restrict current concentration and hot spots in the neck, ankle and wrist, is to measure the current induced in the body. This is not possible for magnetic fields. Instead, for a non-uniform magnetic field below 100 kHz the average magnetic flux density over the whole body and head are valid exposure indicators to protect the central nervous system. The first alternative to analyze exposure to non-sinusoidal magnetic fields below 100 kHz is based on the spectral comparison of each component to the corresponding reference level. In the second alternative the waveform of B or dB/dt is filtered in the time domain with a simple filter, where the attenuation varies proportionally to the reference level as a function of frequency, and the filtered peak value is compared to the peak reference level derived from the ICNIRP reference levels.

Performance Assessment of Bioethanol-Fed Solid Oxide Fuel Cell System Integrated with Distillation Column

This paper investigated the performance of a bioethanol-fed Solid Oxide Fuel Cell (SOFC) system integrated with a distillation column (SOFC-D). Excess heat from the SOFC system was directly utilized in the distillation column where bioethanol (5 mol%) was purified to a desired concentration before feeding to the SOFC system consisting of an air heater, an ethanol/water heater, a reformer, an SOFC preheater, an SOFC stack and an afterburner. The SOFC-D system was simulated using Aspen PlusTM for the distillation portion and MatlabTM for the SOFC portion. The effects of operating parameters; i.e., ethanol concentration, ethanol recovery, fuel utilization and operating voltage on the performance and energy involved in the SOFC-D system (e.g. distillation energy: QD and the net exothermic heat of the SOFC system: QSOFC,Net) were examined. In addition, the performance of the SOFC-D system at the energy sufficient point where QD = QSOFC,Net was considered. The integration of the distillation column with the SOFC system was found to offer superior SOFC performance. The ethanol recovery and fuel utilization significantly influenced the overall electrical efficiency and power density. Quite low performances are obtained when one operated the SOFC-D without an external heat source. The maximum overall efficiency and power density (~35% and 0.22 W cm-2) occured at an ethanol recovery of 80% and Uf of 90%.

Influence of Hydrogen Sulfide in Fuel on Electric Power of Solid Oxide Fuel Cell

Terminal voltage, electric power density and overpotential were measured for the solid oxide fuel cell with gadolinium-doped ceria electrolyte (Ce0.8Gd0.2O1.9, GDC), 30 vol% Ni-GDC anode and Pt cathode using a H2 fuel or biogas (CH4 47, CO2 31, H2 19 vol %) at 1073 K. Addition of 1 ppm H2S in the 3vol % H2O-containing H2 fuel gave no change in the open circuit voltage (0.79 - 0.80 V) and the maximum power density (65 - 72 mW/cm2). Furthermore, no reaction between H2S and Ni in the anode was suggested by the thermodynamic calculation. On the other hand, the terminal voltage and electric power density decreased when 1 ppm H2S gas was mixed with the biogas. After the biogas with 1 ppm H2S flowed into the anode for 8 h, the electric power density decreased from 125 to 90 mW/cm2. The reduced electric power density was also recovered by passing 3 vol % H2O-containing H2 fuel for 2 h.

Analysis of Percent On-Cell Reformation of Methane in SOFC Stacks and the Effects on Thermal, Electrical, and Mechanical Performance

Numerical simulations were performed to determine the effect that varying the percent on-cell steam-methane reformation would have on the thermal, electrical, and mechanical performance of generic, planar solid oxide fuel cell stacks. The study was performed using three-dimensional model geometries for cross-, co-, and counter-flow configuration stacks of 10x10- and 20x20-cm cell sizes. The analysis predicted the stress and temperature difference would be minimized for the 10x10-cm counter- and cross-flow stacks when 40 to 50% of the reformation reaction occurred on the anode. Gross electrical power density was virtually unaffected by the reforming. The co-flow stack benefited most from the on-cell reforming and had the lowest anode stresses of the 20x20-cm stacks. The analyses also suggest that airflows associated with 15% air util

Numerical Simulation of Airfoil Thermal Anti-ice Operation, Part 2:Implementation and Results

We present the implementation and results of an airfoil electrothermal anti-ice mathematical model. From flowfield and supercooled water droplet impingement data up to electrical power density distribution, the numerical code is able to predict airfoil solid surface temperature and runback water mass flow rate distributions around an airfoil provided with ice protection. The numerical predictions were compared with both experimental data and other numerical codes results for selected reference cases

Two-Dimensional Self-Consistent Kinetic Model for Solenoidal Inductively Coupled Plasma

A two-dimensional self-consistent kinetic model was developed tostudy the influence of the various factors on the electron energydistribution function. These factors include gas pressure, thedriving frequency, the radius and length of the inductively coupledplasma equipment, the amplitude of the radio-frequency coil current,and the number of turns of rf coils. The spatial profiles of the rfelectric field and power density have also been calculated under thesame parameters. Numerical results show that the electron energydistribution functions are significantly modified and the spatialprofiles of the rf electric field and rf power density are alsodemonstrated.

FDTD calculation of whole-body average SAR in adult and child models for frequencies from 30 MHz to 3 GHz

Due to the difficulty of the specific absorption rate (SAR) measurement in an actual human body for electromagnetic radio-frequency (RF) exposure, in various compliance assessment procedures the incident electric field or power density is being used as a reference level, which should never yield a larger whole-body average SAR than the basic safety limit. The relationship between the reference level and the whole-body average SAR, however, was established mainly based on numerical calculations for highly simplified human modelling dozens of years ago. Its validity is being questioned by the latest calculation results. In verifying the validity of the reference level with respect to the basic SAR limit for RF exposure, it is essential to have a high accuracy of human modelling and numerical code. In this study, we made a detailed error analysis in the whole-body average SAR calculation for the finite-difference time-domain (FDTD) method in conjunction with the perfectly matched layer (PML) absorbing boundaries. We derived a basic rule for the PML employment based on a dielectric sphere and the Mie theory solution. We then attempted to clarify to what extent the whole-body average SAR may reach using an anatomically based Japanese adult model and a scaled child model. The results show that the whole-body average SAR under the ICNIRP reference level exceeds the basic safety limit nearly 30% for the child model both in the resonance frequency and 2 GHz band.

Fabrication and Fuel Cell Properties of Gd-Doped CeO<sub>2</sub> Micro-Tube Ceramics Reactors Prepared by Gel Precursor

Micro-tube type Gd-doped CeO2(CGO) reactor were prepared by hydrolysis of metal acetate gel at room temperature. The size of anode tube was ca. 0.8mm in diameter, and length was 20mm after sintering at 1400°C. DC conductivity of the prepared dense CGO cell consisting of 500nm grains was about 10 Ohm-cm at 600°C. Electrical power density of the micro-tube fuel cell, which was coated both CGO electrolyte and CGO/La0.6Sr0.4Co0.2Fe0.8O3 cathode on the surface of 40vol%NiO-CGO anode tube, was about 900mW/cm2 at 600°C under 30ml/min H2 gas flowing.

Comparison of numerical and measurement methods of SAR of ellipsoidal phantoms with muscle tissue electrical parameters

PurposeThe assessing of the specific absorption rate (SAR) of living organisms or phantoms is difficult to realize and this paper seeks to do this. SAR much more precisely describes the energy absorbed by biological objects than values of electric field strength (E [V/m]) or power density (S [W/m2]) measured at the point of exposition. However, for living objects the assessing of SAR is not an easy task by measuring methods or even in calculation evaluations. Numerical techniques, especially the finite‐difference time‐domain method (FDTD), offer different possibilities of calculations. The important problem with FDTD method introduced to lossy objects with complex shapes is that this method is not verified with the measuring data.Design/methodology/approachIn this work the results of calculations and measuring data of ellipsoidal phantoms filled with specimen of electrical parameters like muscle tissue are presented. The calculations of SAR have been realized for two cases, e.g. for plane wave incident and for waveguide condition. Measurements for verifying the obtained data were done by waveguide method. The comparison of numerical (the package CONCERTO (Vector Fields Ltd)) and measurement methods were done at frequencies 900 and 1,800 MHz.FindingsCalculations of SAR of lossy objects by FDTD method have been confirmed by measurements and analytical method of calculations. This documents that the package CONCERTO (Vector Fields Ltd) (Concerto User Guide) can be used for such calculations.Originality/valueThis paper presents the results of calculations of SAR of ellipsoidal phantoms filled with specimens of electrical parameters of equivalent muscle tissue.

A Study on the Operation Performance of a Minienvironment System

A minienvironment is a localized environment created by an enclosure to isolate a product or process from the surrounding environment. Minienvironments have been gaining popularity as a means to provide effective containment for critical contamination control. The use of minienvironments can provide several orders of magnitude improvement in particle cleanliness levels, while energy intensity may be shifted from the conventional cleanroom systems to the minienvironments that enclose specific processes. Prior to this study, there was little information available or published to quantify the energy performance of minienvironment systems. This paper will present quantitative results from a recent study of the operation performance of an open-loop minienvironment air system in a ballroom setting, including quantification of operation range, energy performance index, pressure control, electric power density, and airflows. The paper also provides a comparison of the newly measured results from this study with previously measured cleanroom performance. The results can serve as a starting point for identifying areas for energy savings from applying high-performance minienvironments in cleanrooms.

High electrical power density from PbTe-based quantum-dot superlattice unicouple thermoelectric devices

We describe the first demonstration of PbTe-based, cross-plane quantum-dot superlattice (QDSL) unicouple thermoelectric generator devices fabricated from nanostructured, thick-film materials (∼100μm). Both n- and p-type QDSL materials were investigated. With ∼220K temperature difference across small thermoelements (∼95μm length, 4mm2 cross-sectional area), electrical power outputs up to 89mW and power densities up to 2.2W∕cm2 have been demonstrated for both n- and p-type materials. The devices consist of a substrate-free, bulklike slab of molecular beam epitaxy grown PbSeTe∕PbTe QDSL material as the n- or p-type leg and a copper wire as the other p-type leg.

Bound-to-continuum GaInAs-AlAsSb quantum cascade lasers with reduced electric injection power density

Short-wavelength (lambda<4 mum) GaInAs-AlAsSb quantum cascade (QC) lasers have been demonstrated using a bound-to-continuum design for the purpose of reducing the electric injection power density. As a result, we have reduced the low-temperature electric injection power density of the lasers by 40%, compared to that of GaInAs-AlAsSb QC lasers emitting at the same wavelength but adopting a triple-quantum-well design. The lasers in the present report can operate up to room temperature (300 K) in pulsed mode, emitting at short-wavelength lambda~3.7-3.9 mum