The oxidation of CH2O in the intermediate temperature range (943-995 K)

New atmospheric pressure flow reactor data on the oxidation of formaldehyde in the temperature range 943-995 K and over equivalence ratios from 0.013 to 36.7 are reported and discussed. A detailed mechanism assembled from previously published results produced acceptable agreement with the experimental data for the fuel-lean conditions, but failed to predict results for oxidative pyrolysis. Analysis or the very fuel-lean conditions, but failed to modelling results are principally sensitive to CH2O+HO2→HCO+H2O2 (6) and H2O2 +M→OH+OH+M (33). Whereas the specific rate of each reaction cannot be independently determined, it is found that the product k33.k6 is a well defined function of temperature: (3.4±3.0).1028 exp(-(26,800±400)/T). Inadequacies in the mechanism which may be responsible for the disagreement under fuel-rich conditions are discussed. © 1991 Combustion Institute.

The temperature dependence of effective thermal conductivity of open-celled steel alloy foams

The effective thermal conductivity of steel alloy FeCrAlY (Fe-20 wt.% Cr-5 wt.% Al-2 wt.% Y-20 wt.%) foams with a range of pore sizes and porosities was measured between 300 and 800 K, under both vacuum and atmospheric conditions. The results show that the effective thermal conductivity increases rapidly as temperature is increased, particularly in the higher temperature range (500-800 K) where the transport of heat is dominated by thermal radiation. The effective conductivity at temperature 800 K can be three times higher than that at room temperature (300 K). Results obtained under vacuum conditions reveal that the effective conductivity increases with increasing pore size or decreasing porosity. The contribution of natural convection to heat conduction was found to be significant, with the effective thermal conductivity at ambient pressure twice the value of vacuum condition. The results also show that natural convection in metal foams is strongly dependent upon porosity. © 2003 Elsevier B.V. All rights reserved.

Silicon on insulator thermodiode with extremely wide working temperature range

This paper presents for the first time the performance of a silicon-on-insulator (SOI) p-n thermodiode, which can operate in an extremely wide temperature range of 200°C to 700°C while maintaining its linearity. The thermodiode is embedded in a thin dielectric membrane underneath a tungsten microheater, which allows the diode characterization at very high temperature (> 800°C). The effect of the junction area (Aj) on the thermodiode linearity, sensitivity and self-heating is experimentally and theoretically investigated. Results on the long-term diode stability at high temperature are also reported. © 2013 IEEE.

Influence of turbulence-chemistry interaction for n-heptane spray combustion under diesel engine conditions with emphasis on soot formation and oxidation

The influence of the turbulence-chemistry interaction (TCI) for n-heptane sprays under diesel engine conditions has been investigated by means of computational fluid dynamics (CFD) simulations. The conditional moment closure approach, which has been previously validated thoroughly for such flows, and the homogeneous reactor (i.e. no turbulent combustion model) approach have been compared, in view of the recent resurgence of the latter approaches for diesel engine CFD. Experimental data available from a constant-volume combustion chamber have been used for model validation purposes for a broad range of conditions including variations in ambient oxygen (8-21% by vol.), ambient temperature (900 and 1000 K) and ambient density (14.8 and 30 kg/m3). The results from both numerical approaches have been compared to the experimental values of ignition delay (ID), flame lift-off length (LOL), and soot volume fraction distributions. TCI was found to have a weak influence on ignition delay for the conditions simulated, attributed to the low values of the scalar dissipation relative to the critical value above which auto-ignition does not occur. In contrast, the flame LOL was considerably affected, in particular at low oxygen concentrations. Quasi-steady soot formation was similar; however, pronounced differences in soot oxidation behaviour are reported. The differences were further emphasised for a case with short injection duration: in such conditions, TCI was found to play a major role concerning the soot oxidation behaviour because of the importance of soot-oxidiser structure in mixture fraction space. Neglecting TCI leads to a strong over-estimation of soot oxidation after the end of injection. The results suggest that for some engines, and for some phenomena, the neglect of turbulent fluctuations may lead to predictions of acceptable engineering accuracy, but that a proper turbulent combustion model is needed for more reliable results. © 2014 Taylor & Francis.

Characterization of the temperature sensitivity of gain and recombination mechanisms in 1.3-μm AlGaInAs MQW lasers

The potential of 1.3-μm AlGaInAs multiple quantum-well (MQW) laser diodes for uncooled operation in high-speed optical communication systems is experimentally evaluated by characterizing the temperature dependence of key parameters such as the threshold current, transparency current density, optical gain and carrier lifetime. Detailed measurements performed in the 20°C-100°C temperature range indicate a localized T0 value of 68 K at 98°C for a device with a 2.8μm ridge width and 700-μm cavity length. The transparency current density is measured for temperatures from 20°C to 60°C and found to increase at a rate of 7.7 A·cm -2 · °C-1. Optical gain characterizations show that the peak modal gain at threshold is independent of temperature, whereas the differential gain decreases linearly with temperature at a rate of 3 × 10-4 A-1·°C-1. The differential carrier lifetime is determined from electrical impedance measurements and found to decrease with temperature. From the measured carrier lifetime we derive the monomolecular (A), radiative (B), and nonradiative Auger (C) recombination coefficients and determine their temperature dependence in the 20 °C-80 °C range. Our study shows that A is temperature independent, B decreases with temperature, and C exhibits a less pronounced increase with temperature. The experimental observations are discussed and compared with theoretical predictions and measurements performed on other material systems. © 2005 IEEE.

Temperature measurements of the bluff body surface of a Swirl Burner using phosphor thermometry

Flames are often stabilised on bluff-bodies, yet their surface temperatures are rarely measured. This paper presents temperature measurements for the bluff body surface of the Cambridge/Sandia Stratified Swirl Burner. The flame is stabilized by a bluff body, designed to provide a series of turbulent premixed and stratified methane/air flames with a variable degree of swirl and stratification. Recently, modellers have raised concerns about the role of surface temperature on the resulting gas temperatures and the overall heat loss of the burner. Laser-induced phosphorescence is used to measure surface temperatures, with Mg4GeO6F:Mn as the excitation phosphor, creating a spatially resolved temperature map. Results show that the temperature of the bluff body is in the range 550-900 K for different operating conditions. The temperature distribution is strongly correlated with the degree of swirl and local equivalence ratio, reflecting the temperature distribution obtained in the gas phase. The overall heat loss represents only a small fraction (<0.5%) of the total heat load, yet the local surface temperature may affect the local heat transfer and gas temperatures. © 2014 The Combustion Institute.

Bimesogenic liquid crystals: New materials for high performance flexoelectric and blue phase displays

In this paper we will describe new bimesogenic nematic liquid crystals that have high flexoelectro-optic coefficients (e/K),of the order of 1.5 CN 1 m-1, high switching angles, up to 100° and fast response times, of the order of 100μs or less. We will describe devices constructed, using the ULH texture that may be switched to the optimum angle of 45° for a birefringence based device with the fields of 4Vμm-1 over a wide temperature range. Such devices use an "in plane" optical switching mode, have gray scale capability and a wide viewing angle. We will describe devices using the USH or Grandjean texture that have an optically isotropic "field off" black state, uses "in plane" switching E fields, to give an induced birefringence phase device, with switching times of the order of 20μs. We will briefly describe new highly reflective Blue Phase devices stable over a 50V temperature range in which an electric field is used to switch the reflection from red to green, for example. Full RGB reflections may be obtained with switching times of a few milliseconds. Finally we will briefly mention potential applications including high efficiency RGB liquid crystal laser sources. © 2006 SID.

Fabrication and testing of a high resolution extensometer based on resonant MEMS strain sensors

A novel type of linear extensometer with exceptionally high resolution of 4 nm based on MEMS resonant strain sensors bonded on steel and operating in a vacuum package is presented. The tool is implemented by means of a steel thin bar that can be pre-stressed in tension within two fixing anchors. The extension of the bar is detected by using two vacuum-packaged resonant MEMS double- ended tuning fork (DETF) sensors bonded on the bar with epoxy glue, one of which is utilized for temperature compensation. Both sensors are driven by a closed loop self-oscillating transresistance amplifier feedback scheme implemented on a PCB (Printed Circuit Board). On the same board, a microcontroller-based frequency measurement circuit is also implemented, which is able to count the square wave fronts of the MEMS oscillator output with a resolution of 20 nsec. The system provides a frequency noise of 0.2 Hz corresponding to an extension resolution of 4 nm for the extensometer. Nearly perfect temperature compensation of the frequency output is achieved in the temperature range 20-35 C using the reference sensor. © 2011 IEEE.

Spin glass behaviour and spin-dependent scattering in la 0.7Ca 0.3Mn 0.9Cr 0.1O 3 perovskites

The magnetic, electrical and thermal transport properties of the perovskite La 0.7Ca 0.3Mn 0.9Cr 0.1O 3 have been investigated by measuring dc magnetization, ac susceptibility, the magnetoresistance and thermal conductivity in the temperature range of 5-300K. The spin glass behaviour with a spin freezing temperature of 70 K has been well confirmed for this compound, which demonstrates the coexistence and competition between ferromagnetic and antiferromagnetic clusters by the introduction of Cr. Colossal magnetoresistance has been observed over the temperature range investigated. The introduction of Cr causes the "double-bump" feature in electrical resistivity ρ(T). Anomalies on the susceptibility and the thermal conductivity associated with the double-bumps in ρ(T) are observed simultaneously. The imaginary part of ac susceptibility shows a sharp peak at the temperature of insulating-metallic transition where the first resistivity bump was observed, but it is a deep-set valley near the temperature where the second bump in ρ(T) emerges. The thermal conductivity shows an increase below the temperature of the insulating-metallic transition, but the phonon scattering is enhanced accompanying the appearance of the second peak of double-bumps in ρ(T). We relate those observed in magnetic and transport properties of La 0.7Ca 0.3Mn 0.9Cr 0.1O 3 to the spin-dependent scattering. The results reveal that the spin-phonon interaction may be of more significance than the electron (charge)-phonon interaction in the mixed perovskite system. © 2005 Chinese Physical Society and IOP Publishing Ltd.

Autoignition of alcohols and ethers in a rapid compression machine

The autoignition characteristics of methanol, ethanol and MTBE (methyl tert-butyl ether) have been investigated in a rapid compression machine at pressures in the range 20-40 atm and temperatures within 750-1000 K. All three oxygenated fuels tested show higher autoignition temperatures than paraffins, a trend consistent with the high octane number of these fuels. The autoignition delay time for methanol was slightly lower than predicted values using reported reaction mechanisms. However, the experimental and measured values for the activation energy are in very good agreement around 44 kcal/mol. The measured activation energy for ethanol autoignition is in good agreement with previous shock tube results (31 kcal/mol), although ignition times predicted by the shock tube correlation are a factor of three lower than the measured values. The measured activation energy for MTBE, 41.4 kcal/mol, was significantly higher than the value previously observed in shock tubes (28.1 kcal/mol). The onset of preignition, characterized by a slow energy release prior to early ignition was observed in some instances. Possible reasons for these ocurrences are discussed. © Copyright 1993 Society of Automotive engineers, Inc.

Au-catalyzed InP nanowires: The influence of growth temperature and V/III ratio

Growth of Au-catalyzed InP nanowires (NWs) by metalorganic chemical vapor deposition (MOCVD) has been studied in the temperature range of 400-510 °C and V/III ratio of 44-700. We demonstrate that minimal tapering of InP NWs can be achieved at 400 °C and V/III ratio of 350. Zinc-blende (ZB) or wurtzite (WZ) NWs is obtained depending on the growth conditions. 4K microphotoluminescence (μ-PL) studies show that emission energy is blue-shifted as growth temperature increases. By changing these growth parameters, one can tune the emission wavelength of InP NWs which is attractive for applications in developing novel optoelectronic devices. © 2010 IEEE.

Design and market considerations for axial flux superconducting electric machine design

In this paper, the authors investigate a number of design and market considerations for an axial flux superconducting electric machine design that uses high temperature superconductors. The axial flux machine design is assumed to utilise high temperature superconductors in both wire (stator winding) and bulk (rotor field) forms, to operate over a temperature range of 65-77 K, and to have a power output in the range from 10s of kW up to 1 MW (typical for axial flux machines), with approximately 2-3 T as the peak trapped field in the bulk superconductors. The authors firstly investigate the applicability of this type of machine as a generator in small- and medium-sized wind turbines, including the current and forecasted market and pricing for conventional turbines. Next, a study is also carried out on the machine's applicability as an in-wheel hub motor for electric vehicles. Some recommendations for future applications are made based on the outcome of these two studies. Finally, the cost of YBCO-based superconducting (2G HTS) wire is analysed with respect to competing wire technologies and compared with current conventional material costs and current wire costs for both 1G and 2G HTS are still too great to be economically feasible for such superconducting devices.

Thermo-optical characterization of fluorescent rhodamine B based temperature-sensitive nanosensors using a CMOS MEMS micro-hotplate

A custom designed microelectromechanical systems (MEMS) micro-hotplate, capable of operating at high temperatures (up to 700 C), was used to thermo-optically characterize fluorescent temperature-sensitive nanosensors. The nanosensors, 550 nm in diameter, are composed of temperature-sensitive rhodamine B (RhB) fluorophore which was conjugated to an inert silica sol-gel matrix. Temperature-sensitive nanosensors were dispersed and dried across the surface of the MEMS micro-hotplate, which was mounted in the slide holder of a fluorescence confocal microscope. Through electrical control of the MEMS micro-hotplate, temperature induced changes in fluorescence intensity of the nanosensors was measured over a wide temperature range. The fluorescence response of all nanosensors dispersed across the surface of the MEMS device was found to decrease in an exponential manner by 94%, when the temperature was increased from 25 C to 145 C. The fluorescence response of all dispersed nanosensors across the whole surface of the MEMS device and individual nanosensors, using line profile analysis, were not statistically different (p < 0.05). The MEMS device used for this study could prove to be a reliable, low cost, low power and high temperature micro-hotplate for the thermo-optical characterisation of sub-micron sized particles. The temperature-sensitive nanosensors could find potential application in the measurement of temperature in biological and micro-electrical systems. The Authors. © 2013 Published by Elsevier B.V. All rights reserved.