Rapid Heat-up Research Articles

The microstructural origin of a hardness double-peak in an age-hardened EN-AW 6082

In this study, the origin of a double-peak during artificial aging of an EN-AW 6082 is analyzed with (S)TEM. The acquired TEM data is used as an input into a strength model by Holmedal [1] to explore the origin of the double-peak, thus, a broader strength plateau. It is concluded that the first peak arises after about 160min at 175°C from a population of relatively wide β′′-type precipitates with a high number density and a narrow length spread. The second peak occurs after 10h artificial aging and can be traced to a broader size distribution of precipitate lengths of roughly the same type of precipitates as found for the first peak. The longest precipitates, however, act more efficiently as obstacles for gliding dislocations and maintain therefore the high strength. Those long precipitates are of a hybrid type of different, but mainly overaged phases. It is found that this broad strength plateau with a double-peak can arise after a rapid heat-up to the artificial aging temperature. Due to the rapid heat-up, structures of overaged phases are already found within the β′′ precipitates of the first peak making them wider. Ultimately, however, this leads to the evolution of few but very large overaged hybrid-type precipitates co-existing with β′′-type precipitates at the second peak. The mixed morphology counteracts the loss of strength from Ostwald ripening and leads to the second peak. A slower heating rate results in fewer precipitate nucleation sites and in the formation of longer and purer but slimmer βperfect′′ phases.

Non-Destructive characterisation of coke deposit on FCC catalyst and its transient evolution upon Air-Firing and Oxy-Fuel regeneration

In this paper, the regeneration and associated transient evolution of a commercial FCC spent catalyst in both air-firing and oxy-fuel combustion modes (i.e. 0–10% O2 in N2 or CO2, 510–1000°C, and ∼ 4 sec) were studied in a lab-scale drop-tube furnace. A variety of non-destructive techniques including synchrotron NEXAFS, XPS and ATR-FTIR for both non-grounded and grounded spent catalyst and its combustion residues were employed to reveal the speciation, spatial distribution of coke within the catalyst matrix, as well as its evolution upon rapid heart-up and combustion. As have been confirmed, the coke species is highly broad in speciation, covering aliphatic and aromatic compounds as well as graphite that are both physically deposited and chemically adsorbed on acid sites on the catalyst’s exterior surface. The majority of aliphatic hydrocarbons were also embedded deeply within the catalyst matrix, which were presumably caused by the penetration of precursor molecules that are small in size. Irrespective of the combustion mode, upon the initial rapid heat-up, the embedded light hydrocarbons were rapidly volatilised, and diffused outward toward the exterior surface, where it either underwent C-O2/C-CO2 reactions, or simply further recondensed into graphite in the case that oxygen is lean in the air-firing mode. In contrast, in the oxy-firing mode, the coke was confirmed highly reactive for reverse Boudouard reaction and methane drying reaction which were even triggered during the initial particle heat-up stage. Consequently, the initial graphitisation extent of light vapor was mitigated, and the micro-pores of catalysts were opened up to enable a continuous elution of the hydrocarbon vapors to boost the overall coke burn-off. Regarding the competition of the overall C-O2 and C-CO2 reactions on catalyst exterior surface, the former reaction is superior in the case where oxygen is lean (e.g. 3%). In contrast, when the oxygen content is higher (e.g. 10%), the latter one was intensified due to the strong heat feedback from the exothermic C-O2 reactions. As a result, the overall coke including other two species, graphite and aliphatic hydrocarbons were consumed quickly in the O2/CO2 case.

Holistic Engine and EAT Development of Low NO <sub>X</sub> and CO <sub>2</sub> Concepts for HD Diesel Engine Applications

<div class="section abstract"><div class="htmlview paragraph">The latest legislative tendencies for on-highway heavy duty vehicles in the United States such as the feasibility assessment of low NO<sub>X</sub> standards of CARB or EPA’s memorandum forecast further tightening of the NO<sub>X</sub> emissions limits. In addition, the GHG Phase 2 legislation and also phased-in regulations in the EU enforce a continuous reduction in CO<sub>2</sub> emissions resp. fuel consumption. In order to meet such low NO<sub>X</sub> emission limits, a rapid heat-up of the exhaust after-treatment system (EATS) is inevitable. However, the required thermal management results in increased fuel consumption, i.e. CO<sub>2</sub> emissions as shown in numerous previous works also by the authors. A NO<sub>X</sub>-CO<sub>2</sub> trade-off for cumulative cycle emissions can be observed, which can be optimized by using more advance technologies on the engine and/or on the EATS side.</div><div class="htmlview paragraph">In the present study a systematic investigation is carried out by means of model-based holistic approach targeting the definition of a high efficiency engine layout and optimal thermal management calibration. First, the potentials of combustion process optimization (compression ratio, peak firing pressure) and of turbocharger efficiency increase are quantified aiming engine efficiency increase. Afterwards, using holistic engine and EAT concept development approach, conventional and advanced EATS layouts are tested. The advanced EATS layout consist of a close-coupled dual-stage SCR system. In order to explore the benefits of each layouts, the engine heat-up calibrations are varied and the resulting, cumulative NO<sub>X</sub>-CO<sub>2</sub> emissions of the investigated cycle are compared and evaluated. Multiple improvement measures for both engine and EAT system are discussed and an outlook of future powertrain concepts is given.</div></div>

Stability study of SOFC using layered perovskite oxide La1·85Sr0·15CuO4 mixed with ionic conductor as membrane

Long-term stability is of significant importance to energy conversion devices including solid oxide fuel cell (SOFC). In this work, we apply a layered perovskite oxide La1·85Sr0·15CuO4 (LSCO4) mixing with ionic conductor Ce0.8Sm0.2O2-δ (SDC) to get an ionic and electronic conductor composite (IECC) membrane SOFC for the sake of achieving a stable cell. The addition of proper ratio of LSCO4 in the membrane improves cell performance. The IECC fuel cell reaches a stability of over 75 h at 550 °C under 100 mAcm−2 and can resist multiple times of rapid heat-up and cool-down cycles. The factors that influence cell stability are investigated. The covalence states of the IECC are found to change firstly but stabilize after several hours of test. Resulting from anode Ni0·8Co0·15Al0·05LiO2-δ (NCAL) reduction, Li+ is found to migrate to the IECC membrane, leading to IECC membrane densifying and resultantly protecting the IECC from further reduction by hydrogen. However, the continuous online reaction of NCAL electrodes leads to the increase of charge transfer resistance as well as the decrease of gas diffusion pores in the electrode. This study provides important reference for designing stable IECC membrane fuel cell.

Development of a Leuckart–Wallach Reaction in Flow for the Synthesis of Abemaciclib

The development of a route for a key building block in the synthesis of abemaciclib is described. The route proceeds through a Leuckart–Wallach reductive amination in flow followed by an Ullmann amination with aqueous ammonia. Key to the Leuckart–Wallach reductive amination was the addition of trimethyl orthoformate for water removal, running the reaction continuously in a pipes-in-series reactor for rapid heat-up, and building a kinetic model to understand time and temperature parameters for the feed tank storage. The product of the Leuckart–Wallach reductive amination is forward processed in batch and telescoped with the Ullmann amination and subsequent workup. The development resulted in a robust process that has successfully been run on the production scale.

Approaches to understand and predict the influence of rapid heat-up on degradation and strength of carbon fibre polymer matrix composites

This study focuses on understanding and prediction of short-term thermal degradation of polymer matrix composites. One sided irradiation of two commercial composites (HexPly® 8552/IM7 and M18-1/G939) is carried out on specimens of various thickness (2, 4, 6 mm) at different heat fluxes (50 and 80 kW/m2) for various exposure times prior to ignition. The aim is to correlate the amount of the applied thermal energy with the heat damage and the residual mechanical strength. Among the two primary components of each matrix the epoxy resin is observed to degrade faster than the thermoplastic under thermal load, as measured by IR spectroscopy. A correlation is achieved between the interlaminar shear strengths and the relative amount of the residual matrix components. The interlaminar shear strengths and degradation processes are assessed in dependence of the applied energy per volume. The derived relationships and a chemometric analysis of IR spectra, can be used to rapidly estimate mechanical properties, as well as other properties of specimens with unknown thermal preload. Degradation processes are discussed in detail.

Latest SiC Epitaxial Layer Growth Results in a High-Throughput 6×150 mm Warm-Wall Planetary Reactor

Latest results are presented for SiC-epitaxial growths employing a novel 6x150-mm/10x100-mm Warm-Wall Planetary Vapor-Phase Epitaxial (VPE) Reactor. The increased throughput offered by this reactor and 150-mm diameter wafers, is intended to reduce the cost per unit area for SiC epitaxial layers, increasing the market penetration of already successful commercial SiC Schottky and MOSFET devices [1]. Increased growth rates of 30-40 micron/hr and short <2 hr fixed-cycle times (including rapid heat-up and cool-down ramps), while maintaining desirable epitaxial layer quality were achieved. Increased quantities of 150-mm epitaxial wafers now allow statistical analysis of their epitaxial layer properties. Specular epitaxial layer morphology was obtained, with morphological defect densities <0.4 cm-2, consistent with projected 5x5 mm die yields averaging 93% for Si-face epitaxial layers between 10 and 30 microns thick. Intrawafer thickness and doping uniformity are good, averaging 1.7% and 5.1% respectively. Wafer-to-wafer doping variation has also been significantly reduced from ~12 [5] to <3% s/mean. Initial results for C-face growths show excellent morphology (97%) but poor doping uniformity (~16%). Wafer shape is relatively unchanged by epitaxial growth consistent with good epitaxial temperature uniformity.

SiC Epitaxial Layer Growth in a 6x150 mm Warm-Wall Planetary Reactor

Initial results are presented for SiC-epitaxial growths employing a novel 6x150-mm/10x100-mm Warm-Wall Planetary Vapor-Phase Epitaxial (VPE) Reactor. The increased areal throughput offered by this reactor and 150-mm diameter wafers, is intended to reduce the cost per unit area for SiC epitaxial layers, increasing the market penetration of already successful commercial SiC Schottky and MOSFET devices [1]. Growth rates of 20 micron/hr and short <2 hr fixed-cycle times (including rapid heat-up and cool-down ramps), while maintaining desirable epitaxial layer quality were achieved. No significant change in 150 mm diameter wafer shape is observed upon epitaxial growth consistent with good-quality, low-stress substrates and low (<5°C) cross-wafer epitaxial reactor temperature variation. Specular epitaxial layer morphology was obtained, with morphological defect densities consistent with projected 5x5 mm die yields as high as 80% and surface roughness, Ra, of 0.3 nm. Intrawafer thickness uniformity is good, averaging only 1.6% and within a run wafer-to-wafer thickness variation is 2.7%. N-type background doping densities less that 1E14 cm-3 have been measured by CV. Doping uniformity and wafer-to-wafer variation currently average ~12% requiring further improvement. The first 100 m thick 150-mm diameter epitaxial growths are reported.

Delamination of moisture saturated graphite/polyimide composites due to rapid heating

In this study, experimental methods and a theoretical model are developed with aim of understanding and predicting the onset of steam pressure-induced delamination. Experiments are performed by rapid heat-up of moisture saturated T650-35/HFPE-II-52 graphite/polyimide laminates, pre-implanted in the midplane with circular starter cracks. The deformation of these flaws and subsequent delamination growth is measured using custom designed, transverse extensometers. A theoretical model for calculation of internal steam pressure within a deforming circular cavity is derived and combined with a linear elastic fracture mechanics approach to predict the onset of delamination growth. The experimental results and theoretical calculations are used to highlight the effect of heating rate, initial flaw size, initial moisture content, and material toughness on steam-induced delamination. A parametric study is conducted and used to identify conditions required for transition between steam-induced delamination and steam-induced blistering damage.

Modeling of liquid ceramic precursor droplets in a high velocity oxy-fuel flame jet

Production of coatings by high velocity oxy-fuel (HVOF) flame jet processing of liquid precursor droplets can be an attractive alternative method to plasma processing. This article concerns modeling of the thermophysical processes in liquid ceramic precursor droplets injected into an HVOF flame jet. The model consists of several sub-models that include aerodynamic droplet break-up, heat and mass transfer within individual droplets exposed to the HVOF environment and precipitation of ceramic precursors. A parametric study is presented for the initial droplet size, concentration of the dissolved salts and the external temperature and velocity field of the HVOF jet to explore processing conditions and injection parameters that lead to different precipitate morphologies. It is found that the high velocity of the jet induces shear break-up into several μm diameter droplets. This leads to better entrainment and rapid heat-up in the HVOF jet. Upon processing, small droplets (<5 μm) are predicted to undergo volumetric precipitation and form solid particles prior to impact at the deposit location. Droplets larger than 5 μm are predicted to form hollow or precursor containing shells similar to those processed in a DC arc plasma. However, it is found that the lower temperature of the HVOF jet compared to plasma results in slower vaporization and solute mass diffusion time inside the droplet, leading to comparatively thicker shells. These shell-type morphologies may further experience internal pressurization, resulting in possibly shattering and secondary atomization of the trapped liquid. The consequences of these different particle states on the coating microstructure are also discussed in this article.

Modeling of precipitate formation in precursor droplets injected axially into an oxygen/acetylene combustion flame

A computational heat and mass transfer model of ceramic precursor solution containing droplets injected into a combustion flame is presented. Upon heat-up and vaporization, the precursor in droplets precipitate and ultimately form the ceramic material. Temperature and solute concentration distributions were computed to estimate the precipitation zones within droplets based on a simple homogeneous nucleation hypothesis. Effects of droplet size, injection velocity and injection angle were studied parametrically. High relative velocity between the droplets and the hot gas medium results in rapid heat-up and vaporization rates. Consequently, the solute concentration near the droplet surface increases rapidly. It is predicted that small droplets form nearly solid spherical particulates whereas larger droplets form shells and interconnected ceno-spheres. Predicted morphologies are supported by experimental evidence of shell-type structures and spherical particles in the combustion flame experiments performed earlier.

Modeling of axially and transversely injected precursor droplets into a plasma environment

Transport model of droplets injected axially or transversely into a plasma jet is presented. The droplets contain a ceramic precursor that precipitates in the vaporizing droplets. Droplet temperature and solute concentration distributions were predicted to estimate precipitation zones based on a homogeneous nucleation hypothesis. Effects of droplet size, injection velocity and injection angle were parametrically studied and the results were compared for axial and transverse injection. Axial injection is found to result in more rapid heat-up and precipitation than transverse injection. Computations suggest that small droplets form solid spherical particulates whereas larger droplets may form ceno-spheres and thin shell structures.

Comparison of Temperature Conditions in Direct Liquefaction of Selected Low-Rank Coals

The direct liquefaction of one lignitic and two subbituminous coals was studied in laboratory-scale microautoclave reactors. The principal focus of this work was to investigate the effects of three strategies for employing temperature: single-staged liquefaction at one temperature; temperature-staged liquefaction involving rapid heat-up between low- and high-temperature reaction stages; and temperature-programmed liquefaction, with slow heat-up between stages. Both the temperature-staged and temperature-programmed conditions are advantageous relative to the single-staged reaction, particularly for coals that are less easily converted. The benefits of using temperature-staging or programming appear to derive from both physical and chemical processes related to the catalyst and solvent, such as allowing more time for the catalyst precursor to transform into an active form and enhancing solvent−coal interactions. For a highly reactive coal, single-stage conditions appear to be sufficient. In single-stage reactions without solvent or catalyst, or with nonreactive solvent, the conversion of these three coals is related to their organic sulfur content.

In-cylinder sizing of diesel particles by time-resolved laser-induced incandescence (TR-LII)

Laser-induced incandescence (LII) is a technique allowing particle-size distribution measurement and quantifying in an extremely short time. It is especially attractive for rapidly varying conditions as in diesel engine combustion. A special variant is the time-resolved method (TR-LII), which yields almost instantaneous particle-size information. In the present work, the application of particle sizing in the combustion chamber of a diesel engine is demonstrated. The measuring equipment was adapted to a one-cylinder, two-stroke engine with a specially designed cylinder head, yielding highly reproducible signals for particle thermal emission after rapid heatup by a pulsed laser. The characteristic time constant τm of the exponential signal decrease is a measure for the particle size. TR-LII signals for different crank angles and varying motor conditions were measured. A strong dependence of the characteristic emission time constant τm during particle cooling from the measured crank angle and the engine load could be determined. Specialties in signal evaluation due to the higher pressure level during diesel combustion are discussed, and size parameters, such as the count median diameter and the geometric standard deviation of an assumed lognormal size distribution, were determined from the measured optical signals. A comparison of in situ TR-LII particle sizing with the well-established ex situ differential mobility particle-sizing technique was performed. The results are in good agreement.

Foams and gels as fire protection agents

Fire protection foams and gels are used as temporary barriers to protect samples from incident thermal radiation thus delaying their ignition. Comparative measurements of the thermal behavior of these agents are made using a radiant heat exposure. The results of this comparison clearly show that thermal protection is obtained by two different mechanisms. The conduction-dominated gel operates at near saturation conditions (100°C). The radiation-dominated foam provides complete protection at ambient conditions (20–30°C) for about half the transient duration. Thereafter, the residual foam layer cannot prevent a rapid heat-up of the sample. Tests are performed applying the agents to a flat sample that is then positioned vertically and exposed to radiant heat. The lateral ignition and flame spread test (LIFT) apparatus is used to determine the ignition delay time for the gel. Due to the sample size restrictions associated with the LIFT apparatus, data collection for foams is not possible. Therefore, measurements are conducted in a Radiant Exposure Apparatus (REA) which allows for larger samples subjected to uniform heat fluxes up to 18 kW/m 2. The data gathered from the LIFT and REA are compared to establish the consistency between the two measurement sets.

Nitrogen Transformations in Coal during Pyrolysis

X-ray photoelectron spectroscopy (XPS) was used to identify and quantify the changes in organically bound nitrogen forms present in the tars and chars of coals after pyrolysis. For fresh coal, pyrrolic nitrogen is the most abundant form of organically bound nitrogen, followed by pyridinic, quaternary, and amino types. Some of the quaternary nitrogen species initially present in coal are lost upon mild pyrolysis, prior to hydrocarbon devolatilization. These quaternary species are attributed to pyridinic or basic nitrogen species associated with hydroxyl groups from carboxylic acids or phenols. A portion of the quaternary nitrogen species is lost at the very earliest stage of pyrolysis. Upon devolatilization, the resultant tar and char contain mostly pyrrolic and pyridinic forms; however, a portion of the quaternary nitrogen initially present in the coal appears in the coal char and tar. The relatively strong bonding interactions associated with these quaternary species suggests that there may be other quaternary nitrogen, in addition to protonated pyridines, in low-rank coal. For low-rank coal, amino groups are preferentially released and concentrate in the tar. XPS analysis of chars and tars produced during rapid heat-up (104 deg/s) pyrolysis show similar trends. However, severe pyrolysis of the devolatilized char results in the appearance of an asymmetric carbon (1s) line shape indicative of very large polynuclear “graphitic-like” units. This transformation is accompanied by a rise in the relative number of quaternary nitrogen forms and occurs over a relatively narrow temperature range. Quaternary and pyridinic nitrogen forms become the dominant forms in severely pyrolyzed chars. The relatively low level of quaternary nitrogen in the rapid heat-up chars indicates that very large polynuclear aromatic structures are not fully developed under these pyrolysis conditions.

Performance of A Laser-Pulsed Thermal Electron Gun

High-speed electron microscopy strongly demands a high-brightness electron gun in order to increase the number of image forming electrons. A few years ago, a laser-pulsed high-brightness electron gun was introduced. Fig.1 shows the experimental set-up, A standard triode system was supplemented with a Nd:YAG laser, focussing optics and a modified anode, which incorporates the laser deflection mirror. The frequency doubled laser pulse (τ =5 ns, λ = 532 nm) is focused through a window onto the tip of the tungsten hairpin emitter. The laser treated area (≈ 100 μm diameter) is heated well above the melting point, which results in a strong thermal electron emission. Due to rapid heat-up and fast cool-down of the tungsten surface short electron pulses with a duration of 20 ns and a maximum current of 20 mA at 80 kV are emitted. A destruction of the tungsten wire is avoided, too. Laser energies used for the generation of electron pulses are in the range of 100 μJ. Due to these minor modification, the DC operation of the electron gun is not disabled, which allows a convenient adjustment in the DC mode and then switching into the pulsed operation mode. Fig.2 shows a typical electron pulse emitted by the gun. Shorter electron pulses up to 5 ns can be generated by a beam blanking unit.

High-Speed Reflection Electron Microscopy of Laser-Induced Surface Transitions

Micropatterning of bulk material by pulsed laser radiation is a promising technique for many applications, e.g. drilling and data storage. Due to the fact that laser radiation can be applied very localized, high power densities in a small volume of the treated specimen can be realized. As a result of rapid heat-up and cool-down processes, unusual phases and microstructures can be generated.Time-resolving methods, especially imaging with short exposures times are quite useful in order to understand the physics standing behind. As a diagnostic tool electrons are superior to other probes, e.g. light optics, due to their sensitivity to topography, material composition and structure. Unfortunately , the SEM - one of the most common microscopes for surface analysis - cannot be used for investigations in the the nanoseconds time domain due to its far to slow scan time. On the other hand, the reflection electron microscope (REM) is one of the very few instruments, which is capable to image all points of the treated surface simultanously.In order to achieve electron optical images of laser pulse induced processes on surfaces with exposures times of a few nanoseconds, a high-speed REM was developed. This new instrument is based on a conventional TEM, additionally equipped with the following units:- a laser pulsed thermal electron gun, which delivers high-brightness electron pulses with duration of 20ns.

Computer Simulation of a Municipal Solid Waste Combustor

A mathematical model has been developed to study the thermal and chemical processes occurring In a municipal solid waste mass combustor. Treating the solids feed as a mixture of pseudo-components, the model determines the Interrelationships between the solids feed rate, grate travel rate and length, amounts and distributions of primary and secondary air, extent of solids burn out, and the bed and flame temperatures. The model Incorporates the kinetics of pyrolysis of solids and simulates heat and mass transfer within the bed. The temperature and mass flow profiles generated show that much of the grate Is taken up by the heatup and burnout zones. The heatup zone can be reduced by distributing the primary air to maintain minimal air flow In that region, thereby permitting rapid heatup. Increasing the solids feed rate and adjusting the air flow distributions can reduce the length of the burnout zone. The computer program, available on both PCs and mainframe, can be used for different MSW Incinerator dimensio...

ISOTHERMAL PREDICTION OF PARTICLE AND GAS FLOW IN A COAL-FIRED REACTOR

ABSTRACT The steady, turbulent gas flow with entrained coal particles in a laboratory-scale axisymmetric coal gasification reactor is numerically analyzed. The reactor is designed to provide rapid mixing and heatup of the coal in a configuration which results in a nearly isothermal and uniform flow in the main reaction chamber so as to allow controlled study of coal gasification. A detailed knowledge of the reactor dynamics is required in order to interpret experimental results. The nonreacting, isothermal flow pattern is first presented as a base case. Calculations are performed with an iterative, implicit scheme suitable to the elliptic nature of the gas flow equations in an Eulerian frame-work. The turbulent motion is resolved using the eddy-viscosity concept with the standard k-e turbulence model. Coal particle trajectories are then calculated using the Lagrangian form of the momentum equations. The influence of solid particles on the gas phase is neglected. Particle trajectories and residence time di...