Relevant Operating Conditions Research Articles

Application of hot-wire anemometry for experimental investigation of flow distribution in micro-packed bed reactors for synthesis gas conversion

The knowledge of the flow distribution inside microstructured reactors is valuable e.g. for improving the reactor design, developing flow distributors, and optimizing the catalyst loading method. The applicability of the hot-wire anemometry (HWA) technique for experimental determination of the flow distribution inside a multi-stack micro-packed bed reactor is demonstrated for the first time. The anemometry data is then evaluated in relation to the reactor performance for methanol synthesis under relevant industrial operating conditions. A 400 µm long hot-wire connected to a constant temperature anemometer was applied for scanning the flow out of a specially designed reactor model, clamped on a motorized table equipped with a precise positioning system. The anemometry measurements revealed a nonuniformity in the catalyst packing, partially resulting from the reactor design. The flow distribution is poorer for smaller particles and for wider particle size distributions, and worsens as the superficial flow velocity (and the pressure drop) decreases. The effects of the packing nonuniformity on the reactor performance appear minor under methanol synthesis conditions. They could, however, turn out significant upon pushing the overall conversion in the whole reactor towards equilibrium as the synthesis reaction is exothermic, and temperature increase does alleviate the problem. The reactor design should be modified instead.

Mapping the Functional Tortuosity and Spatiotemporal Heterogeneity of Porous Polymer Membranes with Super-Resolution Nanoparticle Tracking.

As particles flow through porous media, they follow complex pathways and experience heterogeneous environments that are challenging to characterize. Tortuosity is often used as a parameter to characterize the complexity of pathways in porous materials and is useful in understanding hindered mass transport in industrial filtration and mass separation processes. However, conventional calculations of tortuosity provide only average values under static conditions; they are insensitive to the intrinsic heterogeneity of porous media and do not account for potential effects of operating conditions. Here, we employ a high-throughput nanoparticle tracking method which enables the observation of actual particle trajectories in polymer membranes under relevant operating conditions. Our results indicate that tortuosity is not simply a structural material property but is instead a functional property that depends on flow rate and particle size. We also resolved the spatiotemporal heterogeneity of flowing particles in these porous media. The distributions of tortuosity and of local residence/retention times were surprisingly broad, exhibiting heavy tails representing a population of highly tortuous trajectories and local regions with anomalously long residence times. Interestingly, local tortuosity and residence times were directly correlated, suggesting the presence of highly confining regions that cause more meandering trajectories and longer retention times. The comprehensive information about tortuosity and spatiotemporal heterogeneity provided by these methods will advance the understanding of complex mass transport and assist rational design and synthesis of porous materials.

Aspects of the Ageing of Elastomeric Materials

Rising raw materials prices and increasing customer demands for reliability and durability mean that there is huge interest in finding more and more ways of improving the service life of elastomeric products, for economic and environmental reasons, by boosting their resistance under the relevant operating conditions. The material-dependent oxygen absorption capacity and oxygen permeability play an important role in oxidative ageing processes and their modelling. Thus, ageing resistance is substantially dependent on the rate of oxygen diffusion into the bulk of the material in the case of thermo-oxidative attack. To evaluate the resistance of materials to external influences, artificial ageing methods are used in practice. The advantage of these methods is that, as a result of intensifying the test parameters, e.g. temperature and humidity, the ageing processes in the vulcanisate are accelerated. Within the scope of this study, the influence of accelerated ageing on the mechanical and viscoelastic properties of mainly carbon-black-filled natural rubber (NR) vulcanisates was studied in an oxygen atmosphere at elevated temperature and in oxygen with solar radiation. The filler content was varied and the antioxidant IPPD was used. The analyses showed that, as well as mechanical properties such as hardness and tensile strength, the viscoelastic properties are also affected, depending on the ageing time and the type of ageing. In addition to the investigation of mechanical properties, a direct evaluation of the material change was carried out for selected samples by means of analytical tests. The investigations showed the deterioration of the antioxidant activity.

The Influence of Carrier Air Preheating on Autoignition of Inline-Injected Hydrogen–Nitrogen Mixtures in Vitiated Air of High Temperature

The use of highly reactive hydrogen-rich fuels in lean premixed combustion systems strongly affects the operability of stationary gas turbines (GT) resulting in higher autoignition and flashback risks. The present study investigates the autoignition behavior and ignition kernel evolution of hydrogen–nitrogen fuel mixtures in an inline co-flow injector configuration at relevant reheat combustor operating conditions. High-speed luminosity and particle image velocimetry (PIV) measurements in an optically accessible reheat combustor are employed. Autoignition and flame stabilization limits strongly depend on temperatures of vitiated air and carrier preheating. Higher hydrogen content significantly promotes the formation and development of different types of autoignition kernels: More autoignition kernels evolve with higher hydrogen content showing the promoting effect of equivalence ratio on local ignition events. Autoignition kernels develop downstream a certain distance from the injector, indicating the influence of ignition delay on kernel development. The development of autoignition kernels is linked to the shear layer development derived from global experimental conditions.

Vehicle response-based track geometry assessment using multi-body simulation

ABSTRACTThe assessment of the geometry of railway tracks is an indispensable requirement for safe rail traffic. Defects which represent a risk for the safety of the train have to be identified and the necessary measures taken. According to current standards, amplitude thresholds are applied to the track geometry parameters measured by recording cars. This geometry-based assessment has proved its value but suffers from the low correlation between the geometry parameters and the vehicle reactions. Experience shows that some defects leading to critical vehicle reactions are underestimated by this approach. The use of vehicle responses in the track geometry assessment process allows identifying critical defects and improving the maintenance operations. This work presents a vehicle response-based assessment method using multi-body simulation. The choice of the relevant operation conditions and the estimation of the simulation uncertainty are outlined. The defects are identified from exceedances of track geometry and vehicle response parameters. They are then classified using clustering methods and the correlation with vehicle response is analysed. The use of vehicle responses allows the detection of critical defects which are not identified from geometry parameters.

Numerical Approach for the Implementation of the Interaction of Pyrolysis Gases and Combustion Products in an Aluminium-Melting Furnace

Aluminium is a key material in modern society and serves the needs because of the unique properties of the metal and its alloys. Scientific evidence and rational economic theories have repeatedly demonstrated that recycling is the most critical and efficient pathway to sustainable human development. Aluminium products like Used Beverage Cans or Containers (UBCs) has been alloyed with other elements to fulfil consumer requirements and contain organic material due to paint and lacquer coatings on the body. The melting and pre-treatment of scrap has an emphasized role in the recycling chain of contaminated aluminium products. The relationship between the amount of contamination, pre-treatment and melting procedure and dross formation attains crucial attention in order to enhance the energy efficiency in existing furnaces. Therefore, understanding the melting and pre-treatment processes includes statistical surveys and systemic modelling. In the present work, numerical simulations were carried out using the commercial software FLUENT for generating a helpful tool in evaluating operational conditions. The main perspective is to analyze the relevant operational conditions inside an aluminium-melting furnace employing oxygen-fuel burner, which is capable to run in the flameless combustion mode. To cope with the challenge of simulating flameless combustion (highly diluted chemical conversion) proved detailed chemistry mechanisms are involved. Further crucial aspect is to evaluate additional in house written codes for the evaporation and gas release due to contaminated input material. Within the scope of the project P5 of the AMAP (Advanced Metals And Processes) research cluster in Aachen a virtual remelting furnace is set up as a CFD (Computational Fluid Dynamics) simulation for evaluating the terms of combustion, pyrolysis/ thermolysis, interaction of combustion products and pyrolysis gases and other crucial phenomena.

Optimization of ESC Performance for Co-Electrolysis Operation

Production of synthetic hydrocarbon fuels from co-electrolysis of steam/CO2 mixtures using renewable energy has been already presented as a promising solution to diminish problems from energy and environmental point of view. The possibility to recycle CO2 into chemicals and value-added fuels helps to reduce the accumulation of atmospheric CO2 and realize the carbon neutral cycling of fuels. The solid oxide cells have great potential within this field and can been used for converting of steam/CO2 mixtures to the syngas for following Fischer-Tropsch conversion by excessive electricity at high temperatures above 750°C. It presents an opportunity for recycling of CO2 into a useful liquid fuel. While the co-electrolysis is more complicated than steam electrolysis, the electrochemical performance electrolyte supported cell with G3 electrodes were investigated over a wide range of operating conditions (SOEC as well as SOFC), varying the ratio of H2O/H2 and CO2/CO, the operating temperature (750–850°C) and current. Comparable activity for operation in the SOEC and SOFC modes was observed and electrodes exhibited similar polarization losses during operation in steam electrolysis and steam/CO2 co-electrolysis. During electrolysis and co-electrolysis operation anomalous increase of polarization resistance during first 50 h on both sides has been observed. The raise of polarization resistance was reversible and diminished after switching to SOFC operation mode. Operating temperature variation during co-electrolysis helped to get insight into relationship between observed performance and electrodes microstructure. Additional experiments and electrochemical testing combined with detailed microstructural analysis have been carried out to better understand the observed phenomena. Obtained performance for single cell has been reproduced also on stack level. To improve electrochemical performance the additional modification of both electrodes, especially of their microstructure, is done. Durability of solid oxide electrolyte supported electrolysis cells (standard G3 and modified) tested at different current densities (from -300 mA/cm2 up to -500 mA/cm2) for high temperature steam or steam/CO2 electrolysis is investigated under stack relevant operating conditions (up to 5,000 h) and showed power degradation rate of ca. 1%/1,000 h for steam electrolysis. The changes in polarization resistance of single cells under different operating conditions as well as during durability tests are performed and discussed on basis of analysis of impedance spectra. Microstructure observations at the interfaces in both electrodes were carried out after long-term tests to understand the reasons for degradation. The cell with optimized fuel and air electrodes was successfully tested for ~2400 hours at 803°C under co-electrolysis conditions (H2/CO2/H2O/CO mixture as fuel, j = -400 mA/cm2). The calculated linear power degradation rate over all durability test (~2400 h) is about 0.4%/1,000 h. Further development of ESC for co-electrolysis and its verification in stack is topic of ongoing activities. Fig. 1 Power density vs. time for long-term test with modified G3 cell based on 165µm 10Sc1CeSZ electrolyte at 803°C in air : (H2/CO2/H2O/CO) mixture (j = - 400 mA/cm2). As reference point the power density in SOFC mode (air : H2/H2O) mixture (j = 300 mA/cm2) is also represented. Figure 1

Lean VOC-Air Mixtures Catalytic Treatment: Cost-Benefit Analysis of Competing Technologies

Various processing routes are available for the treatment of lean VOC-air mixtures, and a cost-benefit analysis is the tool we propose to identify the most suitable technology. Two systems have been compared in this paper, namely a “traditional” plant, with a catalytic fixed-bed reactor with a heat exchanger for heat recovery purposes, and a “non-traditional” plant, with a catalytic reverse-flow reactor, where regenerative heat recovery may be achieved thanks to the periodical reversal of the flow direction. To be useful for decisions-making, the cost-benefit analysis must be coupled to the reliability, or availability, analysis of the plant. Integrated Dynamic Decision Analysis is used for this purpose as it allows obtaining the full set of possible sequences of events that could result in plant unavailability, and, for each of them, the probability of occurrence is calculated. Benefits are thus expressed in terms of out-of-services times, that have to be minimized, while the costs are expressed in terms of extra-cost for maintenance activities and recovery actions. These variable costs must be considered together with the capital (fixed) cost required for building the plant. Results evidenced the pros and cons of the two plants. The “traditional” plant ensures a higher continuity of services, but also higher operational costs. The reverse-flow reactor-based plant exhibits lower operational costs, but a higher number of protection levels are needed to obtain a similar level of out-of-service. The quantification of risks and benefits allows the stakeholders to deal with a complete picture of the behavior of the plants, fostering a more effective decision-making process. With reference to the case under study and the relevant operational conditions, the regenerative system was demonstrated to be more suitable to treat lean mixtures: in terms of time losses following potential failures the two technologies are comparable (Fixed bed plant: 0.35 h/year and Reverse flow plant: 0.56 h/year), while in terms of operational costs, despite its higher complexity, the regenerative system shows lower costs (1200 €/year).

Design, Manufacture, and Test of an 80 kA-Class Nb3Sn Cable-In-Conduit Conductor With Rectangular Geometry and Distributed Pressure Relief Channels

Within the frame of the R&D activities carried out in Europe for the toroidal field coils of the nuclear fusion device DEMO, a fundamental milestone was considered to be the demonstration of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn cable-in-conduit conductors (CICC) performance in the demanding range of interest for DEMO. Among the different technological solutions envisaged, the present paper deals with a wind & react CICC solution, with rectangular geometry, thick steel jacket, and distributed pressure relief channel, designed to operate at 82 kA in a magnetic field of 13 T and with a current sharing temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cs</sub> > 6.5 ,K. The main manufacturing steps of the prototype conductor are described in the present paper, carried out within industrial environment, partly using the facilities and procedures available for the manufacture of ITER conductors. A sample was designed for the EDIPO facility at the Swiss Plasma Center, Switzerland, in the configuration usually adopted for the test of ITER poloidal field conductors, where the two straight conductor legs are part of the same cable length, with a continuous transition through a bottom hairpin-type joint, thus avoiding any resistive connection. The conductor has been characterized in terms of dc performance at relevant operating conditions and the absence of any performance degradation with electro-magnetic load cycles has been verified, thus, qualifying the proposed technological solution. AC losses and thermo-hydraulic tests have also been carried out, providing relevant information for further coil design.

Compact silicon-based optrode with integrated laser diode chips, SU-8 waveguides and platinum electrodes for optogenetic applications

We report on a compact optrode, i.e. a MEMS-based, invasive, bidirectional neural interface allowing to control neural activity using light while neural signals are recorded nearby. The optrode consists of a silicon (Si) base carrying two pairs of bare laser diodes (LDs) emitting at 650 nm and of two 8 mm-long, 250 µm-wide and down to 50 µm-thick shanks extending from the base. Each LD is efficiently coupled to one of four 15 or 20 µm-wide and 13 µm-high SU-8 waveguides (WGs) running in pairs along the shanks. In addition, each shank comprises four 20 µm-diameter platinum electrodes for neural recording near the WG end facets. After encapsulation of the LDs with a Si cover chip blocking stray light and protecting the LDs from the harsh environment to which the probe is destined, the compact base measures only 4 × 4 × 0.43 mm3. The time averaged radiant emittance at the WG end facet is 96.9 mW mm−2 for an LD current of 35 mA at a duty cycle of 5%. The absolute electrode impedance at 1 kHz is 1.54 ± 0.06 MΩ. Using infrared thermography, the temperature increase of the probe during LD operation was determined to be about 1 K under neuroscientifically relevant operating conditions.

Mechanical testing of the IFMIF HFTM-DC prototype during operation in the HELOKA-LP helium loop

The so called High Flux Test Module (HFTM) represents the component of IFMIF (International Fusion Irradiation Facility) in which material specimens are being placed that accumulate high neutron induced damage rates (≥20dpa/fpy). Damage rates of this magnitude are limited to a volume of ∼500cm3 (attenuation in beam direction) behind a beam footprint of 20×5cm2, so the high flux region of the module is contained in a flat faced, cuboid volume of 5.6cm depth. Efforts for a high spatial utilisation and the demand for a high neutron transmission lead to a thin-walled container design. As an efficient, space-saving method to cool the container and the material specimens, an array of mini-channels (1mm gaps) through which low pressure (0.3MPa) helium gas is flowing is established. Installed closely to the target and due to space constraints by other irradiation modules, the HFTM is implemented as a slender and tall construction with features that are challenging for pressure equipment. Experimental studies on a 1:1 prototype of the HFTM-DC (double compartment) have been made in the Helium Loop Karlsruhe – Low Pressure (HELOKA-LP) during 2015. The experiments also included intensive testing to demonstrate the mechanical reliability of the HFTM under IFMIF relevant operation conditions. Therefore, the module was instrumented with numerous sensors which measure displacement, deformation and mechanical strain. The reactions on temperature and pressure loads were studied. In this paper the experimental results will be presented and compared to the numerical (FEM) simulation studies.

Multiscale Computational Fluid Dynamics: Methodology and Application to PECVD of Thin Film Solar Cells

This work focuses on the development of a multiscale computational fluid dynamics (CFD) simulation framework with application to plasma-enhanced chemical vapor deposition of thin film solar cells. A macroscopic, CFD model is proposed which is capable of accurately reproducing plasma chemistry and transport phenomena within a 2D axisymmetric reactor geometry. Additionally, the complex interactions that take place on the surface of a-Si:H thin films are coupled with the CFD simulation using a novel kinetic Monte Carlo scheme which describes the thin film growth, leading to a multiscale CFD model. Due to the significant computational challenges imposed by this multiscale CFD model, a parallel computation strategy is presented which allows for reduced processing time via the discretization of both the gas-phase mesh and microscopic thin film growth processes. Finally, the multiscale CFD model has been applied to the PECVD process at industrially relevant operating conditions revealing non-uniformities greater than 20% in the growth rate of amorphous silicon films across the radius of the wafer.

Materials for Proton Exchange Membrane water electrolyzer bipolar plates

Titanium based BiPolar Plates (BPPs) are commonly used in Proton Exchange Membrane Water Electrolyzers (PEMWEs) today as they can withstand the harsh operating conditions experienced inside an operating PEM water electrolyzer. In particular, the high anode potential and acidic nature of the PEM is crucial for BPP performance. In this work we expand the investigation of non-coated materials at relevant operating conditions to include molybdenum, 254 SMO, tungsten, AISI 316L, AISI 304L, Inconel 625, niobium and tantalum, in addition to Titanium gr. 2. Pre-designed potentiostatic and potentiodynamic tests at potentials up to 2.0 VSHE were performed in addition to Interfacial Contact Resistance (ICR) and weight loss measurements. Scanning Electron Microscopy (SEM) imaging was conducted to observe morphology changes during the electrochemical tests. Titanium, tantalum and niobium experienced little or no weight change during potentiostatic polarization, while for AISI 304L, AISI 316L and tungsten the measured weight loss was much lower than the weight loss calculated from currents produced. When the potentiostatic test was prolonged for titanium, the ICR was found to increase with time. Auger Electron Spectroscopy measurements confirmed that the increase in ICR for titanium, tantalum and niobium is related to an increased thickness of surface oxides.

Numerical modelling and simulation of hydrogen production via four different chemical reforming processes: Process performance and energy requirements

AbstractMethane reforming operated in fluidized bed reactors is modelled and simulated for four different chemical processes: Steam Methane Reforming (SMR) process and the both non‐commercially available Sorption‐Enhanced Steam Methane Reforming (SE‐SMR) process and Chemical Looping Reforming process for non‐autothermal (naCLR) as well as autothermal (aCLR) operation. These processes are operated at relevant operating conditions. The results from the reforming simulations are used as input in a Pressure Swing Adsorption model, where the hydrogen is further purified to about 99.99 % and delivered at 2500 kPa (25 bar) of pressure and 25 °C. The energy consumption for hydrogen production on a mole basis is calculated for each chemical process with and without heat recuperation, with heat recuperation referring in this context to the utilization of the thermal energy available from the cooling of certain fluid streams to power other parts of the process.

SFCOMPO 2.0 – A relational database of spent fuel isotopic measurements, reactor operational histories, and design data

SFCOMPO-2.0 is a database of experimental isotopic concentrations measured in destructive radiochemical analysis of spent nuclear fuel (SNF) samples. The database includes corresponding design description of the fuel rods and assemblies, relevant operating conditions and characteristics of the host reactors necessary for modelling and simulation. Aimed at establishing a thorough, reliable, and publicly available resource for code and data validation of safety-related applications, SFCOMPO-2.0 is developed and maintained by the OECD Nuclear Energy Agency (NEA). The SFCOMPO-2.0 database is a Java application which is downloadable from the NEA website.

Thermal-hydraulic analysis of the coil test facility for CFETR.

BackgroundPerformance test of the China Fusion Engineering Test Reactor (CFETR) central solenoid (CS) and toroidal field (TF) insert coils is of great importance to evaluate the CFETR magnet performance in relevant operation conditions. The superconducting magnet of the coil test facility for CFETR is being designed with the aim of providing a background magnetic field to test the CFETR CS insert and TF insert coils.ResultsThe superconducting magnet consists of the inner module with Nb3Sn coil and the outer module with NbTi coil. The superconducting magnet is designed to have a maximum magnetic field of 12.59 T and a stored energy of 436.6 MJ. An active quench protection circuit and the positive temperature coefficient dump resistor were adopted to transfer the stored magnetic energy.ConclusionsThe temperature margin behavior of the test facility for CFETR satisfies the design criteria. The quench analysis of the test facility shows that the cable temperature and the helium pressure inside the jacket are within the design criteria.

Macroscopic spray characteristics of next-generation bio-derived diesel fuels in comparison to mineral diesel

In this paper, the macroscopic spray characteristics of four next-generation biofuels, namely, hydrotreated vegetable oil (HVO), Palm oil methyl ester (PME), Soybean oil methyl ester (SME) and used cooking oil methyl ester (UCOME) were investigated in detail using a constant volume spray vessel, and benchmarked against reference mineral diesel (B0). During experiments, fuels were heated to 80°C to achieve an engine-like environment before being injected at various compression ignition engine relevant operating conditions. The fuel spray tip penetration, spray cone angle and spray area were investigated analysing images obtained using a direct photography technique. Furthermore, a modified spray model was proposed to extend its scope to include alternative fuels by considering fuel density as part of the spray model. The results show that HVO with the lowest density of all fuels achieves the shortest penetration distance and the highest cone angle, resulting in a more distributed fuel-air mixture. All fuels have very similar spray areas for the same injection conditions, but the specific spray area per injected mass is highest for HVO followed by the three methyl esters. It was concluded that the fuel liquid viscosity was a significant factor on the observed air-fuel mixing process. The spray characteristics were compared with our engine test results and can be used to explain observed engine behaviour when fuelled with biofuels.

Estimation of bubble size distributions and shapes in two-phase bubble column using image analysis and optical probes

A precise estimation of bubble size distributions and shapes is required to characterize the bubble column fluid dynamics at the “bubble-scale”, and to evaluate the heat and mass transfer rate in bubble column reactors. Image analysis methods can be used to measure the bubble size distributions and shapes; unfortunately, these experimental techniques are limited to resolve bubble clusters and large void fractions, and can not be applied under relevant operating conditions (e.g., high temperature and pressure). On the other hand, needle probes (i.e, optical and conductive probes) can be used to measure bubble sizes in dense bubbly flows and under relevant operating conditions; however, needle probes measure chord length distributions, which should be converted into bubble size distributions by using statistical algorithms. These algorithms rely on correlations—generally obtained for single droplets/bubbles—that predicts the bubble shapes, by relating the bubble equivalent diameter to the bubble aspect ratio. In this paper, we contribute to the existing discussion through an experimental study regarding the bubble sizes and aspect ratio in a large air-water bubble column. The experimental investigation has consisted in gas holdup, image analysis and optical probe measurements. First, the gas holdup measurements have been used to identify the flow regime transition between the homogeneous flow regime and the transition flow regime. Secondly, the homogeneous flow regime has been described at the “bubble-scale”: chord length distributions and bubble size distributions have been obtained by using an optical probe and image analysis, respectively. Based on the experimental data from the image analysis, a correlation between the bubble equivalent diameter and the bubble aspect ratio has been proposed and has been compared with existing correlations. Finally, the chord length distributions have been converted into bubble size distributions using a statistical method, supported by the aspect ratio obtained through image analysis. The proposed approach has been able to estimate correctly the bubble size distributions at the center of the column then near the wall. We have also demonstrated that the correlations used to predicts the bubble shapes are the main point of improvement in the method.

Phase Analysis of Scale Deposition in Boiler Tubes Utilizing Steam-Assisted Gravity Drainage Produced Water

Scale buildup on water-side heat transfer surfaces poses a potential operating challenge for steam-assisted gravity drainage (SAGD) boilers used in the production of bitumen since produced water, which has a high dissolved solid content, is recycled. Scale from deposition of dissolved solids on boiler tubes acts as a thermal insulating layer, decreasing heat transfer and lowering boiler efficiency. Understanding scale deposit composition on heat transfer surfaces is beneficial in the determination of adequate boiler maintenance practices and operating parameters. This research determined the effect of feedwater pH (7.5, 9.0, and 10.0) on scale composition resulting from deposition of dissolved solids under commercially relevant boiler operating conditions at 8.96 MPa (1300 psig) and 37.86 kW/m2 (12,000 Btu/h ft2). Scale deposits were analytically investigated using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDS), powder X-ray diffraction (XRD), and Raman spectroscopy. At feedwater pH values of 7.5 and 9.0, anhydrite (CaSO4), xonotlite (Ca6Si6O17(OH)2), and pectolite (NaCa2Si3O8(OH)) were detected. At the pH of 10.0, xonotlite and pectolite were identified in the absence of anhydrite. Furthermore, the magnesium silicate phase, serpentine (Mg3Si2O5(OH)4), was also postulated to be present.

Heat Flow and Solidification Modeling of Industrial Scale, Ingot Casting Operation

A model, based on the concept of effective thermal conductivity, was developed to study thermal fields and the resultant solidification behavior of large, round, industrial size ingots. In this, flow and turbulence phenomena during mold filling as well as subsequent solidification were not modeled explicitly but their influence was accounted for by artificially raising the thermal conductivity of solidifying steel. Thus, a conduction like equation embodying a conjugate approach was applied to simultaneously predict the evolution of temperature fields in the mold as well as in the solidifying ingot following teeming. Prior to comparing model predictions against industrial scale measurements, sensitivity of calculations to grid size, time step height, convergence criterion etc. were rigorously assessed. Similarly, modeling of interfacial resistance, chemical reactions and heat effects in the hot top as well as their influence on predicted results were evaluated computationally. Embodying mixed thermal boundary conditions (free convection + radiation) at the mold wall, temperature fields during solidification of two different industrial large ingots were predicted numerically. Parallely, mold wall temperature was monitored as a function of time and surface temperature of ingot was measured at the instant of mold stripping using hand held, radiation pyrometers. Incorporating relevant operating conditions (viz., mold dimensions and size, ingot and hot top dimensions and material, initial mold and liquid temperature etc.) into the calculation scheme, predictions were made via a computational procedure developed in-house and results thus obtained were compared against equivalent industrial scale measurements. Very reasonable agreement between the two was demonstrated.