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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Heat transfer enhancement due to cold cap motion from bubbling in a waste glass melter

In this study, a computational fluid dynamics (CFD) model was developed to model the motion of a solid cold cap in a waste glass melter. Forced convection bubblers at the base of the melter release air into the molten glass, which forms large bubbles that travel upwards to the cold cap and augment heat transfer from the glass to the cold cap. The CFD model employs the Navier- Stokes equations to solve for the fluctuating flowfield using a rigid body motion dynamic fluid body interaction module. This allows for movement of the floating body in response to the bubbling forces calculated at each time step. Further, the heat flux delivered to the cold cap by the convective bubbling is studied as a function of the bubbling rate. Results for the moving cold cap are compared with the computed heat flux trends for a stationary cold cap. The heat flux delivered to the cold cap from the glass is 25% higher for the case with the moving cold cap. The heat flux was found to be proportional to v0.6 as opposed to v0.9 (where v is the normalized bubbling rate) for the stationary cold cap.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

FY2014 LX-21 Blasting Cap Testing

For a new material to qualify as an Extremely Insensitive Substance (EIS), the material must pass the UN Test 7, EIS Cap Test. This test attempts to measure the shock sensitivity of the material to a standard detonator at its nominal shipping density. The standard detonator specified for this test is based upon the historical number eight, #8, blasting cap. The standard detonator must contain a base charge (output charge) greater than or equal to 450mg and have a detonation velocity of at least 7.0 km/s. The Du Pont E-1A blasting cap, which is no longer made by Du Pont, was originally used to qualify TATB-based insensitive materials in the DOE. This detonator met the requirements of the EIS Cap Test. Several other commercial vendors currently sell products that are listed as equivalent to a number eight blasting cap, but have, in several cases, exceeded the original output energy of the historical number eight. By the loose specification that the number eight contain at least 450mg of output explosive, any product containing at least this quantity can be labeled as a number eight. Indeed, for most applications, higher output energy merely means a better, more reliable product. For standards testing, variation the output energy greatly affects the test results. Pantex has maintained a quantity of the original, number eight blasting caps the DOE used to qualify TATB materials (The DOE uses an IHE qualification, which is similar to the HD 1.6 classification, and requires a similar EIS Cap Test.) In FY-13, we acquired blasting caps from the original Pantex supply and from two commercial vendors for characterization and comparison. Our goals were to first characterize each of the three standard detonators with the intention of using a detonator that was as equivalent to the Du Pont number eight blasting cap as possible. Second, to work with a commercial vendor to produce a number eight equivalent that would either be based on a safer initiation technology such as an exploding bridge wire (EBW) or exploding foil initiator (EFI) – most commercial units hot-wire based, which present considerable safety concerns.

42 ENGINEERING↗
DOE OSTI2015

Cold-Cap Temperature Profile Comparison between the Laboratory and Mathematical Model

The rate of waste vitrification in an electric melter is connected to the feed-to-glass conversion process, which occurs in the cold cap, a layer of reacting feed on top of molten glass. The cold cap consists of two layers: a low temperature (~100°C – ~800°C) region of unconnected feed and a high temperature (~800°C – ~1100°C) region of foam with gas bubbles and cavities mixed in the connected glass melt. A recently developed mathematical model describes the effect of the cold cap on glass production. For verification of the mathematical model, a laboratory-scale melter was used to produce a cold cap that could be cross-sectioned and polished in order to determine the temperature profile related to position in the cold cap. The cold cap from the laboratory-scale melter exhibited an accumulation of feed ~400°C due to radiant heat from the molten glass creating dry feed conditions in the melter, which was not the case in the mathematical model where wet feed conditions were calculated. Through the temperature range from ~500°C – ~1100°C, there was good agreement between the model and the laboratory cold cap. Differences were observed between the two temperature profiles due to the temperature of the glass melts and the lack of secondary foam, large cavities, and shrinkage of the primary foam bubbles upon the cooling of the laboratory-scale cold cap.

Cold Cap↗
DOE OSTI2026

Pull Force Evaluation of CCS Insulated End Caps

Insulated end caps installed on DC pins of Combined Charging System (CCS) inlets have been identified as potential debris sources within electric vehicle supply equipment (EVSE) connectors, increasing the risk of electric shock and fire hazards. Although standards such as IEC 62196-1:2022 specify mechanical pull-force requirements for these end caps, it remains unclear whether these requirements provide adequate robustness under real-world conditions. To address this concern, the National Charging Experience (ChargeX) Consortium's Hardware Task Force conducted evaluations of insulated end caps used in OEM CCS inlets. This study assesses the performance of insulated end caps used in OEM CCS inlets, specifically those installed on DC pins, using the procedures defined in IEC 62196-1:2022 (Section Sign) 26.7 and SAE J3400, supplemented by additional experimental conditioning. To ensure relevance to real-world conditions, NLR collaborated with charging network operators (CNOs) to guide the selection of charging inlet samples. Material analyses of the insulated end cap samples were conducted to confirm that the tested materials reflected the types and properties commonly observed in the field. The selected samples underwent temperature and humidity conditioning followed by pull-force testing to evaluate the end-cap integrity. Although SAE J3400 inlets were not directly tested due to limited diversity in available field data, the underlying end-cap principles between CCS and SAE J3400 are comparable, allowing the study's insights to be relevant to both technologies. Overall, this study provides a structured evaluation framework to inform potential refinements to mechanical pull-force requirements in charging standards.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2013

In-situ subaqueous capping of mercury-contaminated sediments in a fresh-water aquatic system, Part II-evaluation of sorption materials

The function and longevity of traditional, passive, isolation caps can be augmented through the use of more chemically active capping materials which have higher sorptive capacities, ideally rendering metals non-bioavailable. In the case of Hg, active caps also mitigate the rate and extent of methylation. This research examined low cost, readily available, capping materials for their ability to sequester Hg and MeHg. Furthermore, selected capping materials were evaluated to inhibit the methylation of Hg in an incubation study as well as the capacity of a selected capping material to inhibit translocation of Hg and MeHg with respect to ebullition-facilitated contaminant transport in a column study. Results indicated that bauxite had a better capacity for mercury sorption than the other test materials. However, bauxite as well as soil capping materials did not decrease methylation to a significant extent. Materials with larger surface areas, higher organic matter and acid volatile sulfide (AVS) content displayed a larger partitioning coefficient. In the incubation experiments, the presence of a carbon source (lactate), electron acceptor (sulfate) and the appropriate strains of SRB provided the necessary conditions for Hg methylation to occur. The column study showed effectiveness in sequestering Hg and MeHg and retarding transport to the overlying water column; however, disturbances to the soil capping material resulting from gas ebullition negated its effectiveness.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Temperature Distribution within a Cold Cap during Nuclear Waste Vitrification

The kinetics of the feed-to-glass conversion affects the waste vitrification rate in an electric melter. In this study, the primary area of interest in this conversion process is the cold cap, a layer of reacting feed on top of molten glass. Knowing the temperature profile within a cold cap will help determine its characteristics and relate them to the rate of glass production. The work presented here provides an experimental determination of the temperature distribution within the cold cap. Since a direct measurement of the temperature field within the cold cap is impracticable, an indirect method was developed where the textural features in a laboratory-made cold cap with a high-level waste feed were mapped as a function of position using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. To correlate the temperature distribution to microstructures within the cold cap, microstructures were identified of individual feed samples that were heat treated to set temperatures between 400°C and 1200°C and quenched. The temperature distribution within the cold cap was then established by correlating cold-cap regions with the feed samples of nearly identical structures and was compared with the temperature profile from a mathematical model.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Projector-Free Capped-Fragment Scheme within Density Functional Embedding Theory for Covalent and Ionic Compounds

Quantum-mechanics-(QM)-based simulations now routinely aid in understanding and even discovering new chemistries involving molecules and materials exhibiting desired functionalities. Ab initio correlated wavefunction (CW) theories systematically improve QM methods, with many exhibiting high accuracy. However, execution of CW methods requires expensive computations that typically scale poorly with system size. Divide-and-conquer approaches partition large systems into smaller fragments; a lower level of theory treats fragment interactions while a preferred higher level of theory describes the important fragment. These methods offer ways to incorporate CWs into chemical simulations of large systems, e.g., biomolecules, surfaces, large inorganic clusters, bulk crystals, etc. Here we propose a partitioning protocol that utilizes capping atoms to saturate severed covalent bonds at fragment interfaces and density functional embedding theory (DFET) to describe fragment interactions. The capping groups in each fragment provide an ad-hoc potential that approximates the effects of the environment. An embedding potential optimized via DFET then serves as an augmentation of the capping group to simulate the effects of the environment. We concurrently use an auxiliary fragment (a separate system comprised of only the combined capping groups) to account for, and thereby correct, the electron density contributions of all the capping groups added to all of the fragments. This method depends only on the capped-subsystem and auxiliary-fragment electron densities, forgoing, as with the original DFET developed for metallic systems, orbital-based projector approaches that determine a nonlocal action of the embedding potential onto the fragment electrons. By using an auxiliary fragment, the method maintains a purely electron-density-dependent embedding potential, substantially lessening the cost and leading to simpler implementation. In this work, we demonstrate the utility of our capped-DFET and ensuing capped embedded CW method in two contrasting systems, namely, an organic molecule and an ionic metal oxide cluster.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

L-serine capped ZnS:Mn nanocrystals for plant cell biological studies and as a growth enhancing agent for micropropagation of Bacopa monnieri Linn. (Brahmi:Scrophulariaceae)

In the present work, the prospects of ZnS:Mn nanocrystals capped with L- serine, a bio-compatible amino acid, synthesized by wet chemical route, as efficient fluorescent probes for plant cell biological studies have been investigated. The present synthesis route using bio-compatible material is a low cost and easy to control method. The colloidal stability of the capped nano crystals is very good as they remain stable without settling down for long time. It is observed that L- serine significantly modifies the structural and optical characteristics of the ZnS:Mn nanocrystals and hence is suitable as a bio-compatible capping agent. The structural properties of L- serine capped nanocrystals were investigated by XRD technique. The size of the L- serine capped ZnS:Mn nanocrystals is found to be around 2 nm . The optical characterization of the nanocrystals was carried out on the basis of photoluminescence (PL) spectroscopic studies. The intense photoluminescence emission observed around 597nm for L-serine capped ZnS:Mn offers high prospects of applications in bio-imaging fields. The unique optical properties of nanoparticles make them appealing as in vivo and in vitro fluorophores in a variety of biological investigations. In the present study, L-serine capped ZnS:Mn nanocrystals were used as a staining dye in fluorescent microscope for observing cell division, cell structure etc. These nanocrystals were also incorporated into the culture media along with the normal auxin- cytokinin hormone combinations in Murashige and Skoog (MS) medium for micropropagation of Bacopa monnieri Linn. (Brahmi:Scrophulariaceae), an Ayurvedic medicine. The results suggest that L-serine capped ZnS:Mn nanocrystals can act as efficient enhancers towards quick callusing and shoot proliferation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Effect of cold cap coverage and emissivity on the plenum temperature in a pilot-scale waste vitrification melter

Integrated computational fluid dynamics (CFD) models are being developed to model the complex physics occurring within the high-level waste melter for vitrification of legacy tank waste at the Hanford site. Here, we present a validation of the integrated CFD model by using data from two experimental runs in a pilot-scale melter. While the model uses several simplifying assumptions (such as constant heat sinks from a cooling jacket and inleakage of ambient air, steady state feed-to-batch conversion heat, and a cold cap model with a simplified shape), it closely predicts the molten glass (1150°C and 1175°C) and plenum temperatures (550°C) obtained from thermocouples during two pilot-scale tests, with an average cold cap coverage of 80%. Additional simulations were performed to explore the sensitivity of the predicted plenum temperatures to variations in cold cap coverage (fraction of melt surface covered by the glass batch) and batch emissivity. The plenum temperature was found to be in the range of 606°C when cold cap coverage decreased from 95% to 70%. Cold cap emissivity had a smaller effect, increasing the plenum temperature by as much as 179°C when cold cap emissivity increased from 0.2 to 0.8. Maintaining a high cold cap coverage without overfeeding is important for a sustained melter operation with high glass throughput. This work provides a tool for achieving that goal in terms of correlating the plenum temperature with the cold cap coverage.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Shape dependence of laser–particle interaction-induced damage on the protective capping layer of 1 ω high reflector mirror coatings

The response of a potential candidate protective capping layer (SiO 2 or Al 2 O 3 ) to laser exposure of 1 ω (1053 nm) to high-reflector silica-hafnia multilayer coatings in the presence of variously shaped Ti particles is investigated by combining laser damage testing and numerical modeling. Each sample is exposed to a single oblique angle (45°) laser shot (p-polarization, ~10 J/cm 2 , 14 ns) in the presence of spherically or irregularly shaped Ti particles on the surface. The two capping layers show markedly different responses. For the spherical particles, the Al 2 O 3 cap layer exhibits severe damage, with the capping layer becoming completely delaminated at the particle locations. The SiO 2 capping layer is only mildly modified by a shallow depression, likely due to plasma erosion. The different response of the capping layer is attributed to the large difference in the thermal expansion coefficient of the materials, with that of the Al 2 O 3 about 15 times greater than that of the SiO 2 layer. For the irregular particles, the Al 2 O 3 capping layer displays minimal to no damage while the SiO 2 capping layer is significantly damaged. In conclusion, the difference is due to the disparity in mechanical strength with Al 2 O 3 possessing approximately 10 times higher fracture toughness.

1053 nm↗
DOE OSTI2013

Effect of Feeding Rate on the Cold Cap Configuration in a Laboratory-Scale Melter - 13362

High-level-waste melter feed is converted into glass in a joule-heated melter, where it forms a floating layer of reacting feed, called the cold cap. After the glass-forming phase becomes connected, evolving gases produce bubbles that form a foam layer under the feed. The bubbles coalesce into cavities, from which most of the gases are released around the edges of the cold cap while gases also escape through small shafts in the reacting feed. The foam layer insulates the cold cap from the heat transferred from the molten glass below. The cold cap behavior was investigated in a laboratory-scale assembly with a fused silica crucible. A high-alumina waste simulant was fed into the crucible and the feed charging rate was varied from 3 to 7 mL min{sup -1}. After a fixed amount of time (35 min), feed charging was stopped and the crucible was removed from the furnace and quenched on a copper block to preserve the structure of the cold cap during cooling. During the rapid quenching, thermal cracking of the glass and cold cap allowed it to be broken up into sections for analysis. The effect of the charging rate on the height, area and volume of the cold cap was determined. The size of the bubbles collected in the foam layer under the feed increased as the cold cap expanded and the relationship between these bubbles and temperature will be determined for input into a mathematical model. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Cold-cap temperature profile comparison between the laboratory and mathematical model - 15591

The rate of waste vitrification in an electric melter is connected to the feed-to-glass conversion process, which occurs in the cold cap, a layer of reacting feed on top of molten glass. The cold cap consists of two layers: a low-temperature (∼100 deg. C - ∼800 deg. C) region of unconnected, reacting feed and a high-temperature (∼800 deg. C - ∼1100 deg. C) region of molten glass with gas bubbles and cavities. A recently developed mathematical model describes the effect of the cold cap on glass production. For verification of the mathematical model, a cold cap produced in a laboratory-scale melter was subsequently analyzed by correlating structural features of a polished region with those obtained in heat-treated feed samples to determine the temperature profile as a function of cold-cap position. After corrections were made for the diminished volume of bubbles and collapsed cavities that occurred in the cold-cap sample during cooling, the temperature gradients were alike in the model and the laboratory cold cap through the range from ∼500 deg. C to ∼1100 deg. C. The temperature profiles were different in the upper region of the cold cap because the radiant heat from the molten glass in the laboratory-scale melter resulted in dry and hot (∼400 deg. C) surface conditions whereas the model assumed a surface covered by boiling slurry. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Bay capping via acetylene addition to polycyclic aromatic hydrocarbons: Mechanism and kinetics

The bay-capping mechanism on PAH armchair edges and the kinetics of acetylene addition to 6–6–5 and 5–6–5 bays have been explored by ab initio/RRKM-ME calculations. The bays on the edges were modeled by C 21 H 11 and C 20 H 9 radicals produced by H abstractions from 7H-benzo[c]cyclopenta[e]pyrene and dicyclopenta[cf]pyrene. The C 20 H 9 + C 2 H 2 reaction is shown to have a low entrance barrier and to rapidly form the capped product, indaceno[2,1,8,7-cdefg]pyrene, along with ethynyl substituted dicyclopenta[cf]pyrene at temperatures above 1400 K. The reactivity of C 21 H 11 is shown to be governed by the location of the unpaired electron; the π radical R1 formed by H abstraction from the CH 2 group in 7H-benzo[c]cyclopenta[e]pyrene reacts with C 2 H 2 very slowly owing to a high entrance barrier, with the bay-capping rate constant approaching 10 -16 cm 3 molecule -1 s -1 only at temperatures above 2000K. Further, this result reaffirms that the growth of π aryl radicals via acetylene addition is inefficient and reflects the generally low reactivity of such radicals where the spin density is highly delocalized over the entire polyaromatic system. Alternatively, the σ C 21 H 11 radical R2 produced by H abstraction from the five-membered ring at the bay rapidly reacts with C 2 H 2 forming the bay-capped product, with the rate constant on the order of 10 -12 cm 3 molecule -1 s -1 at T≥1500K. Rate constants for the capping reactions at the 6–6–5 and 5–6–5 bays are compared with those at the 6–0–6, 6–6–6, and 6–5–6 bays. The site-specific bay-capping rate constants have been utilized in kMC simulations of the PAH growth and the results showed measurable differences when the 6–6–5 and 5–6–5 bay-capping reactions are taken into account, including an increase of the growth rate and the formation of closed-shell PAH and a rise of the number of embedded five-membered rings accompanied with a slight decrease of their overall amount.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Structure of saguaro cactus virus 3′ translational enhancer mimics 5′ cap for eIF4E binding

The genomes of several plant viruses contain RNA structures at their 3' ends called cap-independent translation enhancers (CITEs) that bind the host protein factors such as mRNA 5' cap-binding protein eIF4E for promoting cap-independent genome translation. However, the structural basis of such 5' cap-binding protein recognition by the uncapped RNA remains largely unknown. Here, we have determined the crystal structure of a 3' CITE, panicum mosaic virus-like translation enhancer (PTE) from the saguaro cactus virus (SCV), using a Fab crystallization chaperone. The PTE RNA folds into a three-way junction architecture with a pseudoknot between the purine-rich R domain and pyrimidine-rich Y domain, which organizes the overall structure to protrude out a specific guanine nucleotide, G18, from the R domain that comprises a major interaction site for the eIF4E binding. The superimposable crystal structures of the wild-type, G18A, G18C, and G18U mutants suggest that the PTE scaffold is preorganized with the flipped-out G18 ready to dock into the eIF4E 5' cap-binding pocket. The binding studies with wheat and human eIF4Es using gel electrophoresis and isothermal titration calorimetry, and molecular docking computation for the PTE–eIF4E complex demonstrated that the PTE structure essentially mimics the mRNA 5' cap for eIF4E binding. Such 5' cap mimicry by the uncapped and structured viral RNA highlights how viruses can exploit RNA structures to mimic the host protein-binding partners and bypass the canonical mechanisms for their genome translation, providing opportunities for a better understanding of virus-host interactions and non-canonical translation mechanisms found in many pathogenic RNA viruses.

3' cap-independent translation enhancers↗
DOE OSTI2013

Kinetics of Cold-Cap Reactions for Vitrification of Nuclear Waste Glass Based on Simultaneous Differential Scanning Calorimetry - Thermogravimetry (DSC-TGA) and Evolved Gas Analysis (EGA)

For vitrifying nuclear waste glass, the feed, a mixture of waste with glass-forming and modifying additives, is charged onto the cold cap that covers 90-100% of the melt surface. The cold cap consists of a layer of reacting molten glass floating on the surface of the melt in an all-electric, continuous glass melter. As the feed moves through the cold cap, it undergoes chemical reactions and phase transitions through which it is converted to molten glass that moves from the cold cap into the melt pool. The process involves a series of reactions that generate multiple gases and subsequent mass loss and foaming significantly influence the mass and heat transfers. The rate of glass melting, which is greatly influenced by mass and heat transfers, affects the vitrification process and the efficiency of the immobilization of nuclear waste. We studied the cold-cap reactions of a representative waste glass feed using both the simultaneous differential scanning calorimetry thermogravimetry (DSC-TGA) and the thermogravimetry coupled with gas chromatography-mass spectrometer (TGA-GC-MS) as complementary tools to perform evolved gas analysis (EGA). Analyses from DSC-TGA and EGA on the cold-cap reactions provide a key element for the development of an advanced cold-cap model. It also helps to formulate melter feeds for higher production rate.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

Characterizing a High-Level Waste Cold Cap via Elemental and Structural Configuration

The process of converting high-level waste feed to an immobilized glass form takes place within a cold cap which covers a high-temperature (1150°C) glass melt in a Joule or induction heated melter. Liquid slurry feed is continuously charged through the top of a melter. Within the cold cap, many glass forming reactions occur and the glass-forming melt becomes connected. Gases trapped in the glass-forming melt arrange into bubbles which create a layer of foam below the reacting feed that collapses into cavities. This foam layer thermally insulates the reacting feed limiting heat transfer from the molten glass below, thus affecting the rate of glass formation. Information about the glass formation is desired for incorporation in a mathematical model designed to simulate the melting in a cold cap. To explore this, a set of high-level waste feed simulant samples were heat-treated at 5 K min-1 to temperatures ranging from 400°C to 1200°C for comparison with cold cap sections generated in a laboratory-scale melter. To estimate the temperature distribution in laboratory-produced cold caps, structural (bubble size and shape) and optical (color) properties of heat-treated samples and cold-cap sections were compared along with elemental maps, the shapes and sizes of the silica particles, and the connectivity of the glass matrix. These results will be used to verify the recently developed mathematical model of the cold-cap.

Cold Cap↗
DOE OSTI2012

ACTIVE CAPPING TECHNOLOGY - NEW APPROACHES FOR IN SITU REMEDIATION OF CONTAMINATED SEDIMENTS

This study evaluated pilot-scale active caps composed of apatite, organoclay, biopolymers, and sand for the remediation of metal-contaminated sediments. The active caps were constructed in Steel Creek, at the Savannah River Site near Aiken, South Carolina. Monitoring was conducted for 12 months. Effectiveness of the caps was based on an evaluation of contaminant bioavailability, resistance to erosion, and impacts on benthic organisms. Active caps lowered metal bioavailability in the sediment during the one-year test period. Biopolymers reduced sediment suspension during cap construction, increased the pool of carbon, and lowered the release of metals. This field validation showed that active caps can effectively treat contaminants by changing their speciation, and that caps can be constructed to include more than one type of amendment to achieve multiple goals.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

Nuclear waste vitrification efficiency: cold cap reactions

The cost and schedule of nuclear waste treatment and immobilization are greatly affected by the rate of glass production. Various factors influence the performance of a waste-glass melter. One of the most significant, and also one of the least understood, is the process of batch melting. Studies are being conducted to gain fundamental understanding of the batch reactions, particularly those that influence the rate of melting, and models are being developed to link batch makeup and melter operation to the melting rate. Batch melting takes place within the cold cap, i.e., a batch layer floating on the surface of molten glass. The conversion of batch to glass consists of various chemical reactions, phase transitions, and diffusion-controlled processes. These include water evaporation (slurry feed contains as high as 60% water), gas evolution, the melting of salts, the formation of borate melt, reactions of borate melt with molten salts and with amorphous oxides (Fe2O3 and Al2O3), the formation of intermediate crystalline phases, the formation of a continuous glass-forming melt, the growth and collapse of primary foam, and the dissolution of residual solids. To this list we also need to add the formation of secondary foam that originates from molten glass but accumulates on the bottom of the cold cap. This study presents relevant data obtained for a high-level-waste melter feed and introduces a one-dimensional (1D) mathematical model of the cold cap as a step toward an advanced three-dimensional (3D) version for a complete model of the waste glass melter. The 1D model describes the batch-to-glass conversion within the cold cap as it progresses in a vertical direction. With constitutive equations and key parameters based on measured data, and simplified boundary conditions on the cold-cap interfaces with the glass melt and the plenum space of the melter, the model provides sensitivity analysis of the response of the cold cap to the batch makeup and melter conditions. The model demonstrates that batch foaming has a decisive influence on the rate of melting. Understanding the dynamics of the foam layer at the bottom of the cold cap and the heat transfer through it appears crucial for a reliable prediction of the rate of melting as a function of the melter-feed makeup and melter operation parameters. Although the study is focused on a batch for waste vitrification, the authors expect that the outcome will also be relevant for commercial glass melting.

Hrma, Pavel R↗