<p>Secondary cooling during continuous casting is a delicate process because the cooling rate of water spray directly affects the slab surface and internal quality. Undercooling may lead to slab surface bulging or even breakout, whereas overcooling can cause deformation and crack of slabs due to excessive thermal residual stresses and strains. Any slab which does not meet the required quality will be downgraded or scrapped and remelted. In order to remain competitive and continuously produce high-quality and high-strength steel at the maximum production rate, the secondary cooling process must be carefully designed and controlled. Efficient and uniform heat removal without deforming or crack the slab is a significant challenge during secondary cooling. In the meantime, the on-site thermal measurement techniques are limited due to the harsh environment. In contrast, experimental measurements are only valid for the tested conditions, and the measurement process is not only labor-intensive, but the result might be inapplicable when changes in the process occur. On the other hand, the high-performance computing (HPC)-powered computational fluid dynamics (CFD) approach has become a powerful tool to gain insights into complex fluid flow and heat transfer problems. Yet, few successful numerical models for heat transfer phenomena during secondary cooling have been reported, primarily due to complex phenomena. </p> <p> </p> <p>Therefore, the current study has proposed two three-dimensional continuum numerical models and a three-step coupling procedure for the transport of mass, momentum, and energy during the secondary cooling process. The first numerical model features the simulation of water spray impingement heat and mass transfer on the surface of a moving slab considering atomization, droplet dispersion, droplet-air interaction, droplet-droplet interaction, droplet-wall impingement, the effect of vapor film, and droplet boiling. The model has been validated against five benchmark experiments in terms of droplet size prior to impingement, droplet impingement pressure, and heat transfer coefficient (HTC) on the slab surface. The validated model has been applied to a series of numerical simulations to investigate the effects of spray nozzle type, spray flow rate, standoff distance, spray direction, casting speed, nozzle-to-nozzle distance, row-to-row distance, arrangement of nozzles, roll and roll pitch, spray angle, spray water temperature, slab surface temperature, and spray cooling on the narrow face. Furthermore, the simulation results have been used to generate a mathematically simple HTC correlation, expressed as a function of nine essential operating parameters. A graphic user interface (GUI) has been developed to facilitate the application of correlations. The calculated two-dimensional HTC distribution is stored in the universal comma-separated values (csv) format, and it can be directly applied as a boundary condition to on-site off-line/on-line solidification calculation at steel mills. The proposed numerical model and the generic methodology for HTC correlations should benefit the steel industry by expediting the development process of HTC correlations, achieving real-time dynamic spray cooling control, supporting nozzle selection, troubleshooting malfunctioning nozzles, and can further improve the accuracy of the existing casting control systems.</p> <p> </p> <p>In the second numerical model, the volume-averaged Enthalpy-Porosity method has been extended to include the slurry effect at low solid fractions through a switching function. With the HTC distribution on the slab surface as the thermal boundary condition, the model has been used to investigate the fluid flow, heat transfer, and solidification inside a slab during the secondary cooling process. The model has been validated against the analytical solution for a stationary thin solidifying body and the simulation for a moving thin solidifying body. The effects of secondary dendrite arm spacing, critical solid fraction, crystal constant, switching function constant, cooling rate, rolls, nozzle-to-nozzle distance, and arrangement of nozzles have been evaluated using the validated model. In addition, <a>the solidification model has been coupled with the predictions from the HTC correlations, and the results have demonstrated the availability of the correlations other than on-site continuous casting control. </a>Moreover, the model, along with the three-step coupling procedure, has been applied to simulate the initial solidification process in continuous casting, where a sufficient cooling rate is required to maintain a proper solidification rate. Otherwise, bulging or breakout might occur. The prediction is in good agreement with the measured shell thickness, which was obtained from a breakout incident. With the help of HPC, such comprehensive simulations will continue to serve as a powerful tool for troubleshooting and optimization.</p>

<p> As space exploration continues to advance, so does the drive to inhabit celestial bodies. In<br> order to expand our civilization to the Moon or even other planets requires an enormous amount of research and development. The Resilient Extra-Terrestrial Habitat Institute is a NASA funded project that aims to develop the technology needed to establish deep-space habitats. Deep-space inhabitation poses many challenges that are not present here on earth. The Moon, for example, has temperatures that range from -233−123°C. Aside from the extreme temperatures, a variety of thermal loads will need to be handled by the Environmental Control and Life Support System (ECLSS). Aside from the research and architecture of the International Space Station’s ECLSS, very little information is known about disturbances related to the thermal management of extra- terrestrial habitats.<br> </p> <p>RETHi is developing a Cyber-Physical Testbed (CPT) that represents a one-fifth scale<br> prototype of a deep space habitat. In order to answer difficult research questions regarding ECLSS and thermal management of a deep-space habitat, a heat pump was modeled and validated with the physical part of the CPT. Once validated, the heat pump model is able to accurately predict the steady state behavior given the indoor and outdoor conditions of the testbed. When coupled with the interior environment (IE) model, it gives insight into the system’s requirements and response. Experimental testing was conducted with the heat pump in order to validate the model. After the model was validated, a series of parametric studies were conducted in order to investigate the effects of varying thermal loads and dehumidification. Since the groundwork was laid through model development and experimentation, future work consists of designing a more versatile heat pump to test a variety of disturbance scenarios. Although the heat pump model is specifically designed for the CPT, it proves to be versatile for other closed and pressurized environments such as aircraft and clean rooms according to the analysis of dehumidification and dependence on pressure. </p>

No description available.

<p>  </p> <p>Metal 3D printing is the industry standard for manufacturing experimental suppressors due to the limitations of conventional, subtractive machining methods. Long print times, difficulty sintering, and cleaning of metal 3D printed suppressor components limit the development time. Plastic printed components are able to be produced quicker, safer, and at a lower cost than their metal 3D printed counterparts. Reducing the time and cost of manufacturing will allow for an increased pace of innovations in suppressor design.</p> <p><br></p> <p>Utilizing Finite Element Analysis (FEA) in combination with Computational Fluid Dynamics (CFD) will expedite the process of designing 3D printed plastic suppressors. Solidworks FEA determined the maximum stress applied to the blast chamber of the plastic suppressor. ANSYS Fluent CFD simulations were used to qualitatively compare the sound pressure levels of an unsuppressed and suppressed 22LR pistol. Comparing the results of the CFD simulations gave insight into the effectiveness of the selected baffle structure.</p> <p><br></p> <p>A prototype 3D printed suppressor was optimized for strength according to manufacturing practices for printed plastic small arms. Testing occurred at an indoor range where peak impulse noise was measured for an unsuppressed 22LR pistol and a plastic printed suppressor. The printed suppressor reduced the small arms impulse noise from 150.5 dB(spl) to 132.4 dB(spl). Impulse noises below the pain threshold of 140 dB(spl) do not require hearing protection for operation. Utilizing FEA, CFD, and FDM prototyping methods in this work has laid the foundation for future works in the rapid prototyping and optimizations of suppressors for small arms.</p>

No description available.

No description available.

<p dir="ltr">An adaptive mesh refinement strategy for shock dominated flows encompassing multiple types of fluids and fluid features. </p>

Thesis (MScIng)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Due to economic and environmental constraints mining operations are placed under increasing pressure to effectively manage and operate tailings disposal operations. Restrictions imposed on water usage and tailings operations footprint have led to higher density and wider particle size distribution slurries conveyed to tailings areas. One means of efficiently disposing the tailings is co-disposal. In this method a concentrated fine vehicle slurry is used to convey a coarser fraction. This produces a higher density of tailings, with a number of advantages both upstream and downstream of the tailings process. Limited research has been conducted on the effect of coarse particles on the non-Newtonian rheological properties of these slurries. This lack of information complicates the design and reliable operation of these systems. This project aims at gaining a clearer understanding as to the mechanisms involved in the addition of coarse particles to a fine clay slurry vehicle; and to provide a means of estimating the measured slurry rheological properties. A number of experiments were designed to test the slurry (both Kaolin only, and Kaolin-coarse particle mixtures) rheological properties using a Couette viscometer (for the dynamic flow properties of yield stress and plastic viscosity) and a vane instrument (for the static yield stress measurements). The slurries were prepared in varying Kaolin clay solids concentrations with reverse osmosis water. Glass beads and two types of industrial sand were used as the coarse fractions. All of the coarse particles had a similar size but varied significantly in shape. Slurry pH and temperature readings were monitored throughout the tests. Tests were done initially on clay only slurries. The rheological properties of these slurries were repeatable, and no noticeable variations of properties with time were observed. The yield stress (both static and dynamic) and plastic viscosity data were well correlated with established relationships. Coarse particles were added to the clay only slurries, and then removed. The remaining clay only slurry exhibited the same rheological properties as the initial clay only slurry. The presence of coarse particles increased all the measured rheological properties (i.e. dynamic yield stress, Bingham viscosity, and static vane yield stress) in a fashion resembling the effect of adding clay to a clay only slurry. In addition, the change in measured rheological property by addition of coarse particle was independent of the clay fraction in the clay slurry. Furthermore, with both the clay only slurries and clay and coarse sand slurries, a constant linear relationship existed between the static and dynamic yield stress. Several correlations from the literature were found to provide reasonable prediction of the rheological property variations observed. These empirical and semi-empirical models however did little to explain the mechanisms involved in coarse particle addition. A new correlation has been proposed, Residual Clay Concentration, which predicts the change in rheological property based on an additional clay concentration, which in turn is a linear function of the coarse particle concentration. The accuracy of this model further strengthens the belief that the coarse particle acts in a similar fashion to a floc. By means of a case study example the importance of selecting an appropriate model for design was illustrated. The Residual Clay Concentration method provided the most conservative results. This combined with its theoretical basis strengthens the models recommendation for use in design. / AFRIKAANSE OPSOMMING: As gevolg van ekonomiese en omgewings beperkinge word mynwese nywerhede onder toenemende druk geplaas om doeltreffende afvalstroom bestuur en operasie toe te pas. Beperkinge geplaas op water gebruik en afvalstroom area-groote ly tot hoër digthede en wyer partikel-grooteverspreidings van flodders vervoer na afval areas. Een manier om van die afval doeltreffend ontslae te raak en te berg is deur medeberging. In die metode word ‘n gekonsentreerde fyn flodder gebruik as draer van ‘n growwer partikel-fraksie. Dit ly tot ‘n hoër digtheid flodder, met verskeie voordele in beide die op – en afstroom prosesse. Beperkte navorsing is gedoen op die effek van growwe partikels op die nie-Newoniese rheolgiese eienskappe van hierdie flodders. Hierdie tekort aan informasie maak die effektiewe, betroubare bedryf en operasie van die sisteme meer ingewikkeld. Hierdie projek is daarheen gemik om ‘n beter begrip te ontwikkel met betrekking tot die meganismes betrokke in die byvoeging van growwe partikels aan ‘n fyn klei-agtige flodder draer; en om ‘n manier te voorsien wat die rheologiese eienskappe kan beraam. Verskeie eksperimente was ontwerp om die flodders (beide slegs Kaolien, en Kaoliengrowwe partikel mengsels) se rheologiese eienskappe te toets deur die gebruik van ‘n Couette-viskometer. Die Couette viskometer was gebruik om die dinamiese eienskappe (van grens-spanning, en plastiese viskositet) te meet. ‘n Vaan apparaat is gebruik om die eienskap van statiese grens-spanning te meet. Die flodders was voorberei in verskeie Kaolien konsentrasies met tru-osmosis water. Glas krale en twee tipes industriële sand is gebruik as die growwe fraksies. Al die growwe partikels het soortgelyke groottes gehad, maar het grootliks verskil in vorm. Die flodder pH en temperatuur lesings is deurentyd nagegaan. Toetse was aanvanklik gedoen op die klei-alleenlike flodders. Die gemete reologiese eienskappe van die flodders was herhaalbaar, en geen opmerkbare veranderinge van die eienskappe met betrekking tot tyd is gemeet nie. Die grens-spanning (beide statiese en dinamiese) en plastiese viskositeit is goed gekorrelleer met gevestigde verhoudinge. Growwe partikels is aan die klei-alleenlike flodders bygevoeg, en daarnae verwyder. Die oorblywende klei-alleenlike flodder het dieselfde gemete rheologiese eienskappe getoon as die oorspronklike klei-allenlike flodder. Die teenwoordigheid van growwe partikels het na ‘n toename van al die gamete rheologiese eienskappe gelei wat fisies baie soortgelyk is aan die byvoeging van klei tot ‘n klei-alleenlike flodder. Verder, met beide die klei-alleenlike en klei-growwe partikel flodders het ‘n konstante liniëre funksie tussen die statiese en dinamiese grens-spannings bestaan. Verskeie verhoudings uit die literatuur het goeie korrelasie bewerkstellig met die waargenome rheologie veranderinge. Hierdie empiriese en semi-empiriese modelle doen egter min om die megansimes betrokke in die toevoeging van growwe partikels te verduidelik. ‘n Nuwe korrelasie is voorgestel, naamlik die Residu Klei Konsentrasie. Hierdie model voorspel die verandering in reologiese eienskappe gebaseer op ‘n addisionele klei konsentrasie, wat ‘n liniëre funkise is van die growwe partikel konsentrasie. Die goeie korrelasie gesien met die model versterk die idée dat die growwe partikel in ‘n soortgelyke manier as ‘n flok gedra in die teenwoordigheid van ander flokke. Deur middel van ‘n tipiese industriële voorbeeld is die belangrikheid in die keuse van die regte korrelasie geillustreer. Die Residu Klei Konsentrasie metode het die mees konservatiewe resultate gelewer. Hierdie feit gekombineerd met die model se soliede teoreitiese beginsels versterk dit as voorgestelde korrelasie vir ontwerp.

Thesis (MScEng (Process Engineering))--Stellenbosch University, 2008. / Please refer to full text to view abstract.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The reactive absorption rate of CO2 into non-aqueous solvents containing the primary amine, mono-ethanolamine (MEA) is recognised as a suitable method for measuring the effective interfacial mass transfer area of separation column internals such as random and structured packing. Currently, this method is used under conditions where the concentration of MEA in the liquid film is unaffected by the reaction and the liquid phase reaction is, therefore, assumed to obey pseudo first order kinetics with respect to CO2. Under pseudo first order conditions, the effect of surface depletion and renewal rates are not accounted for. Previous research indicated that the effective area available for mass transfer is also dependent upon the rate of surface renewal achieved within the liquid film. In order to study the effect of surface depletion and renewal rates on the effective area, a method utilising a fast reaction with appreciable depletion of the liquid phase reagent is required. The homogeneous liquid phase reaction kinetics of CO2 with MEA n-Propanol as alcoholic solvent was investigated in this study. A novel, in-situ Fourier Transform Infra-Red (FTIR) method of analysis was developed to collect real time concentration data from reaction initiation to equilibrium. The reaction was studied in a semi-batch reactor set-up at ambient conditions (T = 25°C, 30°C and 35°C, P = 1 atm (abs)). The concentration ranges investigated were [MEA]:[CO2] = 5:1 and 10:1. The concentration range investigated represents conditions of significant MEA conversion. The reaction kinetic study confirmed the findings of previous research that the reaction of CO2 with MEA is best described by the zwitterion reactive intermediate reaction mechanism. Power rate law and pseudo steady state hypothesis kinetic models (proposed in literature) were found to be insufficient at describing the reaction kinetics accurately. Two fundamentally derived rate expressions (based on the zwitterion reaction mechanism) provided a good quality model fit of the experimental data for the conditions investigated. The rate constants of the full fundamental model were independent of concentration and showed an Arrhenius temperature dependence. The shortened fundamental model rate constants showed a possible concentration dependence, which raises doubt about its applicability. The specific absorption rates (mol/m2.s) of CO2 into solutions of MEA/n-Propanol (0.2 M and 0.08 M, T = 25°C and 30°C, P = ±103 kPa) were investigated on a wetted wall experimental setup. The experimental conditions were designed for a fast reaction in the liquid film to occur with a degree of depletion of MEA in the liquid film. Both interfacial depletion and renewal of MEA may be considered to occur. The gas phase resistance to mass transfer was determined to be negligible. An increase in liquid turbulence caused an increase in the specific absorption rate of CO2 which indicated that an increase in liquid turbulence causes an increase in effective mass transfer area. Image analysis of the wetted wall gas-liquid interface confirmed the increase in wave motion on the surface with an increase in liquid turbulence. The increase in wave motion causes an increase in both interfacial and effective area. A numerical solution strategy based on a concentration diffusion equation incorporating the fundamentally derived rate expressions of this study is proposed for calculating the effective area under conditions where surface depletion and renewal rates are significant. It is recommended that the reaction kinetics of CO2 with MEA in solvents of varying liquid properties is determined and the numerical technique proposed in this study used to calculate effective area from absorption rates into these liquids. From the absorption data an effective area correlation as a function of liquid properties may be derived in future. / AFRIKAANSE OPSOMMING: Die reaktiewe absorpsie van CO2 in nie-waterige oplossings van die primêre amien, monoetanolamien (MEA) word erken as ‘n geskikte metode om die effektiewe massaoordragsarea van gepakte skeidingskolomme te bepaal. Tans word die metode gebruik onder vinnige pseudo eerste orde reaksietoestande met betrekking tot CO2. Die pseudo eersteorde aanname beteken dat die konsentrasie van MEA in die vloeistoffilm onbeduidend beïnvloed word deur die reaksie en effektief konstant bly. Onder pseudo eerste orde toestande word oppervlakverarming- en oppervlakvernuwingseffekte nie in ag geneem nie, juis as gevolg van die konstante konsentrasie van MEA in die vloeistoffilm. Daar is voorheen bevind dat oppervlakverarming en oppervlakvernuwing ‘n beduidende invloed het op die beskikbare effektiewe massaoordragsarea. Hierdie invloed kan slegs bestudeer word met ‘n vinnige reaksie in die vloeistoffilm wat gepaard gaan met beduidende oppervlakverarming van die vloeistoffase reagens. Die homogene vloeistoffase reaksiekinetika van CO2 met MEA in die alkohol oplosmiddel, n- Propanol, is in hierdie studie ondersoek. ‘n Nuwe, in-situ Fourier Transform Infra-Rooi (FTIR) metode van analiese is ontwikkel in hierdie ondersoek. Die reaksie is ondersoek in ‘n semienkelladings reaktor met MEA wat gevoer is tot die reaktor om met die opgeloste CO2 te reageer. Die FTIR metode meet spesiekonsentrasie as ‘n funksie van tyd sodat die konsentrasieprofiele van CO2, MEA en een van die soutprodukte van die reaksie gebruik kan word om verskillende reaksiesnelheidsvergelykings te modelleer. Die reaksie is ondersoek onder matige toestande (T = 25°C, 30°C and 35°C, P = 1 atm (abs)). Die konsentrasiebereik van die ondersoek was [MEA]:[CO2] = 5:1 en 10:1. Hierdie bereik is spesifiek gebruik sodat daar beduidende omsetting van MEA kon plaasvind. Die reaksiekinetieka studie het, ter ondersteuning van bestaande teorie, bevind dat die reaksie van CO2 met MEA in nie-waterige oplosmiddels soos alkohole, beskyf word deur ‘n zwitterioon reaksiemeganisme. Die bestaande reaksiesnelheids modelle (eksponensiële wet en pseudo gestadigde toestand hipotese) kon nie die eksperimentele data met genoegsame akuraatheid beskryf nie. Twee nuwe reaksiesnelheidsvergelykings, afgelei vanaf eerste beginsels en gebaseer op die zwitterioon meganisme, word voorgestel. Hierdie volle fundamentele model het goeie passings op die eksperimentele data getoon oor die volledige temperatuur en konsentrasiebereik van hierdie studie. Die reaksiekonstantes van die fundamentele model was onafhanklik van konsentrasie en tipe oplosmiddel en het ‘n Arrhenius temperatuurafhanklikheid. Die verkorte fundamentele model se reaksiekonstantes het ‘n moontlike konsentrasieafhanlikheid gewys. Dit plaas onsekerheid op die fundamentele basis van hierdie model en kan dus slegs as ‘n eerste benadering beskou word. Die spesifieke absorpsietempos (mol/m2.s) van CO2 in MEA/n-Propanol oplossings (0.2 M en 0.08 M MEA, T = 25°C and 30°C, P = ±103 kPa) is ondersoek met ‘n benatte wand (‘wetted wall’) eksperimentele opstelling. Die eksperimentele toestande is gekies sodat daar ‘n vinnige reaksie in die vloeistoffilm plaasgevind het, met beide beduidende en nie-beduidende MEA omsetting. Die doel met hierdie eksperimentele ontwerp was om die invloed van intervlakverarming en intervlakvernuwing op die spesifieke absorpsietempo te ondersoek. Gas fase weerstand was nie-beduidend onder die eksperimentele toestande nie. Beide intervlakverarming en intervlakvernuwing gebeur gelyktydig en is waargeneem vanuit die eksperimentele data. ‘n Beeldverwerkingstudie van die gas-vloeistof intervlak van die benatte wand het bevind dat daar ‘n toename in golfaksie op die vloeistof oppervlak is vir ‘n toename in vloeistof turbulensie. Hierdie golfaksie dra by tot oppervlakvernuwing en ‘n toename in effektiewe massaoordragsarea. ‘n Numeriese metode word voorgestel om die effektiewe area van beide die benatte wand en gepakte kolomme te bepaal vanaf reaktiewe absorpsietempos. Die metode gebruik die fundamentele reaksiesnelheidsvergelykings, bepaal in hierdie studie, in a konsentrasie diffusievergelyking sodat oppervlakverarming en vernuwing in ag geneem kan word. Daar word voorgestel dat die reaksiekinetika van CO2 met MEA in oplossings met verskillende fisiese eienskappe (digtheid, oppervlakspanning en viskositeit) bepaal word sodat die numeriese metode gebruik kan word om ‘n effektiewe area korrelasie as ‘n funksie van hierdie eienskappe te bepaal.