Using synchrotron-based X-Ray microtomography and functional contrast agents in environmental applications

Despite very rapid development in commercial X-ray tomography technology, synchrotron-based tomography facilities still have a number of advantages over conventional systems. The high photon flux inherent of synchrotron radiation sources allows for (i) high resolution to micro- or nanometer scales depending on the individual beamline, (ii) rapid acquisition times that allow for collection of sufficient data for statistically significant results in a short amount of time as well as prevention of temporal changes that would take place during longer scan times, and (iii) optimal implementation of contrast agents that allow us to resolve features that would not be decipherable in scans obtained with a polychromatic radiation source. This chapter highlights recent advances in capabilities at synchrotron sources, as well as implementation of synchrotron-based computed microtomography (CMT) to two topics of interest to researchers in the soil science, hydrology, and environmental engineering fields, namely multiphase flow in porous media and characterization of biofilm architecture in porous media. In both examples, we make use of contrast agents and photoelectric edge-specic scanning (single- or dual-energy type), in combination with advanced image processing techniques

Methods for Characterizing Multiphase Magnetocaloric Materials

This thesis is aimed to study the characteristics of thermomagnetic phase transitions and the resulting magnetocaloric effect in multiphase magnetocaloric materials, which is a very common scenario in the research of the magnetocaloric effect and can lead to complex situations that need to be properly approached. On the one hand, composites that combine various phases with Curie transitions close to each other are interesting and highly studied as they can lead to an enhanced refrigerant capacity with respect to the pure phases while keeping a large enough response. In this thesis, newly developed Gd + Gd7Pd3 composites are presented as a case in which the mentioned improvement of the refrigerant capacity is achieved. This intentional situation of overlapping Curie transitions has been used for the development of a method for the deconvolution of the magnetocaloric responses by means of the scaling laws of the magnetocaloric effect. On the other hand, materials exhibiting magnetostructural transformation (first-order phase transition) can also show the Curie transitions of the phases (second-order phase transition), where the phase transitions of different type can be concurrent. This situation is approached using Heusler alloys undergoing magnetostructural transformation located close to the Curie transitions of the martensitic and austenitic phases. The competing effect of both types of phase transitions in this case is investigated by experimental and analytical methods. The deconvolution method used for the composites is successfully applied here, enabling the subtraction of the Curie transition to the total response. It has to be noted that these situations of overlapping phase transitions can also occur unintentionally (i.e., due to the presence of impurities during synthesis). Therefore, the developed methods can also be used in these situations to know the effect of additional phase transitions and to gauge the actual response of the desired phase. Additionally, it has also been shown how the overlapping Curie transitions of the phases affect the hysteretic signature of the alloys undergoing magnetostructural transformation. This study is addressed through the emerging Temperature first-order reversal curves (TFORC) method for the study of magnetocaloric materials, using again Heusler alloys as a model case. This part combines experimental results with results from the modelling of the thermomagnetic behavior of the material. This has enabled a direct correlation between the characteristics of the thermomagnetic behavior of the alloys and the features of the TFORC distributions. Finally, the emerging topic of using polymer-based composites for the 3D printing of functional parts is addressed. Here, the main existing problem lies in the fabrication of uniform composite materials that allow the 3D printing of parts with predictable and repeatable functionality without relying on industrial techniques. A novel manufacturing method of polymer-based filaments containing functional fillers is proposed. Soft-magnetic steel particles have been used to manufacture polymer-based magnetic composites as proof of concept of the validity of the method. Once validated, the method is used to manufacture polymer-based magnetocaloric composites for additive manufacturing. The relatively simple method provides highly homogeneous filaments that preserve the magnetic functionality of the fillers. However, the property of the polymeric matrix is significantly affected by the addition of the metallic fillers, which has an important influence on the processability parameters both for the extrusion and printing

Golpe de ariete polifásico : modelado, experimentos e simulación

[Abstract] This thesis deals with the experimental and numerical analysis of the water hammer phenomenon generated by the discharge of a pressurized liquid into a pipeline kept under vacuum conditions. This ow configuration induces several multiphase phenomena such as cavitation and gas desorption that cannot be ignored in the water hammer behavior. The motivation of this research work comes from the liquid propulsion systems used in spacecrafts, which can undergo uid hammer effects threatening the system integrity. Fluid hammer can be particularly adverse during the priming phase, which involves the fast opening of an isolation valve to fill the system with liquid propellant. Due to the initial vacuum conditions in the pipeline system, the water hammer taking place during priming may involve multiphase phenomena, such as cavitation and desorption of a non-condensable gas, which may affect the pressure surges produced in the lines. Even though this ow behavior is known, only few studies model the spacecraft hardware configuration, and a proper characterization of the two-phase ow is still missing. The creation of a reliable database and the physical understanding of the water hammer behavior in propulsion systems are mandatory to improve the physical models implemented in the numerical codes used to simulate this ow configuration. For that purpose, an experimental facility modeling a spacecraft propulsion system has been designed, in which the physical phenomena taking place during priming are generated under controlled conditions in the laboratory using inert uids. An extended experimental campaign was performed on the installation, aiming at analyzing the effect of various working parameters on the uid hammer behavior, such as the initial pressure in the line, liquid saturation with the pressurant gas, liquid properties and pipe configuration. The in uence of the desorbed gas during water hammer occurrence is found to have a great importance on the whole process, due to the added compressibility and lower speed of sound by an increasing amount of non-condensable gas in the liquid + gas mixture. This results in lower pressure levels and faster pressure peaks attenuation, compared to uids without desorption. The two-phase ow was characterized by means of ow visualization of the liquid front at the location where the uid hammer is generated. The front arrival was found to be preceded by a foamy mixture of liquid, vapor and non-condensable gas, and the pressure wave re ected at the tank may induce the liquid column separation at the bottom end. While column separation takes place, the successive pressure peaks are generated by the impact of the column back against the bottom end. The resulting experimental database is then confronted to the predictions of the 1D numerical code EcosimPro/ESPSS used to assess the propulsion system designs. Simulations are performed with the ow configuration described before, modeling the experimental facility. The comparison of the numerical results against the experimental data shows that aspects such as speed of sound computation with a dissolved gas and friction modeling need to be improved.[Resumen] Esta tesis presenta un estudio experimental y numérico del fenómeno de golpe de ariete generado por la descarga de un líquido presurizado en una conducción bajo condiciones de vacío. Esta configuración de ujo induce varios fenómenos multifásicos, tales como cavitación y desorción de gases no condensables, que no pueden ser ignorados en el análisis del problema. La motivación de este trabajo de investigación tiene su origen en los sistemas de propulsión con combustibles líquidos utilizados en aplicaciones aeroespaciales, donde el fenómeno de golpe de ariete y el incremento de presión ocasionado puede afectar la integridad del sistema. El golpe de ariete es particularmente adverso durante la fase de cebado, donde la apertura rápida de una válvula de aislamiento permite el llenado de las líneas de combustible, las cuales se encuentran inicialmente al vacío. Debido a esto, junto al fenómeno de golpe de ariete también tiene lugar la cavitación del uido y la desorción de un gas no condensable, los cuales afectan a los incrementos de presión que se producen en las líneas. A pesar de que todos estos fenómenos han sido ampliamente tratados en la literatura científica, existen muy pocos estudios que traten la configuración de ujo descrita y que aborden todos los fenómenos multifásicos ocasionados de forma simultánea. Es por ello que la creación de una extensa base de datos, con las condiciones experimentales bien definidas, es una necesidad para validar y mejorar los modelos físicos implementados en los códigos numéricos, los cuales se utilizan para evaluar el comportamiento de los sistemas de propulsión durante la fase de diseño. Para tal fin, se ha diseñado una instalación experimental que reproduce un sistema de propulsión, de forma que todos los fenómenos físicos que tienen lugar durante el cebado del combustible se generan en el laboratorio bajo condiciones controladas. El estudio experimental llevado a cabo ha permitido analizar el efecto de diversos parámetros de trabajo en el comportamiento del golpe de ariete, tales como la presión inicial de vacío en la línea, saturación del líquido con el gas presurizante, propiedades del líquido y configuración de la conducción. Los resultados muestran como la desorción del gas no condensable afecta de forma significativa el comportamiento del uido durante el golpe de ariete, debido al incremento de compresibilidad y la reducción de la velocidad del frente de onda al aumentar la presencia de gas en la mezcla bifásica. Esto se traduce en menores incrementos de presión y atenuación más rápida de los picos de presión, en comparaci ón con el mismo uido bajo condiciones donde la desorción no tiene lugar. La visualización del ujo allí donde se genera el golpe de ariete ha permitido caracterizar el comportamiento bifásico del uido. El avance del frente líquido en la línea está precedido por una mezcla multifásica de líquido, vapor y gas no condensable, y las ondas de expansión pueden inducir la separación de la columna líquida en el extremo cerrado de la conducción donde impacta el uido. Siempre que la separación de columna tenga lugar, los sucesivos picos de presión se generan por el impacto de la columna líquida contra el extremo cerrado de la línea tras la separación. La base de datos experimental resultante se ha comparado con las predicciones del código numérico 1D EcosimPro/ESPSS simulando la configuración experimental. La comparación de los resultados numéricos con los datos experimentales muestran que es necesario reformular el cálculo de la velocidad del frente de onda cuando existe una fase gaseosa disuelta en el volumen líquido. Además, es preciso incluir en el código un modelo de fricción no estacionario que mejore las predicciones del modelo de fricción quasi-estacionario utilizado actualmente.[Resumo] Esta tese presenta un estudo experimental e numérico do fenómeno de golpe de ariete xerado pola descarga dun líquido presurizado nunha condución baixo condicións de baleiro. Esta configuración de uxo induce varios fenómenos multif ásicos, tales como cavitación e desorción de gases non condensables, que non poden ser ignorados na análise do problema. A motivación deste traballo de investigación ten a súa orixe nos sistemas de propulsión con combustibles líquidos utilizados en aplicacións aeroespaciais, onde o fenómeno de golpe de ariete e o incremento de presión ocasionado pode afectar a integridade do sistema. O golpe de ariete é particularmente adverso durante a fase de cebado, onde a apertura rápida dunha válvula de illamento permite a enchedura das liñas de combustible, as cales se encontran inicialmente ao baleiro. Debido a isto, xunto ao fenómeno de golpe de ariete tamén ten lugar a cavitación do fluído e a desorción dun gas non condensable, os cales afectan aos incrementos de presión que se producen nas liñas. A pesar de que todos estes fenómenos foron amplamente tratados na literatura científica, existen moi poucos estudos que traten a configuración de uxo descrita e que aborden todos os fenómenos multif ásicos ocasionados de forma simultánea. É por iso que a creación dunha extensa base de datos, coas condicións experimentais ben definidas, é unha necesidade para validar e mellorar os modelos físicos implementar nos códigos numéricos, os cales se utilizan para avaliar o comportamento dos sistemas de propulsión durante a fase de deseño. Para tal fin, deseñouse unha instalación experimental que reproduce un sistema de propulsión, de forma que todos os fenómenos físicos que teñen lugar durante o cebado do combustible se xeran no laboratorio baixo condicións controladas. O estudo experimental levado a cabo permitiu analizar o efecto de diversos parámetros de traballo no comportamento do golpe de ariete, tales como a presión inicial de baleiro na liña, saturación do líquido co gas presurizante, propiedades do líquido e configuración da condución. Os resultados mostran como a desorción do gas non condensable afecta de forma significativa o comportamento do fluído durante o golpe de ariete, debido ao incremento de compresibilidade e a redución da velocidade da fronte de onda ao aumentar a presenza de gas na mestura bifásica. Isto tradúcese en menores incrementos de presión e atenuación máis rápida dos picos de presión, en comparación co mesmo fluído baixo condicións onde a desorción non ten lugar. A visualización do uxo alí onde se xera o golpe de ariete permitiu caracteri zar o comportamento bifásico do fluído. O avance da fronte líquida na liña está precedido por unha mestura multifásica de líquido, vapor e gas non condensable, e as ondas de expansión poden inducir a separación da columna líquida no extremo pechado da condución onde impacta o fluído. Sempre que a separación de columna teña lugar, os sucesivos picos de presión xéranse polo impacto da columna líquida contra o extremo pechado da liña tras a separación. A base de datos experimental resultante comparouse coas predicións do código numérico 1D EcosimPro/ESPSS simulando a configuración experimental. A comparaci ón dos resultados numéricos cos datos experimentais mostran que é necesario reformular o cálculo da velocidade da fronte de onda cando existe unha fase gasosa disolta no volume líquido. Ademais, é preciso incluír no código un modelo de fricción non estacionario que mellore as predicións do modelo de fricción quasi-estacionario utilizado actualmente

Dry Chemical Fire Suppression System Discharge Modeling and Testing

An engineering method has been developed for calculating the blowdown of agent from a pressurized dry chemical fire suppression system supply cylinder, and the flow rate of agent through a piping delivery system. Its goal is to provide the means to determine the blowdown time and agent delivery capabilities of pre-engineered and simple engineered systems. The method is based on the treatment of the two-phase powder-gas flow as an equivalent fluid with thermodynamic properties that account for agent composition and the relative proportions of agent and gas propellant. The mixture is treated as compressible, and the expansion in the supply tank is assumed isentropic. A key assumption in the model is that the agent (powder) mass fraction remains constant, in both the tank and delivery system. Laboratory tests were conducted to examine the validity of the model and its assumptions. Simple systems were discharged to measure pressures in the cylinder and nozzle inlet during discharge, and the mass of agent discharged. A 0.43 cubic foot cylinder containing 0-25 lbm of either sodium bicarbonate or moammonium phosphate, pressurized at up to 300 psig of nitrogen, was discharged, either alone, or with an 8-foot length of piping and a single nozzle. For the cylinder by itself, gas alone pressurized to 300 psig discharged in 1.5 seconds, while 25 lbm of sodium bicarbonate agent pressurized to 300 psig discharged in 5.2 seconds with 0.10 lbm of agent remaining in the cylinder after discharge. There was no significant difference in the discharge times or residual masses in the cylinder after discharge between the sodium bicarbonate and monoammonium phosphate agents. For a cylinder-pipe-nozzle system, gas-alone discharges pressurized to 300 psig took 7 seconds, while 25 lbm of sodium bicarbonate agent pressurized to 300 psig discharged in 26 seconds with 0.64 lbm of residual agent in the cylinder after discharge. Predictions generated by the model were compared with test results. Cylinder alone gas-only discharge model predictions agreed well with test data for the full duration of tests using a discharge coefficient of 0.380 to characterize the gas flow through the dip tube / valve assembly; a simple isentropic analytical model gave a good prediction using a discharge coefficient of 0.430. Gas-solids predictions using a discharge coefficient of 0.500 agreed well with test data up to the observed inflection point near the end of discharge. This inflection point is caused by the agent in the cylinder reaching the bottom of the dip tube, resulting in reduced flow of agent from the cylinder, and thus reducing the mass fraction of the flow. Cylinder-pipe-nozzle model discharge predictions for gas-only discharges agreed well with test data for the full duration of tests using a discharge coefficient of 0.470 for the 0.173-inch diameter nozzle used in the testing. Model predictions agreed well with the gas-solids mixture test data up to the inflection point, using a discharge coefficient of 0.999. The constant mass fraction assumption results in residual agent mass predictions of 2.0 lbm or more after discharge. Test data shows 0.6 lbm or less of residual. This residual discrepancy, and the presence of the inflection point observed in solids-gas tests, suggests that the constant mass fraction assumption is not adequate to accurately model agent discharge from the cylinder. Using an appropriate discharge coefficient, the model can be used to determine approximate discharge times for simple systems

A Method to Represent Heterogeneous Materials for Rapid Prototyping: The Matryoshka Approach

Purpose—The purpose of this paper is to present a new method for representing heterogeneous materials using nested STL shells, based, in particular, on the density distributions of human bones. Design/methodology/approach—Nested STL shells, called Matryoshka models, are described, based on their namesake Russian nesting dolls. In this approach, polygonal models, such as STL shells, are “stacked” inside one another to represent different material regions. The Matryoshka model addresses the challenge of representing different densities and different types of bone when reverse engineering from medical images. The Matryoshka model is generated via an iterative process of thresholding the Hounsfield Unit (HU) data using computed tomography (CT), thereby delineating regions of progressively increasing bone density. These nested shells can represent regions starting with the medullary (bone marrow) canal, up through and including the outer surface of the bone. Findings—The Matryoshka approach introduced can be used to generate accurate models of heterogeneous materials in an automated fashion, avoiding the challenge of hand-creating an assembly model for input to multi-material additive or subtractive manufacturing. Originality/Value—This paper presents a new method for describing heterogeneous materials: in this case, the density distribution in a human bone. The authors show how the Matryoshka model can be used to plan harvesting locations for creating custom rapid allograft bone implants from donor bone. An implementation of a proposed harvesting method is demonstrated, followed by a case study using subtractive rapid prototyping to harvest a bone implant from a human tibia surrogate

Density-based topology optimization for 3D-printable building structures

This paper presents the study of a new penalty method for density-based topology optimization. The focus is on 3D-printable building structures with optimized stiffness and thermal insulation properties. The first part of the paper investigates the homogenized properties of 3D-printed infill patterns and in the second part a new penalty method is proposed and demonstrated. The method presents an alternative way to implement multi-material topology optimization without increasing computational cost. A single interpolation function is created, based on the homogenized properties of a triangular infill pattern. The design variables are linked to the different possible infill densities of the pattern. A high density represents a solid structure with high stiffness, but weak thermal properties, while an intermediate density provides the structure with good insulation qualities. On the other hand, when the air cavities become too large (i.e., low infill densities), the heat flow by convection and radiation again decreases the thermal performances of the material. The optimization study is performed using the GCMMA algorithm combined with a weighted-sum dual objective. One part of the equation aims to maximize stiffness, while the other attempts to minimize the thermal transmittance. Different case studies are presented to demonstrate the effectiveness of this multi-physics optimization strategy. Results show a series of optimized topologies with a perfect trade-off between structural and thermal efficienc

Toward a microgravity research strategy

Recommendations of the Committee on Microgravity Research (CMGR) of the Space Studies Board of the National Research Council are found in the Summary and Recommendations in the front of the report. The CMGR recommends a long-range research strategy. The main rationale for the microgravity research program should be to improve our fundamental scientific and technical knowledge base, particularly in the areas that are likely to lead to improvements in processing and manufacturing on earth. The CMGR recommends research be categorized as Biological science and technology, Combustion, Fluid science, Fundamental phenomena, Materials, and Processing science and technology. The committee also recommends that NASA apply a set of value criteria and measurement indicators to define the research and analysis program more clearly. The CMGR recommends that the funding level for research and analysis in microgravity science be established as a fixed percentage of the total program of NASA's Microgravity Science and Applications Division in order to build a strong scientific base for future experiments. The committee also recommends a cost-effective approach to experiments. Finally the CMGR recommends that a thorough technical review of the centers for commercial development of space be conducted to determine the quality of their activities and to ascertain to what degree their original mission has been accomplished