Study of Microfluidic Mixing and Droplet Generation for 3D Printing of Nuclear Fuels

Internal gelation and 3D printing processes were proposed to combine in a process that is promising to produce nuclear fuels with simplified production route and enhanced in-core performance [1]. The process relies on in-situ mixing of feed solutions that bear actinides and uranium nitrates with the methenamine and urea mixture. These feed solutions should be thoroughly mixed and kept at low temperature up to an inkjet printing head, where an inkjet printing process is used to deposit controlled volumes of the mixed solution on the pellet under-fabrication. Microwave and/or laser-heating are then used to trigger the gelation reaction and to solidify these printed dots and later to drive out the excess water and pre-sinter the gelled oxides. The current study is an initial approach to optimize the upfront parameters of the 3D printing process. The feed solutions need be mixed in a passive microfluidic mixer, where the first optimization parameter is the minimum mixing time in the microfluidic mixer that will yield an acceptable mixing level. To do so, CFD modelling using OpenFOAM for different designs of microfluidic mixers was conducted to select the most efficient conception. To validate the CFD results, simulation of microfluidic mixers similar to some literature cases were performed and compared. The uncertainty of selected parameters in the CFD models was used to evaluate a conservative retention time and length. Secondly, the next printing step was modeled with OpenFOAM, which is the droplet generation process. The objective from these models was to correlate the feed parameters like the flow rate and the usage of an acoustic mechanical vibrator to the printed droplets size, generation rate, and the required stand-off distance of the printing head. To perform these CFD simulations with the right solution parameters, rheology and diffusivity measurements were conducted. A proposed empirical approach was investigated for the evaluation of the diffusivity of multi-species solutions. The resultant parameters from the current study are the mixing times and lengths for given microfluidic mixers that are industrially feasible, also, the rate and volume at which the droplets of the broth mixture are generated. These results can be used as guidelines for designing the inkjet printing head and to highlight areas where further investigations are required for an efficient production process

Investigation into vibration assisted micro milling: theory, modelling and applications

PhD ThesisPrecision micro components are increasingly in demand for various engineering industries, such as biomedical engineering, MEMS, electro-optics, aerospace and communications. The proposed requirements of these components are not only in high accuracy, but also in good surface performance, such as drag reduction, wear resistance and noise reduction, which has become one of the main bottlenecks in the development of these industries. However, processing these difficult-to-machine materials efficiently and economically is always a challenging task, which stimulates the development and subsequent application of vibration assisted machining (VAM) over the past few decades. Vibration assisted machining employs additional external energy sources to generate high frequency vibration in the conventional machining process, changing the machining (cutting) mechanism, thus reducing cutting force and cutting heat and improving machining quality. The current awareness on VAM technology is incomplete and effective implementation of the VAM process depends on a wide range of technical issues, including vibration device design and setup, process parameters optimization and performance evaluation. In this research, a 2D non-resonant vibration assisted system is developed and evaluated. Cutting mechanism and relevant applications, such as functional surface generation and microfluidic chips manufacturing is studies through both experimental and finite element analysis (FEA) method. A new two-dimensional piezoelectric actuator driven vibration stage is proposed and prototyped. A double parallel four-bar linkage structure with double layer flexible hinges is designed to guide the motion and reduce the displacement coupling effect between the two directions. The compliance modelling and dynamic analysis are carried out based on the matrix method and lagrangian principle, and the results are verified by finite element analysis. A closed loop control system is developed and proposed based on LabVIEW program consisting of data acquisition (DAQ) devices and capacitive sensors. Machining experiments have been carried out to evaluate the performance of the vibration stage and the results show a good agreement with the tool tip trajectory simulation results, which demonstrates the feasibility and effectiveness of the vibration stage for vibration assisted micro milling. The textured surface generation mechanism is investigated through both modelling and experimental methods. A surface generation model based on homogenous matrices transformation is proposed by considering micro cutter geometry and kinematics of vibration assisted milling. On this basis, series of simulations are performed to provide insights into the effects of various vibration parameters (frequency, amplitude and phase difference) on the generation mechanism of typical textured surfaces in 1D and 2D vibration-assisted micro milling. Furthermore, the wettability tests are performed on the machined surfaces with various surface texture topographies. A new contact model, which considers both liquid infiltration effects and air trapped in the microstructure, is proposed for predicting the wettability of the fish scales surface texture. The following surface textures are used for T-shaped and Y-shaped microchannels manufacturing to achieve liquid one-way flow and micro mixer applications, respectively. The liquid flow experiments have been carried out and the results indicate that liquid flow can be controlled effectively in the proposed microchannels at proper inlet flow rates. Burr formation and tool wear suppression mechanisms are studied by using both finite element simulation and experiment methods. A finite element model of vibration assisted micro milling using ABAQUS is developed based on the Johnson-Cook material and damage models. The tool-workpiece separation conditions are studied by considering the tool tip trajectories. The machining experiments are carried out on Ti-6Al-4V with coated micro milling tool (fine-grain tungsten carbides substrate with ZrO2-BaCrO4 (ZB) coating) under different vibration frequencies (high, medium and low) and cutting states (tool-workpiece separation or nonseparation). The results show that tool wear can be reduced effectively in vibration assisted micro milling due to different wear suppression mechanisms. The relationship between tool wear and cutting performance is studied, and the results indicate that besides tool wear reduction, better surface finish, lower burrs and smaller chips can also be obtained as vibration assistance is added

Characterisation of Monodisperse Regimes of a Droplet Stream Generator

The interest in studying droplet related phenomena has been increasing over the last decades. In the fluid dispensing equipment industry, a major problem is to minimise droplet diameter and to eject droplets in a controlled manner with a low-cost device. Micro-droplet generation has gained its popularity for its multiple applications, such as biotechnology, manufacturing engineering, and fuel dispensing. Taking all this into account, a new low-cost droplet stream generator was designed and fabricated. The material used to manufacture the stream droplet generator structure was PLA, since it is a 3D printable material, which allowed to minimise the device cost. This structure has three separated components: lid, fluid chamber, and pinhole holder. In order to simplify the disturbance mechanism, it was decided that the disruption waves should be applied directly to the fluid. To achieve that, a piezoelectric cell that vibrates through the variation of waveform parameters was placed above the liquid chamber, creating disturbances directly onto the liquid surface in a parallel direction, making this device a push mode generator. The interchangeable nozzle used was a round stainlesssteel high precision optical pinhole with three different sizes: 100 µm, 150 µm, and 200 µm. Jet attribute properties (droplet diameter, droplet velocity, and distance between droplets) were measured as the different conditions changed (piezoelectric diaphragm frequency, outlet pressure, and nozzle size). The present work studied the spray characteristics for water, jet fuel and a jet fuel and biofuel mixture, and different monodisperse regimes were found. A full characterisation of them is presented and discussed in detail. It was found that the range of droplet diameter for a pinhole size of 200 µm that can be used for all three fluids is 401 µm to 472 µm and a range of velocity of 1.24 m/s to 2.48m/s, while for a pinhole size of 150 µm the droplet diameter range that can be obtained is 287 µm to 340 µm and a range of velocity of 2.04 m/s to 4.38 m/s for all three fluids. For a pinhole size of 100 µm the droplet diameter range for all three fluids is 206 µm to 258 µm and the velocity range is 2.36 m/s to 5.99 m/s. It was found that both droplet diameter and spacing decrease with the increase of inlet flow rate and frequency, and the most important property in the jet formation is the nozzle size. The jet velocity is also highly influenced by the flow rate and nozzle size. When compared, the three fluids behave in a different manner, resulting in different droplet diameter and velocity values. This can be explained by the fluids properties, where the mixture of jet fuel and biofuel presents higher viscosity than the other two fluids.O interesse em estudar fenómenos relacionados com as gotas tem vindo a aumentar nas últimas décadas. Na indústria de equipamentos de ejeção de fluidos, um grande problema é minimizar o diâmetro das gotas e ejetá-las de forma controlada utilizando um dispositivo de baixo custo. A geração de micro-gotas ganhou popularidade pelas suas múltiplas aplicações, como biotecnologia, engenharia de fabricação e ejeção de combustível. Tendo tudo isto em conta, um novo gerador de gotas contínuas, de baixo custo, foi projetado e fabricado. PLA foi o material usado para fabricar a estrutura do gerador de gotas dado que é um material de impressão 3D, o que permite minimizar o custo do dispositivo. Esta estrutura tem três componentes separados: tampa da célula piezoelétrica, câmara de fluido e suporte do pinhole. A fim de simplificar o mecanismo de perturbação, foi decidido que as ondas de perturbação devem ser aplicadas diretamente no fluido. Para conseguir isso, uma célula piezoelétrica foi colocada acima da câmara de fluido. O ”nozzle” utilizado é um pinhole óptico redondo de alta precisão, feito de de aço inoxidável e com três tamanhos diferentes: 100 µm, 150 µm e 200 µm. As propriedades do jato (diâmetro da gota, velocidade da gota e distância entre gotas) foram medidas de para diferentes propriedades (frequência da célula piezoelétrica, pressão de fluído e tamanho do ”nozzle”). O presente trabalho estudou as características do spray para três fluidos diferentes (àgua, jet fuel e mistura de biocombustível) e diferentes regimes monodispersos foram encontrados. Uma caracterização destes parametros é apresentada e discutida com detalhe. Verificou-se que o intervalo do diâmetro das gotas para um ”nozzle” com tamanho de 200 µm, que pode ser usado para todos os três fluidos, é de 401 µm até 472 µm e o intervalo de velocidade é de 1, 24 m/s até 2, 48 m/s, enquanto que para um ”nozzle” com um tamanho de 150 µm, a gama de diâmetros que pode ser obtido é de 287 µm até 340 µm e um intervalo de velocidade de 2, 04 m/s até 4, 38 m/s, para os três fluidos. Para um tamanho de pinhole de 100 µm, o intervalo de diâmetros das gotas para todos os três fluidos é de 206 µm a 258 µm e o intervalo de velocidade é 2, 36 m/s a 5, 99 m/s. Verificou-se que, tanto o diâmetro da gota como o espaçamento, diminuem com o aumento da fluxo da entrada e frequência, e a propriedade mais importante na formação do jato é o tamanho do ”nozzle”. A velocidade do jato é muito influenciada pela velocidade do fluxo e pelo tamanho do ”nozzle”. Quando comparados, os três fluidos comportam-se de uma forma diferente, resultando em diferentes diâmetro de gotas e velocidade do jato. Isto pode ser explicado pelas propriedades dos fluidos, onde a mistura de biocombustível apresenta maior viscosidade do que os outros dois fluídos

Recent advances in micro-electro-mechanical devices for controlled drug release applications

In recent years, controlled release of drugs has posed numerous challenges with the aim of optimizing parameters such as the release of the suitable quantity of drugs in the right site at the right time with the least invasiveness and the greatest possible automation. Some of the factors that challenge conventional drug release include long-term treatments, narrow therapeutic windows, complex dosing schedules, combined therapies, individual dosing regimens, and labile active substance administration. In this sense, the emergence of micro-devices that combine mechanical and electrical components, so called micro-electro-mechanical systems (MEMS) can offer solutions to these drawbacks. These devices can be fabricated using biocompatible materials, with great uniformity and reproducibility, similar to integrated circuits. They can be aseptically manufactured and hermetically sealed, while having mobile components that enable physical or analytical functions together with electrical components. In this review we present recent advances in the generation of MEMS drug delivery devices, in which various micro and nanometric structures such as contacts, connections, channels, reservoirs, pumps, valves, needles, and/or membranes can be included in their design and manufacture. Implantable single and multiple reservoir-based and transdermal-based MEMS devices are discussed in terms of fundamental mechanisms, fabrication, performance, and drug release applications.Fil: Villarruel Mendoza, Luis A.. Comisión Nacional de Energía Atómica. Gerencia de Área de Investigación y Aplicaciones no Nucleares. Gerencia de Desarrollo Tecnológico y Proyectos Especiales. Departamento de Micro y Nanotecnología; ArgentinaFil: Scilletta, Natalia Antonela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área de Investigación y Aplicaciones no Nucleares. Gerencia de Desarrollo Tecnológico y Proyectos Especiales. Departamento de Micro y Nanotecnología; ArgentinaFil: Bellino, Martin Gonzalo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Constituyentes | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Constituyentes.; ArgentinaFil: Desimone, Martín Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; ArgentinaFil: Catalano, Paolo Nicolás. Comisión Nacional de Energía Atómica. Gerencia de Área de Investigación y Aplicaciones no Nucleares. Gerencia de Desarrollo Tecnológico y Proyectos Especiales. Departamento de Micro y Nanotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentin

Electrospun Nanofibers for Biomedical Applications

Electrospinning is a versatile and effective technique widely used to manufacture nanofibrous structures from a diversity of materials (synthetic, natural or inorganic). The electrospun nanofibrous meshes’ composition, morphology, porosity, and surface functionality support the development of advanced solutions for many biomedical applications. The Special Issue on “Electrospun Nanofibers for Biomedical Applications” assembles a set of original and highly-innovative contributions showcasing advanced devices and therapies based on or involving electrospun meshes. It comprises 13 original research papers covering topics that span from biomaterial scaffolds’ structure and functionalization, nanocomposites, antibacterial nanofibrous systems, wound dressings, monitoring devices, electrical stimulation, bone tissue engineering to first-in-human clinical trials. This publication also includes four review papers focused on drug delivery and tissue engineering applications

Nonreciprocity Applications in Acoustics and Microfluidic Systems

Breaking reciprocity in linear acoustic systems and designing a novel actuator for the nonreciprocal valveless pumps are studied in this dissertation. The first part was started by deriving the acoustic governing equations in a moving wave propagation medium. It was shown thatthe Coriolis acceleration term appears ina cross-product term with the wave vector. It means the main reason for breaking reciprocity in the circular fluid flow is the Coriolis acceleration term. Finally, the governing equations were solved numerically by COMSOL Multiphysics software. Moreover, Green`s second identity was used as a complimentary method to prove breaking reciprocityin such a system with moving medium. It is concluded that the non-reciprocity is magnified by increasing the angular velocity of the fluid system. The second part of this thesis is about achieving non-reciprocity utilizing the arrangement of a nozzle and diffuser as the inlet and outlet ports. This part’s goal is to design a novel flexible actuator design for a valveless pump. The actuation mechanism which is novel in its own term, uses liquid metal called galinstan, a non-magnetic but electrically conducting alloy. In the designed device, an alternating current (AC) is applied onto a microchannel filled with galinstan. This device is placed between two permanent magnets with opposing poles. Due to the Lorentz force law, there will be radial in-plane forces on the polymeric flexible substrate. These in-plane forces radially contract and expand the circular diaphragm to provide an upward and downward out of plane bending moment, which causes an oscillatory reciprocating movement similar to a piezoelectric actuator`s movement. Compared to the traditional piezo electric materials such as Lead Zirconate Titanate (PZT), this actuator has numerous advantages such as being flexible, having the ability to be scaled down, being formed as an integrated structure, and being fabricated by a considerably simple process. The prototype of the pump could be fabricated easily with Platinum Silicone rubber and some low-cost 3D printed elements. Although the prototype has been fabricated in a relatively large size, it is considered as a proper conceptual model representing the performance of the pump