Experimental investigations on micro-scale thermal fluid phenomena by using advance flow diagnostic techniques

Two-fluid mixing is an essential process for many microfluidic or lab-on-a-chip devices. Effective mixing of two fluids inside microchannels could be very challenging since turbulence is usually absent due to the nature of low Reynolds numbers of microflows. In the present study, a parametric study is carried out to elucidate underlying physics and to quantify the effectiveness of manipulating Electro-Kinetic-Instabilities (EKI) to actively control/enhance fluid mixing inside Y-shaped microchannels. Epi-fluorescence imaging technique is used to conduct qualitative flow visualization and quantitative scalar concentration field measurements to quantify the fluid mixing process inside the Y-shaped microchannels in terms of scalar concentration distributions, shedding frequency of the EKI waves and scalar mixing efficiency. The effects of the relevant parameters, such as the conductivity ratio of the two mixing streams, the strength of the applied static electric fields, the frequency and amplitude of the applied alternating perturbations, and micro-structures inside the microchannels on the evolution of the EKI waves and resultant fluid mixing process are investigated systematically. Micro-flows and heat transfer process inside small surface droplets have many interesting applications associated with microfluidics such as DNA molecule imaging, micro-pumps, and ink-jet printing. The second component of present study is to investigate the unsteady flow and heat transfer phenomena inside small surface droplets over a solid substrate at different temperature levels. Particle Image Velocimetry (PIV) technique is used to quantify the dynamics of the evaporation process and surface-tension induced Marangoni flows inside the small surface droplets. Molecular Tagging Thermometry (MTT) technique is used to map the transient temperature distributions inside the droplets to quantify the unsteady heat transfer process. The effects of the substrate temperature on the evaporation process, surface-tension induced Marangoni flows and micros-scale heat transfer process inside the surface droplets are quantified in detail

Microfluidics and Nanofluidics Handbook

The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals

Multi-Functional System for Biomedical Application Using AC Electrokinetics

Manipulation of fluids in a small volume is often a challenge in the field of Microfluidics. While many research groups have addressed this issue with robust methodologies, manipulating fluids remains a scope of study due to the ever-changing technology (Processing Tools) and increase in the demand for “Lab-On-a-Chip” devices in biological applications. This thesis peruses the flow pattern of the orthogonal electrode pattern and circular electrode providing, examples of the flow patterns and the process micromixing. Characteristics of a multifunctional system were demonstrated using orthogonal electrode and circular electrode patterned device. Conductivity of the fluids were chosen such they reflect perfect biological conditions to determine the working conditions of the proposed devices under different AC voltage and frequency levels. Experimental results were then compared with simulated results which were obtained using COMSOL simulation software

Application of Experimental and Numerical Techniques to Microscale Devices

Two of the areas that have become relevant recently are the areas of mixing in micro-scale devices, and manufacturing of functional nanoparticles. MicroPIV experiments were performed on two different mixers, one a wide microchannel with the surface grooves, in the laminar regime, and the other, a confined impinging jets reactor, in the laminar and turbulent regimes. In the wide microchannel with surface grooves, microPIV data were collected at the interface and the midplane at the Reynolds numbers of 0.08, 0.8, and 8. The experiments were performed on three internal angles of the chevrons, namely 135°, 90°, and 45°. The normalized transverse velocity generated in the midplane due to the presence of the grooves, is the strongest for the internal angle of 135°, and in that, the normalized transverse velocity is maximum at the Reynolds numbers of 0.08 and 0.8. MicroPIV experiments were performed in a confined impinging jets reactors at Reynolds numbers of 200, 1000, and 1500. The data was collected in the midplane, and turbulent statistics were further computed. The high velocity jets impinge along the centerline of the reactor. Upon impinging, part of the fluid turns towards the top wall and the majority of it turn towards the outlet. This high velocity impingement causes and unstable zone called the impingement zone, which moves about the centerline line, causing the jets to flap back and forth. Spatial correlations were computed to get an estimate of the size of the coherent structures. Large eddy simulation was performed on the CIJR for the Reynolds numbers of 1000 and 1500, using OpenFOAM. The Reynolds number is based on the inlet jet hydraulic diameter. Excellent agreement was found with the experimental and simulation data. Turbulent reactive mixing in a rectangular microscale confined impinging-jets reactor (CIJR) was investigated using the pH indicator phenolphthalein in this study for three di_erent jet Reynolds numbers of 25, 1000 and 1500. Laminar flow regime was observed at Reynolds number of 25 whereas the flow was turbulent at Reynolds numbers of 1000 and 1500. An image processing technique was applied to instantaneous images to extract quantitative mixing data by identifying regions with pH ≥ 9.3 and regions with pH \u3c 9.3. The ensemble-averages were computed using these thresholded images to compare mixing performance between different Reynolds numbers. Finally, the spatial auto-correlation fields of the thresholded images fluctuations were evaluated, based on which large-scale turbulent structure were analyzed

COUPLED EQUIVALENT CIRCUIT MODEL FOR FLUID FLOW AND HEAT TRANSFER IN LARGE CONNECTED MICROCHANNEL NETWORKS

Ph.DDOCTOR OF PHILOSOPH

Microfluidic system for cell separation and deformation assessment by using passive methods

Tese de doutoramento em Biomedical EngineeringOs sistemas microfluídicos têm sido usados com sucesso em muitas aplicações biomédicas. As principais vantagens destes sistemas consistem na utilização de volumes de amostras reduzidos e com tempos de ensaios curtos. Além disso, os sistemas microfluídicos possibilitam a execução de várias tarefas em paralelo numa única plataforma microfluídica, como por exemplo a separação e medição da deformabilidade de células/partículas. Em dispositivos microfluídicos, existem dois métodos principais para separar células: métodos passivos, baseados em microestruturas e escoamentos laminares, e métodos ativos, baseados em campos de forças externos. Muitos estudos têm sido realizados com métodos passivos, pois estes não necessitam de forças externas. Nesta tese serão apresentadas diferentes geometrias passivas para um dispositivo microfluídico, constituído por vários filtros de fluxo cruzado e multiníveis com o intuito de separar células/partículas em função do seu tamanho. Outra característica importante é a implementação de microcanais hiperbólicos a montante das saídas por forma a criar um escoamento extensional homogéneo e consequentemente medir a deformabilidade das células de forma controlada. Após a separação e avaliação da deformação, a quantidade de glóbulos vermelhos será quantificada por um método de espectrofotometria. Os resultados indicam que várias geometrias mostraram uma boa taxa de separação, confirmada pelas medidas de camada livre de células e pela espectrofotometria. Verificou-se também que os sistemas microfluídicos testados são capazes de separar amostras patológicas de sangue, demostrando assim o seu potencial em realizar simultaneamente a separação e deformação de células patológicas, como por exemplo células provenientes de pacientes diagnosticados com malária e/ou diabetes.Microfluidic systems have been successfully used at many biomedical applications. Their great advantages allow working with minimal sample volumes and with short assays times. Additionally, microfluidic systems allow parallel operations in a single microfluidic platform such as separation and measurement of single cell/particles deformability. In microfluidic devices, there are two main methods for cells separation: passive methods, based on microstructures and laminar flow, and active methods, based on external force fields. Many studies have been made using passive methods because they do not require external forces. In this thesis it will be presented different geometrical passive approaches for a microfluidic device, that will have crossflow filters and multilevel steps that will separate the cells/particles by their size. Another important feature is the implementation of hyperbolic microchannels upstream the outlets in order to create a homogeneous extensional flow and consequently to measure the cells deformability in a controlled way. After the separation and deformation assessment, the amount of RBCs will be quantified by a spectrophotometry method. The results indicate that several geometries have shown a good separation rate, confirmed by the cell free layer and spectrophotometry measurements. It was also verified that the tested microfluidic systems are able to separate pathological blood samples, showing its potential to perform simultaneously separation and deformation assessments of blood diseases, such as malaria and diabetes.I want to acknowledge the financial support provided by scholarship SFRH/BD/99696/2014 from FCT (Science and Technology Foundation), COMPETE 2020, Portugal 2020 and POCH, that allow the successful development of this PhD project

Multi-parameter quantitative mapping of microfluidic devices

Fluorescence lifetime imaging microscopy (FLIM) is a powerful technique to non-invasively map the physical and chemical environment within microfluidic devices. In this work FLIM has been used in conjunction with a variety of other techniques to provide a greater insight into flow behaviour and fluid properties at the microscale. The pH-sensitive fluorescent dyes, fluorescein and C-SNARF 1, have been used to generate pH maps of microfluidic devices with a time-gated camera and a time-and-space-correlated single photon counting (TSCSPC) detector, respectively. Using time-gated detection and fluorescein, the fluorescence lifetime images allow for direct reading of the pH. The relative contribution to fluorescence of the acid and basic forms of C-SNARF 1 was spatially resolved on the basis of pre-exponential factors, giving quantitative mapping of the pH in the microfluidic device. Three dimensional maps of solvent composition have been generated using 2-photon excitation FLIM (2PE-FLIM) in order to observe the importance of gravitational effects in microfluidic devices. Two fluidic systems have been studied: glycerol concentration in the microfluidic device was measured using Kiton red; water concentration in a methanolic solution was measured using ANS. The density mismatch between two solutions of different composition induced a rotation of the interface between two streams travelling side by side in a microchannel. The experiment has provided evidence of non-negligible gravitational effects in microflows. 2PE-FLIM has superior capability than methods used previously to assess similar phenomena. FLIM and micro-particle imaging velocimetry (μ-PIV) have been implemented on a custom-built open frame microscope and used simultaneously for multimodal mapping of fluid properties and flow characteristics. It has been shown that viscosity mismatch between two streams induces a non-constant advective transport across the channel and results in a flow profile that deviates from the usual Poiseuille profile, characteristic of pressure driven flow in microfluidic devices

Micro/nano devices for blood analysis

[Excerpt] The development of microdevices for blood analysis is an interdisciplinary subject that demandsan integration of several research fields such as biotechnology, medicine, chemistry, informatics, optics,electronics, mechanics, and micro/nanotechnologies.Over the last few decades, there has been a notably fast development in the miniaturization ofmechanical microdevices, later known as microelectromechanical systems (MEMS), which combineelectrical and mechanical components at a microscale level. The integration of microflow and opticalcomponents in MEMS microdevices, as well as the development of micropumps and microvalves,have promoted the interest of several research fields dealing with fluid flow and transport phenomenahappening at microscale devices. [...