Numerical Investigation of Bubble Movement in Magnetic Nanofluids

Department of Mechanical EngineeringIn this study, the idea to generate electrical energy by using waste heat is suggested. In this idea, the electrical energy can be generated by a magnetic nanofluid and bubble movement. Thus, bubble movement in a magnetic fluid is numerically investigated using the commercial CFD package COMSOL Multiphysics for effective energy generation. The slug characteristics are also investigated because it can be generated by merging each bubble. The level-set method and phase-field method are used to simulate the bubble and slug movement, respectively. For the investigation, EFH1 and EFH3 are selected as working fluidsthey are commercial magnetic fluids manufactured by Ferrotec, and each fluid contains different amounts of magnetic particles. The solvers are validated by comparing the numerical results with previous research studies and experimental data for reliable results. The properties of a fluid can be changed by solid particles if the particles are dispersed in the fluid. These particles can affect the bubble and slug characteristics, such as shape, velocity and wake. Thus, the effect of solid particles is first studied by observing the bubble and slug movement in each magnetic fluid. In the slug investigation, the effects of some parameters are also studied, such as slug length and liquid backflow. The patterns of bubble and slug movement are investigated to predict the effective condition for the energy generation. The effective bubble and slug movements are predicted by evaluating the disturbance of the surrounding magnetic fluid for each flow pattern. A magnetic force can be created, and it can affect any phenomena when the magnetic field is applied to the system. Thus, the effect of the magnetic force is also investigated because the magnetic field should be applied to the system for the electrical energy generation. Finally, the important factor for energy generation is identified by comparing the results.ope

Recovery of magnetic catalysts: advanced design for process intensification

The design of microdevices in which components with magnetic character must be separated and recovered from reactive media benefits from the advantages of microfluidics and meets the criteria for process intensification; however, there are open questions, such as the design of the most appropriate magnet arrangement, that need further research in order to increase the magnetic gradient exerted on the particles. Herein, we focus on the continuous recovery of magnetic microparticles, that can be used as support to facilitate the recovery of biocatalysts (magnetic microcatalysts, MMCs) from biological fluids. We analyze and compare the performance of two typical magnetophoretic microdevices for addressing bead recovery: (i) annular channels with a quadrupole orientation of the permanent magnets (quadrupole magnetic sorter, QMS) and (ii) the standard design, which consists of rectangular channels with a single permanent magnet to generate the magnetic field. To this end, an experimentally validated computational fluid dynamics (CFD) numerical model has been employed. Our results reveal that for devices with the same width and length, the micro QMS, in comparison to a rectangular channel, could accomplish the complete particle retrieval while (i) processing more than 4 times higher fluid velocities, treating more than 360 times higher flow rates or (ii) working with smaller particles, thus reducing by 55% the particle mass. Additionally, the parallel performance of +/-300 micro-QMSs fulfills the processing of flow rates as high as 200 L·h-1 while entirely capturing the magnetic beads. Thereby, this work shows the potential of the QMS advanced design in the intensification of the recovery of catalysts supports of magnetic character.Financial support from the Spanish Ministry of Science, Innovation and Universities under the project RTI2018- 093310-B-I00 is gratefully acknowledged. Cristina González-Fernández acknowledges the FPU (FPU18/03525) postgraduate research grants. We also wish to thank the United States National Institutes of Health (1R01HL131720-01A1, CA62349) and the United States Defense Advanced Research Projects Agency (BAA07-21) for financial assistance

Modeling and Performance Analysis of A Sloshing Ferrofluid Based Electromagnetic Energy Harvester

Computational modeling and performance analysis are carried out for a ferrofluid based electromagnetic energy harvester which converts ambient vibratory energy into electromotive force through sloshing motion of a ferrofluid. The system consists of a tank partially filled with ferrofluid, magnets placed on the opposite sides of the tank and a copper coil wound around the tank. In the presence of an external magnetic field, magnetic dipoles in the ferrofluid rotate and produce a net magnetic moment aligned in the direction of the field. When the device is subjected to an external excitation, the ferrofluid in the tank undergoes a sloshing motion which induces a time-varying magnetization in the fluid, causing a time-varying magnetic flux and electromotive force in the copper coil according to Faraday\u27s law of induction. Compared to traditional solid-state vibratory energy harvesters, this liquid-state harvester provides better conformability, sensitivity, tunability and response bandwidth. This study provides useful insights for designing high performance ferrofluid based energy harvesters and is divided into three sections. First, A continuum level finite element model is developed and implemented for the multi-physics computational analysis of the energy harvester. The model solves the coupled magnetic scalar potential equation and Navier-Stokes equations for the dynamic behavior of the magnetic field and fluid motion. The model is validated against experimental results for eight configurations of the system. The validated model is then employed to study the underlying mechanisms that determine the electromotive force of the energy harvester. Furthermore, computational analysis is performed to test the effects of several modeling aspects, such as three-dimensional effect, surface tension and type of the ferrofluid-magnetic field coupling, on the accuracy of the model prediction. Second, a series of numerical simulations are performed to investigate the influence of several design parameters on the electromotive force of the energy harvester. From the eight configurations used for model validation, two configurations that give the highest electromotive forces are chosen for further performance analysis. The design parameters considered in this investigation include the device\u27s geometric parameters, external excitation amplitude and material properties of the ferrofluid, which affect either the magnetic flux in the device or the sloshing behavior of the ferrofluid. Third, non-equilibrium molecular dynamics (NEMD) simulations are employed to obtain an understanding of the dynamic magnetization behavior of the ferromagnetic nano-particles and microscopic structures of the ferrofluid. The results from the continuum level numerical simulations reveal that the magnetic susceptibility/magnetization of ferrofluid greatly influences the performance of the energy harvester. Since the ferrofluid in the energy harvester undergoes sloshing motion under external mechanical excitations, it is also expected that fluid motion would significantly influence the aggregation behavior of the nano-particles, thereby playing an important role in determining the magnetization of the ferrofluid and the performance of the energy harvester. In this study, ferrofluid systems containing both small and large particles under the influence of both magnetic field and shear flow are considered. The computational model involves long-range dipolar interaction as well as short-range repulsive interaction of the nano-particles. The factors investigated include solvent friction coefficients, particle size, magnetic field strength and direction, and shear rate

Study on Removal of Particles from Used Turbine Oil

Turbine oil is usually use in gas turbines, and other applications requiring supreme quality turbine oil. Turbine oil cleanliness continues to cause concern because to have optimum performance the oil has to be significantly clean. The current inventions of turbine oil filtration are widely categorized under different types of filtration methods depending on its objectives or applications. The existence of iron components in industrial turbine oil makes magnetic filter is the effective tools for capturing as well as recycling of small sized magnetic particles. Turbine oil correction can be quite exhaustive and detailed in nature. Most commercial oil analysis laboratories do not have this capability or technical expertise. Some of the machines also very bulky and not portable. This problem had inspired the author to develop a new design of magnetic filter which is smaller in size and simpler process to remove particles from used turbine oils. The method used in designing the magnetic filter are modeling and simulation software.After performing calculations and software simulation, the best method in filtering particles in used turbine oil is by using off-line magnetic filter. Agitation is introduced in getting optimum result

Magnetic Nanoparticle Enhanced Actuation Strategy for mixing, separation, and detection of biomolecules in a Microfluidic Lab-on-a-Chip System

Magnetic nanoparticle (MNP) combined with biomolecules in a microfluidic system can be efficiently used in various applications such as mixing, pre-concentration, separation and detection. They can be either integrated for point-of care applications or used individually in the area of bio-defense, drug delivery, medical diagnostics, and pharmaceutical development. The interaction of magnetic fields with magnetic nanoparticles in microfluidic flows will allow simplifying the complexity of the present generation separation and detection systems. The ability to understand the dynamics of these interactions is a prerequisite for designing and developing more efficient systems. Therefore, in this work proof-of-concept experiments are combined with advanced numerical simulation to design, develop and optimize the magnetic microfluidic systems for mixing, separation and detection. Different strategies to combine magnetism with microfluidic technology are explored; a time-dependent magnetic actuation is used for efficiently mixing low volume of samples whereas tangential microfluidic channels were fabricated to demonstrate a simple low cost magnetic switching for continuous separation of biomolecules. A simple low cost generic microfluidic platform is developed using assembly of readily available permanent magnets and electromagnets. Microfluidic channels were fabricated at much lower cost and with a faster construction time using our in-house developed micromolding technique that does not require a clean room. Residence-time distribution (RTD) analysis obtained using dynamic light scattering data from samples was successfully used for the first time in microfluidic system to characterize the performance. Both advanced multiphysics finite element models and proof of concept experimentation demonstrates that MNPs when tagged with biomolecules can be easily manipulated within the microchannel. They can be precisely captured, separated or detected with high efficiency and ease of operation. Presence of MNPs together with time-dependent magnetic actuation also helps in mixing as well as tagging biomolecules on chip, which is useful for point-of-care applications. The advanced mathematical model that takes into account mass and momentum transport, convection & diffusion, magnetic body forces acting on magnetic nanoparticles further demonstrates that the performance of microfluidic surface-based bio-assay can be increased by incorporating the idea of magnetic actuation. The numerical simulations were helpful in testing and optimizing key design parameters and demonstrated that fluid flow rate, magnetic field strength, and magnetic nanoparticle size had dramatic impact on the performance of microfluidic systems studied. This work will also emphasize the importance of considering magnetic nanoparticles interactions for a complete design of magnetic nanoparticle-based Lab-on-a-chip system where all the laboratory unit operations can be easily integrated. The strategy demonstrated in this work will not only be easy to implement but also allows for versatile biochip design rules and provides a simple approach to integrate external elements for enhancing mixing, separation and detection of biomolecules. The vast applications of this novel concept studied in this work demonstrate its potential of to be applied to other kinds of on-chip immunoassays in future. We think that the possibility of integrating magnetism with microfluidic-based bioassay on a disposable chip is a very promising and versatile approach for point-of care diagnostics especially in resource-limited settings

A novel phenomenological model for dynamic behavior of magnetorheological elastomers in tension-compression mode

Tension-compression operation in MR elastomers (MREs) offers both the most compact design and superior stiffness in many vertical load-bearing applications, such as MRE bearing isolators in bridges and buildings, suspension systems and engine mounts in cars, and vibration control equipment. It suffers, however, from lack of good computational models to predict device performance, and as a result shear-mode MREs are widely used in the industry, despite their low stiffness and load-bearing capacity. We start with a comprehensive review of modeling of MREs and their dynamic characteristics, showing previous studies have mostly focused on dynamic behavior of MREs in shear mode, though the MRE strength and MR effect are greatly decreased at high strain amplitudes, due to increasing distance between the magnetic particles. Moreover, the characteristic parameters of the current models assume either frequency, or strain, or magnetic field are constant; hence, new model parameters must be recalculated for new loading conditions. This is an experimentally time consuming and computationally expensive task, and no models capture the full dynamic behavior of the MREs at all loading conditions. In this study, we present an experimental setup to test MREs in a coupled tension-compression mode, as well as a novel phenomenological model which fully predicts the stress-strain material behavior as a function of magnetic flux density, loading frequency and strain. We use a training set of experiments to find the experimentally derived model parameters, from which can predict by interpolation the MRE behavior in a relatively large continuous range of frequency, strain and magnetic field. We also challenge the model to make extrapolating predictions and compare to additional experiments outside the training experimental data set with good agreement. Further development of this model would allow design and control of engineering structures equipped with tension-compression MREs and all the advantages they offer.We acknowledge funding from the European Research Council grant EMATTER 280078

Continuous focusing and separation of microparticles with acoustic and magnetic fields

Microfluidics enables a diverse range of manipulations (e.g., focusing, separating, trapping, and enriching) of micrometer-sized objects, and has played an increasingly important role for applications that involve single cell biology and the detection and diagnosis of diseases. In microfluidic devices, methods that are commonly used to manipulate cells or particles include the utilization of hydrodynamic effects and externally applied field gradients that induce forces on cells/particles, such as electrical fields, optical fields, magnetic fields, and acoustic fields. However, these conventional methods often involve complex designs or strongly depend on the properties of the flow medium or the interaction between the fluid and fluidic channels, so this dissertation aims to propose and demonstrate novel and low-cost techniques to fabricate microfluidic devices to separate microparticles with different sizes, materials and shapes by the optimized acoustic and magnetic fields. The first method is to utilize acoustic bubble-enhanced pinched flow for microparticle separation; the microfluidic separation of magnetic particles with soft magnetic microstructures is achieved in the second part; the third technique separates and focuses microparticles by multiphase ferrofluid flows; the fourth method realizes the fabrication and integration of microscale permanent magnets for particle separation in microfluidics; magnetic separation of microparticles by shape is proposed in the fifth technique. The methods demonstrated in this dissertation not only address some of the limitations of conventional microdevices, but also provide simple and efficient method for the separation of microparticles and biological cells with different sizes, materials and shapes, and will benefit practical microfluidic platforms concerning micron sized particles/cells --Abstract, page iv