Recently, the suspension of hybrid nanoparticles in conventional fluids has been investigated as a technique for improving the thermophysical properties of nanofluids. The dearth of documentation on ...the trio influence of volume concentration, base fluid, and temperature on the electrical conductivity and viscosity of hybrid alumina–ferrofluids Al
2
O
3
–Fe
2
O
3
(25:75 mass%) has led to this study. The effective viscosity and electrical conductivity of the deionized water (DW)-based and ethylene glycol (EG)–DW-based (50:50 vol%) hybrid alumina–ferrofluids were measured at temperatures of 20–50 °C and volume concentrations of 0.05–0.75%. Based on the importance of soft computing methods to engineers, adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) were used for predicting the relative viscosity and electrical conductivity of the two types of hybrid ferrofluids. The measured data for viscosity and electrical conductivity were used in the modeling. Model performances were evaluated using the root mean squared error index. Viscosity was enhanced by 3.23–43.64% and 2.79–49.38%, while electrical conductivity was increased by 163.37–1692.16% and 717.14–7618.89% for the DW- and EG–DIW-based hybrid ferrofluids, respectively, compared with the respective base fluids. Increasing volume concentration augmented the viscosity and electrical conductivity of all the hybrid alumina–ferrofluids, whereas a rise in temperature enhanced their electrical conductivity and detracted the viscosity. DW-based hybrid alumina–ferrofluid was observed to have a lower viscosity and higher electrical conductivity than the EG–DW-based counterpart. The results showed that the optimum ANN and ANFIS models have a maximum error of less than 4.5% and 3.9% for relative viscosity and electrical conductivity, respectively, which were lower than those proposed using regression analysis. With the hybrid alumina–ferrofluids possessing a lower viscosity relative to single-particle ferrofluids, they are recommended for engineering application.
Developing microrobots with multiple deformabilities has become extremely challenging due to the lack of materials that are soft enough at the microscale level and the inability to be reconfigured ...after fabrication. In this study, it is aimed to prove that liquid microrobots composed of ferrofluid droplets are inherently deformable and they can be controlled, individually or in aggregate, with multiple programmable deformabilities. For example, the liquid‐microrobot monomer (LRM) can pass through narrow channels via elongation and achieve scaling via splitting and coalescence. LRMs can also reassemble into various kinds of functional liquid‐robot aggregates, such as microsticks, micropies, microtrains, microkayaks, and microrollingpins. Thus, they can respond to multi‐terrain surfaces or perform various complex tasks. Moreover, the authors' physics‐based theoretical model demonstrates dynamic self‐assembly and group behavior of a multiple LRM system, which is conducive to investigating the mechanisms behind it. These ferrofluid droplet robots provide novel solutions for some potential applications, such as untethered micromanipulation and targeted cargo delivery.
Liquid microrobots composed of ferrofluid droplets with multiple deformabilities are designed in this work. The resulting microrobots can be controlled individually or in aggregate to achieve many complex tasks, such as crossing narrow channels, collectively passing through gullies and transporting multiple, large objects. This approach presents a valuable avenue for drug delivery and manipulation on a micro scale.
•A flat-plate solar collector with ferrofluid under magnetic field is studied.•Without magnetic field, the collector's efficiency increased with flow rate increase.•Without field, the maximum ...efficiency increase is 39.9% for 0.8 vol% and 0.05 kg/s.•The field effect on the efficiency enhancement increased with decreasing flow rate.•The maximum efficiency enhancement of is 52.15% for 0.8 vol%, 0.0083 kg/s, 1.0 T.
Mn–Zn Fe2O4 magnetic nanoparticles have high magnetization capability. They can be stimulated well with an external magnetic field for producing a high magnetic body force, which is added to the momentum equation. Applying an Mn–Zn Fe2O4 ferrofluid in a flat-plate solar collector influenced by a strong magnetic field can be a compelling method in improving the thermal efficiency of the collector compared with other nanofluid-based ones. This experimental investigation, for the first time, presents an Mn–Zn Fe2O4/water ferrofluid-based flat-plate solar collector, equipped with a set of permanent magnets, to study the impact of the non-uniform magnetic field on the collector efficiency based on ASHRAE Standard. Simultaneous effect of the various parameters like the nanoparticles volume fraction (φ = 0, 0.2, 0.4, and 0.8%), the fluid flow rate (ṁ = 0.0083–0.05 kg/s), and the remanent magnetization of the magnets (Br = 0.0–1.0 T) on the collector efficiency have been taken into the consideration. According to the results, using the ferrofluid-based collector has a relatively significant impact on the collector efficiency than other nanofluid-based collectors. For the ferrofluid case studies without a magnetic field, the maximum enhancement in the collector efficiency compared to water is 39.9% for the case with φ = 0.8% and ṁ = 0.05 kg/s. Also, when the magnets are used, the collector efficiency is improved with volume fraction augmentation and decreasing the fluid flow rate. Finally, with applying the magnetic field, the maximum enhancement in the efficiency has been 52.15% obtained for φ = 0.8%, ṁ = 0.0083 kg/s, and Br = 1.0 T.
Ferrofluids exhibit unusual hydrodynamic effects owing to the magnetic nature of their constituents. As magnetization increases, a classical ferrofluid undergoes a Rosensweig instability and creates ...self-organized, ordered surface structures or droplet crystals. Quantum ferrofluids such as Bose-Einstein condensates with strong dipolar interactions also display superfluidity. The field of dipolar quantum gases is motivated by the search for new phases of matter that break continuous symmetries. The simultaneous breaking of continuous symmetries such as the phase invariance in a superfluid state and the translational symmetry in a crystal provides the basis for these new states of matter. However, interaction-induced crystallization in a superfluid has not yet been observed. Here we use in situ imaging to directly observe the spontaneous transition from an unstructured superfluid to an ordered arrangement of droplets in an atomic dysprosium Bose-Einstein condensate. By using a Feshbach resonance to control the interparticle interactions, we induce a finite-wavelength instability and observe discrete droplets in a triangular structure, the number of which grows as the number of atoms increases. We find that these structured states are surprisingly long-lived and observe hysteretic behaviour, which is typical for a crystallization process and in close analogy to the Rosensweig instability. Our system exhibits both superfluidity and, as we show here, spontaneous translational symmetry breaking. Although our observations do not probe superfluidity in the structured states, if the droplets establish a common phase via weak links, then our system is a very good candidate for a supersolid ground state.
•The SAXS is well described in terms of independent aggregates for dilute ferrofluids.•The effective structure-factor analysis revealed secondary aggregation for concentrated ferrofluids.•Particle ...correlations in the aggregate are dependent on the surfactant coating.
Small-angle X-ray scattering is applied to study particle correlations in concentrated (up to 7.5 vol% magnetite) aqueous magnetic fluids with double-layer coating by either oleic or lauric acids. The structure of aggregates in these fluids is analyzed when diluting samples with the goal of finding out a concentration threshold at which the aggregates can be considered weakly interacting independent formations. For dilute systems, suitable models fitting experimental scattering curves are proposed, which take into account the polydispersity of both particles and aggregates. It is shown that particle correlations found in aggregates are dependent on the surfactant coating.
Droplet Manipulation
In article number 2100178, Fernando Benito‐Lopez, Lourdes Basabe‐Desmonts, and Vahid Nasirimarekani show that the interaction between an oil‐based ferrofluid and a drop of water ...results in the formation of a ferrofluid ring around the drop of water. The ring behaves like a soft matter dipole, disappearing once the magnetic field is removed. The set takes the shape of a cupcake and allows precise movement of the drop on a surface, even on inverted surfaces.
Tunable Superparamagnetic Ring Nasirimarekani, Vahid; Fernando Benito‐Lopez; Lourdes Basabe‐Desmonts
Advanced functional materials,
08/2021, Letnik:
31, Številka:
32
Journal Article
Recenzirano
Droplet ManipulationIn article number 2100178, Fernando Benito‐Lopez, Lourdes Basabe‐Desmonts, and Vahid Nasirimarekani show that the interaction between an oil‐based ferrofluid and a drop of water ...results in the formation of a ferrofluid ring around the drop of water. The ring behaves like a soft matter dipole, disappearing once the magnetic field is removed. The set takes the shape of a cupcake and allows precise movement of the drop on a surface, even on inverted surfaces.
Many astonishing biological collective behaviors exist in nature, and artificial microrobotic swarms have been developed by emulating these scenarios. However, these microswarms typically have single ...structures and lack the adaptability that many biological swarms exhibit to thrive in complex environments. Inspired by viscoelastic fire ant aggregations and using a combination of experiment and simulation, a strategy to trigger ferrofluid droplets into forming microswarms exhibiting both liquid‐like and solid‐like behaviors is reported. By spatiotemporally programming an applied magnetic field, microswarms can be liquefied to implement reversible elongation with a high aspect ratio and solidified into entireties to perform overturning and bending behaviors. It is demonstrated that reconfigurability enables the microswarm to be a mobile dexterous micromanipulator, acting not only as a soft “octopus arm” to explore a confined environment and grasp a targeted object but also adaptively navigate multiple terrains, such as uneven surfaces, curved grooves, complex mazes, high steps, narrow channels, and even wide gaps. This microrobotic swarm can reconfigure both shapes and tasks based on the demands of the environment, presenting novel solutions for a variety of applications.
Inspired by viscoelastic fire ant aggregations, the ferrofluid microdroplets are triggered into microswarms with both liquid‐like and solid‐like behavior by spatiotemporally programming an applied magnetic field. This microrobotic swarm has flexibility, adaptability, and polymorphism and so may inspire investigations of the fundamentals of biological swarms and presents novel solutions for a variety of applications.
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•On-demand ferrofluid drop formation at a T-junction by a magnetic pulse is studied.•The drop generation under a Pulse-Width-Modulation magnetic field was investigated.•A new kind of ...drop formation named as beating regime is observed for the first time.•The regime map is presented in terms of magnetic Bond and Capillary numbers.•A correlation for predicting the dimensionless drop diameter is presented.
Micro-magnetofluidics offers a promising tool to regulate the drop formation process with versatile applications in engineering and biomedicine. In the present study, on-demand ferrofluid drop generation at a T-junction is investigated utilizing a magnetic pulse. Also, a novel method for ferrofluid droplet formation is introduced using a non-uniform Pulse-Width Modulation (PWM) magnetic field. A novel mechanism of drop generation named “beating regime” was seen for the first time in which the ferrofluid moves back and forth before the breakup. The effect of the magnetic induction, continuous phase flow rate, duty cycle, and applied frequency on the generation frequency and drop diameter was investigated under the PWM magnetic field and compared with those under the DC magnetic field. The results showed that greater values of drop diameter and generation frequency are obtained either when the magnetic induction and/or duty cycle increases or when the applied frequency decreases. The regime maps of ferrofluid droplet formation were presented for different magnetic Bond and Capillary numbers under both PWM and DC magnetic fields and compared with each other. Finally, a correlation was presented to estimate the dimensionless drop diameter on the basis of four nondimensionalized parameters, showing a 7.2 % average relative error.
Abstract
The necessity of the magnetic track research from the moving object is substantiated. An optical system has been developed to detect a magnetic track at sea depth from the moving magnetic ...object. A method of processing and decoding optical images formed using a ferrofluid cell and laser radiation is proposed. The results of experimental studies are presented.
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