The investigated ferrofluid was divided into three samples and placed in identical transparent glass vials.

The paper reports on the effect of prolonged exposure to light of a water-based ferrofluid, with magnetite particles, double stabilized with oleic acid, on its low frequency complex magnetic permeability. In addition, we also explain how the magnetic fluid transmits its magnetic force to the stator and rotor, respectively. Numerical analysis and experimental results show the validity of this approach. Then, we show that the virtual work principle in appropriate approach can calculate the output torque of the nonmagnetic rotor due to pressure of the magnetic fluid. To illustrate this, we use an experimental motor made of a nonmagnetic rotor immersed in a magnetic fluid. To resolve this problem, this paper shows that the calculation of the torque of these applications should not only use the magnetic force calculation method, but also consider the mechanical pressure using an indirect approach, such as the virtual work principle. However, obtaining magnetic body force density is still under controversy. The standard method is to solve the Navier–Stokes equation. If the magnetic fluid is involved, the force and torque also include the effect of pressure caused by the fluid. In magnetomechanical applications, it is necessary to calculate the magnetic force or torque of specific objects. This pump is then compared with similar pumps developed in the past. Phase separation is also carried out with an existing decanter design, modified using electromagnetism to work without a selective membrane, usually necessary for phase separation at this scale. To operate this pump continuously and to be able to regulate the phase ratio, an electromagnetic non-invasive valve is developed. Conveying concepts using permanent magnets in the immediate vicinity of the flow are investigated. It uses magnetic gradients to manipulate two-phase flow, one of which is a magnetically active phase. A considerably energy-efficient, non-invasive alternative, with reduced mechanical interfacing is suggested in this work. The microflow is also disturbed by the invasive nature of these pumps.

Micro-gear pumps and syringe pumps, with their traditional mechanical components, result in parts degrading over time due to fatigue caused by pressure differentials and corrosive chemicals. A ferrofluid with reproducible properties is produced and, together with another phase, stable slug flow is generated. This work aids in this by using magnetofluidics to manipulate these parameters. Knowledge of the flow properties in microchannels along variables’ controllability (e.g., phase ratio, slug length along with classical variables, such as pressure, temperature, and flow velocity) during operation is crucial. Liquid–liquid slug flow in a microcapillary, with its improved heat and mass transfer properties and narrow residence time, plays a vital role in process intensification. The originality of this study is that it uses visualization to describe the current state of research and development patterns instead of thousands of papers, providing valuable reference information for existing researchers and practitioners. Finally, by analyzing the current status of each application, we summarize two challenges, that is to strengthen the research on the micromechanism of ferrofluid and to prepare a ferrofluid with better performance. Next, we focus on ferrofluid applications in six engineering fields and summarize the development history and research status. In particular, we draw connections between publication year and novel engineering applications and show how they impact future development-the increasing use of ferrofluids in microfluidic environments and the increasing study of their soft and reshapable properties. This list greatly helps researchers to understand the authoritative papers as well as the latest results. By analyzing the number of papers and citations at a given institution, we obtained a list of influential institutions and schools and indicated the current research directions of these institutions.

Visualization to highlight important schools and organizations.

We have got several important research directions (basic physics research, medical applications, and engineering applications) using keywords as an entry point by visualizing the cluster analysis. To obtain systematic analytical results and to help researchers gain insight into the dynamics of ferrofluid research, in this review, we first track and summarize the ferrofluid research over the past 15 years to assay how ferrofluid can contribute to modern technology. With the broader use of ferrofluid in industry and the sciences, ferrofluid research has produced many new branches.

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