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Circulating tumor cells (CTCs) largely contribute to cancer metastasis and show potential prognostic significance in cancer isolation and detection. Miniaturization has progressed significantly in the last decade which in turn enabled the development of several microfluidic systems. The microfluidic systems offer a controlled microenvironment for studies of fundamental cell biology, resulting in the rapid development of microfluidic isolation of CTCs. Due to the inherent ability of magnets to provide forces at a distance, the technology of CTCs isolation based on the magnetophoresis mechanism has become a routine methodology. This historical review aims to introduce two principles of magnetic isolation and recent techniques, facilitating research in this field and providing alternatives for researchers in their study of magnetic isolation. Researchers intend to promote effective CTC isolation and analysis as well as active development of next‐generation cancer treatment. The first part of this review summarizes the primary principles based on positive and negative magnetophoretic isolation and describes the metrics for isolation performance. The second part presents a detailed overview of the factors that affect the performance of CTC magnetic isolation, including the magnetic field sources, functionalized magnetic nanoparticles, magnetic fluids, and magnetically driven microfluidic systems. [ABSTRACT FROM AUTHOR]

The paper presents a concept of thermal-to-electrical energy conversion by using the oscillatory motion of magnetic fluid slugs which has potential to be applied in the field of sensors. A pulsating heat pipe (PHP) is introduced to produce vapor-magnetic fluid plug–slug flow in a snake-shaped capillary tube. As the magnetic fluid is magnetized by the permanent magnet, the slugs of magnetic fluid passing through the copper coils make the magnetic flux vary and produce the electromotive force. The peak values of induced voltage observed in our tests are from 0.1 mV to 4.4 mV. The effects of the slug velocity, heat input and magnetic particle volume concentration on the electromotive force are discussed. Furthermore, a theoretical model considering the fluid velocity of the working fluid, the inner radius of the PHP and the contact angle between the working fluid and the pipe wall is established. At the same time, the theoretical and experimental results are compared, and the influences of tube inner radius, working fluid velocity and contact angle on the induced electromotive force are analyzed. [ABSTRACT FROM AUTHOR]

The ability to focus biological particles into a designated position of a microchannel is vital for various biological applications. This paper reports particle focusing under vertical and inclined magnetic fields. We analyzed the effect of the angle of rotation (θ) of the permanent magnets and the critical Reynolds number (Rec) on the particle focusing in depth. We found that a rotation angle of 10° is preferred; a particle loop has formed when Re < Rec and Rec of the inclined magnetic field is larger than that of the vertical magnetic field. We also conducted experiments with polystyrene particles (10.4 μm in diameter) to prove the calculations. Experimental results show that the focusing effectiveness improved with increasing applied magnetic field strength or decreasing inlet flow rate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Behaviors of a ferrofluid droplet in vertical gradient magnetic fields were studied. [•] The droplet undergoes significant deformation as increasing the field gradient. [•] A theoretical model is proposed to predict the droplet velocity. [•] Velocity depends on field gradient, droplet size and surrounding liquid viscosity. [•] Interaction of a pair of droplets under current magnetic fields was also studied. [Copyright &y& Elsevier]

• A concept of kinetic-to-electrical energy conversion is presented. • The idea can be used as a non-contact sensor to monitor the flow state. • Formula to explain the variation of the electromotive force is derived. • The corresponding voltage waveforms of flow patterns are obtained. This paper presents a mechanical-to-electrical energy conversion concept by using the upward movement of air bubbles in ferrofluids. As ferrofluids are magnetized by a magnetic field, the air bubbles passing through the induction coils will change magnetic flux in the coils and produce electromotive force. Therefore, the kinetic energy of air bubbles converts into electricity. The idea possesses a promising prospect to be applied in the non-contact sensor field, which can monitor the flow states of boiling two-phase flow in a heat exchanger and warn the deterioration of heat transfer. A millivolt-level induced voltage with a waveform like a sine wave can be generated. The induced voltage's peak value is approximately proportional to the air bubble's volume and velocity and tends to saturate as the magnetic field strength increases. [ABSTRACT FROM AUTHOR]

Ferrofluids have more excellent thermal performance than their carrier liquids, but the magnetoviscous effects under magnetic fields will increase the flow resistance to weaken this enhancement. We investigated the flow and convective heat transfer performance of ferrofluids in the tube under a magnetic field by the experimental method. A non-magnetic stainless-steel tube with 476 mm length and an inner diameter of 2.46 mm is used in our test. The maximum field intensity ranges from 22 to 97.2 kA/m. The friction coefficient and Nusselt number for water and ferrofluids are measured and compared under various conditions, including Reynolds number, nanoparticles concentration, magnetic field strength, heat flux, and magnets arrangement mode. The results indicate that the magnetoviscous effects induced by the external fields offset the possible convective heat transfer enhancement, which challenges the current view that ferrofluids can be used as a potential heat transfer medium, especially in a strong magnetic field. • Two arrangements of permanent magnets are designed. • Magnetoviscous effect is greatly affected by particle concentration. • A higher particle concentration of ferrofluids increases the laminar friction coefficient. • Strong magnetic field weakens the heat transfer due to magnetoviscous effects. [ABSTRACT FROM AUTHOR]