Investigation into ferrofluid magnetoviscous effects under an oscillating shear flow

Pinho, Marcos; Brouard, Bruno; Génevaux, Jean-Michel; Lanfranchi, Vincent; Volkova, Olga; Mezière, Hervé; Collas, Patrick

doi:10.1016/j.jmmm.2011.05.002

Cited by 15 publications

(6 citation statements)

References 17 publications

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“…These chains increase the resistance to the flow, thereby increasing viscosity. This is consistent with previous studies [8,[18][19][20][21].…”

Section: Transport Properties Viscositysupporting

confidence: 94%

“…Table A2 in the appendix compiles past experimental results for ferrofluid viscosity. Past experimental results have agreed that viscosity increases with an increasing solid volume concentration and magnetic flux strength, and viscosity decreases with increasing temperature [8,[18][19][20][21]. Li et al [18] and Wang et al [19] found that the rate of increase in viscosity is reduced with increasing solid volume concentration, magnetic flux strength and temperature.…”

Section: 2mentioning

confidence: 77%

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Ferrofluids for heat transfer enhancement under an external magnetic field

Gui

Stanley

Nguyen

et al. 2018

International Journal of Heat and Mass Transfer

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Overheating of power electronic devices has become a significant issue due to their continued miniaturization and increased heat flux that needs to be dissipated. Ferrofluids (magnetic nanofluids) have been shown to have higher thermal conductivity than their base aqueous or oil based fluids due to the solid magnetic nanoparticles that make up the ferrofluid. This allows higher convective heat transfer rates and, importantly, the ability to externally effect the flow using a magnetic field. In this paper, we focus on material characterization of ferrofluids and measurement of heat transfer rates for single-phase ferrofluidic forced convective flow in microchannels. We show that heat transfer properties of the flow are enhanced with the use of ferrofluids and that the material make-up of the ferrofluid affects these properties. In this paper, we argue that generally, convective heat transfer rates for ferrofluids are increased by increasing the solid volume concentration of magnetic particles (~0.2-0.4%). Interestingly, increasing magnetic flux was shown to decrease heat transfer enhancement. This was due to a reduction in the thermal conductivity of the bulk fluid caused by magnetic nanoparticles being drawn out of the isotropic mixture and becoming pinned to the channel wall in the region of strongest magnetic field. We show that there is good correlation between both theory and experimental visualization of this phenomenon.

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“…These chains increase the resistance to the flow, thereby increasing viscosity. This is consistent with previous studies [8,[18][19][20][21].…”

Section: Transport Properties Viscositysupporting

confidence: 94%

Section: 2mentioning

confidence: 77%

Ferrofluids for heat transfer enhancement under an external magnetic field

Gui

Stanley

Nguyen

et al. 2018

International Journal of Heat and Mass Transfer

View full text Add to dashboard Cite

show abstract

“…It is also observed that the critical strain marking the onset of nonlinearity decreases with magnetic field up to 160 mT and slightly increases thereafter. The response of ferrofluid to an oscillatory shear studied by Pinho et al 29 reveals that the viscosity increases with magnetic field and monotonically decreases with oscillation frequency. A similar observation was recorded for the viscous damping force on an oscillating plate in contact with ferrofluid subjected to a constant magnetic field.…”

Section: Resultsmentioning

confidence: 99%

“…On the other hand, ferrofluids with fairly monodisperse particles and excellent long-term stability can be tailored. The magneto-rheological properties of ferrofluids have been studied both theoretically and experimentally. , Though steady shear behavior of ferrofluids has been well characterized, only a few studies concentrate on their oscillatory behavior, , where the particles are considered to be noninteracting.…”

Section: Introductionmentioning

confidence: 99%

Probing of Field-Induced Structures and Their Dynamics in Ferrofluids Using Oscillatory Rheology

Felicia

Philip

2014

Langmuir

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We probe field-induced structures and their dynamics in ferrofluids using oscillatory rheology. The magnetic field dependence of the relaxation time and crossover modulus showed two distinct regions, indicating the different microstructures in those regions. The observed relaxation at various magnetic field strengths indicates that side chains are attached to the pinned single-sphere-width chains between the rheometer plates. Our results suggest that the ferrofluid under a magnetic field exhibits a soft solidlike behavior whose relaxation is governed by the imposed strain rate and the magnetic field. Using the scaling factors obtained from the frequency and modulus at the crossover point in the oscillatory rheological measurements, the constant strain-rate frequency sweep data is superimposed onto a single master curve. The frequency scaling factor increases with the strain rate as a power law with an exponent close to unity, whereas the amplitude scaling factor is almost strain-rate-independent at high magnetic field strengths. These findings are useful for a better understanding of field-induced ordering of nanoparticles in fluids and their optimization for practical applications.

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“…Surprisingly, oscillatory shear experiments have received little application in the study of ferrofluids, even though chain formation, deformation, and breakage are also important processes that determine the magnetorheological properties of ferrofluids [47]. Recently, Pinho et al [48] reported a series of oscillatory shear measurements with commercial ferrofluids in applied magnetic fields. They only reported viscous damping of the force on an oscillating plate in contact with ferrofluid subjected to a constant magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Oscillatory shear response of dilute ferrofluids: Predictions from rotational Brownian dynamics simulations and ferrohydrodynamics modeling

2011

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Ferrofluids are colloidal suspensions of magnetic nanoparticles that exhibit normal liquid behavior in the absence of magnetic fields but respond to imposed magnetic fields by changing their viscosity without loss of fluidity. The response of ferrofluids to constant shear and magnetic fields has received a lot of attention, but the response of ferrofluids to oscillatory shear remains largely unexplored. In the present work we used rotational Brownian dynamics to study the dynamic properties of ferrofluids with thermally blocked nanoparticles under oscillatory shear and constant magnetic fields. Comparisons between simulations and modeling using the ferrohydrodynamics equations were also made. Simulation results show that, for small rotational Péclet number, the in-phase and out-of-phase components of the complex viscosity depend on the magnitude of the magnetic field and frequency of the shear, following a Maxwell-like model with field-dependent viscosity and characteristic time equal to the field-dependent transverse magnetic relaxation time of the nanoparticles. Comparison between simulations and the numerical solution of the ferrohydrodynamic equations shows that the oscillatory rotational magnetoviscosity for an oscillating shear field obtained using the kinetic magnetization relaxation equation quantitatively agrees with simulations for a wide range of Péclet number and Langevin parameter but has quantitative deviations from the simulations at high values of the Langevin parameter. These predictions indicate an apparent elastic character to the rheology of these suspensions, even though we are considering the infinitely dilute limit in which there are negligible particle-particle interactions and, as such, chains do not form. Additionally, an asymptotic analytical solution of the ferrohydrodynamics equations, valid for Pe<<2, was used to demonstrate that the Cox-Merz rule applies for dilute ferrofluids under conditions of small shear rates. At higher shear rates the Cox-Merz rule ceases to apply.

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Investigation into ferrofluid magnetoviscous effects under an oscillating shear flow

Cited by 15 publications

References 17 publications

Ferrofluids for heat transfer enhancement under an external magnetic field

Ferrofluids for heat transfer enhancement under an external magnetic field

Probing of Field-Induced Structures and Their Dynamics in Ferrofluids Using Oscillatory Rheology

Oscillatory shear response of dilute ferrofluids: Predictions from rotational Brownian dynamics simulations and ferrohydrodynamics modeling

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