Effective viscosity of magnetic nanofluids through capillaries

Rajesh Patel

Phys. Rev. E 85, 026316 – Published 23 February 2012

Abstract

The simultaneous effect of magnetic field and temperature on the capillary viscosity of magnetic nanofluid is an important parameter for a new class of applications such as nanoduct flow, nanomotors, micro- and nanofluidic devices, for transformer cooling, magnetic targeted drug delivery, etc. The effective viscosity of a nanofluid is explained based on the rotation of the particles and the effect of torque on it due to an externally applied magnetic field. Two types of fluids are used here, temperature-sensitive and non-temperature-sensitive magnetic nanofluids. In both types of fluids, decrease in effective viscosity with temperature is observed, but in both cases the mechanism for the decrement is quite different. One is due to temperature dependence of the magnetic moment and the other is due to removal of the secondary surfactant. For temperature-sensitive magnetic nanofluids, a Curie temperature of $\sim$ 80 $^{\circ}$ C is extracted from this study. For non-temperature-sensitive magnetic nanofluids $\sim$ 65 $%$ of the secondary surfactant is removed for a change in temperature, $Δ$ $T$ $=$ 40 $^{\circ}$ C. This is analogous with removal of a drug from magnetic particles for targeted drug delivery. Further, a linear dependence of effective viscosity with different capillary size and $ξ$ (angle between magnetic field and flow direction, $ξ$ $\in$ [0, $π$ /2]) is also observed. This linear dependence can also be a good approximation for the study of magnetic drug targeting, as in the human body the capillaries are of different sizes, and the externally applied magnetic field is not always parallel or perpendicular to the drug flow direction.

Received 10 May 2011

DOI:https://doi.org/10.1103/PhysRevE.85.026316

Authors & Affiliations

Rajesh Patel^*

Department of Physics, Bhavangar University, Bhavnagar 364022, Gujarat, India

^*rjp@bhavuni.edu; rpat7@yahoo.com

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Issue

Vol. 85, Iss. 2 — February 2012

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Images

Figure 1
Effective viscosity of magnetic nanofluid as a function of magnetic field in two directions, parallel to the flow direction and perpendicular to the flow direction. It is observed that $Δ$ $η$ $_{∥}$ ≈ 2 $Δ$ $η$ $_{⊥}$ . The solid line is fit to Eq. (1).Reuse & Permissions
Figure 2
(a) Schematic of the particle rotation, flow direction, and angular dependence of applied magnetic field with respect to the flow direction. (b) Effective viscosity as a function of magnetic field intensity for different angles, $ξ$ , which is the angle between direction of magnetic field intensity and the flow direction. The solid line is fit to Eq. (1). (c) Linear relation between effective viscosity and the angle $ξ$ .Reuse & Permissions
Figure 3
Effective viscosity as a function of magnetic field for different capillary diameters. Here the direction of the magnetic field is kept perpendicular to the flow direction. As the diameter of the capillary decreases, the hindrance to the rotation of the particle increases due to increase in the local density of magnetic particles within the magnetic field region, causing the increase in the effective viscosity of the nanofluid. The inset shows the linear relation between the effective viscosity and the capillary diameter measured for the field intensity 0.05 T.Reuse & Permissions
Figure 4
(a) Effect of temperature on the effective viscosity of temperature-sensitive magnetic nanofluids as a function of external magnetic field. As the temperature increases the effective viscosity decreases due to decrease of domain magnetization and magnetic moment of the particles with increase in temperature. (b) Variation of $M_{d}$ and $μ$ as a function of temperature for temperature-sensitive MZ5 magnetic nanofluids.Reuse & Permissions
Figure 5
(a) Variation of effective viscosity as a function of magnetic field for different temperatures for magnetite magnetic fluid whose Curie temperature is $\sim$ 585 $^{\circ}$ C, which is higher than the temperature range of the experiment. Hence, the decrease in viscosity is due to the temperature dependent removal of secondary surfactant from the magnetic particles, causing more free rotation of the particles inside the fluid which results in a decrease in the effective viscosity. Results are corrected for the decrease in viscosity of the carrier (water) with temperature. (b) Variation of hydrodynamic size of the magnetite particle as a function of temperature. The decrease in the hydrodynamic size is due to the removal of the secondary surfactant with increasing temperature. The inset shows the percentage removal of surfactant as a function of change in temperature. The second inset shows the two layers on the surface of the magnetic nanoparticle. The first layer is chemiadsorbed on the surface of the particle whereas the tail of the second layer is physiadsorbed with the first layer.Reuse & Permissions

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