Effect of magnetic field on laminar convective heat transfer characteristics of ferrofluid flowing through a circular stainless steel tube

https://doi.org/10.1016/j.ijheatfluidflow.2016.01.009Get rights and content

Highlights

Abstract

Ferrofluids have promising potential for heat transfer applications, as they can be easily controlled and manipulated by applied magnetic field produced by either permanent magnets or electromagnets. The present study reports the effect of magnetic field on the convective heat transfer characteristics of ferrofluid flowing through a circular stainless steel (SS) tube (2 mm ID × 2.6 mm OD) under constant heat flux conditions. The convective heat transfer coefficient for various ferrofluid flow rates and applied magnetic field gradients is reported using infrared thermography (IRT) technique. COMSOL simulation has been carried out to calculate the magnetic field and magnetic force distribution inside the SS tube. Bright field visualization of clusters of nanoparticles and aggregation of nanoparticles at the inner wall of the SS tube in the presence of magnetic field have also been carried out in order to explain the possible mechanism for heat transfer enhancement for ferrofluid in the presence of magnetic field. The convective heat transfer coefficient for ferrofluid flow in the presence of magnetic field may increase or decrease depending upon several factors such as, ratio of magnetic force to inertia force acting on the ferrofluid, interaction of ferrofluid flow with the aggregate of nanoparticles formed at the wall of the tube near the vicinity of the magnets, and enhancement in local thermal conductivity of ferrofluid flow resulting from the chain like clusters of nanoparticles within the ferrofluid in the presence of magnetic field.

Section snippets

Abbreviations

    DLS

    dynamics light scattering

    ID

    inner diameter

    IR

    infrared

    IRT

    infrared thermography

    IONP

    iron oxide nanoparticle

    OD

    outer diameter

    OA-IONP

    oleic acid coated iron oxide nanoparticle

    SS

    stainless steel

    TEM

    transmission electron microscopy

    VSM

    vibration sample magnetometer

Synthesis and thermophysical properties of water-based ferrofluid

Iron oxide nano-particles (IONPs) were chemically synthesized by the co-precipitation method from an aqueous mixture of Fe3+/Fe2+ (2:1) solutions. The chemical reaction responsible for this synthesis is expressed as: Fe+2 + 2Fe+3 + 8OH→Fe3O4 + 4H2O

After the synthesis of IONPs, oleic acid is added as a surfactant to prevent the agglomeration of IONPs. The oleic acid coated IONPs (OA-IONPs) were then dispersed in DI-water to prepare suspensions of IONPs or ferrofluids. The OA-IONPs are found to be

Simulation of magnetic flux density and magnetic force distribution

Distributions of the magnetic field and the resulting Kelvin's magnetic body force acting on the iron oxide nanoparticles of ferrofluid for the given configurations of the permanent magnets have been simulated using commercial software COMSOL–Multiphysics V4.3 (COMSOL Inc.). The magnetic flux density (B) and the magnetic force (F) distributions were simulated based on the Eqs. (8) and (9) as mentioned below. B=μ0μrH+BrF=MHwhere B is the magnetic flux density, μ0 is the magnetic

Variation of Nusselt number for DI-water flow

Prior to using the IR camera for estimation of local heat transfer coefficients, the bench marking exercise was performed to instill confidence in the subsequent estimation of local heat transfer coefficients of ferrofluid flow with and without the applied magnetic field. A series of experiments were performed for benchmarking the thermography technique using DI-water as the working fluid at flow rates of 20 and 40 mL/min (corresponding to Peclet numbers of 1467 and 2934 respectively) through

Mechanism of heat transfer enhancement

Many research groups (Maïga et al., 2005, Bianco et al., 2009, Kalteh et al., 2012) have discussed the mechanism by which the presence of nanoparticles (magnetic or non-magnetic) can enhance convective heat transfer coefficients relative to its base fluid. However, based on different observations it still remains as a debatable issue. One of the proposed mechanisms for heat transfer enhancement in nanofluids is the enhancement in thermal conductivity of nanofluid compared to its base fluid.

Summary and conclusions

The laminar convective heat transfer characteristics of ferrofluid flowing through a circular SS tube under constant heat flux condition and in the presence of applied magnetic field is experimentally investigated using IRT technique. The magnetic field and magnetic force distribution for different arrangement of magnets have been calculated using COMSOL simulation in order to support the experimental results. The major conclusions of the present study are as follows:

  • There is no enhancement in

Acknowledgements

The authors wish to thank Mr. Mohammed Anwar (Nano-formulation laboratory, Faculty of pharmacy, Jamia Hamdard, New Delhi) for providing water based ferrofluid for conducting the experiments. The authors also thank Mr. Ram Krishna Saha (Department of Mechanical Engineering, IIT Kanpur) for helping us in conducting the COMSOL simulations reported in the present work.

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