Experimental Study of an On-Demand Thermomagnetic Micropump
Souvik Pal1,a, Achintya Mukhopadhyay2,d, Swarnendu Sen2,e, Amitava Datta1,b, Ranjan Ganguly1,c and Kallol Bandopadhyay3
1Department of Power Engineering, Jadavpur University, Kolkata 700 098, India.
asouviktor@gmail.com
bamdatta_ju@yahoo.com
crgangu2@yahoo.com
2Department of Mechanical Engineering, Jadavpur University, Kolkata 700 032, India.
dmukhopadhyay@mech.jdvu.ac.in
edrssen@mech.jdvu.ac.in
3Machine Dynamics Division, BARC, Trombay, Mumbai 400 085, India.
kallol13@rediffmail.com
ABSTRACT
Ferrofluids are colloidal suspensions of single domain superparamagnetic nanoparticles, typically of the order of 10 nm in diameter, in nonmagnetic liquids. In the absence of an external magnetic field, the individual particle dipoles are randomly oriented due to thermal agitation, and the fluid does not show any permanent magnetization. However, the fluid bulk exhibits magnetic behavior when an external magnetic field is imposed. The nanoparticles are stabilized by coating them with surfactant molecules, so that a ferrofluid can often be treated as a single homogeneous liquid, which can be steered and collected into homogeneous aggregates by applying external magnetic fields. This “action at a distance” offers various promising microfluidic applications using ferrofluids, e.g., ferrofluid micropumping. The present study demonstrates, at a proof-of-concept level, the feasibility of using a thermomagnetic micropump, where suitably imposed temperature and magnetic field gradients are used to pump a known volume of ferrofluid in a microfluidic channel without application of any external pressure gradient. Such a pump can operate in a hermetically sealed MEMS configuration without any moving part, and is capable of handling extremely hazardous materials with little risk of contamination.
In the experiment, ferrofluid in a glass capillary tube is exposed to a magnetic field using a solenoid, and small resistive heaters are used to create temperature gradient in such a way that the Kelvin body force in the medium has a net unbalanced axial component. This causes a thermomagnetic pumping action, transporting the ferrofluid in the capillary tube from the colder end to the warmer end. Performance of the thermomagnetic pump is investigated experimentally to characterize the pressure head and response time of the pumps under different working conditions, namely, the magnetic field strength, heating power, ferrofluid properties, etc. Results of the study will provide the operating characteristics of an on-demand MEMS-scale thermomagnetic pump.
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