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ABSTRACT
Ferrofluids are widely employed in versatile applications like in sealing, as loud speaker coolant, lubricants, in pressure sensors, in display devices, in biomedical applications like targeted drug delivery, hyperthermia, as a low side effect MRI contrasting agent, as magnetically tunable optical filters, as tunable diffraction gratings, as magnetic field and moment sensor etc [1-11]. This chapter describes these applications of ferrofluids. Optical, non linear optical and biomedical applications of ferrofluids are elaborated in detail in the previous chapters. Hence this chapter mainly concentrates on the industrial application of ferrofluids.
Ferrofluids are widely employed in industry. Ferrofluid filled loud speakers are already in markets as dampers. Laser head in a CD or DVD player most probably has a drop of ferrofluid as a damper. They are widely used as different type of sensors. Ferrofluids used as seals and coolants. Each of these applications are detailed in the following sections.
FERROFLUID SEALS
One of the most important industrial applications of ferrofluids is their employment as fluid seals [1-11]. They are used extensively to form liquid seals around the spinning drive shafts in hard disks. The rotating shaft is surrounded by magnets. A small amount of ferrofluid, placed in the gap between the magnet and the shaft, will be held in place by its attraction to the magnet. The fluid of magnetic particles forms a barrier which prevents debris from entering the interior of the hard drive. The most important advantage is that the amount of liquid seal needed is very less as a tiny drop of magnetic fluid will go on rotating with the magnetic field.
Ferrofluid based rotary seals operate with no maintenance and extremely low leakage in a very wide range of applications. They are used widely in variety of industrial and scientific applications. Generally, they are packaged in mechanical seal assemblies called rotary feedthroughs. Rotary feedthroughs consist of mainly 3 parts,
1. A central shaft
2. Ball bearings
3. An outer housing
The ball bearings are used to maintain the shaft within the seal gap as well as to support external loads. The bearings are the only mechanical wear-items, as the dynamic seal is actually a series of ferrofluid rings made of ultra-low vapour pressure, oil-based liquid held magnetically between the rotor...