Abstract
Ferrofluid rotary seals are mechanical contact-free magnetic liquid seals that are characterised by their simple structure, low friction and ability to hermetically seal. Although ferrofluid rotary seals for sealing vacuum and gases are part of a well established industry, the sealing of liquids has not been implemented yet. Literature learns that degradation of the ferrofluid seal over time when it dynamically contacts a liquid results into premature seal failure. This paper presents a new type of ferrofluid rotary seal in which a ferrofluid replenishment system is implemented that renews the ferrofluid in the sealing ring while sealing capacity is maintained. By replacing the degraded ferrofluid in the seal at a sufficient rate, service life of the ferrofluid rotary seal can theoretically be unlimited. An analytical model and FEM analysis are used to design the ferrofluid sealing device and to predict its sealing capacity. An experimental test setup has been built on which the sealing capacity and service life of the device has been tested for different sealing conditions. It is demonstrated that the ferrofluid replenishment system successfully extends and controls the service life of the ferrofluid rotary seal that dynamically seals pressurised water.
Highlights
In the 1960’s the world’s first patented magnetic fluid was created by adding magnetic properties to rocket fuel, enabling control of the fluid in outer space using magnets [1]
Ferrofluid rotary seals are mechanical contact-free magnetic liquid seals that are characterised by their simple structure, low friction and ability to hermetically seal
This paper presents a new type of ferrofluid rotary seal in which a ferrofluid replenishment system is implemented that renews the ferrofluid in the sealing ring while sealing capacity is maintained
Summary
In the 1960’s the world’s first patented magnetic fluid was created by adding magnetic properties to rocket fuel, enabling control of the fluid in outer space using magnets [1]. The driving mechanisms causing this premature failure are not fully understood and prevent current implementation for sealing liquids Many authors attribute this limited service life to the arise of interfacial instabilities between the liquid that is sealed and the ferrofluid of the seal [13,18]. The acquired knowledge is used to design an experimental test setup for a series of experiments in order to identify both static and dynamic sealing capacity of the system These results are used to perform a series of experiments in order to validate the hypothesis that the ferrofluid replenishment system improves the service life of the ferrofluid rotary seal that is used to seal high pressure water on a rotating shaft
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