One of the main engineering applications of ferrofluids is in magnetic fluid seals, working in rotary motion. An area, which has so far been insufficiently examined, is the mechanism of leaks between seal stages in this type of seal. This is an important issue in order to understand the principle of the seal operation and to properly design this type of seal. This paper presents the results of research into the mechanism of leaks between stages in multi-stage magnetic fluid seals. The tests were conducted when the pressure of the sealing air increased and reached its maximum value. The influence of the magnetic fluid properties, such as saturation magnetization or dynamic viscosity, was taken into account. Studies were performed for different seal temperatures. Experiments allowed models for determining the maximum pressure of the multi-stage seal to be proposed, based on the information about this pressure for a one-stage seal. This paper presents the comparative results of the critical pressure value obtained from experimental studies and calculations based on numerical simulations.

Ferrofluids have various engineering applications; one of them is magnetic fluid seals. There are various constructions this type of seals. Development for this design is a complex process which requires knowledge about ferrofluid physical properties and magnetic field distribution inside the sealing gap. One of the most important parameters of ferromagnetic fluid seals is critical pressure value. It is a pressure at which rapid leakage will occur. This publication presents the results of critical pressure value obtained from, experimental studies and calculations based on numerical simulations. Shape of sealing stage, volume of ferrofluid and volume of permanent magnet used in seal construction were taken into account. Experiments and calculations were performed for four ferrofluids differ in saturation magnetization, density and zero magnetic field viscosity.

Purpose: – The purpose of this publication is to determine the influence of selected factors on the durability and the tightness of ferrofluid seals working in water environments. Ferromagnetic fluid (FF) seals are one of the most common applications of magnetic fluid. New applications can be developed by extending the capabilities of these seals in fluid environments, especially in water. Design/methodology/approach: – Tests were performed using ferrofluids with differing physical properties like density, dynamic viscosity and saturation magnetization. Working conditions, such as water pressure and peripheral speed, were taken into account. Findings: – A mathematical description which allows the selection of an appropriate ferrofluid and the determination of the operating parameters of an FF seal was developed. Originality/value: – This study concerns the influence of peripheral speed, water pressure and magnetic fluid properties on seal tightness.

Magnetic fluid seals are among the most common ferrofluid applications. One interesting area is the use of numerical simulations to determine the critical pressure, which is a basic parameter determining the possible range of seal operating pressures. The purpose of this study is to present the method of critical pressure calculations in magnetic fluid seals based on magnetic field numerical simulations, which will provide better results than the methods used previously. It is a relatively simple method and can help to reduce the difference between simulations and experiments. Different seal stage shapes, such as symmetric trapezoidal, asymmetric trapezoidal, and rectangular, were taken into account. The research shows that an increase in the magnetic fluid volume applied at the seal stage and a magnetic saturation increase in the seal gap allow the manufacturing inaccuracy influence to be reduced, meaning that the difference between the simulation and experiment results is smaller. In addition, in this paper, the pressure transfer mechanism between liquid rings of the multistage seal is analyzed to show its influence on the critical pressure value calculated based on simulations.

Magnetic fluid seals are among the most common applications of ferrofluids. In such seals, the torque friction results only from the internal friction in the fluid and there is no direct contact between seal elements. Despite this, the heat generated during operation can be significant due to the low volume of the ferrofluid in the seal and high rotational speeds. The difficulty in calculating the torque friction is because the ferrofluid is a non-Newtonian fluid and changes its viscosity under the influence of a magnetic field. In order to measure torque friction in magnetic fluid seals, a special test stand was built. Tests were performed at different rotation speeds, different temperatures, and two seal stage geometries (rectangle and trapezoid). Numerical simulations were performed to determine the magnetic field distribution in the seal. Dynamic viscosity under the influence of the magnetic field was measured on a rotary rheometer. Mathematical models were compared with laboratory results. The results obtained from the calculations in some cases gave overstated values almost twice in value. An additional correction in the case of ferrofluid viscosity is proposed.

The advantages of magnetic fluid seals, such as low friction moment, high tightness, and high durability, have been known for many years. However, they are used particularly in air or vacuum environments and the application of this type of seal in water still remains a problem. This is mainly due to the friction occurring between the two fluids and interfacial instability. This publication focuses on investigating the influence of magnetic fluid properties on the mechanism of pressure transfer between sealing stages. The main aim was to better understand the leak mechanism in this type of seal and to be able to select ferrofluids (FFs) resistant to water for long-term operation after short-term testing. The tested seals rotated over 4.3 million times without failure. The results of the research carried out are recommendations for the selection of magnetic fluid, sealing stage width, and FF volume.