Length Measurement of Chain-Like Structure of Micron Magnetic Particles Dispersing in Carrier Fluid Effected by Magnetic Field

The chain-like structure and motion of the magnetic particles (MPs) in magnetorheological fluid (MRF) determine the rheological properties of MRF. In order to investigate the appearance and motion state of the chain-like structure of MPs under both static and flowing states of MRF, the formation process of MP chains in a stationary MRF under the action of an external magnetic field was observed by microscope. And the length of MP chains was measured by an objective micrometer to reveal the key factors affecting the length of formed chain. The MP chains broke after the magnet rotated by 90 degrees. The MRF was injected into a microchannel to observe the motion of MP chains. The speeds of the MP chains were measured by micrometer under different magnetic field strengths and inflow rates. The static test results show that the particle diameter has the greatest influence on the length of chain. The maximum length of the MP chains is 978.2 μm with a magnetic field strength of 130.31 mT; the diameter and mass fraction of the MPs are 2 μm and 3%. The MP chains will break from a long chain into short chains and rotate at a certain angle due to the rotation of magnetic field. The test results at different inflow rates show that the moving speed of MP chains in the microchannel increases with the increase of inflow rate and the decrease of magnetic field strength. In addition, the MP chains can withstand a carrier fluid flow rate of up to 0.32 m/s.