Study on viscosity and yield stress of magnetic fluid applied to low temperature magnetic fluid seal

Magnetic fluid seal is one of the most mature applications of magnetic fluid and is widely used in numerous fields. However, magnetic fluid seals used in low-temperature environments often encounter the problem of high starting torque. The rheometers commonly employed to characterize the rheological properties of magnetic fluid seal are limited by their temperature range, making it challenging to evaluate the properties of magnetic fluid seal under extremely low temperatures (such as -55 °C). Meanwhile, the standing time on the yield stress of magnetic fluid or the starting torque of magnetic fluid seal in low-temperature should be added to characterization especially for analyzing the magnetic fluid seal in low temperature. Additionally, the commonly used Herschel-Bulkley (H-B) model struggles to accurately fit the static yield stress of magnetic fluid seal. To address this issue, a stress-strain method was proposed to fit the static yield stress of magnetic fluid seal, and empirical formulas for viscosity and yield stress were developed. The effects of temperature, magnetic field, and resting time on yield stress were analyzed, and the starting torque of magnetic fluid seals under specific operating conditions was calculated. The results obtained from this method will provide valuable guidance for engineering applications.