Research on Measurement of Nano Magnetic Fluid Viscosity in Variable Magnetic Field

To measure viscosity of magnetic fluids (MFs) in adjustable magnetic field, this paper presented a novel method using a double tube and a torque measuring motor. The inner tube was fixed and the outer tube was driven by a motor. Mathematical analysis indicated that the viscosity of MFs in the gap between the two tubes could be determined by the rotational speed. A magnetic circuit constructed by some permanent magnets and yokes provided the magnetic field for the MFs in the gap. Changing the number of the magnets could adjust the magnetic density easily. Taking the temperature’s influence on the viscosity into account, an extrapolation method was adopted to measure and control the MFs’ temperature precisely. This method was calibrated by the standard liquid with the known viscosity, which showed that the mean error was less than 0.82%. This method was used to measure the viscosity of MFs composed of MnZnFeO4 nanoparticles, oleic acid surfactants and lubricant carrier liquid in variable magnetic field at the different temperatures.