VISCOMETRY OF NANODISPERSE MAGNETIC LIQUIDS AND LUBRICATING OILS. 1. INSTRUMENTATION FOR RHEOLOGICAL STUDIES OF MAGNETIC NANODISPERSE LIQUID MEDIA

Abstract

Analysis of the literature sources shows that the existing viscometers are not always and not completely able to provide comprehensive studies of magnetic nanofluids for scientific and practical purposes. Design has been developed of a magnetic rotary viscometer which makes it possible to carry out investigations in a wide range of the magnetic field induction. The magnetic field in the device is directed orthogonally to the shear stress and can vary from zero to 1,7·10^5 A/m. The device has two measuring gaps filled with liquid, that increases the accuracy of the results of studies of low-viscosity liquids. The viscometer allows you to measure the standard characteristics of magnetic nanofluids (viscosity coefficient, plastic viscosity, ultimate shear stress, etc.), as well as to study the structural features of liquids under shear stresses. The shear rate in the liquid can be stably maintained in a wide range of (1÷5)·10^3 s^(-1). The viscosity of the studied liquids can vary from 10^(-3) Pa·s to ≈10^2 Pa·s. For studies on a viscometer, a small amount of magnetic nanofluid with a volume of about 3,5 cm^3 is required. Using experimental data, the mathematical description of the process of laminar fluid flow in the annular gap of the viscometer made it possible to optimize its geometric dimensions and obtain formulas for calculating the viscosity coefficient, shear stress and shear rate.

Keywords

• magnetic nanofluid
• rheology
• coaxial viscometer
• shear stress
• shear rate
• coefficient of viscosity
• magnetic field
• external and internal friction