Miniviscometer: A small Couette instrument

Abstract

Miniviscometer is a Couette instrument that can determine the viscosity vs shear-rate relation of a 0.2 cm³ sample of fluid. The inner member, the one that docs not rotate, is entirely surrounded by the outer member. It is kept from rotating by a magnetic field produced by an electromagnet. The electromagnet current just sufficient to prevent rotation is proportional to the viscous torque, and thus to the product of shear rate and viscosity.

The inner member has a conical bottom end that mates with a slightly blunter conical cavity in the outer member. This maintains across the bottom the same shear rate as that between the cylindrical surfaces of inner and outer, and serves as a bearing to keep the inner member centralized. Friction of this bearing is kept low by making the inner member as a Cartesian diver and adjusting its density so it just barely sinks in the liquid under investigation.