Precise Viscosity Measurements Very Close to Critical Points

A torsion oscillator is being developed to measure the viscosity of fluids at moderate temperatures (0-100 C) and pressures (0-10 MPa) at very low frequencies (0.5 Hz) and very low shear rates (0.05/sec). These conditions are required to measure the shear viscosity of fluids extremely close to the critical point. The oscillator, thermostat, vacuum system, and instrumentation were assembled and are undergoing debugging. Preliminary measurements indicate that the system has a noise corresponding to 0.2% of the viscosity of methanol-cyclohexane mixtures near the consolute point.