Imperfect squeezing flow viscosimetry of Newtonian liquids - Theoretical and practical considerations

imperfect squeezing flow viscosimetry is an experimental procedure based on pressing a liquid specimen in a shallow container by a wide plate. Unlike in proper squeezing flow viscosimetry the specimen does not have a perfect cylindrical shape. Consequently, the flow regime is affected by factors other than squeezing and hence the name. Newtonian fluids, silicone oils of known viscosity and two honeys, were employed to evaluate the roles of the hydrostatic pressure and entry effects on the method's performance. Because of these, the shape of the initial parr of the flow curve differs significantly from the ideal and it appears that a fully developed squeezing flow is only reached after a penetration of several millimeters. The magnitude of the viscosity calculated through nonlinear regression is extremely sensitive to the mathematical model used. Thus, added terms, to account for secondary effects, which improve the fit almost to perfection, can also result in a substantial error - or underestimate of the viscosity. Theoretical analysis shows that with a sensor of a size of Petri dish (plate and container diameters on the order of 120 and 140 mm respectively, and a specimen height on the order of 5 mm) the method is only suitable for fluids whose viscosity is in excess of about 100 Pa.s. Nevertheless, the method was still sensitive enough to monitor differences in the viscosity of commercial honeys which was merely on the order of 5-10 Pa.s at ambient temperature.