OPPOSING-JET VISCOMETRY OF FLUIDS WITH VISCOSITY APPROACHING THAT OF WATER

Flows which were predominantly uniaxial in extension were generated through 0.5 mm diameter aligned jets. The torque required to keep the jets at a fixed distance apart, and thus the apparent stress generated by the fluid, was measured by a torque rebalance transducer attached to one of the moveable jet arms. Strain rates from 1000 to 20 000 s-1 were spanned. Data are presented for 1 to approximately 150 centipoise (cP) Newtonian water and glycerol/water mixtures. The trends found were consistent with a contribution to the measured torque by the inertia of the fluid, becoming negligibly small as the shear viscosity of the fluid approached approximately 75 cP. A method for correcting opposing-jet measurements made on fluids of viscosity less than 75 cP is described and the extent of the correction illustrated on a series of solutions with identical shear viscosities prepared from polyethylene glycols of molecular weight 8 x 10(3) to 1 x 10(6). The validity of the correction method for use on non-Newtonian fluids is discussed. The corrected results for the polyethylene glycol solutions of identical shear viscosity clearly illustrate the influence of molecular weight on extensional flow properties.