An oscillating cup viscometer interfaced to an automatic data acquisition and processing system (computer, interface, software) was built for viscosity measurements in molten salts below 1400 K.In order to avoid the "meniscus effect", the main source of errors of the method, the measurements were carried out in the so-called "full cup" condition, i.e. with the height of the liquid column (h) of 11.2 cm, the overall height of the cup being 11.9 cm. An adequate software supplied values at each temperature, as function of R, I, 6, h, p and T values in air and with liquid containing cup. The viscosity of molten KNO3 and NaCI, both of "standard salt purity", was reinvestigated over a temperature range of 100 K above their melting points. The standard deviation of the data obtained was +0.38%. These data were systematically lower (3% for qNacl and 2% for q K N~, ) than those obtained earlier by the same method, but agree within +0.9% with the recommended Janz's "calibration quality viscosity data".One can conclude that the method gives accurate results only if operated in "full cup" condition.
The errors in viscosity measurements by the oscillating cup method were calculated as a function of the limit of accuracy imposed by the uncertainty in determining the constants of the oscillating system R, I, T0, δ0 and the limit of precision resulting from errors in determining the experimental parameters δ , T , h, ρ.
Thus, by evaluating the fractional error of each of the parameters and implicitly its distinct contribution to the total standard error, it was established that the “meniscus error” Δh, which is difficult to be controlled or avoided, represents the major source of imprecision of oscillating cup viscometers.
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