Study of the temperature dependences of abnormal oil viscosity using rotational and vibrational viscometers

Principle of operation, advantages and disadvantages of the recently introduced a vibrational viscometer SV-10 are discussed. The results of measuring the viscosity of Newtonian and non-Newtonian oils on a HAAKE VT550 rotary viscometer are compared with that obtained on a vibratory viscometer in the temperature range wherein the non-Newtonian properties of oil appear and disappear. It is shown that when measuring the viscosity of Newtonian liquids, including light unstructured oils, in the temperature range where non-Newtonian properties are not manifested, the rotational and vibrational viscometers provide similar results regarding both the viscosity values and temperature dependence of the viscosity. However, when the oil temperature drops to the range of the abnormal properties, each value of the oil viscosity measured on SV-10 corresponds to the effective shear rate on the flow curve for a given temperature recorded on a rotational viscometer VT550 (the higher the viscosity, the smaller the effective shear rate). Hence, when studying the rheology of non-Newtonian structured liquids, e.g., high-paraffin oils, it is necessary to use rotational rheometers, which provide recording the entire flow curve and determining the viscosity values in transient and steady-state flow regimes. The vibration viscometer measures the viscosity of non-Newtonian structured media for some “effective” shear rate values, which are not set by the device and can be determined as a result of separate experiments with calibrated samples thus providing relative rather than absolute measurements of the viscosity. Recommendations for practical use of SV-10 vibrational viscometers are specified proceeding from the results of studying the rheological characteristics of oils obtained on both types of the viscometers.

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