VISCOMETRIC PERFORMANCE EVALUATION OF OIL WITH RESPECT TO SHEAR RATE, TEMPERATURE AND SHEARING TIME

In this study, we evaluate the fundamental behaviour of mineral oil (Mobil Extra 2T) that was stressed from stagnant condition to a shear rate of 1900 1/s in different shearing time (60, 300 and 900 s), remained at constant shear rate of 1900 1/s between 30 to 60 s, and continued by decreasing shear rate to stagnant condition at specific shearing time of 60, 300 and 900 s. This process was repeated from 40 to 100 °C with an interval of 20 °C. Viscosity measurement was carried out by ThermoHaake (Rheometer model RS600) and temperature control (Haake - Phoenix model C1 35P). Failure of rheological models in modeling the relationship of viscosityshear rate was demonstrated and alternative model i.e. Fourier series was proposed as a substitution with a high R-squared value of 0.99. Integration of Fourier series from 0 to 1900 1/s was carried out on increasing and decreasing shear rate-generated curves. Results showed a consistent trend of lost-shear stress ( τ L ), represented by the difference of integration value of increasing and decreasing shear rate-generated curves, at specific temperature and shearing time. This method is proposed to evaluate the performance of oil on viscosity recovery after historical treatment of shear rate.