The purpose of this work was to determine a viscosity-temperature relationship for SAE 10W-60 engine oil. The rheological properties of this engine oil, for a temperature range of 20÷60 C, were obtained with RheolabQC rotational rheometer. For the first reference temperature of 40 C, the experimental result was obtained with a relative error of 1.29%. The temperature-dependent viscosity was modelled, comparatively, with the Arrhenius and the 3 rd degree polynomial models. Comparing the graphs of the fits with prediction bounds for 95% confidence level, as well as the goodness-of-fit statistics, the preliminary conclusion was that the 3 rd degree polynomial could be the best fit model. However, the fit model should be used also for extrapolation, for the second reference temperature of 100 C. This new approach changes the fit models order, the Arrhenius equation becoming the best fit model, because of the completely failed to predict the extrapolated value with the polynomial model.
Mathematical models that describe the variation of soybean oil viscosity with temperature according to the recent WLF and VTF (or VFT) equations and traditionally by the Arrhenius equation. The Arrhenius equation shows that the viscosity of the oil is proportional to the absolute temperature and is determined by the activation energy parameter. In Arrhenius' equation the absolute temperature is replaced by T + b where both adjustable T and b are in ° C. The mathematical models described by the equations WLF and VTF, are equal to each other. All three equations are in the same model when used for experimental data of temperature-viscosity dependence, they give exactly the same very high regression coefficient.
Viscosity is one of the most important parameters for vegetable oil. A new mathematical viscosity model was developed based on freely sliding molecules with Lennard-Jones’ potential and linear density-temperature relation. According to the functions derived from the new model, viscosity gradually decreases with temperature at atmospheric pressure. Viscosity increases with density, however, due to the molecular momentum transfer and statistical effect of average molecular potential. After the temperature dependent function is fitted to the 417 experimental data points collected from references and distributed among the ranges: 278.15–453.15 K and 2.6-192.6 mPa.s, it was found that the calculated data agreed well with experimental data with R2 ≥ 0.961 for 13 oil samples. The density dependent function was also satisfactorily fitted to the 143 viscosity data points versus density from 5 oil samples with R2 ≥ 0.917.
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