That is what led to my confusion in the first place. Since my calculations show that the tabulated values of VBN were obtained using log e, I can only conclude that some people use log to mean the natural logarithm. It is interesting that the patent presents the Refutas equation (their equation 13) as VBI = 14.534 × log + 10.975 with no explanation of whether base 10 or base e applies.
I then calculated the VBN values using log e in the Refutas equation and obtained exactly the same values as tabulated in the patent. I found a number of tabulated data on the viscosity (in centistokes) at a given temperature and the correspomding VBN at the same temperature for a good many different refinery streams in this patent: http:/ /tent_pdf/p atents/US6 662116.pdf which was assigned to Exxon Research and Engineering. The Refutas equation for calculating Viscosity Blending Numbers (VBN) in my original posting definitely uses the natural logarithm Log e (often but not always denoted as ln). RE: The Calculation of Viscosity Blending Indices Using the Refutas Equation jmw (Industrial) 2 Oct 07 05:54 but I am only interested in the above equation. I know that there are many other charts, tables, nomograms and equations for calculating Viscosity Blending Indices. Does the equation require the use of the log to the base 10 or the natural log to the base e? Not a single one of the publications I read clearly states whether log base 10 or log base e is required.Ĭan anyone tell me which log to use and provide me with a reference that clearly and definitively verifies it. Seeing the equation published in the literature in both of the above forms leaves me confused. The following equation for calculating the Viscosity Blending Index (VBI) of heavy oils is often referred to as the Refutas method and I have seen it published in the technical literature in both of the forms below:
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