Where VBN is the viscosity blending number of the blend and e is the transcendental number 2.71828, also known as Euler's number. Once the viscosity blending number of a blend has been calculated using equation (2), the third and final step is to determine the viscosity of the blend by using the invert of equation (1): Where w is the weight fraction (i.e., weight % ÷ 100) of each component of the blend. The next step is to calculate the VBN of the blend, using this equation: It is important that the viscosity of each component of the blend be obtained at the same temperature. Calculator for viscosity index (VI) according to ASTM D2270 and ISO. v, and v, can be found by solving these equations respect to interchange of indices. Standard practice for calculating viscosity index from kinematic viscosity at 40 and 100C. Where v is the viscosity in square millimeters per second (mm²/s) or centistokes (cSt) and ln is the natural logarithm (log e). mole fraction in the calculation of the viscosity of the mixture. Better yet, you can enter a single known viscosity (and temperature) and VI (commonly found on a lubricants product data sheet) to calculate the viscosity of. Calculate the viscosity using the viscosity index. The first step is to calculate the Viscosity Blending Index (VBI) of each component of the liquid blend using the following equation: Liquid viscosity blending calculations to determine the viscosity of a blend of two or more liquids having different viscosities are best performed by using what is known as the Refutas equation in a three-step procedure.
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