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. A high VI-value indicates smaller viscosity changes with temperature. Then the viscosity at temperature T is calculated with Ubbelohde-Walther equation according ASTM-D341. Calculation according ISO 2909 / ASTM D2270-226.

The next step is to calculate the VBN of the blend, using this equation: First the viscosity at 100☌ is calculated using the viscosity at 40☌ and the Viscosity Index. It is important that the viscosity of each component of the blend be obtained at the same temperature. The viscosity-temperature coefficient for hydraulic oil can vary by a factor of 10 depending on the. Viscosity index obtained with the calculator program is 69 lower than that obtained by graphical method and the equation (1). Where v is the viscosity in square millimeters per second (mm²/s) or centistokes (cSt) and ln is the natural logarithm (log e). Viscosity index calculation was performed with a computer program using kinematic viscosity at 40☌ and 100☌. The first step is to calculate the Viscosity Blending Index (VBI) of each component of the liquid blend using the following equation: Scope 1.1 The tables and equations included in these methods provide a means for calculating the viscosity index of a petroleum product or lubricant from. The standard establishes two methods for calculating the viscosity index (VI) of lubricating oils based on their kinematic viscosity at 40 and 100 : A. 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.