
Member • Oct 3, 2007
Viscosity blending equations
(1) VBI = 14.534 × ln[ln(v + 0.8)] + 10.975
where v is the viscosity in centistokes and ln is the natural logarithm (Log[sub]e[/sub]).
The second step involves using this equation:
(2) VBI[sub]Blend[/sub] = [w[sub]A[/sub] × VBI[sub]A[/sub]] + [w[sub]B[/sub] × VBI[sub]B[/sub]] + ... + [w[sub]X[/sub] × VBI[sub]X[/sub]]
where w is the weight fraction (i.e., % ÷ 100) of each component of the blend. In using the above blending equation, it is necessary that all viscosities are determined at the same temperature, for example, 100 [sup]o[/sup]C.
(Reference: Robert E. Maples (2000), Petroleum Refinery Process Economics, 2nd Edition, Pennwell Books, ISBN 0-87814-779-9)
Once the viscosity blending number of a blend is obtained with equation (2), the viscosity of the blend can be determined by using the invert of equation (1):
(3) v = e[sup]e[sup](VBN - 10.975) ÷ 14.534[/sup][/sup] - 0.8
where VBN is the viscosity blending number of the blend and e is the transcendental number 2.71828, also known as Euler's number.