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Viscosity Blending Index calculation
Viscosity blending equations
Calculating the viscosity blending index of a liquid consisting oftwo or more liquids having different viscosities is a two stepprocedure. The first step involves calculation of the ViscosityBlending Index (VBI) of each component of the blend using thefollowing equation (known as a Refutas equation):
(1) VBI = 14.534 × ln[ln(v + 0.8)] + 10.975
where v is the viscosity in centistokes and ln is the naturallogarithm (Loge).
The second step involves using this equation:
(2) VBIBlend = [wA × VBIA] + [wB × VBIB] + ... + [wX × VBIX]
where w is the weight fraction (i.e., % ÷ 100) of each componentof the blend. In using the above blending equation, it is necessarythat all viscosities are determined at the same temperature, forexample, 100 oC.
(Reference: Robert E. Maples (2000), Petroleum Refinery ProcessEconomics, 2nd Edition, Pennwell Books, ISBN 0-87814-779-9)
Once the viscosity blending number of a blend is obtained withequation (2), the viscosity of the blend can be determined by usingthe invert of equation (1):
(3) v = ee(VBN - 10.975) ÷ 14.534 - 0.8
where VBN is the viscosity blending number of the blend and e isthe transcendental number 2.71828, also known as Euler'snumber.
