mbeychok

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.