Calculating the viscosity of a blended liquid consisting of two or more liquids having different viscosities is a three step procedure. The first step involves calculation of the Viscosity Blending Index (VBI) of each component of the blend using the following 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 natural logarithm (Log_e).

 

The second step involves using this blending equation:

 

(2) VBI_Blend = [w_A × VBI_A] + [w_B × VBI_B] + ... + [w_X × VBI_X]

 

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 ^oC.

 

The third and final step is to determine the viscosity of the blend by using the invert of equation (1):

 

(3) v = e^{e(VBI - 10.975) ÷ 14.534} − 0.8

 

where VBI is the Viscosity Blending Index of the blend and e is the transcendental number 2.71828, also known as [[Euler's number]].

This version is no more interesting or correct that this one.

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